Enable golangci-lint (#49)

## Summary:
It would be nice to have some linting beyond `go vet`!  Now we do.  I
started by copying the config from Khan/webapp.  I did remove a couple
of staticcheck checks that I didn't feel were useful.  (Note also that
exportloopref is the replacement for scopelint in newer golangci-lint.)

Included are all the needed lint fixes; most are stylistic but the
changes in the example are a (minor) bugfix.

Fixes #22.
Issue: https://github.com/Khan/genqlient/issues/22

## Test plan:
make check

Author: benjaminjkraft

Reviewers: aberkan, dnerdy, benjaminjkraft, csilvers, MiguelCastillo

Required Reviewers: 

Approved by: aberkan, dnerdy

Checks: ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Test (1.13), ✅ Lint, ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Test (1.13), ✅ Lint

Pull request URL: https://github.com/Khan/genqlient/pull/49

generate/comments.go

@@ -65,8 +65,8 @@ type GenqlientDirective struct {
 	Pointer *bool
 }
 
-func (g *GenqlientDirective) GetOmitempty() bool { return g.Omitempty != nil && *g.Omitempty }
-func (g *GenqlientDirective) GetPointer() bool   { return g.Pointer != nil && *g.Pointer }
+func (dir *GenqlientDirective) GetOmitempty() bool { return dir.Omitempty != nil && *dir.Omitempty }
+func (dir *GenqlientDirective) GetPointer() bool   { return dir.Pointer != nil && *dir.Pointer }
 
 func setBool(dst **bool, v *ast.Value) error {
 	ei, err := v.Value(nil) // no vars allowed

generate/example_test.go

@@ -21,7 +21,7 @@ func getRepoRoot(t *testing.T) string {
 }
 
 func TestGenerateExample(t *testing.T) {
-	configFilename := filepath.Join(getRepoRoot(t), "example/genqlient.yaml")
+	configFilename := filepath.Join(getRepoRoot(t), "example", "genqlient.yaml")
 	config, err := ReadAndValidateConfig(configFilename)
 	if err != nil {
 		t.Fatal(err)

generate/generate.go

@@ -152,7 +152,6 @@ func (g *generator) addOperation(op *ast.OperationDefinition) error {
 
 	args := make([]argument, len(op.VariableDefinitions))
 	for i, arg := range op.VariableDefinitions {
-		var err error
 		args[i], err = g.getArgument(op.Name, arg, directive)
 		if err != nil {
 			return err

generate/generate_test.go

@@ -68,7 +68,6 @@ func TestGenerate(t *testing.T) {
 				t.Run(filename, func(t *testing.T) {
 					testutil.Cupaloy.SnapshotT(t, string(content))
 				})
-				// TODO(benkraft): Also check that the code at least builds!
 			}
 
 			t.Run("Build", func(t *testing.T) {

generate/imports.go

@@ -9,8 +9,8 @@ import (
 )
 
 func (g *generator) addImportFor(pkgPath string) (alias string) {
-	if alias, ok := g.imports[pkgPath]; ok {
-		return alias
+	if existingAlias, ok := g.imports[pkgPath]; ok {
+		return existingAlias
 	}
 
 	pkgName := pkgPath[strings.LastIndex(pkgPath, "/")+1:]

generate/parse.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	goAst "go/ast"
 	goParser "go/parser"
-	"go/token"
 	goToken "go/token"
 	"io/ioutil"
 	"path/filepath"
@@ -134,7 +133,7 @@ func getQueriesFromGo(text string, basedir, filename string) ([]*ast.QueryDocume
 		}
 
 		basicLit, ok := node.(*goAst.BasicLit)
-		if !ok || basicLit.Kind != token.STRING {
+		if !ok || basicLit.Kind != goToken.STRING {
 			return true // recurse
 		}
 

generate/types.go

@@ -281,8 +281,8 @@ func (builder *typeBuilder) writeType(name, namePrefix string, typ *ast.Type, fi
 	def := builder.schema.Types[typ.Name()]
 	goName, ok := builder.Config.Scalars[def.Name]
 	if ok {
-		name, err := builder.addRef(goName)
-		builder.WriteString(name)
+		newName, err := builder.addRef(goName)
+		builder.WriteString(newName)
 		return err
 	}
 	goName, ok = builtinTypes[def.Name]
@@ -303,7 +303,7 @@ func (builder *typeBuilder) writeTypedef(
 	typedef *ast.Definition,
 	pos *ast.Position,
 	fields []field,
-	options *GenqlientDirective,
+	options *GenqlientDirective, //nolint:unparam // it is used!
 	description string, // defaults to typedef.Description
 ) (err error) {
 	defer func() {