go.tools/cmd/vet: the composite test is about keys, not tags

Fix the confusion.
No semantic change, just some renamings.

Fixes golang/go#6017.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/12394043

cmd/vet/composite.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file contains the test for untagged struct literals.
+// This file contains the test for unkeyed struct literals.
 
 package main
 
@@ -14,9 +14,9 @@ import (
 
 var compositeWhiteList = flag.Bool("compositewhitelist", true, "use composite white list; for testing only")
 
-// checkUntaggedLiteral checks if a composite literal is a struct literal with
-// untagged fields.
-func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
+// checkUnkeyedLiteral checks if a composite literal is a struct literal with
+// unkeyed fields.
+func (f *File) checkUnkeyedLiteral(c *ast.CompositeLit) {
 	if !vet("composites") {
 		return
 	}
@@ -36,9 +36,9 @@ func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
 	case *ast.MapType:
 		return
 	case *ast.StructType:
-		return // a literal struct type does not need to use tags
+		return // a literal struct type does not need to use keys
 	case *ast.Ident:
-		// A simple type name like t or T does not need tags either,
+		// A simple type name like t or T does not need keys either,
 		// since it is almost certainly declared in the current package.
 		// (The exception is names being used via import . "pkg", but
 		// those are already breaking the Go 1 compatibility promise,
@@ -59,7 +59,7 @@ func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
 
 	// It's a struct, or we can't tell it's not a struct because we don't have types.
 
-	// Check if the CompositeLit contains an untagged field.
+	// Check if the CompositeLit contains an unkeyed field.
 	allKeyValue := true
 	for _, e := range c.Elts {
 		if _, ok := e.(*ast.KeyValueExpr); !ok {
@@ -88,11 +88,11 @@ func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
 		return
 	}
 	typeName := path + "." + s.Sel.Name
-	if *compositeWhiteList && untaggedLiteralWhitelist[typeName] {
+	if *compositeWhiteList && unkeyedLiteralWhitelist[typeName] {
 		return
 	}
 
-	f.Warn(c.Pos(), typeString+" composite literal uses untagged fields")
+	f.Warn(c.Pos(), typeString+" composite literal uses unkeyed fields")
 }
 
 // pkgPath returns the import path "image/png" for the package name "png".
@@ -118,7 +118,7 @@ func pkgPath(f *File, pkgName string) (path string) {
 	return ""
 }
 
-var untaggedLiteralWhitelist = map[string]bool{
+var unkeyedLiteralWhitelist = map[string]bool{
 	/*
 		These types are actually slices. Syntactically, we cannot tell
 		whether the Typ in pkg.Typ{1, 2, 3} is a slice or a struct, so we

cmd/vet/doc.go

@@ -49,9 +49,9 @@ Non-standard signatures for methods with familiar names, including:
 
 Struct tags that do not follow the format understood by reflect.StructTag.Get.
 
-4. Untagged composite literals, flag -composites
+4. Unkeyed composite literals, flag -composites
 
-Composite struct literals that do not use the type-tagged syntax.
+Composite struct literals that do not use the field-keyed syntax.
 
 
 Usage:

cmd/vet/main.go

@@ -38,7 +38,7 @@ var report = map[string]*bool{
 	"assign":      flag.Bool("assign", false, "check for useless assignments"),
 	"atomic":      flag.Bool("atomic", false, "check for common mistaken usages of the sync/atomic package"),
 	"buildtags":   flag.Bool("buildtags", false, "check that +build tags are valid"),
-	"composites":  flag.Bool("composites", false, "check that composite literals used type-tagged elements"),
+	"composites":  flag.Bool("composites", false, "check that composite literals used field-keyed elements"),
 	"methods":     flag.Bool("methods", false, "check that canonically named methods are canonically defined"),
 	"printf":      flag.Bool("printf", false, "check printf-like invocations"),
 	"rangeloops":  flag.Bool("rangeloops", false, "check that range loop variables are used correctly"),
@@ -400,7 +400,7 @@ func (f *File) walkCallExpr(call *ast.CallExpr) {
 
 // walkCompositeLit walks a composite literal.
 func (f *File) walkCompositeLit(c *ast.CompositeLit) {
-	f.checkUntaggedLiteral(c)
+	f.checkUnkeyedLiteral(c)
 }
 
 // walkFieldTag walks a struct field tag.

cmd/vet/testdata/composite.go

@@ -50,7 +50,7 @@ var Okay4 = MyStruct{
 // Testing is awkward because we need to reference things from a separate package
 // to trigger the warnings.
 
-var BadStructLiteralUsedInTests = flag.Flag{ // ERROR "untagged fields"
+var BadStructLiteralUsedInTests = flag.Flag{ // ERROR "unkeyed fields"
 	"Name",
 	"Usage",
 	nil, // Value

cmd/vet/types.go

@@ -40,7 +40,7 @@ func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) error {
 // isStruct reports whether the composite literal c is a struct.
 // If it is not (probably a struct), it returns a printable form of the type.
 func (pkg *Package) isStruct(c *ast.CompositeLit) (bool, string) {
-	// Check that the CompositeLit's type is a slice or array (which needs no tag), if possible.
+	// Check that the CompositeLit's type is a slice or array (which needs no field keys), if possible.
 	typ := pkg.types[c]
 	// If it's a named type, pull out the underlying type. If it's not, the Underlying
 	// method returns the type itself.