cmd, pkg/go/*: fix "go vet" warnings for go/ast and go/printer

struct literals.

R=gri
CC=golang-dev
https://golang.org/cl/5653073

src/cmd/fix/httpfs.go

@@ -39,7 +39,10 @@ func httpfs(f *ast.File) bool {
 		}
 		dir, prefix := call.Args[0], call.Args[1]
 		call.Args = []ast.Expr{&ast.CallExpr{
-			Fun:  &ast.SelectorExpr{ast.NewIdent("http"), ast.NewIdent("Dir")},
+			Fun: &ast.SelectorExpr{
+				X:   ast.NewIdent("http"),
+				Sel: ast.NewIdent("Dir"),
+			},
 			Args: []ast.Expr{dir},
 		}}
 		wrapInStripHandler := true
@@ -53,7 +56,10 @@ func httpfs(f *ast.File) bool {
 			call.Args = []ast.Expr{
 				prefix,
 				&ast.CallExpr{
-					Fun:  &ast.SelectorExpr{ast.NewIdent("http"), ast.NewIdent("FileServer")},
+					Fun: &ast.SelectorExpr{
+						X:   ast.NewIdent("http"),
+						Sel: ast.NewIdent("FileServer"),
+					},
 					Args: call.Args,
 				},
 			}

src/cmd/fix/main.go

@@ -104,8 +104,8 @@ const (
 )
 
 var printConfig = &printer.Config{
-	printerMode,
-	tabWidth,
+	Mode:     printerMode,
+	Tabwidth: tabWidth,
 }
 
 func gofmtFile(f *ast.File) ([]byte, error) {

src/cmd/fix/reflect.go

@@ -188,7 +188,7 @@ func reflectFn(f *ast.File) bool {
 			}
 			*n = v
 		case *ast.IfStmt:
-			x := &ast.ExprStmt{n.Cond}
+			x := &ast.ExprStmt{X: n.Cond}
 			if reflectFixTypecheck(&n.Init, nil, []ast.Stmt{x, n.Body, n.Else}) {
 				n.Cond = x.X
 				fixed = true

src/cmd/godoc/codewalk.go

@@ -119,7 +119,7 @@ func loadCodewalk(filename string) (*Codewalk, error) {
 	d.Entity = xml.HTMLEntity
 	err = d.Decode(cw)
 	if err != nil {
-		return nil, &os.PathError{"parsing", filename, err}
+		return nil, &os.PathError{Op: "parsing", Path: filename, Err: err}
 	}
 
 	// Compute file list, evaluate line numbers for addresses.

src/cmd/godoc/godoc.go

@@ -383,7 +383,7 @@ func writeNode(w io.Writer, fset *token.FileSet, x interface{}) {
 	//           with an another printer mode (which is more efficiently
 	//           implemented in the printer than here with another layer)
 	mode := printer.TabIndent | printer.UseSpaces
-	err := (&printer.Config{mode, *tabwidth}).Fprint(&tconv{output: w}, fset, x)
+	err := (&printer.Config{Mode: mode, Tabwidth: *tabwidth}).Fprint(&tconv{output: w}, fset, x)
 	if err != nil {
 		log.Print(err)
 	}

src/cmd/godoc/parser.go

@@ -40,7 +40,7 @@ func parseFiles(fset *token.FileSet, filenames []string) (pkgs map[string]*ast.P
 		pkg, found := pkgs[name]
 		if !found {
 			// TODO(gri) Use NewPackage here; reconsider ParseFiles API.
-			pkg = &ast.Package{name, nil, nil, make(map[string]*ast.File)}
+			pkg = &ast.Package{Name: name, Files: make(map[string]*ast.File)}
 			pkgs[name] = pkg
 		}
 		pkg.Files[filename] = file

src/cmd/godoc/snippet.go

@@ -62,7 +62,14 @@ func genSnippet(fset *token.FileSet, d *ast.GenDecl, id *ast.Ident) *Snippet {
 	}
 
 	// only use the spec containing the id for the snippet
-	dd := &ast.GenDecl{d.Doc, d.Pos(), d.Tok, d.Lparen, []ast.Spec{s}, d.Rparen}
+	dd := &ast.GenDecl{
+		Doc:    d.Doc,
+		TokPos: d.Pos(),
+		Tok:    d.Tok,
+		Lparen: d.Lparen,
+		Specs:  []ast.Spec{s},
+		Rparen: d.Rparen,
+	}
 
 	return newSnippet(fset, dd, id)
 }
@@ -73,7 +80,12 @@ func funcSnippet(fset *token.FileSet, d *ast.FuncDecl, id *ast.Ident) *Snippet {
 	}
 
 	// only use the function signature for the snippet
-	dd := &ast.FuncDecl{d.Doc, d.Recv, d.Name, d.Type, nil}
+	dd := &ast.FuncDecl{
+		Doc:  d.Doc,
+		Recv: d.Recv,
+		Name: d.Name,
+		Type: d.Type,
+	}
 
 	return newSnippet(fset, dd, id)
 }

src/cmd/gofmt/gofmt.go

@@ -118,7 +118,7 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 	}
 
 	var buf bytes.Buffer
-	err = (&printer.Config{printerMode, *tabWidth}).Fprint(&buf, fset, file)
+	err = (&printer.Config{Mode: printerMode, Tabwidth: *tabWidth}).Fprint(&buf, fset, file)
 	if err != nil {
 		return err
 	}

src/cmd/gofmt/long_test.go

@@ -37,7 +37,7 @@ func gofmt(filename string, src *bytes.Buffer) error {
 	}
 	ast.SortImports(fset, f)
 	src.Reset()
-	return (&printer.Config{printerMode, *tabWidth}).Fprint(src, fset, f)
+	return (&printer.Config{Mode: printerMode, Tabwidth: *tabWidth}).Fprint(src, fset, f)
 }
 
 func testFile(t *testing.T, b1, b2 *bytes.Buffer, filename string) {

src/pkg/go/doc/reader.go

@@ -439,8 +439,10 @@ func (r *reader) readFile(src *ast.File) {
 						// gets to (re-)use the declaration documentation
 						// if there's none associated with the spec itself
 						fake := &ast.GenDecl{
-							d.Doc, d.Pos(), token.TYPE, token.NoPos,
-							[]ast.Spec{s}, token.NoPos,
+							Doc:    d.Doc,
+							TokPos: d.Pos(),
+							Tok:    token.TYPE,
+							Specs:  []ast.Spec{s},
 						}
 						r.readType(fake, s)
 					}
@@ -460,7 +462,7 @@ func (r *reader) readFile(src *ast.File) {
 				// non-empty BUG comment; collect comment without BUG prefix
 				list := append([]*ast.Comment(nil), c.List...) // make a copy
 				list[0].Text = text[m[1]:]
-				r.bugs = append(r.bugs, (&ast.CommentGroup{list}).Text())
+				r.bugs = append(r.bugs, (&ast.CommentGroup{List: list}).Text())
 			}
 		}
 	}
@@ -530,7 +532,7 @@ func customizeRecv(f *Func, recvTypeName string, embeddedIsPtr bool, level int)
 	_, origRecvIsPtr := newField.Type.(*ast.StarExpr)
 	var typ ast.Expr = ast.NewIdent(recvTypeName)
 	if !embeddedIsPtr && origRecvIsPtr {
-		typ = &ast.StarExpr{token.NoPos, typ}
+		typ = &ast.StarExpr{X: typ}
 	}
 	newField.Type = typ