non-ridiculous handling of scalars

generate/generate.go

@@ -56,7 +56,7 @@ func fromASTArg(arg *ast.VariableDefinition, schema *ast.Schema) argument {
 	}
 }
 
-func fromASTOperation(op *ast.OperationDefinition, schema *ast.Schema) operation {
+func fromASTOperation(op *ast.OperationDefinition, schema *ast.Schema) (operation, error) {
 	// TODO: we may have to actually get the precise query text, in case we
 	// want to be hashing it or something like that.  Although maybe
 	// there's no reasonable way to do that with several queries in one
@@ -72,6 +72,12 @@ func fromASTOperation(op *ast.OperationDefinition, schema *ast.Schema) operation
 	for i, arg := range op.VariableDefinitions {
 		args[i] = fromASTArg(arg, schema)
 	}
+
+	typ, err := typeForOperation(op, schema)
+	if err != nil {
+		return operation{}, fmt.Errorf("could not compute return-type for query: %v", err)
+	}
+
 	return operation{
 		Type: op.Operation,
 		Name: op.Name,
@@ -85,14 +91,18 @@ func fromASTOperation(op *ast.OperationDefinition, schema *ast.Schema) operation
 
 		// TODO: configure ResponseName format
 		ResponseName: op.Name + "Response",
-		ResponseType: typeForOperation(op, schema),
+		ResponseType: typ,
-	}
+	}, nil
 }
 
 func Generate(schema *ast.Schema, document *ast.QueryDocument) ([]byte, error) {
+	var err error
 	operations := make([]operation, len(document.Operations))
 	for i, op := range document.Operations {
-		operations[i] = fromASTOperation(op, schema)
+		operations[i], err = fromASTOperation(op, schema)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	data := templateParams{
@@ -102,7 +112,7 @@ func Generate(schema *ast.Schema, document *ast.QueryDocument) ([]byte, error) {
 	}
 
 	var buf bytes.Buffer
-	err := tmpl.Execute(&buf, data)
+	err = tmpl.Execute(&buf, data)
 	if err != nil {
 		return nil, fmt.Errorf("could not render template: %v", err)
 	}

generate/types.go

@@ -7,12 +7,10 @@ import (
 	"github.com/vektah/gqlparser/ast"
 )
 
-func typeForOperation(operation *ast.OperationDefinition, schema *ast.Schema) string {
+func typeForOperation(operation *ast.OperationDefinition, schema *ast.Schema) (string, error) {
 	var builder strings.Builder
-
+	err := writeSelectionSetStruct(&builder, operation.SelectionSet, schema)
-	writeSelectionSetStruct(&builder, operation.SelectionSet, schema)
+	return builder.String(), err
-
-	return builder.String()
 }
 
 func typeForInputType(typ *ast.Type, schema *ast.Schema) string {
@@ -25,7 +23,7 @@ func typeForInputType(typ *ast.Type, schema *ast.Schema) string {
 	return builder.String()
 }
 
-func writeSelectionSetStruct(builder *strings.Builder, selectionSet ast.SelectionSet, schema *ast.Schema) {
+func writeSelectionSetStruct(builder *strings.Builder, selectionSet ast.SelectionSet, schema *ast.Schema) error {
 	builder.WriteString("struct {\n")
 	for _, selection := range selectionSet {
 		switch selection := selection.(type) {
@@ -52,15 +50,29 @@ func writeSelectionSetStruct(builder *strings.Builder, selectionSet ast.Selectio
 			builder.WriteRune('\n')
 
 		case *ast.FragmentSpread, *ast.InlineFragment:
-			panic("TODO")
+			return fmt.Errorf("not implemented: %T", selection)
 		default:
-			panic(fmt.Errorf("invalid selection type: %v", selection))
+			return fmt.Errorf("invalid selection type: %v", selection)
 		}
 	}
 	builder.WriteString("}")
+	return nil
 }
 
-func writeType(builder *strings.Builder, typ *ast.Type, selectionSet ast.SelectionSet, schema *ast.Schema) {
+var graphQLNameToGoName = map[string]string{
+	"Int":     "int", // TODO: technically int32 is always enough, use that?
+	"Float":   "float64",
+	"String":  "string",
+	"Boolean": "bool",
+	"ID":      "string", // TODO: named type for IDs?
+}
+
+func writeType(builder *strings.Builder, typ *ast.Type, selectionSet ast.SelectionSet, schema *ast.Schema) error {
+	// gqlgen does slightly different things here since it defines names for
+	// all the intermediate types, but its implementation may be useful to crib
+	// from:
+	// https://github.com/99designs/gqlgen/blob/master/plugin/modelgen/models.go#L113
+	// TODO: or maybe we should do that?
 	if typ.Elem != nil {
 		// Type is a list.
 		builder.WriteString("[]")
@@ -70,12 +82,14 @@ func writeType(builder *strings.Builder, typ *ast.Type, selectionSet ast.Selecti
 	}
 
 	if selectionSet != nil {
-		writeSelectionSetStruct(builder, selectionSet, schema)
+		return writeSelectionSetStruct(builder, selectionSet, schema)
-		return
 	}
 
-	// TODO: actually handle scalars.  or can we instead use gqlgen's
+	// TODO: handle enums better.  (do unions need special handling?)
-	// converter?  they're doing mostly the same thing.  if not, crib from it:
+	goName := graphQLNameToGoName[typ.Name()]
-	// https://github.com/99designs/gqlgen/blob/master/plugin/modelgen/models.go#L113
+	if goName == "" {
-	builder.WriteString(strings.ToLower(typ.Name()))
+		return fmt.Errorf("unknown scalar name: %s", typ.Name())
+	}
+	builder.WriteString(goName)
+	return nil
 }