Add support for binding with a custom marshal/unmarshal function (#104)

## Summary:
This is useful if you want to bind to a type you don't control (or use
for other things) but need different serialization than its default.
This is a feature gqlgen has and we've found it very useful.  For
example, in webapp we want to bind `DateTime` to `time.Time`, but its
default serialization is not compatible with Python, so currently we
have to bind to a wrapper type and cast all over the place, which is
exactly the sort of boilerplate genqlient is supposed to avoid.

For unmarshaling, the implementation basically just follows the existing
support for abstract types; instead of calling our own generated
helper, we now call your specified function.  This required some
refactoring to abstract the handling of custom unmarshalers generally
from abstract types specifically, and to wire in not only the
unmarshaler-name but also the `generator` (in order to compute the right
import alias).

For marshaling, I had to implement all that stuff over again; it's
mostly parallel to unmarshaling (and I made a few minor changes to
unmarshaling to make the two more parallel).  Luckily, after #103 I at
least only had to do it once, rather than implementing the same
functionality for arguments and for input-type fields.  It was still
quite a bit of code; I didn't try to be quite as completionist about the
tests as with unmarshal but still had to add a few.

Issue: https://github.com/Khan/genqlient/issues/38

## Test plan:
make check


Author: benjaminjkraft

Reviewers: StevenACoffman, dnerdy, benjaminjkraft, aberkan, jvoll, mahtabsabet, MiguelCastillo

Required Reviewers: 

Approved By: StevenACoffman, dnerdy

Checks: ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint, ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint

Pull Request URL: https://github.com/Khan/genqlient/pull/104

generate/config.go

@@ -44,6 +44,8 @@ type Config struct {
 type TypeBinding struct {
 	Type              string `yaml:"type"`
 	ExpectExactFields string `yaml:"expect_exact_fields"`
+	Marshaler         string `yaml:"marshaler"`
+	Unmarshaler       string `yaml:"unmarshaler"`
 }
 
 // ValidateAndFillDefaults ensures that the configuration is valid, and fills

generate/convert.go

@@ -125,6 +125,7 @@ func (g *generator) convertOperation(
 		},
 		Fields:    fields,
 		Selection: operation.SelectionSet,
+		Generator: g,
 	}
 
 	return g.addType(goType, goType.GoName, operation.Position)
@@ -188,6 +189,7 @@ func (g *generator) convertArguments(
 			// fake name, used by addType
 			GraphQLName: name,
 		},
+		Generator: g,
 	}
 	goTypAgain, err := g.addType(goTyp, goTyp.GoName, operation.Position)
 	if err != nil {
@@ -217,7 +219,9 @@ func (g *generator) convertType(
 	localBinding := options.Bind
 	if localBinding != "" && localBinding != "-" {
 		goRef, err := g.ref(localBinding)
-		return &goOpaqueType{goRef, typ.Name()}, err
+		// TODO(benkraft): Add syntax to specify a custom (un)marshaler, if
+		// it proves useful.
+		return &goOpaqueType{GoRef: goRef, GraphQLName: typ.Name()}, err
 	}
 
 	if typ.Elem != nil {
@@ -269,11 +273,16 @@ func (g *generator) convertDefinition(
 			}
 		}
 		goRef, err := g.ref(globalBinding.Type)
-		return &goOpaqueType{goRef, def.Name}, err
+		return &goOpaqueType{
+			GoRef:       goRef,
+			GraphQLName: def.Name,
+			Marshaler:   globalBinding.Marshaler,
+			Unmarshaler: globalBinding.Unmarshaler,
+		}, err
 	}
 	goBuiltinName, ok := builtinTypes[def.Name]
 	if ok {
-		return &goOpaqueType{goBuiltinName, def.Name}, nil
+		return &goOpaqueType{GoRef: goBuiltinName, GraphQLName: def.Name}, nil
 	}
 
 	// Determine the name to use for this type.
@@ -337,6 +346,7 @@ func (g *generator) convertDefinition(
 			Fields:          fields,
 			Selection:       selectionSet,
 			descriptionInfo: desc,
+			Generator:       g,
 		}
 		return g.addType(goType, goType.GoName, pos)
 
@@ -346,6 +356,7 @@ func (g *generator) convertDefinition(
 			Fields:          make([]*goStructField, len(def.Fields)),
 			descriptionInfo: desc,
 			IsInput:         true,
+			Generator:       g,
 		}
 		// To handle recursive types, we need to add the type to the type-map
 		// *before* converting its fields.
@@ -700,6 +711,7 @@ func (g *generator) convertNamedFragment(fragment *ast.FragmentDefinition) (goTy
 			Fields:          fields,
 			Selection:       fragment.SelectionSet,
 			descriptionInfo: desc,
+			Generator:       g,
 		}
 		g.typeMap[fragment.Name] = goType
 		return goType, nil
@@ -729,6 +741,7 @@ func (g *generator) convertNamedFragment(fragment *ast.FragmentDefinition) (goTy
 				Fields:          implFields,
 				Selection:       fragment.SelectionSet,
 				descriptionInfo: implDesc,
+				Generator:       g,
 			}
 			goType.Implementations[i] = implTyp
 			g.typeMap[implTyp.GoName] = implTyp

generate/generate_test.go

@@ -83,8 +83,13 @@ func TestGenerate(t *testing.T) {
 				ExportOperations: queriesFilename,
 				ContextType:      "-",
 				Bindings: map[string]*TypeBinding{
-					"ID":          {Type: "github.com/Khan/genqlient/internal/testutil.ID"},
-					"DateTime":    {Type: "time.Time"},
+					"ID":       {Type: "github.com/Khan/genqlient/internal/testutil.ID"},
+					"DateTime": {Type: "time.Time"},
+					"Date": {
+						Type:        "time.Time",
+						Marshaler:   "github.com/Khan/genqlient/internal/testutil.MarshalDate",
+						Unmarshaler: "github.com/Khan/genqlient/internal/testutil.UnmarshalDate",
+					},
 					"Junk":        {Type: "interface{}"},
 					"ComplexJunk": {Type: "[]map[string]*[]*map[string]interface{}"},
 					"Pokemon": {

generate/marshal.go.tmpl

@@ -0,0 +1,52 @@
+{{/* See unmarshal.go.tmpl for more on how this works; this is mostly just
+     parallel (and simplified -- we don't need to handle embedding). */}}
+
+func (v *{{.GoName}}) MarshalJSON() ([]byte, error) {
+    {{/* We do the two passes in the opposite order of unmarshal: first, we
+         marshal the special fields, then we assign those to the wrapper struct
+         and finish marshaling the whole object.  But first we set up the
+         object for the second part, so we can assign to it as we go. */}}
+    var fullObject struct{
+        *{{.GoName}}
+        {{range .Fields -}}
+        {{if .NeedsMarshaler -}}
+        {{.GoName}} {{repeat .GoType.SliceDepth "[]"}}{{ref "encoding/json.RawMessage"}} `json:"{{.JSONName}}"`
+        {{end -}}
+        {{end -}}
+        {{ref "github.com/Khan/genqlient/graphql.NoMarshalJSON"}}
+    }
+    fullObject.{{.GoName}} = v
+
+    {{range $field := .Fields -}}
+    {{if $field.NeedsMarshaler -}}
+    {
+        {{/* Here dst is the json.RawMessage, and src is the Go type */}}
+        dst := &fullObject.{{$field.GoName}}
+        src := v.{{$field.GoName}}
+        {{range $i := intRange $field.GoType.SliceDepth -}}
+        *dst = make(
+            {{repeat (sub $field.GoType.SliceDepth $i) "[]"}}{{ref "encoding/json.RawMessage"}},
+            len(src))
+        for i, src := range src {
+            dst := &(*dst)[i]
+        {{end -}}
+        var err error
+        *dst, err = {{$field.Marshaler $.Generator}}(
+            {{/* src is a pointer to the struct-field (or field-element, etc.).
+                 We want to pass a pointer to the type you specified, so if
+                 there's a pointer on the field that's exactly what we want,
+                 and if not we need to take the address. */ -}}
+            {{if not $field.GoType.IsPointer}}&{{end}}src)
+        if err != nil {
+            return nil, fmt.Errorf(
+                "Unable to marshal {{$.GoName}}.{{$field.GoName}}: %w", err)
+        }
+        {{range $i := intRange $field.GoType.SliceDepth -}}
+        }
+        {{end -}}
+    }
+    {{end -}}
+    {{end}}
+
+    return {{ref "encoding/json.Marshal"}}(&fullObject)
+}

generate/testdata/queries/CustomMarshal.graphql

@@ -0,0 +1,6 @@
+query CustomMarshal($date: Date!) {
+  usersBornOn(date: $date) {
+    id
+    birthdate
+  }
+}

generate/testdata/queries/CustomMarshalSlice.graphql

@@ -0,0 +1,8 @@
+query CustomMarshalSlice(
+  $datesss: [[[Date!]!]!]!,
+  # @genqlient(pointer: true)
+  $datesssp: [[[Date!]!]!]!,
+) {
+  acceptsListOfListOfListsOfDates(datesss: $datesss)
+  withPointer: acceptsListOfListOfListsOfDates(datesss: $datesssp)
+}

generate/testdata/queries/schema.graphql

@@ -3,6 +3,7 @@
 We don't really have anything useful to do with this description though.
 """
 scalar DateTime
+scalar Date
 scalar Junk
 scalar ComplexJunk
 
@@ -44,6 +45,7 @@ input UserQueryInput {
   role: Role
   names: [String]
   hasPokemon: PokemonInput
+  birthdate: Date
 }
 
 type AuthMethod {
@@ -66,6 +68,7 @@ type User {
   authMethods: [AuthMethod!]!
   pokemon: [Pokemon!]
   greeting: Clip
+  birthdate: Date
 }
 
 """An audio clip, such as of a user saying hello."""
@@ -153,6 +156,9 @@ type Query {
 
   """usersWithRole looks a user up by role."""
   usersWithRole(role: Role!): [User!]!
+
+  usersBornOn(date: Date!): [User!]!
+
   root: Topic!
   randomItem: Content!
   randomLeaf: LeafContent!
@@ -163,6 +169,7 @@ type Query {
   listOfListsOfLists: [[[String!]!]!]!
   listOfListsOfListsOfContent: [[[Content!]!]!]!
   recur(input: RecursiveInput!): Recursive
+  acceptsListOfListOfListsOfDates(datesss: [[[Date!]!]!]!): Boolean
 }
 
 type Mutation {

generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.go

@@ -55,15 +55,15 @@ func (v *ComplexInlineFragmentsConflictingStuffTopic) implementsGraphQLInterface
 // GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsConflictingStuffContent.
 func (v *ComplexInlineFragmentsConflictingStuffTopic) GetTypename() string { return v.Typename }
 
-func __unmarshalComplexInlineFragmentsConflictingStuffContent(v *ComplexInlineFragmentsConflictingStuffContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsConflictingStuffContent(b []byte, v *ComplexInlineFragmentsConflictingStuffContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -71,13 +71,13 @@ func __unmarshalComplexInlineFragmentsConflictingStuffContent(v *ComplexInlineFr
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsConflictingStuffArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsConflictingStuffVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsConflictingStuffTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -142,15 +142,15 @@ func (v *ComplexInlineFragmentsNestedStuffTopic) implementsGraphQLInterfaceCompl
 // GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffContent.
 func (v *ComplexInlineFragmentsNestedStuffTopic) GetTypename() string { return v.Typename }
 
-func __unmarshalComplexInlineFragmentsNestedStuffContent(v *ComplexInlineFragmentsNestedStuffContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsNestedStuffContent(b []byte, v *ComplexInlineFragmentsNestedStuffContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -158,13 +158,13 @@ func __unmarshalComplexInlineFragmentsNestedStuffContent(v *ComplexInlineFragmen
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsNestedStuffArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsNestedStuffVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsNestedStuffTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -182,6 +182,10 @@ type ComplexInlineFragmentsNestedStuffTopic struct {
 
 func (v *ComplexInlineFragmentsNestedStuffTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*ComplexInlineFragmentsNestedStuffTopic
 		Children []json.RawMessage `json:"children"`
@@ -195,15 +199,15 @@ func (v *ComplexInlineFragmentsNestedStuffTopic) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]ComplexInlineFragmentsNestedStuffTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal ComplexInlineFragmentsNestedStuffTopic.Children: %w", err)
@@ -229,6 +233,10 @@ type ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTop
 
 func (v *ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopic
 		Children []json.RawMessage `json:"children"`
@@ -242,15 +250,15 @@ func (v *ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParen
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopic.Children: %w", err)
@@ -344,15 +352,15 @@ func (v *ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParen
 	return v.Name
 }
 
-func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent(v *ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent(b []byte, v *ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -360,13 +368,13 @@ func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenArticleParentConte
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenArticleParentContentParentTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -447,15 +455,15 @@ func (v *ComplexInlineFragmentsNestedStuffTopicChildrenTopic) GetTypename() stri
 // GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffTopicChildrenContent.
 func (v *ComplexInlineFragmentsNestedStuffTopicChildrenTopic) GetId() testutil.ID { return v.Id }
 
-func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenContent(v *ComplexInlineFragmentsNestedStuffTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenContent(b []byte, v *ComplexInlineFragmentsNestedStuffTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -463,13 +471,13 @@ func __unmarshalComplexInlineFragmentsNestedStuffTopicChildrenContent(v *Complex
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsNestedStuffTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -565,15 +573,15 @@ func (v *ComplexInlineFragmentsRandomItemTopic) GetId() testutil.ID { return v.I
 // GetName is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
 func (v *ComplexInlineFragmentsRandomItemTopic) GetName() string { return v.Name }
 
-func __unmarshalComplexInlineFragmentsRandomItemContent(v *ComplexInlineFragmentsRandomItemContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsRandomItemContent(b []byte, v *ComplexInlineFragmentsRandomItemContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -581,13 +589,13 @@ func __unmarshalComplexInlineFragmentsRandomItemContent(v *ComplexInlineFragment
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsRandomItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsRandomItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsRandomItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -721,15 +729,15 @@ func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetName() string { return v.N
 // GetOtherName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
 func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetOtherName() string { return v.OtherName }
 
-func __unmarshalComplexInlineFragmentsRepeatedStuffContent(v *ComplexInlineFragmentsRepeatedStuffContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalComplexInlineFragmentsRepeatedStuffContent(b []byte, v *ComplexInlineFragmentsRepeatedStuffContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -737,13 +745,13 @@ func __unmarshalComplexInlineFragmentsRepeatedStuffContent(v *ComplexInlineFragm
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ComplexInlineFragmentsRepeatedStuffArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ComplexInlineFragmentsRepeatedStuffVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ComplexInlineFragmentsRepeatedStuffTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -789,6 +797,10 @@ type ComplexInlineFragmentsResponse struct {
 
 func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*ComplexInlineFragmentsResponse
 		RandomItem       json.RawMessage `json:"randomItem"`
@@ -805,10 +817,10 @@ func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalComplexInlineFragmentsRandomItemContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal ComplexInlineFragmentsResponse.RandomItem: %w", err)
@@ -816,10 +828,10 @@ func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RepeatedStuff
-		raw := firstPass.RepeatedStuff
+		dst := &v.RepeatedStuff
+		src := firstPass.RepeatedStuff
 		err = __unmarshalComplexInlineFragmentsRepeatedStuffContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal ComplexInlineFragmentsResponse.RepeatedStuff: %w", err)
@@ -827,10 +839,10 @@ func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.ConflictingStuff
-		raw := firstPass.ConflictingStuff
+		dst := &v.ConflictingStuff
+		src := firstPass.ConflictingStuff
 		err = __unmarshalComplexInlineFragmentsConflictingStuffContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal ComplexInlineFragmentsResponse.ConflictingStuff: %w", err)
@@ -838,10 +850,10 @@ func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.NestedStuff
-		raw := firstPass.NestedStuff
+		dst := &v.NestedStuff
+		src := firstPass.NestedStuff
 		err = __unmarshalComplexInlineFragmentsNestedStuffContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal ComplexInlineFragmentsResponse.NestedStuff: %w", err)

generate/testdata/snapshots/TestGenerate-ComplexNamedFragments.graphql-ComplexNamedFragments.graphql.go

@@ -17,6 +17,10 @@ type ComplexNamedFragmentsResponse struct {
 
 func (v *ComplexNamedFragmentsResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*ComplexNamedFragmentsResponse
 		graphql.NoUnmarshalJSON
@@ -77,15 +81,15 @@ func (v *ContentFieldsTopic) GetName() string { return v.Name }
 // GetUrl is a part of, and documented with, the interface ContentFields.
 func (v *ContentFieldsTopic) GetUrl() string { return v.Url }
 
-func __unmarshalContentFields(v *ContentFields, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalContentFields(b []byte, v *ContentFields) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -93,13 +97,13 @@ func __unmarshalContentFields(v *ContentFields, m json.RawMessage) error {
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ContentFieldsArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ContentFieldsVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ContentFieldsTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -148,6 +152,10 @@ type InnerQueryFragment struct {
 
 func (v *InnerQueryFragment) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragment
 		RandomItem json.RawMessage `json:"randomItem"`
@@ -163,10 +171,10 @@ func (v *InnerQueryFragment) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalInnerQueryFragmentRandomItemContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InnerQueryFragment.RandomItem: %w", err)
@@ -174,10 +182,10 @@ func (v *InnerQueryFragment) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomLeaf
-		raw := firstPass.RandomLeaf
+		dst := &v.RandomLeaf
+		src := firstPass.RandomLeaf
 		err = __unmarshalInnerQueryFragmentRandomLeafLeafContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InnerQueryFragment.RandomLeaf: %w", err)
@@ -185,10 +193,10 @@ func (v *InnerQueryFragment) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.OtherLeaf
-		raw := firstPass.OtherLeaf
+		dst := &v.OtherLeaf
+		src := firstPass.OtherLeaf
 		err = __unmarshalInnerQueryFragmentOtherLeafLeafContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InnerQueryFragment.OtherLeaf: %w", err)
@@ -205,6 +213,10 @@ type InnerQueryFragmentOtherLeafArticle struct {
 
 func (v *InnerQueryFragmentOtherLeafArticle) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentOtherLeafArticle
 		graphql.NoUnmarshalJSON
@@ -250,15 +262,15 @@ func (v *InnerQueryFragmentOtherLeafVideo) implementsGraphQLInterfaceInnerQueryF
 // GetTypename is a part of, and documented with, the interface InnerQueryFragmentOtherLeafLeafContent.
 func (v *InnerQueryFragmentOtherLeafVideo) GetTypename() string { return v.Typename }
 
-func __unmarshalInnerQueryFragmentOtherLeafLeafContent(v *InnerQueryFragmentOtherLeafLeafContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInnerQueryFragmentOtherLeafLeafContent(b []byte, v *InnerQueryFragmentOtherLeafLeafContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -266,10 +278,10 @@ func __unmarshalInnerQueryFragmentOtherLeafLeafContent(v *InnerQueryFragmentOthe
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InnerQueryFragmentOtherLeafArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InnerQueryFragmentOtherLeafVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing LeafContent.__typename")
@@ -288,6 +300,10 @@ type InnerQueryFragmentOtherLeafVideo struct {
 
 func (v *InnerQueryFragmentOtherLeafVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentOtherLeafVideo
 		graphql.NoUnmarshalJSON
@@ -323,6 +339,10 @@ type InnerQueryFragmentRandomItemArticle struct {
 
 func (v *InnerQueryFragmentRandomItemArticle) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentRandomItemArticle
 		graphql.NoUnmarshalJSON
@@ -401,15 +421,15 @@ func (v *InnerQueryFragmentRandomItemTopic) GetId() testutil.ID { return v.Id }
 // GetName is a part of, and documented with, the interface InnerQueryFragmentRandomItemContent.
 func (v *InnerQueryFragmentRandomItemTopic) GetName() string { return v.Name }
 
-func __unmarshalInnerQueryFragmentRandomItemContent(v *InnerQueryFragmentRandomItemContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInnerQueryFragmentRandomItemContent(b []byte, v *InnerQueryFragmentRandomItemContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -417,13 +437,13 @@ func __unmarshalInnerQueryFragmentRandomItemContent(v *InnerQueryFragmentRandomI
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InnerQueryFragmentRandomItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InnerQueryFragmentRandomItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InnerQueryFragmentRandomItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -444,6 +464,10 @@ type InnerQueryFragmentRandomItemTopic struct {
 
 func (v *InnerQueryFragmentRandomItemTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentRandomItemTopic
 		graphql.NoUnmarshalJSON
@@ -475,6 +499,10 @@ type InnerQueryFragmentRandomItemVideo struct {
 
 func (v *InnerQueryFragmentRandomItemVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentRandomItemVideo
 		graphql.NoUnmarshalJSON
@@ -507,6 +535,10 @@ type InnerQueryFragmentRandomLeafArticle struct {
 
 func (v *InnerQueryFragmentRandomLeafArticle) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentRandomLeafArticle
 		graphql.NoUnmarshalJSON
@@ -552,15 +584,15 @@ func (v *InnerQueryFragmentRandomLeafVideo) implementsGraphQLInterfaceInnerQuery
 // GetTypename is a part of, and documented with, the interface InnerQueryFragmentRandomLeafLeafContent.
 func (v *InnerQueryFragmentRandomLeafVideo) GetTypename() string { return v.Typename }
 
-func __unmarshalInnerQueryFragmentRandomLeafLeafContent(v *InnerQueryFragmentRandomLeafLeafContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInnerQueryFragmentRandomLeafLeafContent(b []byte, v *InnerQueryFragmentRandomLeafLeafContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -568,10 +600,10 @@ func __unmarshalInnerQueryFragmentRandomLeafLeafContent(v *InnerQueryFragmentRan
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InnerQueryFragmentRandomLeafArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InnerQueryFragmentRandomLeafVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing LeafContent.__typename")
@@ -591,6 +623,10 @@ type InnerQueryFragmentRandomLeafVideo struct {
 
 func (v *InnerQueryFragmentRandomLeafVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InnerQueryFragmentRandomLeafVideo
 		graphql.NoUnmarshalJSON
@@ -637,6 +673,10 @@ type MoreVideoFieldsParentTopic struct {
 
 func (v *MoreVideoFieldsParentTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*MoreVideoFieldsParentTopic
 		Children []json.RawMessage `json:"children"`
@@ -656,15 +696,15 @@ func (v *MoreVideoFieldsParentTopic) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]MoreVideoFieldsParentTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalMoreVideoFieldsParentTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal MoreVideoFieldsParentTopic.Children: %w", err)
@@ -712,15 +752,15 @@ func (v *MoreVideoFieldsParentTopicChildrenTopic) implementsGraphQLInterfaceMore
 // GetTypename is a part of, and documented with, the interface MoreVideoFieldsParentTopicChildrenContent.
 func (v *MoreVideoFieldsParentTopicChildrenTopic) GetTypename() *string { return v.Typename }
 
-func __unmarshalMoreVideoFieldsParentTopicChildrenContent(v *MoreVideoFieldsParentTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalMoreVideoFieldsParentTopicChildrenContent(b []byte, v *MoreVideoFieldsParentTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -728,13 +768,13 @@ func __unmarshalMoreVideoFieldsParentTopicChildrenContent(v *MoreVideoFieldsPare
 	switch tn.TypeName {
 	case "Article":
 		*v = new(MoreVideoFieldsParentTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(MoreVideoFieldsParentTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(MoreVideoFieldsParentTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -757,6 +797,10 @@ type MoreVideoFieldsParentTopicChildrenVideo struct {
 
 func (v *MoreVideoFieldsParentTopicChildrenVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*MoreVideoFieldsParentTopicChildrenVideo
 		graphql.NoUnmarshalJSON
@@ -786,6 +830,10 @@ type QueryFragment struct {
 
 func (v *QueryFragment) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*QueryFragment
 		graphql.NoUnmarshalJSON
@@ -818,6 +866,10 @@ type VideoFields struct {
 
 func (v *VideoFields) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*VideoFields
 		graphql.NoUnmarshalJSON

generate/testdata/snapshots/TestGenerate-CustomMarshal.graphql-CustomMarshal.graphql.go

@@ -0,0 +1,118 @@
+package test
+
+// Code generated by github.com/Khan/genqlient, DO NOT EDIT.
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"github.com/Khan/genqlient/graphql"
+	"github.com/Khan/genqlient/internal/testutil"
+)
+
+// CustomMarshalResponse is returned by CustomMarshal on success.
+type CustomMarshalResponse struct {
+	UsersBornOn []CustomMarshalUsersBornOnUser `json:"usersBornOn"`
+}
+
+// CustomMarshalUsersBornOnUser includes the requested fields of the GraphQL type User.
+// The GraphQL type's documentation follows.
+//
+// A User is a user!
+type CustomMarshalUsersBornOnUser struct {
+	// id is the user's ID.
+	//
+	// It is stable, unique, and opaque, like all good IDs.
+	Id        testutil.ID `json:"id"`
+	Birthdate time.Time   `json:"-"`
+}
+
+func (v *CustomMarshalUsersBornOnUser) UnmarshalJSON(b []byte) error {
+
+	if string(b) == "null" {
+		return nil
+	}
+
+	var firstPass struct {
+		*CustomMarshalUsersBornOnUser
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoUnmarshalJSON
+	}
+	firstPass.CustomMarshalUsersBornOnUser = v
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		dst := &v.Birthdate
+		src := firstPass.Birthdate
+		err = testutil.UnmarshalDate(
+			src, dst)
+		if err != nil {
+			return fmt.Errorf(
+				"Unable to unmarshal CustomMarshalUsersBornOnUser.Birthdate: %w", err)
+		}
+	}
+	return nil
+}
+
+// __CustomMarshalInput is used internally by genqlient
+type __CustomMarshalInput struct {
+	Date time.Time `json:"-"`
+}
+
+func (v *__CustomMarshalInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*__CustomMarshalInput
+		Date json.RawMessage `json:"date"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.__CustomMarshalInput = v
+
+	{
+
+		dst := &fullObject.Date
+		src := v.Date
+		var err error
+		*dst, err = testutil.MarshalDate(
+			&src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal __CustomMarshalInput.Date: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
+}
+
+func CustomMarshal(
+	client graphql.Client,
+	date time.Time,
+) (*CustomMarshalResponse, error) {
+	__input := __CustomMarshalInput{
+		Date: date,
+	}
+	var err error
+
+	var retval CustomMarshalResponse
+	err = client.MakeRequest(
+		nil,
+		"CustomMarshal",
+		`
+query CustomMarshal ($date: Date!) {
+	usersBornOn(date: $date) {
+		id
+		birthdate
+	}
+}
+`,
+		&retval,
+		&__input,
+	)
+	return &retval, err
+}
+

generate/testdata/snapshots/TestGenerate-CustomMarshal.graphql-CustomMarshal.graphql.json

@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "CustomMarshal",
+      "query": "\nquery CustomMarshal ($date: Date!) {\n\tusersBornOn(date: $date) {\n\t\tid\n\t\tbirthdate\n\t}\n}\n",
+      "sourceLocation": "testdata/queries/CustomMarshal.graphql"
+    }
+  ]
+}

generate/testdata/snapshots/TestGenerate-CustomMarshalSlice.graphql-CustomMarshalSlice.graphql.go

@@ -0,0 +1,126 @@
+package test
+
+// Code generated by github.com/Khan/genqlient, DO NOT EDIT.
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"github.com/Khan/genqlient/graphql"
+	"github.com/Khan/genqlient/internal/testutil"
+)
+
+// CustomMarshalSliceResponse is returned by CustomMarshalSlice on success.
+type CustomMarshalSliceResponse struct {
+	AcceptsListOfListOfListsOfDates bool `json:"acceptsListOfListOfListsOfDates"`
+	WithPointer                     bool `json:"withPointer"`
+}
+
+// __CustomMarshalSliceInput is used internally by genqlient
+type __CustomMarshalSliceInput struct {
+	Datesss  [][][]time.Time  `json:"-"`
+	Datesssp [][][]*time.Time `json:"-"`
+}
+
+func (v *__CustomMarshalSliceInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*__CustomMarshalSliceInput
+		Datesss  [][][]json.RawMessage `json:"datesss"`
+		Datesssp [][][]json.RawMessage `json:"datesssp"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.__CustomMarshalSliceInput = v
+
+	{
+
+		dst := &fullObject.Datesss
+		src := v.Datesss
+		*dst = make(
+			[][][]json.RawMessage,
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
+			*dst = make(
+				[][]json.RawMessage,
+				len(src))
+			for i, src := range src {
+				dst := &(*dst)[i]
+				*dst = make(
+					[]json.RawMessage,
+					len(src))
+				for i, src := range src {
+					dst := &(*dst)[i]
+					var err error
+					*dst, err = testutil.MarshalDate(
+						&src)
+					if err != nil {
+						return nil, fmt.Errorf(
+							"Unable to marshal __CustomMarshalSliceInput.Datesss: %w", err)
+					}
+				}
+			}
+		}
+	}
+	{
+
+		dst := &fullObject.Datesssp
+		src := v.Datesssp
+		*dst = make(
+			[][][]json.RawMessage,
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
+			*dst = make(
+				[][]json.RawMessage,
+				len(src))
+			for i, src := range src {
+				dst := &(*dst)[i]
+				*dst = make(
+					[]json.RawMessage,
+					len(src))
+				for i, src := range src {
+					dst := &(*dst)[i]
+					var err error
+					*dst, err = testutil.MarshalDate(
+						src)
+					if err != nil {
+						return nil, fmt.Errorf(
+							"Unable to marshal __CustomMarshalSliceInput.Datesssp: %w", err)
+					}
+				}
+			}
+		}
+	}
+
+	return json.Marshal(&fullObject)
+}
+
+func CustomMarshalSlice(
+	client graphql.Client,
+	datesss [][][]time.Time,
+	datesssp [][][]*time.Time,
+) (*CustomMarshalSliceResponse, error) {
+	__input := __CustomMarshalSliceInput{
+		Datesss:  datesss,
+		Datesssp: datesssp,
+	}
+	var err error
+
+	var retval CustomMarshalSliceResponse
+	err = client.MakeRequest(
+		nil,
+		"CustomMarshalSlice",
+		`
+query CustomMarshalSlice ($datesss: [[[Date!]!]!]!, $datesssp: [[[Date!]!]!]!) {
+	acceptsListOfListOfListsOfDates(datesss: $datesss)
+	withPointer: acceptsListOfListOfListsOfDates(datesss: $datesssp)
+}
+`,
+		&retval,
+		&__input,
+	)
+	return &retval, err
+}
+

generate/testdata/snapshots/TestGenerate-CustomMarshalSlice.graphql-CustomMarshalSlice.graphql.json

@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "CustomMarshalSlice",
+      "query": "\nquery CustomMarshalSlice ($datesss: [[[Date!]!]!]!, $datesssp: [[[Date!]!]!]!) {\n\tacceptsListOfListOfListsOfDates(datesss: $datesss)\n\twithPointer: acceptsListOfListOfListsOfDates(datesss: $datesssp)\n}\n",
+      "sourceLocation": "testdata/queries/CustomMarshalSlice.graphql"
+    }
+  ]
+}

generate/testdata/snapshots/TestGenerate-InputObject.graphql-InputObject.graphql.go

@@ -3,6 +3,10 @@ package test
 // Code generated by github.com/Khan/genqlient, DO NOT EDIT.
 
 import (
+	"encoding/json"
+	"fmt"
+	"time"
+
 	"github.com/Khan/genqlient/graphql"
 	"github.com/Khan/genqlient/internal/testutil"
 )
@@ -54,6 +58,32 @@ type UserQueryInput struct {
 	Role       Role             `json:"role"`
 	Names      []string         `json:"names"`
 	HasPokemon testutil.Pokemon `json:"hasPokemon"`
+	Birthdate  time.Time        `json:"-"`
+}
+
+func (v *UserQueryInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*UserQueryInput
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.UserQueryInput = v
+
+	{
+
+		dst := &fullObject.Birthdate
+		src := v.Birthdate
+		var err error
+		*dst, err = testutil.MarshalDate(
+			&src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal UserQueryInput.Birthdate: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
 }
 
 // __InputObjectQueryInput is used internally by genqlient

generate/testdata/snapshots/TestGenerate-InterfaceListField.graphql-InterfaceListField.graphql.go

@@ -26,6 +26,10 @@ type InterfaceListFieldRootTopic struct {
 
 func (v *InterfaceListFieldRootTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceListFieldRootTopic
 		Children []json.RawMessage `json:"children"`
@@ -39,15 +43,15 @@ func (v *InterfaceListFieldRootTopic) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]InterfaceListFieldRootTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalInterfaceListFieldRootTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal InterfaceListFieldRootTopic.Children: %w", err)
@@ -123,15 +127,15 @@ func (v *InterfaceListFieldRootTopicChildrenTopic) GetId() testutil.ID { return
 // GetName is a part of, and documented with, the interface InterfaceListFieldRootTopicChildrenContent.
 func (v *InterfaceListFieldRootTopicChildrenTopic) GetName() string { return v.Name }
 
-func __unmarshalInterfaceListFieldRootTopicChildrenContent(v *InterfaceListFieldRootTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceListFieldRootTopicChildrenContent(b []byte, v *InterfaceListFieldRootTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -139,13 +143,13 @@ func __unmarshalInterfaceListFieldRootTopicChildrenContent(v *InterfaceListField
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceListFieldRootTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceListFieldRootTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceListFieldRootTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -181,6 +185,10 @@ type InterfaceListFieldWithPointerTopic struct {
 
 func (v *InterfaceListFieldWithPointerTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceListFieldWithPointerTopic
 		Children []json.RawMessage `json:"children"`
@@ -194,15 +202,15 @@ func (v *InterfaceListFieldWithPointerTopic) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]InterfaceListFieldWithPointerTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal InterfaceListFieldWithPointerTopic.Children: %w", err)
@@ -278,15 +286,15 @@ func (v *InterfaceListFieldWithPointerTopicChildrenTopic) GetId() testutil.ID {
 // GetName is a part of, and documented with, the interface InterfaceListFieldWithPointerTopicChildrenContent.
 func (v *InterfaceListFieldWithPointerTopicChildrenTopic) GetName() string { return v.Name }
 
-func __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(v *InterfaceListFieldWithPointerTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(b []byte, v *InterfaceListFieldWithPointerTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -294,13 +302,13 @@ func __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(v *InterfaceLi
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceListFieldWithPointerTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceListFieldWithPointerTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceListFieldWithPointerTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")

generate/testdata/snapshots/TestGenerate-InterfaceListOfListsOfListsField.graphql-InterfaceListOfListsOfListsField.graphql.go

@@ -86,15 +86,15 @@ func (v *InterfaceListOfListOfListsFieldListOfListsOfListsOfContentTopic) GetNam
 	return v.Name
 }
 
-func __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(v *InterfaceListOfListOfListsFieldListOfListsOfListsOfContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(b []byte, v *InterfaceListOfListOfListsFieldListOfListsOfListsOfContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -102,13 +102,13 @@ func __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(v *In
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceListOfListOfListsFieldListOfListsOfListsOfContentArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceListOfListOfListsFieldListOfListsOfListsOfContentVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceListOfListOfListsFieldListOfListsOfListsOfContentTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -150,6 +150,10 @@ type InterfaceListOfListOfListsFieldResponse struct {
 
 func (v *InterfaceListOfListOfListsFieldResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceListOfListOfListsFieldResponse
 		ListOfListsOfListsOfContent [][][]json.RawMessage `json:"listOfListsOfListsOfContent"`
@@ -164,25 +168,25 @@ func (v *InterfaceListOfListOfListsFieldResponse) UnmarshalJSON(b []byte) error
 	}
 
 	{
-		target := &v.ListOfListsOfListsOfContent
-		raw := firstPass.ListOfListsOfListsOfContent
-		*target = make(
+		dst := &v.ListOfListsOfListsOfContent
+		src := firstPass.ListOfListsOfListsOfContent
+		*dst = make(
 			[][][]InterfaceListOfListOfListsFieldListOfListsOfListsOfContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
-			*target = make(
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
+			*dst = make(
 				[][]InterfaceListOfListOfListsFieldListOfListsOfListsOfContent,
-				len(raw))
-			for i, raw := range raw {
-				target := &(*target)[i]
-				*target = make(
+				len(src))
+			for i, src := range src {
+				dst := &(*dst)[i]
+				*dst = make(
 					[]InterfaceListOfListOfListsFieldListOfListsOfListsOfContent,
-					len(raw))
-				for i, raw := range raw {
-					target := &(*target)[i]
+					len(src))
+				for i, src := range src {
+					dst := &(*dst)[i]
 					err = __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(
-						target, raw)
+						src, dst)
 					if err != nil {
 						return fmt.Errorf(
 							"Unable to unmarshal InterfaceListOfListOfListsFieldResponse.ListOfListsOfListsOfContent: %w", err)
@@ -193,26 +197,26 @@ func (v *InterfaceListOfListOfListsFieldResponse) UnmarshalJSON(b []byte) error
 	}
 
 	{
-		target := &v.WithPointer
-		raw := firstPass.WithPointer
-		*target = make(
+		dst := &v.WithPointer
+		src := firstPass.WithPointer
+		*dst = make(
 			[][][]*InterfaceListOfListOfListsFieldWithPointerContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
-			*target = make(
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
+			*dst = make(
 				[][]*InterfaceListOfListOfListsFieldWithPointerContent,
-				len(raw))
-			for i, raw := range raw {
-				target := &(*target)[i]
-				*target = make(
+				len(src))
+			for i, src := range src {
+				dst := &(*dst)[i]
+				*dst = make(
 					[]*InterfaceListOfListOfListsFieldWithPointerContent,
-					len(raw))
-				for i, raw := range raw {
-					target := &(*target)[i]
-					*target = new(InterfaceListOfListOfListsFieldWithPointerContent)
+					len(src))
+				for i, src := range src {
+					dst := &(*dst)[i]
+					*dst = new(InterfaceListOfListOfListsFieldWithPointerContent)
 					err = __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(
-						*target, raw)
+						src, *dst)
 					if err != nil {
 						return fmt.Errorf(
 							"Unable to unmarshal InterfaceListOfListOfListsFieldResponse.WithPointer: %w", err)
@@ -290,15 +294,15 @@ func (v *InterfaceListOfListOfListsFieldWithPointerTopic) GetId() *testutil.ID {
 // GetName is a part of, and documented with, the interface InterfaceListOfListOfListsFieldWithPointerContent.
 func (v *InterfaceListOfListOfListsFieldWithPointerTopic) GetName() *string { return v.Name }
 
-func __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(v *InterfaceListOfListOfListsFieldWithPointerContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(b []byte, v *InterfaceListOfListOfListsFieldWithPointerContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -306,13 +310,13 @@ func __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(v *InterfaceLi
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceListOfListOfListsFieldWithPointerArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceListOfListOfListsFieldWithPointerVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceListOfListOfListsFieldWithPointerTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")

generate/testdata/snapshots/TestGenerate-InterfaceNesting.graphql-InterfaceNesting.graphql.go

@@ -24,6 +24,10 @@ type InterfaceNestingRootTopic struct {
 
 func (v *InterfaceNestingRootTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceNestingRootTopic
 		Children []json.RawMessage `json:"children"`
@@ -37,15 +41,15 @@ func (v *InterfaceNestingRootTopic) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]InterfaceNestingRootTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalInterfaceNestingRootTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal InterfaceNestingRootTopic.Children: %w", err)
@@ -127,15 +131,15 @@ func (v *InterfaceNestingRootTopicChildrenTopic) GetParent() InterfaceNestingRoo
 	return v.Parent
 }
 
-func __unmarshalInterfaceNestingRootTopicChildrenContent(v *InterfaceNestingRootTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceNestingRootTopicChildrenContent(b []byte, v *InterfaceNestingRootTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -143,13 +147,13 @@ func __unmarshalInterfaceNestingRootTopicChildrenContent(v *InterfaceNestingRoot
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceNestingRootTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceNestingRootTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceNestingRootTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -168,6 +172,10 @@ type InterfaceNestingRootTopicChildrenContentParentTopic struct {
 
 func (v *InterfaceNestingRootTopicChildrenContentParentTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceNestingRootTopicChildrenContentParentTopic
 		Children []json.RawMessage `json:"children"`
@@ -181,15 +189,15 @@ func (v *InterfaceNestingRootTopicChildrenContentParentTopic) UnmarshalJSON(b []
 	}
 
 	{
-		target := &v.Children
-		raw := firstPass.Children
-		*target = make(
+		dst := &v.Children
+		src := firstPass.Children
+		*dst = make(
 			[]InterfaceNestingRootTopicChildrenContentParentTopicChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalInterfaceNestingRootTopicChildrenContentParentTopicChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal InterfaceNestingRootTopicChildrenContentParentTopic.Children: %w", err)
@@ -265,15 +273,15 @@ func (v *InterfaceNestingRootTopicChildrenContentParentTopicChildrenTopic) GetId
 	return v.Id
 }
 
-func __unmarshalInterfaceNestingRootTopicChildrenContentParentTopicChildrenContent(v *InterfaceNestingRootTopicChildrenContentParentTopicChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceNestingRootTopicChildrenContentParentTopicChildrenContent(b []byte, v *InterfaceNestingRootTopicChildrenContentParentTopicChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -281,13 +289,13 @@ func __unmarshalInterfaceNestingRootTopicChildrenContentParentTopicChildrenConte
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceNestingRootTopicChildrenContentParentTopicChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceNestingRootTopicChildrenContentParentTopicChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceNestingRootTopicChildrenContentParentTopicChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")

generate/testdata/snapshots/TestGenerate-InterfaceNoFragments.graphql-InterfaceNoFragments.graphql.go

@@ -76,15 +76,15 @@ func (v *InterfaceNoFragmentsQueryRandomItemTopic) GetId() testutil.ID { return
 // GetName is a part of, and documented with, the interface InterfaceNoFragmentsQueryRandomItemContent.
 func (v *InterfaceNoFragmentsQueryRandomItemTopic) GetName() string { return v.Name }
 
-func __unmarshalInterfaceNoFragmentsQueryRandomItemContent(v *InterfaceNoFragmentsQueryRandomItemContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceNoFragmentsQueryRandomItemContent(b []byte, v *InterfaceNoFragmentsQueryRandomItemContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -92,13 +92,13 @@ func __unmarshalInterfaceNoFragmentsQueryRandomItemContent(v *InterfaceNoFragmen
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceNoFragmentsQueryRandomItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceNoFragmentsQueryRandomItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryRandomItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -196,15 +196,15 @@ func (v *InterfaceNoFragmentsQueryRandomItemWithTypeNameTopic) GetId() testutil.
 // GetName is a part of, and documented with, the interface InterfaceNoFragmentsQueryRandomItemWithTypeNameContent.
 func (v *InterfaceNoFragmentsQueryRandomItemWithTypeNameTopic) GetName() string { return v.Name }
 
-func __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(v *InterfaceNoFragmentsQueryRandomItemWithTypeNameContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(b []byte, v *InterfaceNoFragmentsQueryRandomItemWithTypeNameContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -212,13 +212,13 @@ func __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(v *Interf
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceNoFragmentsQueryRandomItemWithTypeNameArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceNoFragmentsQueryRandomItemWithTypeNameVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryRandomItemWithTypeNameTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -254,6 +254,10 @@ type InterfaceNoFragmentsQueryResponse struct {
 
 func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*InterfaceNoFragmentsQueryResponse
 		RandomItem             json.RawMessage `json:"randomItem"`
@@ -269,10 +273,10 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalInterfaceNoFragmentsQueryRandomItemContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.RandomItem: %w", err)
@@ -280,10 +284,10 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItemWithTypeName
-		raw := firstPass.RandomItemWithTypeName
+		dst := &v.RandomItemWithTypeName
+		src := firstPass.RandomItemWithTypeName
 		err = __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.RandomItemWithTypeName: %w", err)
@@ -291,11 +295,11 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.WithPointer
-		raw := firstPass.WithPointer
-		*target = new(InterfaceNoFragmentsQueryWithPointerContent)
+		dst := &v.WithPointer
+		src := firstPass.WithPointer
+		*dst = new(InterfaceNoFragmentsQueryWithPointerContent)
 		err = __unmarshalInterfaceNoFragmentsQueryWithPointerContent(
-			*target, raw)
+			src, *dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.WithPointer: %w", err)
@@ -377,15 +381,15 @@ func (v *InterfaceNoFragmentsQueryWithPointerTopic) GetId() *testutil.ID { retur
 // GetName is a part of, and documented with, the interface InterfaceNoFragmentsQueryWithPointerContent.
 func (v *InterfaceNoFragmentsQueryWithPointerTopic) GetName() *string { return v.Name }
 
-func __unmarshalInterfaceNoFragmentsQueryWithPointerContent(v *InterfaceNoFragmentsQueryWithPointerContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalInterfaceNoFragmentsQueryWithPointerContent(b []byte, v *InterfaceNoFragmentsQueryWithPointerContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -393,13 +397,13 @@ func __unmarshalInterfaceNoFragmentsQueryWithPointerContent(v *InterfaceNoFragme
 	switch tn.TypeName {
 	case "Article":
 		*v = new(InterfaceNoFragmentsQueryWithPointerArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(InterfaceNoFragmentsQueryWithPointerVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryWithPointerTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")

generate/testdata/snapshots/TestGenerate-Omitempty.graphql-Omitempty.graphql.go

@@ -3,6 +3,8 @@ package test
 // Code generated by github.com/Khan/genqlient, DO NOT EDIT.
 
 import (
+	"encoding/json"
+	"fmt"
 	"time"
 
 	"github.com/Khan/genqlient/graphql"
@@ -70,6 +72,32 @@ type UserQueryInput struct {
 	Role       Role             `json:"role"`
 	Names      []string         `json:"names"`
 	HasPokemon testutil.Pokemon `json:"hasPokemon"`
+	Birthdate  time.Time        `json:"-"`
+}
+
+func (v *UserQueryInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*UserQueryInput
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.UserQueryInput = v
+
+	{
+
+		dst := &fullObject.Birthdate
+		src := v.Birthdate
+		var err error
+		*dst, err = testutil.MarshalDate(
+			&src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal UserQueryInput.Birthdate: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
 }
 
 // __OmitEmptyQueryInput is used internally by genqlient

generate/testdata/snapshots/TestGenerate-Pointers.graphql-Pointers.graphql.go

@@ -3,6 +3,8 @@ package test
 // Code generated by github.com/Khan/genqlient, DO NOT EDIT.
 
 import (
+	"encoding/json"
+	"fmt"
 	"time"
 
 	"github.com/Khan/genqlient/graphql"
@@ -77,6 +79,32 @@ type UserQueryInput struct {
 	Role       *Role             `json:"role"`
 	Names      []*string         `json:"names"`
 	HasPokemon *testutil.Pokemon `json:"hasPokemon"`
+	Birthdate  *time.Time        `json:"-"`
+}
+
+func (v *UserQueryInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*UserQueryInput
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.UserQueryInput = v
+
+	{
+
+		dst := &fullObject.Birthdate
+		src := v.Birthdate
+		var err error
+		*dst, err = testutil.MarshalDate(
+			src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal UserQueryInput.Birthdate: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
 }
 
 // __PointersQueryInput is used internally by genqlient

generate/testdata/snapshots/TestGenerate-PointersInline.graphql-PointersInline.graphql.go

@@ -3,6 +3,8 @@ package test
 // Code generated by github.com/Khan/genqlient, DO NOT EDIT.
 
 import (
+	"encoding/json"
+	"fmt"
 	"time"
 
 	"github.com/Khan/genqlient/graphql"
@@ -77,6 +79,32 @@ type UserQueryInput struct {
 	Role       Role             `json:"role"`
 	Names      []string         `json:"names"`
 	HasPokemon testutil.Pokemon `json:"hasPokemon"`
+	Birthdate  time.Time        `json:"-"`
+}
+
+func (v *UserQueryInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*UserQueryInput
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.UserQueryInput = v
+
+	{
+
+		dst := &fullObject.Birthdate
+		src := v.Birthdate
+		var err error
+		*dst, err = testutil.MarshalDate(
+			&src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal UserQueryInput.Birthdate: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
 }
 
 // __PointersQueryInput is used internally by genqlient

generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.go

@@ -77,15 +77,15 @@ func (v *SimpleInlineFragmentRandomItemTopic) GetId() testutil.ID { return v.Id
 // GetName is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
 func (v *SimpleInlineFragmentRandomItemTopic) GetName() string { return v.Name }
 
-func __unmarshalSimpleInlineFragmentRandomItemContent(v *SimpleInlineFragmentRandomItemContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalSimpleInlineFragmentRandomItemContent(b []byte, v *SimpleInlineFragmentRandomItemContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -93,13 +93,13 @@ func __unmarshalSimpleInlineFragmentRandomItemContent(v *SimpleInlineFragmentRan
 	switch tn.TypeName {
 	case "Article":
 		*v = new(SimpleInlineFragmentRandomItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(SimpleInlineFragmentRandomItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(SimpleInlineFragmentRandomItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -133,6 +133,10 @@ type SimpleInlineFragmentResponse struct {
 
 func (v *SimpleInlineFragmentResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*SimpleInlineFragmentResponse
 		RandomItem json.RawMessage `json:"randomItem"`
@@ -146,10 +150,10 @@ func (v *SimpleInlineFragmentResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalSimpleInlineFragmentRandomItemContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal SimpleInlineFragmentResponse.RandomItem: %w", err)

generate/testdata/snapshots/TestGenerate-SimpleNamedFragment.graphql-SimpleNamedFragment.graphql.go

@@ -76,15 +76,15 @@ func (v *SimpleNamedFragmentRandomItemTopic) GetId() testutil.ID { return v.Id }
 // GetName is a part of, and documented with, the interface SimpleNamedFragmentRandomItemContent.
 func (v *SimpleNamedFragmentRandomItemTopic) GetName() string { return v.Name }
 
-func __unmarshalSimpleNamedFragmentRandomItemContent(v *SimpleNamedFragmentRandomItemContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalSimpleNamedFragmentRandomItemContent(b []byte, v *SimpleNamedFragmentRandomItemContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -92,13 +92,13 @@ func __unmarshalSimpleNamedFragmentRandomItemContent(v *SimpleNamedFragmentRando
 	switch tn.TypeName {
 	case "Article":
 		*v = new(SimpleNamedFragmentRandomItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(SimpleNamedFragmentRandomItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(SimpleNamedFragmentRandomItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -127,6 +127,10 @@ type SimpleNamedFragmentRandomItemVideo struct {
 
 func (v *SimpleNamedFragmentRandomItemVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*SimpleNamedFragmentRandomItemVideo
 		graphql.NoUnmarshalJSON
@@ -177,15 +181,15 @@ func (v *SimpleNamedFragmentRandomLeafVideo) implementsGraphQLInterfaceSimpleNam
 // GetTypename is a part of, and documented with, the interface SimpleNamedFragmentRandomLeafLeafContent.
 func (v *SimpleNamedFragmentRandomLeafVideo) GetTypename() string { return v.Typename }
 
-func __unmarshalSimpleNamedFragmentRandomLeafLeafContent(v *SimpleNamedFragmentRandomLeafLeafContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalSimpleNamedFragmentRandomLeafLeafContent(b []byte, v *SimpleNamedFragmentRandomLeafLeafContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -193,10 +197,10 @@ func __unmarshalSimpleNamedFragmentRandomLeafLeafContent(v *SimpleNamedFragmentR
 	switch tn.TypeName {
 	case "Article":
 		*v = new(SimpleNamedFragmentRandomLeafArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(SimpleNamedFragmentRandomLeafVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing LeafContent.__typename")
@@ -214,6 +218,10 @@ type SimpleNamedFragmentRandomLeafVideo struct {
 
 func (v *SimpleNamedFragmentRandomLeafVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*SimpleNamedFragmentRandomLeafVideo
 		graphql.NoUnmarshalJSON
@@ -241,6 +249,10 @@ type SimpleNamedFragmentResponse struct {
 
 func (v *SimpleNamedFragmentResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*SimpleNamedFragmentResponse
 		RandomItem json.RawMessage `json:"randomItem"`
@@ -255,10 +267,10 @@ func (v *SimpleNamedFragmentResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalSimpleNamedFragmentRandomItemContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal SimpleNamedFragmentResponse.RandomItem: %w", err)
@@ -266,10 +278,10 @@ func (v *SimpleNamedFragmentResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomLeaf
-		raw := firstPass.RandomLeaf
+		dst := &v.RandomLeaf
+		src := firstPass.RandomLeaf
 		err = __unmarshalSimpleNamedFragmentRandomLeafLeafContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal SimpleNamedFragmentResponse.RandomLeaf: %w", err)

generate/testdata/snapshots/TestGenerate-StructOption.graphql-StructOption.graphql.go

@@ -62,6 +62,10 @@ type StructOptionRootTopicChildrenContentParentTopic struct {
 
 func (v *StructOptionRootTopicChildrenContentParentTopic) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*StructOptionRootTopicChildrenContentParentTopic
 		InterfaceChildren []json.RawMessage `json:"interfaceChildren"`
@@ -75,15 +79,15 @@ func (v *StructOptionRootTopicChildrenContentParentTopic) UnmarshalJSON(b []byte
 	}
 
 	{
-		target := &v.InterfaceChildren
-		raw := firstPass.InterfaceChildren
-		*target = make(
+		dst := &v.InterfaceChildren
+		src := firstPass.InterfaceChildren
+		*dst = make(
 			[]StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent,
-			len(raw))
-		for i, raw := range raw {
-			target := &(*target)[i]
+			len(src))
+		for i, src := range src {
+			dst := &(*dst)[i]
 			err = __unmarshalStructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent(
-				target, raw)
+				src, dst)
 			if err != nil {
 				return fmt.Errorf(
 					"Unable to unmarshal StructOptionRootTopicChildrenContentParentTopic.InterfaceChildren: %w", err)
@@ -169,15 +173,15 @@ func (v *StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenTopic)
 	return v.Id
 }
 
-func __unmarshalStructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent(v *StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalStructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent(b []byte, v *StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -185,13 +189,13 @@ func __unmarshalStructOptionRootTopicChildrenContentParentTopicInterfaceChildren
 	switch tn.TypeName {
 	case "Article":
 		*v = new(StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -218,6 +222,10 @@ type StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenVideo struc
 
 func (v *StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenVideo) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*StructOptionRootTopicChildrenContentParentTopicInterfaceChildrenVideo
 		graphql.NoUnmarshalJSON

generate/testdata/snapshots/TestGenerate-TypeNames.graphql-TypeNames.graphql.go

@@ -65,15 +65,15 @@ func (v *ItemTopic) GetId() testutil.ID { return v.Id }
 // GetName is a part of, and documented with, the interface Item.
 func (v *ItemTopic) GetName() string { return v.Name }
 
-func __unmarshalItem(v *Item, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalItem(b []byte, v *Item) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -81,13 +81,13 @@ func __unmarshalItem(v *Item, m json.RawMessage) error {
 	switch tn.TypeName {
 	case "Article":
 		*v = new(ItemArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(ItemVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Topic":
 		*v = new(ItemTopic)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing Content.__typename")
@@ -134,6 +134,10 @@ type Resp struct {
 
 func (v *Resp) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*Resp
 		RandomItem json.RawMessage `json:"randomItem"`
@@ -147,10 +151,10 @@ func (v *Resp) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomItem
-		raw := firstPass.RandomItem
+		dst := &v.RandomItem
+		src := firstPass.RandomItem
 		err = __unmarshalItem(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal Resp.RandomItem: %w", err)

generate/testdata/snapshots/TestGenerate-UnionNoFragments.graphql-UnionNoFragments.graphql.go

@@ -40,15 +40,15 @@ func (v *UnionNoFragmentsQueryRandomLeafVideo) implementsGraphQLInterfaceUnionNo
 // GetTypename is a part of, and documented with, the interface UnionNoFragmentsQueryRandomLeafLeafContent.
 func (v *UnionNoFragmentsQueryRandomLeafVideo) GetTypename() string { return v.Typename }
 
-func __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(v *UnionNoFragmentsQueryRandomLeafLeafContent, m json.RawMessage) error {
-	if string(m) == "null" {
+func __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(b []byte, v *UnionNoFragmentsQueryRandomLeafLeafContent) error {
+	if string(b) == "null" {
 		return nil
 	}
 
 	var tn struct {
 		TypeName string `json:"__typename"`
 	}
-	err := json.Unmarshal(m, &tn)
+	err := json.Unmarshal(b, &tn)
 	if err != nil {
 		return err
 	}
@@ -56,10 +56,10 @@ func __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(v *UnionNoFragmentsQu
 	switch tn.TypeName {
 	case "Article":
 		*v = new(UnionNoFragmentsQueryRandomLeafArticle)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "Video":
 		*v = new(UnionNoFragmentsQueryRandomLeafVideo)
-		return json.Unmarshal(m, *v)
+		return json.Unmarshal(b, *v)
 	case "":
 		return fmt.Errorf(
 			"Response was missing LeafContent.__typename")
@@ -81,6 +81,10 @@ type UnionNoFragmentsQueryResponse struct {
 
 func (v *UnionNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 
+	if string(b) == "null" {
+		return nil
+	}
+
 	var firstPass struct {
 		*UnionNoFragmentsQueryResponse
 		RandomLeaf json.RawMessage `json:"randomLeaf"`
@@ -94,10 +98,10 @@ func (v *UnionNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 	}
 
 	{
-		target := &v.RandomLeaf
-		raw := firstPass.RandomLeaf
+		dst := &v.RandomLeaf
+		src := firstPass.RandomLeaf
 		err = __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(
-			target, raw)
+			src, dst)
 		if err != nil {
 			return fmt.Errorf(
 				"Unable to unmarshal UnionNoFragmentsQueryResponse.RandomLeaf: %w", err)

generate/testdata/snapshots/TestGenerate-unexported.graphql-unexported.graphql.go

@@ -3,6 +3,10 @@ package test
 // Code generated by github.com/Khan/genqlient, DO NOT EDIT.
 
 import (
+	"encoding/json"
+	"fmt"
+	"time"
+
 	"github.com/Khan/genqlient/graphql"
 	"github.com/Khan/genqlient/internal/testutil"
 )
@@ -34,6 +38,32 @@ type UserQueryInput struct {
 	Role       Role             `json:"role"`
 	Names      []string         `json:"names"`
 	HasPokemon testutil.Pokemon `json:"hasPokemon"`
+	Birthdate  time.Time        `json:"-"`
+}
+
+func (v *UserQueryInput) MarshalJSON() ([]byte, error) {
+
+	var fullObject struct {
+		*UserQueryInput
+		Birthdate json.RawMessage `json:"birthdate"`
+		graphql.NoMarshalJSON
+	}
+	fullObject.UserQueryInput = v
+
+	{
+
+		dst := &fullObject.Birthdate
+		src := v.Birthdate
+		var err error
+		*dst, err = testutil.MarshalDate(
+			&src)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"Unable to marshal UserQueryInput.Birthdate: %w", err)
+		}
+	}
+
+	return json.Marshal(&fullObject)
 }
 
 // __unexportedInput is used internally by genqlient

generate/types.go

@@ -61,8 +61,9 @@ type (
 	// goOpaqueType represents a user-defined or builtin type, often used to
 	// represent a GraphQL scalar.  (See Config.Bindings for more context.)
 	goOpaqueType struct {
-		GoRef       string
-		GraphQLName string
+		GoRef                  string
+		GraphQLName            string
+		Marshaler, Unmarshaler string
 	}
 	// goSliceType represents the Go type []Elem, used to represent GraphQL
 	// list types.
@@ -132,6 +133,7 @@ type goStructType struct {
 	IsInput   bool
 	Selection ast.SelectionSet
 	descriptionInfo
+	Generator *generator // for the convenience of the template
 }
 
 type goStructField struct {
@@ -156,10 +158,74 @@ func (field *goStructField) IsEmbedded() bool {
 	return field.GoName == ""
 }
 
+// unmarshaler returns:
+// - the name of the function to use to unmarshal this field
+// - true if this is a fully-qualified name (false if it is a package-local
+//   unqualified name)
+// - true if we need to generate an unmarshaler at all, false if the default
+//   behavior will suffice
+func (field *goStructField) unmarshaler() (qualifiedName string, needsImport bool, needsUnmarshaler bool) {
+	switch typ := field.GoType.Unwrap().(type) {
+	case *goOpaqueType:
+		if typ.Unmarshaler != "" {
+			return typ.Unmarshaler, true, true
+		}
+	case *goInterfaceType:
+		return "__unmarshal" + typ.Reference(), false, true
+	}
+	return "encoding/json.Unmarshal", true, field.IsEmbedded()
+}
+
+// NeedsUnmarshaler returns true if this field needs special handling when
+// unmarshaling, e.g. if it's of interface type, embedded, or has a
+// user-specified custom unmarshaler.
+func (field *goStructField) NeedsUnmarshaler() bool {
+	_, _, ok := field.unmarshaler()
+	return ok
+}
+
+// Unmarshaler returns the Go name of the function to use to unmarshal this
+// field (which may be "json.Unmarshal" if there's not a special one).
+func (field *goStructField) Unmarshaler(g *generator) (string, error) {
+	name, needsImport, _ := field.unmarshaler()
+	if needsImport {
+		return g.ref(name)
+	}
+	return name, nil
+}
+
+// marshaler returns:
+// - the fully-qualified name of the function to use to marshal this field
+// - true if we need to generate an marshaler at all, false if the default
+//   behavior will suffice
+func (field *goStructField) marshaler() (qualifiedName string, needsMarshaler bool) {
+	// (there are no interfaces on the input side)
+	opaque, ok := field.GoType.Unwrap().(*goOpaqueType)
+	if ok && opaque.Marshaler != "" {
+		return opaque.Marshaler, true
+	}
+	return "encoding/json.Marshal", field.IsEmbedded()
+}
+
+// NeedsMarshaler returns true if this field needs special handling when
+// marshaling, e.g. if it has a user-specified custom marshaler.
+func (field *goStructField) NeedsMarshaler() bool {
+	_, ok := field.marshaler()
+	return ok
+}
+
+// Marshaler returns the Go name of the function to use to marshal this
+// field (which may be "json.Marshal" if there's not a special one).
+func (field *goStructField) Marshaler(g *generator) (string, error) {
+	name, _ := field.marshaler()
+	// Unlike unmarshaler, we never have a local name, and always need g.ref.
+	return g.ref(name)
+}
+
 func (typ *goStructType) WriteDefinition(w io.Writer, g *generator) error {
 	writeDescription(w, structDescription(typ))
 
-	needUnmarshaler := false
+	needUnmarshaler, needMarshaler := false, false
 	fmt.Fprintf(w, "type %s struct {\n", typ.GoName)
 	for _, field := range typ.Fields {
 		writeDescription(w, field.Description)
@@ -168,24 +234,24 @@ func (typ *goStructType) WriteDefinition(w io.Writer, g *generator) error {
 			jsonTag += ",omitempty"
 		}
 		jsonTag += `"`
-		if field.IsAbstract() {
-			// abstract types are handled in our UnmarshalJSON (see below)
+		if !typ.IsInput && field.NeedsUnmarshaler() {
+			// certain types are handled in our UnmarshalJSON (see below)
 			needUnmarshaler = true
 			jsonTag = `"-"`
 		}
-		if field.IsEmbedded() {
-			// embedded fields also need UnmarshalJSON handling (see below)
-			needUnmarshaler = true
-			fmt.Fprintf(w, "\t%s `json:\"-\"`\n", field.GoType.Unwrap().Reference())
-		} else {
-			fmt.Fprintf(w, "\t%s %s `json:%s`\n",
-				field.GoName, field.GoType.Reference(), jsonTag)
+		if typ.IsInput && field.NeedsMarshaler() {
+			needMarshaler = true
+			jsonTag = `"-"`
 		}
+		// Note for embedded types field.GoName is "", which produces the code
+		// we want!
+		fmt.Fprintf(w, "\t%s %s `json:%s`\n",
+			field.GoName, field.GoType.Reference(), jsonTag)
 	}
 	fmt.Fprintf(w, "}\n")
 
-	// Now, if needed, write the unmarshaler.  We need one if we have any
-	// interface-typed fields, or any embedded fields.
+	// Now, if needed, write the marshaler/unmarshaler.  We need one if we have
+	// any interface-typed fields, or any embedded fields.
 	//
 	// For interface-typed fields, ideally we'd write an UnmarshalJSON method
 	// on the field, but you can't add a method to an interface.  So we write a
@@ -204,13 +270,28 @@ func (typ *goStructType) WriteDefinition(w io.Writer, g *generator) error {
 	// JSON library will only fill one of those (the least-nested one); we want
 	// to fill them all.
 	//
+	// For fields with a custom marshaler or unmarshaler, we do basically the
+	// same thing as interface-typed fields, except the user has defined the
+	// helper.
+	//
+	// Note that in all cases we need only write an unmarshaler if this is an
+	// input type, and a marshaler if it's an output type.
+	//
 	// TODO(benkraft): If/when proposal #5901 is implemented (Go 1.18 at the
 	// earliest), we may be able to do some of this a simpler way.
-	if !needUnmarshaler {
-		return nil
+	if needUnmarshaler {
+		err := g.render("unmarshal.go.tmpl", w, typ)
+		if err != nil {
+			return err
+		}
 	}
-
-	return g.render("unmarshal.go.tmpl", w, typ)
+	if needMarshaler {
+		err := g.render("marshal.go.tmpl", w, typ)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (typ *goStructType) Reference() string              { return typ.GoName }

generate/unmarshal.go.tmpl

@@ -2,23 +2,25 @@
      UnmarshalJSON from the function it follows) */}}
 
 func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
-    {{/* We want to specially handle the abstract or embedded fields, but
-         unmarshal everything else normally.  To handle abstract fields,
-         first we unmarshal them into a json.RawMessage, and then handle those
-         further, below.  Embedded fields we just unmarshal directly into the
-         embedded value.  For the rest, we just want to call json.Unmarshal.
-         But if we do that naively on a value of type `.Type`, it will call
-         this function again, and recurse infinitely.  So we make a wrapper
-         type which embeds both this type and NoUmnarshalJSON, which prevents
-         either's UnmarshalJSON method from being promoted.  For more on why
-         this is so difficult, see
+    {{/* Standard convention for unmarshalers is to no-op on null. */}}
+    if string(b) == "null" {
+        return nil
+    }
+
+    {{/* We want to specially handle certain fields, but unmarshal everything
+         else normally.  To handle abstract fields and fields with custom
+         unmarshalers, first we unmarshal them into a json.RawMessage, and then
+         handle those further, below.  Embedded fields don't need the
+         json.RawMessage; we just use our input again.  Either way, we first
+         want to call json.Unmarshal on the receiver (v).  But if we do that
+         naively on a value of type `.Type`, it will call this function again,
+         and recurse infinitely.  So we make a wrapper type which embeds both
+         this type and NoUmnarshalJSON, which prevents either's UnmarshalJSON
+         method from being promoted.  For more on why this is so difficult, see
          https://github.com/benjaminjkraft/notes/blob/master/go-json-interfaces.md.
          (Note there are a few different ways "hide" the method, but this one
          seems to be the best option that works if this type has embedded types
          with UnmarshalJSON methods.)
-         TODO(benkraft)): Ensure `{{.Type}}Wrapper` won't collide with any
-         other type we need.  (For the most part it being locally-scoped saves
-         us; it's not clear if this can be a problem in practice.)
     */}}
 
     {{/* TODO(benkraft): Omit/simplify the first pass if all fields are
@@ -26,7 +28,7 @@ func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
     var firstPass struct{
         *{{.GoName}}
         {{range .Fields -}}
-        {{if and .IsAbstract (not .IsEmbedded) -}}
+        {{if and .NeedsUnmarshaler (not .IsEmbedded) -}}
         {{.GoName}} {{repeat .GoType.SliceDepth "[]"}}{{ref "encoding/json.RawMessage"}} `json:"{{.JSONName}}"`
         {{end -}}
         {{end -}}
@@ -43,77 +45,71 @@ func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
 
     {{/* Now, handle the fields needing special handling. */}}
     {{range $field := .Fields -}}
+    {{if $field.NeedsUnmarshaler -}}
     {{if $field.IsEmbedded -}}
     {{/* Embedded fields are easier: we just unmarshal the same input into
          them.  (They're also easier because they can't be lists, since they
          arise from GraphQL fragment spreads.) */ -}}
-    {{if $field.IsAbstract -}}
-    {{/* Except if they're both abstract and embedded, in which case we need to
-         call the unmarshal-helper instead.  Luckily, we don't embed
-         slice-typed fields, so we don't need the full generality we handle
-         below. */ -}}
-    err = __unmarshal{{$field.GoType.Unwrap.Reference}}(
+    err = {{$field.Unmarshaler $.Generator}}(
         b, &v.{{$field.GoType.Unwrap.Reference}})
-    {{else -}}
-    err = json.Unmarshal(
-        b, &v.{{$field.GoType.Unwrap.Reference}})
-    {{end -}}{{/* inner if .IsAbstract */ -}}
     if err != nil {
         return err
     }
-    {{else if $field.IsAbstract -}}
-    {{/* First, for abstract fields, call the unmarshal-helper.
-         This gets a little complicated because we may have a slice field.
-         So what we do is basically, for each field of type `[][]...[]MyType`:
+    {{else -}}
+    {{/* For other fields (abstract or custom unmarshaler), first, call the
+         unmarshaler (our unmarshal-helper, or the user-specified one,
+         respectively).  This gets a little complicated because we may have
+         a slice field.  So what we do is basically, for each field of type
+         `[][]...[]MyType`:
 
-            target := &v.MyField      // *[][]...[]MyType
-            raw := firstPass.MyField  // [][]...[]json.RawMessage
+            dst := &v.MyField      // *[][]...[]MyType
+            src := firstPass.MyField  // [][]...[]json.RawMessage
 
             // repeat the following three lines n times; each time, inside
-            // the loop we have one less layer of slice on raw and target
-            *target = make([][]...[]MyType, len(raw))
-            for i, raw := range raw {
-                // We need the &(*target)[i] because at each stage we want to
-                // keep target as a pointer.  (It only really has to be a
+            // the loop we have one less layer of slice on src and dst
+            *dst = make([][]...[]MyType, len(src))
+            for i, src := range src {
+                // We need the &(*dst)[i] because at each stage we want to
+                // keep dst as a pointer.  (It only really has to be a
                 // pointer at the innermost level, but it's easiest to be
                 // consistent.)
-                target := &(*target)[i]
-            
-                // (now we have `target *MyType` and `raw json.RawMessage`)
-                __unmarshalMyType(target, raw)
+                dst := &(*dst)[i]
+           
+                // (now we have `dst *MyType` and `src json.RawMessage`)
+                __unmarshalMyType(dst, src)
 
             } // (also n times)
 
          Note that if the field also uses a pointer (`[][]...[]*MyType`), we
          now pass around `*[][]...[]*MyType`; again in principle
          `[][]...[]*MyType` would work but require more special-casing.  Thus
-         in the innermost loop, `target` is of type `**MyType`, so we have to
-         pass `*target` to the unmarshal-helper.  Of course, since MyType is an
+         in the innermost loop, `dst` is of type `**MyType`, so we have to
+         pass `*dst` to the unmarshaler.  Of course, since MyType is an
          interface, I'm not sure why you'd any of that anyway.
 
          One additional trick is we wrap everything above in a block ({ ... }),
-         so that the variables target and raw may take on different types for
+         so that the variables dst and src may take on different types for
          each field we are handling, which would otherwise conflict.  (We could
          instead suffix the names, but that makes things much harder to read.)
     */}}
     {
-        target := &v.{{$field.GoName}}
-        raw := firstPass.{{$field.GoName}}
+        dst := &v.{{$field.GoName}}
+        src := firstPass.{{$field.GoName}}
         {{range $i := intRange $field.GoType.SliceDepth -}}
-        *target = make(
+        *dst = make(
             {{repeat (sub $field.GoType.SliceDepth $i) "[]"}}{{if $field.GoType.IsPointer}}*{{end}}{{$field.GoType.Unwrap.Reference}},
-            len(raw))
-        for i, raw := range raw {
-            target := &(*target)[i]
+            len(src))
+        for i, src := range src {
+            dst := &(*dst)[i]
         {{end -}}
         {{if $field.GoType.IsPointer -}}
         {{/* In this case, the parent for loop did `make([]*MyType, ...)` and
              we have a pointer into that list.  But we actually still need to
              initialize the *elements* of the list. */ -}}
-        *target = new({{$field.GoType.Unwrap.Reference}})
+        *dst = new({{$field.GoType.Unwrap.Reference}})
         {{end -}}
-        err = __unmarshal{{$field.GoType.Unwrap.Reference}}(
-            {{if $field.GoType.IsPointer}}*{{end}}target, raw)
+        err = {{$field.Unmarshaler $.Generator}}(
+            src, {{if $field.GoType.IsPointer}}*{{end}}dst)
         if err != nil {
             return fmt.Errorf(
                 "Unable to unmarshal {{$.GoName}}.{{$field.GoName}}: %w", err)
@@ -122,7 +118,8 @@ func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
         }
         {{end -}}
     }
-    {{end -}}{{/* end if .IsEmbedded + else if .IsAbstract */ -}}
+    {{end -}}{{/* end if/else .IsEmbedded */ -}}
+    {{end -}}{{/* end if .NeedsUnmarshaler */ -}}
     {{end}}{{/* end range .Fields */ -}}
 
     return nil

generate/unmarshal_helper.go.tmpl

@@ -1,15 +1,15 @@
 {{/* (the blank lines at the start are intentional, to separate
      the helper from the function it follows) */}}
 
-func __unmarshal{{.GoName}}(v *{{.GoName}}, m {{ref "encoding/json.RawMessage"}}) error {
-    if string(m) == "null" {
+func __unmarshal{{.GoName}}(b []byte, v *{{.GoName}}) error {
+    if string(b) == "null" {
         return nil
     }
 
     var tn struct {
         TypeName string `json:"__typename"`
     }
-    err := {{ref "encoding/json.Unmarshal"}}(m, &tn)
+    err := {{ref "encoding/json.Unmarshal"}}(b, &tn)
     if err != nil {
         return err
     }
@@ -18,7 +18,7 @@ func __unmarshal{{.GoName}}(v *{{.GoName}}, m {{ref "encoding/json.RawMessage"}}
     {{range .Implementations -}}
     case "{{.GraphQLName}}":
         *v = new({{.GoName}})
-        return {{ref "encoding/json.Unmarshal"}}(m, *v)
+        return {{ref "encoding/json.Unmarshal"}}(b, *v)
     {{end -}}
     case "":
         {{/* Likely if we're making a request to a mock server and the author