vet: add a check for untagged struct literals.

R=rsc, dsymonds
CC=golang-dev, gri
https://golang.org/cl/5622045

src/cmd/vet/main.go

@@ -175,6 +175,8 @@ func (f *File) Visit(node ast.Node) ast.Visitor {
 	switch n := node.(type) {
 	case *ast.CallExpr:
 		f.walkCallExpr(n)
+	case *ast.CompositeLit:
+		f.walkCompositeLit(n)
 	case *ast.Field:
 		f.walkFieldTag(n)
 	case *ast.FuncDecl:
@@ -190,6 +192,11 @@ func (f *File) walkCall(call *ast.CallExpr, name string) {
 	f.checkFmtPrintfCall(call, name)
 }
 
+// walkCompositeLit walks a composite literal.
+func (f *File) walkCompositeLit(c *ast.CompositeLit) {
+	f.checkUntaggedLiteral(c)
+}
+
 // walkFieldTag walks a struct field tag.
 func (f *File) walkFieldTag(field *ast.Field) {
 	if field.Tag == nil {

src/cmd/vet/taglit.go

@@ -0,0 +1,120 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// 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.
+
+package main
+
+import (
+	"go/ast"
+	"strings"
+)
+
+// checkUntaggedLiteral checks if a composite literal is an struct literal with
+// untagged fields.
+func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
+	// Check if the CompositeLit contains an untagged field.
+	allKeyValue := true
+	for _, e := range c.Elts {
+		if _, ok := e.(*ast.KeyValueExpr); !ok {
+			allKeyValue = false
+			break
+		}
+	}
+	if allKeyValue {
+		return
+	}
+
+	// Check that the CompositeLit's type has the form pkg.Typ.
+	s, ok := c.Type.(*ast.SelectorExpr)
+	if !ok {
+		return
+	}
+	pkg, ok := s.X.(*ast.Ident)
+	if !ok {
+		return
+	}
+
+	// Convert the package name to an import path, and compare to a whitelist.
+	path := pkgPath(f, pkg.Name)
+	if path == "" {
+		f.Warnf(c.Pos(), "unresolvable package for %s.%s literal", pkg.Name, s.Sel.Name)
+		return
+	}
+	typ := path + "." + s.Sel.Name
+	if untaggedLiteralWhitelist[typ] {
+		return
+	}
+
+	f.Warnf(c.Pos(), "%s struct literal uses untagged fields", typ)
+}
+
+// pkgPath returns the import path "image/png" for the package name "png".
+//
+// This is based purely on syntax and convention, and not on the imported
+// package's contents. It will be incorrect if a package name differs from the
+// leaf element of the import path, or if the package was a dot import.
+func pkgPath(f *File, pkgName string) (path string) {
+	for _, x := range f.file.Imports {
+		s := strings.Trim(x.Path.Value, `"`)
+		if x.Name != nil {
+			// Catch `import pkgName "foo/bar"`.
+			if x.Name.Name == pkgName {
+				return s
+			}
+		} else {
+			// Catch `import "pkgName"` or `import "foo/bar/pkgName"`.
+			if s == pkgName || strings.HasSuffix(s, "/"+pkgName) {
+				return s
+			}
+		}
+	}
+	return ""
+}
+
+var untaggedLiteralWhitelist = 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
+		whitelist all the standard package library's exported slice types.
+
+		find $GOROOT/src/pkg -type f | grep -v _test.go | xargs grep '^type.*\[\]' | \
+			grep -v ' map\[' | sed 's,/[^/]*go.type,,' | sed 's,.*src/pkg/,,' | \
+			sed 's, ,.,' |  sed 's, .*,,' | grep -v '\.[a-z]' | sort
+	*/
+	"crypto/x509/pkix.RDNSequence":                  true,
+	"crypto/x509/pkix.RelativeDistinguishedNameSET": true,
+	"database/sql.RawBytes":                         true,
+	"debug/macho.LoadBytes":                         true,
+	"encoding/asn1.ObjectIdentifier":                true,
+	"encoding/asn1.RawContent":                      true,
+	"encoding/json.RawMessage":                      true,
+	"encoding/xml.CharData":                         true,
+	"encoding/xml.Comment":                          true,
+	"encoding/xml.Directive":                        true,
+	"exp/norm.Decomposition":                        true,
+	"exp/types.ObjList":                             true,
+	"go/scanner.ErrorList":                          true,
+	"image/color.Palette":                           true,
+	"net.HardwareAddr":                              true,
+	"net.IP":                                        true,
+	"net.IPMask":                                    true,
+	"sort.Float64Slice":                             true,
+	"sort.IntSlice":                                 true,
+	"sort.StringSlice":                              true,
+	"unicode.SpecialCase":                           true,
+
+	// These image and image/color struct types are frozen. We will never add fields to them.
+	"image/color.Alpha16": true,
+	"image/color.Alpha":   true,
+	"image/color.Gray16":  true,
+	"image/color.Gray":    true,
+	"image/color.NRGBA64": true,
+	"image/color.NRGBA":   true,
+	"image/color.RGBA64":  true,
+	"image/color.RGBA":    true,
+	"image/color.YCbCr":   true,
+	"image.Point":         true,
+	"image.Rectangle":     true,
+}