libgo: Update to weekly.2012-02-14 release.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@184798 138bc75d-0d04-0410-961f-82ee72b054a4

35 files changed, 1266 insertions, 315 deletions

diff --git a/libgo/go/go/ast/resolve.go b/libgo/go/go/ast/resolve.go
index c7c8e7c101e..908e61c5da0 100644
--- a/libgo/go/go/ast/resolve.go
+++ b/libgo/go/go/ast/resolve.go
@@ -14,12 +14,12 @@ import (
 )
 
 type pkgBuilder struct {
-	scanner.ErrorVector
-	fset *token.FileSet
+	fset   *token.FileSet
+	errors scanner.ErrorList
 }
 
 func (p *pkgBuilder) error(pos token.Pos, msg string) {
-	p.Error(p.fset.Position(pos), msg)
+	p.errors.Add(p.fset.Position(pos), msg)
 }
 
 func (p *pkgBuilder) errorf(pos token.Pos, format string, args ...interface{}) {
@@ -169,5 +169,6 @@ func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer,
 		pkgScope.Outer = universe // reset universe scope
 	}
 
-	return &Package{pkgName, pkgScope, imports, files}, p.GetError(scanner.Sorted)
+	p.errors.Sort()
+	return &Package{pkgName, pkgScope, imports, files}, p.errors.Err()
 }
diff --git a/libgo/go/go/build/dir.go b/libgo/go/go/build/dir.go
index 0917e736aa4..6b30f76265b 100644
--- a/libgo/go/go/build/dir.go
+++ b/libgo/go/go/build/dir.go
@@ -25,10 +25,11 @@ import (
 
 // A Context specifies the supporting context for a build.
 type Context struct {
-	GOARCH     string   // target architecture
-	GOOS       string   // target operating system
-	CgoEnabled bool     // whether cgo can be used
-	BuildTags  []string // additional tags to recognize in +build lines
+	GOARCH      string   // target architecture
+	GOOS        string   // target operating system
+	CgoEnabled  bool     // whether cgo can be used
+	BuildTags   []string // additional tags to recognize in +build lines
+	UseAllFiles bool     // use files regardless of +build lines, file names
 
 	// By default, ScanDir uses the operating system's
 	// file system calls to read directories and files.
@@ -225,6 +226,7 @@ func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
 
 	var Sfiles []string // files with ".S" (capital S)
 	var di DirInfo
+	var firstFile string
 	imported := make(map[string][]token.Position)
 	testImported := make(map[string][]token.Position)
 	fset := token.NewFileSet()
@@ -237,7 +239,7 @@ func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
 			strings.HasPrefix(name, ".") {
 			continue
 		}
-		if !ctxt.goodOSArchFile(name) {
+		if !ctxt.UseAllFiles && !ctxt.goodOSArchFile(name) {
 			continue
 		}
 
@@ -250,12 +252,13 @@ func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
 			continue
 		}
 
-		// Look for +build comments to accept or reject the file.
 		filename, data, err := ctxt.readFile(dir, name)
 		if err != nil {
 			return nil, err
 		}
-		if !ctxt.shouldBuild(data) {
+
+		// Look for +build comments to accept or reject the file.
+		if !ctxt.UseAllFiles && !ctxt.shouldBuild(data) {
 			continue
 		}
 
@@ -281,9 +284,6 @@ func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
 		}
 
 		pkg := string(pf.Name.Name)
-		if pkg == "main" && di.Package != "" && di.Package != "main" {
-			continue
-		}
 		if pkg == "documentation" {
 			continue
 		}
@@ -293,15 +293,11 @@ func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
 			pkg = pkg[:len(pkg)-len("_test")]
 		}
 
-		if pkg != di.Package && di.Package == "main" {
-			// Found non-main package but was recording
-			// information about package main.  Reset.
-			di = DirInfo{}
-		}
 		if di.Package == "" {
 			di.Package = pkg
+			firstFile = name
 		} else if pkg != di.Package {
-			return nil, fmt.Errorf("%s: found packages %s and %s", dir, pkg, di.Package)
+			return nil, fmt.Errorf("%s: found packages %s (%s) and %s (%s)", dir, di.Package, firstFile, pkg, name)
 		}
 		if pf.Doc != nil {
 			if di.PackageComment != nil {
diff --git a/libgo/go/go/build/path.go b/libgo/go/go/build/path.go
index 7e931faff19..e160ac3b280 100644
--- a/libgo/go/go/build/path.go
+++ b/libgo/go/go/build/path.go
@@ -12,6 +12,9 @@ import (
 	"runtime"
 )
 
+// ToolDir is the directory containing build tools.
+var ToolDir = filepath.Join(runtime.GOROOT(), "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
+
 // Path is a validated list of Trees derived from $GOROOT and $GOPATH at init.
 var Path []*Tree
 
diff --git a/libgo/go/go/doc/doc_test.go b/libgo/go/go/doc/doc_test.go
index 9ffe72032c2..f957ede4abf 100644
--- a/libgo/go/go/doc/doc_test.go
+++ b/libgo/go/go/doc/doc_test.go
@@ -14,12 +14,14 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 	"text/template"
 )
 
 var update = flag.Bool("update", false, "update golden (.out) files")
+var files = flag.String("files", "", "consider only Go test files matching this regular expression")
 
 const dataDir = "testdata"
 
@@ -66,14 +68,26 @@ type bundle struct {
 }
 
 func test(t *testing.T, mode Mode) {
-	// get all packages
+	// determine file filter
+	filter := isGoFile
+	if *files != "" {
+		rx, err := regexp.Compile(*files)
+		if err != nil {
+			t.Fatal(err)
+		}
+		filter = func(fi os.FileInfo) bool {
+			return isGoFile(fi) && rx.MatchString(fi.Name())
+		}
+	}
+
+	// get packages
 	fset := token.NewFileSet()
-	pkgs, err := parser.ParseDir(fset, dataDir, isGoFile, parser.ParseComments)
+	pkgs, err := parser.ParseDir(fset, dataDir, filter, parser.ParseComments)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	// test all packages
+	// test packages
 	for _, pkg := range pkgs {
 		importpath := dataDir + "/" + pkg.Name
 		doc := New(pkg, importpath, mode)
diff --git a/libgo/go/go/doc/example.go b/libgo/go/go/doc/example.go
index d5b58d26643..1c23b0d95c3 100644
--- a/libgo/go/go/doc/example.go
+++ b/libgo/go/go/doc/example.go
@@ -9,6 +9,7 @@ package doc
 import (
 	"go/ast"
 	"go/printer"
+	"go/token"
 	"strings"
 	"unicode"
 	"unicode/utf8"
@@ -21,28 +22,47 @@ type Example struct {
 }
 
 func Examples(pkg *ast.Package) []*Example {
-	var examples []*Example
-	for _, src := range pkg.Files {
-		for _, decl := range src.Decls {
+	var list []*Example
+	for _, file := range pkg.Files {
+		hasTests := false // file contains tests or benchmarks
+		numDecl := 0      // number of non-import declarations in the file
+		var flist []*Example
+		for _, decl := range file.Decls {
+			if g, ok := decl.(*ast.GenDecl); ok && g.Tok != token.IMPORT {
+				numDecl++
+				continue
+			}
 			f, ok := decl.(*ast.FuncDecl)
 			if !ok {
 				continue
 			}
+			numDecl++
 			name := f.Name.Name
+			if isTest(name, "Test") || isTest(name, "Benchmark") {
+				hasTests = true
+				continue
+			}
 			if !isTest(name, "Example") {
 				continue
 			}
-			examples = append(examples, &Example{
+			flist = append(flist, &Example{
 				Name: name[len("Example"):],
 				Body: &printer.CommentedNode{
 					Node:     f.Body,
-					Comments: src.Comments,
+					Comments: file.Comments,
 				},
 				Output: f.Doc.Text(),
 			})
 		}
+		if !hasTests && numDecl > 1 && len(flist) == 1 {
+			// If this file only has one example function, some
+			// other top-level declarations, and no tests or
+			// benchmarks, use the whole file as the example.
+			flist[0].Body.Node = file
+		}
+		list = append(list, flist...)
 	}
-	return examples
+	return list
 }
 
 // isTest tells whether name looks like a test, example, or benchmark.
diff --git a/libgo/go/go/doc/exports.go b/libgo/go/go/doc/exports.go
index 68dd3841bed..146be5d8707 100644
--- a/libgo/go/go/doc/exports.go
+++ b/libgo/go/go/doc/exports.go
@@ -22,12 +22,38 @@ func filterIdentList(list []*ast.Ident) []*ast.Ident {
 	return list[0:j]
 }
 
+// removeErrorField removes anonymous fields named "error" from an interface.
+// This is called when "error" has been determined to be a local name,
+// not the predeclared type.
+//
+func removeErrorField(ityp *ast.InterfaceType) {
+	list := ityp.Methods.List // we know that ityp.Methods != nil
+	j := 0
+	for _, field := range list {
+		keepField := true
+		if n := len(field.Names); n == 0 {
+			// anonymous field
+			if fname, _ := baseTypeName(field.Type); fname == "error" {
+				keepField = false
+			}
+		}
+		if keepField {
+			list[j] = field
+			j++
+		}
+	}
+	if j < len(list) {
+		ityp.Incomplete = true
+	}
+	ityp.Methods.List = list[0:j]
+}
+
 // filterFieldList removes unexported fields (field names) from the field list
 // in place and returns true if fields were removed. Anonymous fields are
 // recorded with the parent type. filterType is called with the types of
 // all remaining fields.
 //
-func (r *reader) filterFieldList(parent *namedType, fields *ast.FieldList) (removedFields bool) {
+func (r *reader) filterFieldList(parent *namedType, fields *ast.FieldList, ityp *ast.InterfaceType) (removedFields bool) {
 	if fields == nil {
 		return
 	}
@@ -37,9 +63,15 @@ func (r *reader) filterFieldList(parent *namedType, fields *ast.FieldList) (remo
 		keepField := false
 		if n := len(field.Names); n == 0 {
 			// anonymous field
-			name := r.recordAnonymousField(parent, field.Type)
-			if ast.IsExported(name) {
+			fname := r.recordAnonymousField(parent, field.Type)
+			if ast.IsExported(fname) {
+				keepField = true
+			} else if ityp != nil && fname == "error" {
+				// possibly the predeclared error interface; keep
+				// it for now but remember this interface so that
+				// it can be fixed if error is also defined locally
 				keepField = true
+				r.remember(ityp)
 			}
 		} else {
 			field.Names = filterIdentList(field.Names)
@@ -86,14 +118,14 @@ func (r *reader) filterType(parent *namedType, typ ast.Expr) {
 	case *ast.ArrayType:
 		r.filterType(nil, t.Elt)
 	case *ast.StructType:
-		if r.filterFieldList(parent, t.Fields) {
+		if r.filterFieldList(parent, t.Fields, nil) {
 			t.Incomplete = true
 		}
 	case *ast.FuncType:
 		r.filterParamList(t.Params)
 		r.filterParamList(t.Results)
 	case *ast.InterfaceType:
-		if r.filterFieldList(parent, t.Methods) {
+		if r.filterFieldList(parent, t.Methods, t) {
 			t.Incomplete = true
 		}
 	case *ast.MapType:
@@ -116,9 +148,12 @@ func (r *reader) filterSpec(spec ast.Spec) bool {
 			return true
 		}
 	case *ast.TypeSpec:
-		if ast.IsExported(s.Name.Name) {
+		if name := s.Name.Name; ast.IsExported(name) {
 			r.filterType(r.lookupType(s.Name.Name), s.Type)
 			return true
+		} else if name == "error" {
+			// special case: remember that error is declared locally
+			r.errorDecl = true
 		}
 	}
 	return false
diff --git a/libgo/go/go/doc/headscan.go b/libgo/go/go/doc/headscan.go
index 37486b126fd..f5593476382 100644
--- a/libgo/go/go/doc/headscan.go
+++ b/libgo/go/go/doc/headscan.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 /*
 	The headscan command extracts comment headings from package files;
 	it is used to detect false positives which may require an adjustment
diff --git a/libgo/go/go/doc/reader.go b/libgo/go/go/doc/reader.go
index dcf49f68fd3..bdfb294adb0 100644
--- a/libgo/go/go/doc/reader.go
+++ b/libgo/go/go/doc/reader.go
@@ -17,7 +17,7 @@ import (
 //
 // Internally, we treat functions like methods and collect them in method sets.
 
-// methodSet describes a set of methods. Entries where Decl == nil are conflict
+// A methodSet describes a set of methods. Entries where Decl == nil are conflict
 // entries (more then one method with the same name at the same embedding level).
 //
 type methodSet map[string]*Func
@@ -110,6 +110,9 @@ func baseTypeName(x ast.Expr) (name string, imported bool) {
 	return
 }
 
+// An embeddedSet describes a set of embedded types.
+type embeddedSet map[*namedType]bool
+
 // A namedType represents a named unqualified (package local, or possibly
 // predeclared) type. The namedType for a type name is always found via
 // reader.lookupType.
@@ -119,9 +122,9 @@ type namedType struct {
 	name string       // type name
 	decl *ast.GenDecl // nil if declaration hasn't been seen yet
 
-	isEmbedded bool                // true if this type is embedded
-	isStruct   bool                // true if this type is a struct
-	embedded   map[*namedType]bool // true if the embedded type is a pointer
+	isEmbedded bool        // true if this type is embedded
+	isStruct   bool        // true if this type is a struct
+	embedded   embeddedSet // true if the embedded type is a pointer
 
 	// associated declarations
 	values  []*Value // consts and vars
@@ -152,6 +155,10 @@ type reader struct {
 	values  []*Value // consts and vars
 	types   map[string]*namedType
 	funcs   methodSet
+
+	// support for package-local error type declarations
+	errorDecl bool                 // if set, type "error" was declared locally
+	fixlist   []*ast.InterfaceType // list of interfaces containing anonymous field "error"
 }
 
 func (r *reader) isVisible(name string) bool {
@@ -173,7 +180,7 @@ func (r *reader) lookupType(name string) *namedType {
 	// type not found - add one without declaration
 	typ := &namedType{
 		name:     name,
-		embedded: make(map[*namedType]bool),
+		embedded: make(embeddedSet),
 		funcs:    make(methodSet),
 		methods:  make(methodSet),
 	}
@@ -210,6 +217,10 @@ func (r *reader) readDoc(comment *ast.CommentGroup) {
 	r.doc += "\n" + text
 }
 
+func (r *reader) remember(typ *ast.InterfaceType) {
+	r.fixlist = append(r.fixlist, typ)
+}
+
 func specNames(specs []ast.Spec) []string {
 	names := make([]string, 0, len(specs)) // reasonable estimate
 	for _, s := range specs {
@@ -274,7 +285,7 @@ func (r *reader) readValue(decl *ast.GenDecl) {
 	// determine values list with which to associate the Value for this decl
 	values := &r.values
 	const threshold = 0.75
-	if domName != "" && domFreq >= int(float64(len(decl.Specs))*threshold) {
+	if domName != "" && r.isVisible(domName) && domFreq >= int(float64(len(decl.Specs))*threshold) {
 		// typed entries are sufficiently frequent
 		if typ := r.lookupType(domName); typ != nil {
 			values = &typ.values // associate with that type
@@ -315,7 +326,7 @@ func (r *reader) readType(decl *ast.GenDecl, spec *ast.TypeSpec) {
 		return // no name or blank name - ignore the type
 	}
 
-	// A type should be added at most once, so info.decl
+	// A type should be added at most once, so typ.decl
 	// should be nil - if it is not, simply overwrite it.
 	typ.decl = decl
 
@@ -543,7 +554,8 @@ func customizeRecv(f *Func, recvTypeName string, embeddedIsPtr bool, level int)
 
 // collectEmbeddedMethods collects the embedded methods of typ in mset.
 //
-func (r *reader) collectEmbeddedMethods(mset methodSet, typ *namedType, recvTypeName string, embeddedIsPtr bool, level int) {
+func (r *reader) collectEmbeddedMethods(mset methodSet, typ *namedType, recvTypeName string, embeddedIsPtr bool, level int, visited embeddedSet) {
+	visited[typ] = true
 	for embedded, isPtr := range typ.embedded {
 		// Once an embedded type is embedded as a pointer type
 		// all embedded types in those types are treated like
@@ -557,8 +569,11 @@ func (r *reader) collectEmbeddedMethods(mset methodSet, typ *namedType, recvType
 				mset.add(customizeRecv(m, recvTypeName, thisEmbeddedIsPtr, level))
 			}
 		}
-		r.collectEmbeddedMethods(mset, embedded, recvTypeName, thisEmbeddedIsPtr, level+1)
+		if !visited[embedded] {
+			r.collectEmbeddedMethods(mset, embedded, recvTypeName, thisEmbeddedIsPtr, level+1, visited)
+		}
 	}
+	delete(visited, typ)
 }
 
 // computeMethodSets determines the actual method sets for each type encountered.
@@ -568,12 +583,19 @@ func (r *reader) computeMethodSets() {
 		// collect embedded methods for t
 		if t.isStruct {
 			// struct
-			r.collectEmbeddedMethods(t.methods, t, t.name, false, 1)
+			r.collectEmbeddedMethods(t.methods, t, t.name, false, 1, make(embeddedSet))
 		} else {
 			// interface
 			// TODO(gri) fix this
 		}
 	}
+
+	// if error was declared locally, don't treat it as exported field anymore
+	if r.errorDecl {
+		for _, ityp := range r.fixlist {
+			removeErrorField(ityp)
+		}
+	}
 }
 
 // cleanupTypes removes the association of functions and methods with
diff --git a/libgo/go/go/doc/testdata/b.0.golden b/libgo/go/go/doc/testdata/b.0.golden
index 7c33300616d..9d93392eaa5 100644
--- a/libgo/go/go/doc/testdata/b.0.golden
+++ b/libgo/go/go/doc/testdata/b.0.golden
@@ -12,18 +12,46 @@ FILENAMES
 
 CONSTANTS
 	// 
+	const (
+		C1	notExported	= iota
+		C2
+	
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
 	const Pi = 3.14	// Pi
 
 
 VARIABLES
 	// 
+	var (
+		U1, U2, U4, U5	notExported
+	
+		U7	notExported	= 7
+	)
+
+	// 
 	var MaxInt int	// MaxInt
 
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, V4, V5 notExported
+
 
 FUNCTIONS
 	// 
 	func F(x int) int
 
+	// 
+	func F1() notExported
+
 	// Always under the package functions list. 
 	func NotAFactory() int
 
diff --git a/libgo/go/go/doc/testdata/b.1.golden b/libgo/go/go/doc/testdata/b.1.golden
index f30380516bd..66c47b5c2a7 100644
--- a/libgo/go/go/doc/testdata/b.1.golden
+++ b/libgo/go/go/doc/testdata/b.1.golden
@@ -38,8 +38,42 @@ TYPES
 	// 
 	func (x *T) M()
 
+	// 
+	type notExported int
+
+	// 
+	const (
+		C1	notExported	= iota
+		C2
+		c3
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
+	var (
+		U1, U2, u3, U4, U5	notExported
+		u6			notExported
+		U7			notExported	= 7
+	)
+
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, v3, V4, V5 notExported
+
+	// 
+	func F1() notExported
+
+	// 
+	func f2() notExported
+
 	// Should only appear if AllDecls is set. 
-	type uint struct{}
+	type uint struct{}	// overrides a predeclared type uint
 
 	// Associated with uint type if AllDecls is set. 
 	func UintFactory() uint
diff --git a/libgo/go/go/doc/testdata/b.2.golden b/libgo/go/go/doc/testdata/b.2.golden
index 7c33300616d..9d93392eaa5 100644
--- a/libgo/go/go/doc/testdata/b.2.golden
+++ b/libgo/go/go/doc/testdata/b.2.golden
@@ -12,18 +12,46 @@ FILENAMES
 
 CONSTANTS
 	// 
+	const (
+		C1	notExported	= iota
+		C2
+	
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
 	const Pi = 3.14	// Pi
 
 
 VARIABLES
 	// 
+	var (
+		U1, U2, U4, U5	notExported
+	
+		U7	notExported	= 7
+	)
+
+	// 
 	var MaxInt int	// MaxInt
 
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, V4, V5 notExported
+
 
 FUNCTIONS
 	// 
 	func F(x int) int
 
+	// 
+	func F1() notExported
+
 	// Always under the package functions list. 
 	func NotAFactory() int
 
diff --git a/libgo/go/go/doc/testdata/b.go b/libgo/go/go/doc/testdata/b.go
index 28660f9be7c..e50663b3dfa 100644
--- a/libgo/go/go/doc/testdata/b.go
+++ b/libgo/go/go/doc/testdata/b.go
@@ -6,6 +6,7 @@ package b
 
 import "a"
 
+// ----------------------------------------------------------------------------
 // Basic declarations
 
 const Pi = 3.14   // Pi
@@ -28,3 +29,30 @@ func uintFactory() uint {}
 
 // Should only appear if AllDecls is set.
 type uint struct{} // overrides a predeclared type uint
+
+// ----------------------------------------------------------------------------
+// Exported declarations associated with non-exported types must always be shown.
+
+type notExported int
+
+const C notExported = 0
+
+const (
+	C1 notExported = iota
+	C2
+	c3
+	C4
+	C5
+)
+
+var V notExported
+var V1, V2, v3, V4, V5 notExported
+
+var (
+	U1, U2, u3, U4, U5 notExported
+	u6                 notExported
+	U7                 notExported = 7
+)
+
+func F1() notExported {}
+func f2() notExported {}
diff --git a/libgo/go/go/doc/testdata/e.0.golden b/libgo/go/go/doc/testdata/e.0.golden
index 096a50ff41f..6987e5867cf 100644
--- a/libgo/go/go/doc/testdata/e.0.golden
+++ b/libgo/go/go/doc/testdata/e.0.golden
@@ -40,3 +40,70 @@ TYPES
 		T4
 	}
 
+	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		// contains filtered or unexported fields
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
diff --git a/libgo/go/go/doc/testdata/e.1.golden b/libgo/go/go/doc/testdata/e.1.golden
index 28be74a1fd6..cbe22e0bf63 100644
--- a/libgo/go/go/doc/testdata/e.1.golden
+++ b/libgo/go/go/doc/testdata/e.1.golden
@@ -43,6 +43,73 @@ TYPES
 	}
 
 	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		*u5
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
+	// 
 	type t1 struct{}
 
 	// t1.M should not appear as method in a Tx type. 
@@ -70,3 +137,8 @@ TYPES
 	// t2.M should not appear as method in a Tx type. 
 	func (t2e) M()
 
+	// 
+	type u5 struct {
+		*U4
+	}
+
diff --git a/libgo/go/go/doc/testdata/e.2.golden b/libgo/go/go/doc/testdata/e.2.golden
index f9a2b816774..e7b05e80faf 100644
--- a/libgo/go/go/doc/testdata/e.2.golden
+++ b/libgo/go/go/doc/testdata/e.2.golden
@@ -43,3 +43,88 @@ TYPES
 	// T4.M should appear as method of T5 only if AllMethods is set. 
 	func (*T5) M()
 
+	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (U2) N()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (U3) M()
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		// contains filtered or unexported fields
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (V1) M()
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (V2) M()
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (V3) M()
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (V5) M()
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
diff --git a/libgo/go/go/doc/testdata/e.go b/libgo/go/go/doc/testdata/e.go
index 526a91f4f00..19dd138cf40 100644
--- a/libgo/go/go/doc/testdata/e.go
+++ b/libgo/go/go/doc/testdata/e.go
@@ -1,4 +1,4 @@
-// Copyright 2011 The Go Authors. All rights reserved.
+// 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.
 
@@ -77,3 +77,71 @@ func (*T4) M() {}
 type T5 struct {
 	T4
 }
+
+// ----------------------------------------------------------------------------
+// Recursive type declarations must not lead to endless recursion.
+
+type U1 struct {
+	*U1
+}
+
+// U1.M should appear as method of U1.
+func (*U1) M() {}
+
+type U2 struct {
+	*U3
+}
+
+// U2.M should appear as method of U2 and as method of U3 only if AllMethods is set.
+func (*U2) M() {}
+
+type U3 struct {
+	*U2
+}
+
+// U3.N should appear as method of U3 and as method of U2 only if AllMethods is set.
+func (*U3) N() {}
+
+type U4 struct {
+	*u5
+}
+
+// U4.M should appear as method of U4. 
+func (*U4) M() {}
+
+type u5 struct {
+	*U4
+}
+
+// ----------------------------------------------------------------------------
+// A higher-level embedded type (and its methods) wins over the same type (and
+// its methods) embedded at a lower level.
+
+type V1 struct {
+	*V2
+	*V5
+}
+
+type V2 struct {
+	*V3
+}
+
+type V3 struct {
+	*V4
+}
+
+type V4 struct {
+	*V5
+}
+
+type V5 struct {
+	*V6
+}
+
+type V6 struct{}
+
+// V4.M should appear as method of V2 and V3 if AllMethods is set.
+func (*V4) M() {}
+
+// V6.M should appear as method of V1 and V5 if AllMethods is set.
+func (*V6) M() {}
diff --git a/libgo/go/go/doc/testdata/error1.0.golden b/libgo/go/go/doc/testdata/error1.0.golden
new file mode 100644
index 00000000000..6c6fe5d49bd
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error1.0.golden
@@ -0,0 +1,30 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/libgo/go/go/doc/testdata/error1.1.golden b/libgo/go/go/doc/testdata/error1.1.golden
new file mode 100644
index 00000000000..a8dc2e71dc3
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error1.1.golden
@@ -0,0 +1,32 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// In struct types, an embedded error must only be visible
+		// if AllDecls is set.
+		error
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/libgo/go/go/doc/testdata/error1.2.golden b/libgo/go/go/doc/testdata/error1.2.golden
new file mode 100644
index 00000000000..6c6fe5d49bd
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error1.2.golden
@@ -0,0 +1,30 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/libgo/go/go/doc/testdata/error1.go b/libgo/go/go/doc/testdata/error1.go
new file mode 100644
index 00000000000..3c777a78005
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error1.go
@@ -0,0 +1,24 @@
+// 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.
+
+package error1
+
+type I0 interface {
+	// When embedded, the predeclared error interface
+	// must remain visible in interface types.
+	error
+}
+
+type T0 struct {
+	ExportedField interface {
+		// error should be visible
+		error
+	}
+}
+
+type S0 struct {
+	// In struct types, an embedded error must only be visible
+	// if AllDecls is set.
+	error
+}
diff --git a/libgo/go/go/doc/testdata/error2.0.golden b/libgo/go/go/doc/testdata/error2.0.golden
new file mode 100644
index 00000000000..dedfe412a0f
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error2.0.golden
@@ -0,0 +1,27 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// contains filtered or unexported methods
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// contains filtered or unexported methods
+		}
+	}
+
diff --git a/libgo/go/go/doc/testdata/error2.1.golden b/libgo/go/go/doc/testdata/error2.1.golden
new file mode 100644
index 00000000000..776bd1b3e40
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error2.1.golden
@@ -0,0 +1,37 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the the locally declared error interface
+		// is only visible if all declarations are shown.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// In struct types, an embedded error must only be visible
+		// if AllDecls is set.
+		error
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should not be visible
+			error
+		}
+	}
+
+	// This error declaration shadows the predeclared error type. 
+	type error interface {
+		Error() string
+	}
+
diff --git a/libgo/go/go/doc/testdata/error2.2.golden b/libgo/go/go/doc/testdata/error2.2.golden
new file mode 100644
index 00000000000..dedfe412a0f
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error2.2.golden
@@ -0,0 +1,27 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// contains filtered or unexported methods
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// contains filtered or unexported methods
+		}
+	}
+
diff --git a/libgo/go/go/doc/testdata/error2.go b/libgo/go/go/doc/testdata/error2.go
new file mode 100644
index 00000000000..6cc36feef3e
--- /dev/null
+++ b/libgo/go/go/doc/testdata/error2.go
@@ -0,0 +1,29 @@
+// 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.
+
+package error2
+
+type I0 interface {
+	// When embedded, the the locally declared error interface
+	// is only visible if all declarations are shown.
+	error
+}
+
+type T0 struct {
+	ExportedField interface {
+		// error should not be visible
+		error
+	}
+}
+
+type S0 struct {
+	// In struct types, an embedded error must only be visible
+	// if AllDecls is set.
+	error
+}
+
+// This error declaration shadows the predeclared error type.
+type error interface {
+	Error() string
+}
diff --git a/libgo/go/go/doc/testdata/f.go b/libgo/go/go/doc/testdata/f.go
index a3051e1fb3b..7e9add90784 100644
--- a/libgo/go/go/doc/testdata/f.go
+++ b/libgo/go/go/doc/testdata/f.go
@@ -1,4 +1,4 @@
-// Copyright 2011 The Go Authors. All rights reserved.
+// 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.
 
diff --git a/libgo/go/go/parser/interface.go b/libgo/go/go/parser/interface.go
index f1b4ce34d1a..5c203a7846e 100644
--- a/libgo/go/go/parser/interface.go
+++ b/libgo/go/go/parser/interface.go
@@ -80,13 +80,25 @@ const (
 // are returned via a scanner.ErrorList which is sorted by file position.
 //
 func ParseFile(fset *token.FileSet, filename string, src interface{}, mode Mode) (*ast.File, error) {
+	// get source
 	text, err := readSource(filename, src)
 	if err != nil {
 		return nil, err
 	}
+
+	// parse source
 	var p parser
 	p.init(fset, filename, text, mode)
-	return p.parseFile(), p.errors()
+	f := p.parseFile()
+
+	// sort errors
+	if p.mode&SpuriousErrors == 0 {
+		p.errors.RemoveMultiples()
+	} else {
+		p.errors.Sort()
+	}
+
+	return f, p.errors.Err()
 }
 
 // ParseDir calls ParseFile for the files in the directory specified by path and
diff --git a/libgo/go/go/parser/parser.go b/libgo/go/go/parser/parser.go
index 6bee8de9f65..6a0b61eb48c 100644
--- a/libgo/go/go/parser/parser.go
+++ b/libgo/go/go/parser/parser.go
@@ -18,8 +18,8 @@ import (
 
 // The parser structure holds the parser's internal state.
 type parser struct {
-	file *token.File
-	scanner.ErrorVector
+	file    *token.File
+	errors  scanner.ErrorList
 	scanner scanner.Scanner
 
 	// Tracing/debugging
@@ -58,7 +58,8 @@ func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mod
 	if mode&ParseComments != 0 {
 		m = scanner.ScanComments
 	}
-	p.scanner.Init(p.file, src, p, m)
+	eh := func(pos token.Position, msg string) { p.errors.Add(pos, msg) }
+	p.scanner.Init(p.file, src, eh, m)
 
 	p.mode = mode
 	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
@@ -74,14 +75,6 @@ func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mod
 	p.openLabelScope()
 }
 
-func (p *parser) errors() error {
-	m := scanner.Sorted
-	if p.mode&SpuriousErrors == 0 {
-		m = scanner.NoMultiples
-	}
-	return p.GetError(m)
-}
-
 // ----------------------------------------------------------------------------
 // Scoping support
 
@@ -334,7 +327,7 @@ func (p *parser) next() {
 }
 
 func (p *parser) error(pos token.Pos, msg string) {
-	p.Error(p.file.Position(pos), msg)
+	p.errors.Add(p.file.Position(pos), msg)
 }
 
 func (p *parser) errorExpected(pos token.Pos, msg string) {
@@ -342,7 +335,7 @@ func (p *parser) errorExpected(pos token.Pos, msg string) {
 	if pos == p.pos {
 		// the error happened at the current position;
 		// make the error message more specific
-		if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
+		if p.tok == token.SEMICOLON && p.lit == "\n" {
 			msg += ", found newline"
 		} else {
 			msg += ", found '" + p.tok.String() + "'"
@@ -363,6 +356,17 @@ func (p *parser) expect(tok token.Token) token.Pos {
 	return pos
 }
 
+// expectClosing is like expect but provides a better error message
+// for the common case of a missing comma before a newline.
+//
+func (p *parser) expectClosing(tok token.Token, construct string) token.Pos {
+	if p.tok != tok && p.tok == token.SEMICOLON && p.lit == "\n" {
+		p.error(p.pos, "missing ',' before newline in "+construct)
+		p.next()
+	}
+	return p.expect(tok)
+}
+
 func (p *parser) expectSemi() {
 	if p.tok != token.RPAREN && p.tok != token.RBRACE {
 		p.expect(token.SEMICOLON)
@@ -1063,7 +1067,7 @@ func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
 		p.next()
 	}
 	p.exprLev--
-	rparen := p.expect(token.RPAREN)
+	rparen := p.expectClosing(token.RPAREN, "argument list")
 
 	return &ast.CallExpr{fun, lparen, list, ellipsis, rparen}
 }
@@ -1118,7 +1122,7 @@ func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
 		elts = p.parseElementList()
 	}
 	p.exprLev--
-	rbrace := p.expect(token.RBRACE)
+	rbrace := p.expectClosing(token.RBRACE, "composite literal")
 	return &ast.CompositeLit{typ, lbrace, elts, rbrace}
 }
 
@@ -2123,7 +2127,7 @@ func (p *parser) parseFile() *ast.File {
 	// Don't bother parsing the rest if we had errors already.
 	// Likely not a Go source file at all.
 
-	if p.ErrorCount() == 0 && p.mode&PackageClauseOnly == 0 {
+	if p.errors.Len() == 0 && p.mode&PackageClauseOnly == 0 {
 		// import decls
 		for p.tok == token.IMPORT {
 			decls = append(decls, p.parseGenDecl(token.IMPORT, parseImportSpec))
diff --git a/libgo/go/go/printer/performance_test.go b/libgo/go/go/printer/performance_test.go
index dbd942292b5..0c6a4e71f13 100644
--- a/libgo/go/go/printer/performance_test.go
+++ b/libgo/go/go/printer/performance_test.go
@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // This file implements a simple printer performance benchmark:
-// gotest -bench=BenchmarkPrint 
+// go test -bench=BenchmarkPrint 
 
 package printer
 
diff --git a/libgo/go/go/printer/printer.go b/libgo/go/go/printer/printer.go
index fe99e675eb0..c9949205e8a 100644
--- a/libgo/go/go/printer/printer.go
+++ b/libgo/go/go/printer/printer.go
@@ -6,7 +6,6 @@
 package printer
 
 import (
-	"bytes"
 	"fmt"
 	"go/ast"
 	"go/token"
@@ -51,22 +50,22 @@ type printer struct {
 	fset *token.FileSet
 
 	// Current state
-	output      bytes.Buffer // raw printer result
+	output      []byte       // raw printer result
 	indent      int          // current indentation
 	mode        pmode        // current printer mode
 	impliedSemi bool         // if set, a linebreak implies a semicolon
 	lastTok     token.Token  // the last token printed (token.ILLEGAL if it's whitespace)
 	wsbuf       []whiteSpace // delayed white space
 
-	// The (possibly estimated) position in the generated output;
-	// in AST space (i.e., pos is set whenever a token position is
-	// known accurately, and updated dependending on what has been
-	// written).
-	pos token.Position
-
-	// The value of pos immediately after the last item has been
-	// written using writeItem.
-	last token.Position
+	// Positions
+	// The out position differs from the pos position when the result
+	// formatting differs from the source formatting (in the amount of
+	// white space). If there's a difference and SourcePos is set in
+	// ConfigMode, //line comments are used in the output to restore
+	// original source positions for a reader.
+	pos  token.Position // current position in AST (source) space
+	out  token.Position // current position in output space
+	last token.Position // value of pos after calling writeString
 
 	// The list of all source comments, in order of appearance.
 	comments        []*ast.CommentGroup // may be nil
@@ -89,6 +88,8 @@ type printer struct {
 func (p *printer) init(cfg *Config, fset *token.FileSet, nodeSizes map[ast.Node]int) {
 	p.Config = *cfg
 	p.fset = fset
+	p.pos = token.Position{Line: 1, Column: 1}
+	p.out = token.Position{Line: 1, Column: 1}
 	p.wsbuf = make([]whiteSpace, 0, 16) // whitespace sequences are short
 	p.nodeSizes = nodeSizes
 	p.cachedPos = -1
@@ -151,41 +152,57 @@ func (p *printer) lineFor(pos token.Pos) int {
 	return p.cachedLine
 }
 
-// writeByte writes ch to p.output and updates p.pos.
-func (p *printer) writeByte(ch byte) {
-	p.output.WriteByte(ch)
-	p.pos.Offset++
-	p.pos.Column++
-
-	if ch == '\n' || ch == '\f' {
-		// write indentation
-		// use "hard" htabs - indentation columns
-		// must not be discarded by the tabwriter
-		const htabs = "\t\t\t\t\t\t\t\t"
-		j := p.indent
-		for j > len(htabs) {
-			p.output.WriteString(htabs)
-			j -= len(htabs)
-		}
-		p.output.WriteString(htabs[0:j])
+// atLineBegin emits a //line comment if necessary and prints indentation.
+func (p *printer) atLineBegin(pos token.Position) {
+	// write a //line comment if necessary
+	if p.Config.Mode&SourcePos != 0 && pos.IsValid() && (p.out.Line != pos.Line || p.out.Filename != pos.Filename) {
+		p.output = append(p.output, tabwriter.Escape) // protect '\n' in //line from tabwriter interpretation
+		p.output = append(p.output, fmt.Sprintf("//line %s:%d\n", pos.Filename, pos.Line)...)
+		p.output = append(p.output, tabwriter.Escape)
+		// p.out must match the //line comment
+		p.out.Filename = pos.Filename
+		p.out.Line = pos.Line
+	}
 
-		// update p.pos
-		p.pos.Line++
-		p.pos.Offset += p.indent
-		p.pos.Column = 1 + p.indent
+	// write indentation
+	// use "hard" htabs - indentation columns
+	// must not be discarded by the tabwriter
+	for i := 0; i < p.indent; i++ {
+		p.output = append(p.output, '\t')
 	}
+
+	// update positions
+	i := p.indent
+	p.pos.Offset += i
+	p.pos.Column += i
+	p.out.Column += i
 }
 
-// writeByteN writes ch n times to p.output and updates p.pos.
-func (p *printer) writeByteN(ch byte, n int) {
-	for n > 0 {
-		p.writeByte(ch)
-		n--
+// writeByte writes ch n times to p.output and updates p.pos.
+func (p *printer) writeByte(ch byte, n int) {
+	if p.out.Column == 1 {
+		p.atLineBegin(p.pos)
+	}
+
+	for i := 0; i < n; i++ {
+		p.output = append(p.output, ch)
+	}
+
+	// update positions
+	p.pos.Offset += n
+	if ch == '\n' || ch == '\f' {
+		p.pos.Line += n
+		p.out.Line += n
+		p.pos.Column = 1
+		p.out.Column = 1
+		return
 	}
+	p.pos.Column += n
+	p.out.Column += n
 }
 
-// writeString writes the string s to p.output and updates p.pos.
-// If isLit is set, s is escaped w/ tabwriter.Escape characters
+// writeString writes the string s to p.output and updates p.pos, p.out,
+// and p.last. If isLit is set, s is escaped w/ tabwriter.Escape characters
 // to protect s from being interpreted by the tabwriter.
 //
 // Note: writeString is only used to write Go tokens, literals, and
@@ -195,64 +212,69 @@ func (p *printer) writeByteN(ch byte, n int) {
 // avoids processing extra escape characters and reduces run time of the
 // printer benchmark by up to 10%.
 //
-func (p *printer) writeString(s string, isLit bool) {
+func (p *printer) writeString(pos token.Position, s string, isLit bool) {
+	if p.out.Column == 1 {
+		p.atLineBegin(pos)
+	}
+
+	if pos.IsValid() {
+		// update p.pos (if pos is invalid, continue with existing p.pos)
+		// Note: Must do this after handling line beginnings because
+		// atLineBegin updates p.pos if there's indentation, but p.pos
+		// is the position of s.
+		p.pos = pos
+		// reset state if the file changed
+		// (used when printing merged ASTs of different files
+		// e.g., the result of ast.MergePackageFiles)
+		if p.last.IsValid() && p.last.Filename != pos.Filename {
+			p.indent = 0
+			p.mode = 0
+			p.wsbuf = p.wsbuf[0:0]
+		}
+	}
+
 	if isLit {
 		// Protect s such that is passes through the tabwriter
 		// unchanged. Note that valid Go programs cannot contain
 		// tabwriter.Escape bytes since they do not appear in legal
 		// UTF-8 sequences.
-		p.output.WriteByte(tabwriter.Escape)
+		p.output = append(p.output, tabwriter.Escape)
 	}
 
-	p.output.WriteString(s)
+	if debug {
+		p.output = append(p.output, fmt.Sprintf("/*%s*/", pos)...) // do not update p.pos!
+	}
+	p.output = append(p.output, s...)
 
-	// update p.pos
+	// update positions
 	nlines := 0
-	column := p.pos.Column + len(s)
+	var li int // index of last newline; valid if nlines > 0
 	for i := 0; i < len(s); i++ {
+		// Go tokens cannot contain '\f' - no need to look for it
 		if s[i] == '\n' {
 			nlines++
-			column = len(s) - i
+			li = i
 		}
 	}
 	p.pos.Offset += len(s)
-	p.pos.Line += nlines
-	p.pos.Column = column
+	if nlines > 0 {
+		p.pos.Line += nlines
+		p.out.Line += nlines
+		c := len(s) - li
+		p.pos.Column = c
+		p.out.Column = c
+	} else {
+		p.pos.Column += len(s)
+		p.out.Column += len(s)
+	}
 
 	if isLit {
-		p.output.WriteByte(tabwriter.Escape)
+		p.output = append(p.output, tabwriter.Escape)
 	}
-}
 
-// writeItem writes data at position pos. data is the text corresponding to
-// a single lexical token, but may also be comment text. pos is the actual
-// (or at least very accurately estimated) position of the data in the original
-// source text. writeItem updates p.last to the position immediately following
-// the data.
-//
-func (p *printer) writeItem(pos token.Position, data string, isLit bool) {
-	if pos.IsValid() {
-		// continue with previous position if we don't have a valid pos
-		if p.last.IsValid() && p.last.Filename != pos.Filename {
-			// the file has changed - reset state
-			// (used when printing merged ASTs of different files
-			// e.g., the result of ast.MergePackageFiles)
-			p.indent = 0
-			p.mode = 0
-			p.wsbuf = p.wsbuf[0:0]
-		}
-		p.pos = pos
-	}
-	if debug {
-		// do not update p.pos - use write0
-		fmt.Fprintf(&p.output, "/*%s*/", pos)
-	}
-	p.writeString(data, isLit)
 	p.last = p.pos
 }
 
-const linePrefix = "//line "
-
 // writeCommentPrefix writes the whitespace before a comment.
 // If there is any pending whitespace, it consumes as much of
 // it as is likely to help position the comment nicely.
@@ -262,14 +284,14 @@ const linePrefix = "//line "
 // next item is a keyword.
 //
 func (p *printer) writeCommentPrefix(pos, next token.Position, prev, comment *ast.Comment, isKeyword bool) {
-	if p.output.Len() == 0 {
+	if len(p.output) == 0 {
 		// the comment is the first item to be printed - don't write any whitespace
 		return
 	}
 
 	if pos.IsValid() && pos.Filename != p.last.Filename {
 		// comment in a different file - separate with newlines
-		p.writeByteN('\f', maxNewlines)
+		p.writeByte('\f', maxNewlines)
 		return
 	}
 
@@ -309,7 +331,7 @@ func (p *printer) writeCommentPrefix(pos, next token.Position, prev, comment *as
 				// with a blank instead of a tab
 				sep = ' '
 			}
-			p.writeByte(sep)
+			p.writeByte(sep, 1)
 		}
 
 	} else {
@@ -373,23 +395,17 @@ func (p *printer) writeCommentPrefix(pos, next token.Position, prev, comment *as
 		}
 
 		if n > 0 {
-			// turn off indent if we're about to print a line directive
-			indent := p.indent
-			if strings.HasPrefix(comment.Text, linePrefix) {
-				p.indent = 0
-			}
 			// use formfeeds to break columns before a comment;
 			// this is analogous to using formfeeds to separate
 			// individual lines of /*-style comments
-			p.writeByteN('\f', nlimit(n))
-			p.indent = indent // restore indent
+			p.writeByte('\f', nlimit(n))
 		}
 	}
 }
 
 // Split comment text into lines
 // (using strings.Split(text, "\n") is significantly slower for
-// this specific purpose, as measured with: gotest -bench=Print)
+// this specific purpose, as measured with: go test -bench=Print)
 func split(text string) []string {
 	// count lines (comment text never ends in a newline)
 	n := 1
@@ -564,30 +580,33 @@ func stripCommonPrefix(lines []string) {
 
 func (p *printer) writeComment(comment *ast.Comment) {
 	text := comment.Text
+	pos := p.posFor(comment.Pos())
 
-	if strings.HasPrefix(text, linePrefix) {
-		pos := strings.TrimSpace(text[len(linePrefix):])
-		i := strings.LastIndex(pos, ":")
-		if i >= 0 {
-			// The line directive we are about to print changed
-			// the Filename and Line number used by go/token
-			// as it was reading the input originally.
-			// In order to match the original input, we have to
-			// update our own idea of the file and line number
-			// accordingly, after printing the directive.
-			file := pos[:i]
-			line, _ := strconv.Atoi(pos[i+1:])
-			defer func() {
-				p.pos.Filename = file
-				p.pos.Line = line
-				p.pos.Column = 1
-			}()
+	const linePrefix = "//line "
+	if strings.HasPrefix(text, linePrefix) && (!pos.IsValid() || pos.Column == 1) {
+		// possibly a line directive
+		ldir := strings.TrimSpace(text[len(linePrefix):])
+		if i := strings.LastIndex(ldir, ":"); i >= 0 {
+			if line, err := strconv.Atoi(ldir[i+1:]); err == nil && line > 0 {
+				// The line directive we are about to print changed
+				// the Filename and Line number used for subsequent
+				// tokens. We have to update our AST-space position
+				// accordingly and suspend indentation temporarily.
+				indent := p.indent
+				p.indent = 0
+				defer func() {
+					p.pos.Filename = ldir[:i]
+					p.pos.Line = line
+					p.pos.Column = 1
+					p.indent = indent
+				}()
+			}
 		}
 	}
 
 	// shortcut common case of //-style comments
 	if text[1] == '/' {
-		p.writeItem(p.posFor(comment.Pos()), text, true)
+		p.writeString(pos, text, true)
 		return
 	}
 
@@ -598,14 +617,13 @@ func (p *printer) writeComment(comment *ast.Comment) {
 
 	// write comment lines, separated by formfeed,
 	// without a line break after the last line
-	pos := p.posFor(comment.Pos())
 	for i, line := range lines {
 		if i > 0 {
-			p.writeByte('\f')
+			p.writeByte('\f', 1)
 			pos = p.pos
 		}
 		if len(line) > 0 {
-			p.writeItem(pos, line, true)
+			p.writeString(pos, line, true)
 		}
 	}
 }
@@ -643,7 +661,7 @@ func (p *printer) writeCommentSuffix(needsLinebreak bool) (wroteNewline, dropped
 
 	// make sure we have a line break
 	if needsLinebreak {
-		p.writeByte('\n')
+		p.writeByte('\n', 1)
 		wroteNewline = true
 	}
 
@@ -671,7 +689,7 @@ func (p *printer) intersperseComments(next token.Position, tok token.Token) (wro
 		if last.Text[1] == '*' && p.lineFor(last.Pos()) == next.Line {
 			// the last comment is a /*-style comment and the next item
 			// follows on the same line: separate with an extra blank
-			p.writeByte(' ')
+			p.writeByte(' ', 1)
 		}
 		// ensure that there is a line break after a //-style comment,
 		// before a closing '}' unless explicitly disabled, or at eof
@@ -722,7 +740,7 @@ func (p *printer) writeWhitespace(n int) {
 			}
 			fallthrough
 		default:
-			p.writeByte(byte(ch))
+			p.writeByte(byte(ch), 1)
 		}
 	}
 
@@ -886,12 +904,12 @@ func (p *printer) print(args ...interface{}) {
 				if droppedFF {
 					ch = '\f' // use formfeed since we dropped one before
 				}
-				p.writeByteN(ch, n)
+				p.writeByte(ch, n)
 				impliedSemi = false
 			}
 		}
 
-		p.writeItem(next, data, isLit)
+		p.writeString(next, data, isLit)
 		p.impliedSemi = impliedSemi
 	}
 }
@@ -1027,7 +1045,7 @@ unsupported:
 type trimmer struct {
 	output io.Writer
 	state  int
-	space  bytes.Buffer
+	space  []byte
 }
 
 // trimmer is implemented as a state machine.
@@ -1038,6 +1056,11 @@ const (
 	inText          // inside text
 )
 
+func (p *trimmer) resetSpace() {
+	p.state = inSpace
+	p.space = p.space[0:0]
+}
+
 // Design note: It is tempting to eliminate extra blanks occurring in
 //              whitespace in this function as it could simplify some
 //              of the blanks logic in the node printing functions.
@@ -1062,36 +1085,33 @@ func (p *trimmer) Write(data []byte) (n int, err error) {
 		case inSpace:
 			switch b {
 			case '\t', ' ':
-				p.space.WriteByte(b) // WriteByte returns no errors
+				p.space = append(p.space, b)
 			case '\n', '\f':
-				p.space.Reset() // discard trailing space
+				p.resetSpace() // discard trailing space
 				_, err = p.output.Write(aNewline)
 			case tabwriter.Escape:
-				_, err = p.output.Write(p.space.Bytes())
+				_, err = p.output.Write(p.space)
 				p.state = inEscape
 				m = n + 1 // +1: skip tabwriter.Escape
 			default:
-				_, err = p.output.Write(p.space.Bytes())
+				_, err = p.output.Write(p.space)
 				p.state = inText
 				m = n
 			}
 		case inEscape:
 			if b == tabwriter.Escape {
 				_, err = p.output.Write(data[m:n])
-				p.state = inSpace
-				p.space.Reset()
+				p.resetSpace()
 			}
 		case inText:
 			switch b {
 			case '\t', ' ':
 				_, err = p.output.Write(data[m:n])
-				p.state = inSpace
-				p.space.Reset()
-				p.space.WriteByte(b) // WriteByte returns no errors
+				p.resetSpace()
+				p.space = append(p.space, b)
 			case '\n', '\f':
 				_, err = p.output.Write(data[m:n])
-				p.state = inSpace
-				p.space.Reset()
+				p.resetSpace()
 				_, err = p.output.Write(aNewline)
 			case tabwriter.Escape:
 				_, err = p.output.Write(data[m:n])
@@ -1110,8 +1130,7 @@ func (p *trimmer) Write(data []byte) (n int, err error) {
 	switch p.state {
 	case inEscape, inText:
 		_, err = p.output.Write(data[m:n])
-		p.state = inSpace
-		p.space.Reset()
+		p.resetSpace()
 	}
 
 	return
@@ -1120,16 +1139,19 @@ func (p *trimmer) Write(data []byte) (n int, err error) {
 // ----------------------------------------------------------------------------
 // Public interface
 
-// General printing is controlled with these Config.Mode flags.
+// A Mode value is a set of flags (or 0). They coontrol printing. 
+type Mode uint
+
 const (
-	RawFormat uint = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
+	RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
 	TabIndent                  // use tabs for indentation independent of UseSpaces
 	UseSpaces                  // use spaces instead of tabs for alignment
+	SourcePos                  // emit //line comments to preserve original source positions
 )
 
 // A Config node controls the output of Fprint.
 type Config struct {
-	Mode     uint // default: 0
+	Mode     Mode // default: 0
 	Tabwidth int  // default: 8
 }
 
@@ -1170,7 +1192,7 @@ func (cfg *Config) fprint(output io.Writer, fset *token.FileSet, node interface{
 	}
 
 	// write printer result via tabwriter/trimmer to output
-	if _, err = output.Write(p.output.Bytes()); err != nil {
+	if _, err = output.Write(p.output); err != nil {
 		return
 	}
 
diff --git a/libgo/go/go/printer/printer_test.go b/libgo/go/go/printer/printer_test.go
index 9adf48cda61..fa133cd35f0 100644
--- a/libgo/go/go/printer/printer_test.go
+++ b/libgo/go/go/printer/printer_test.go
@@ -67,6 +67,13 @@ func runcheck(t *testing.T, source, golden string, mode checkMode) {
 	}
 	res := buf.Bytes()
 
+	// formatted source must be valid
+	if _, err := parser.ParseFile(fset, "", res, 0); err != nil {
+		t.Error(err)
+		t.Logf("\n%s", res)
+		return
+	}
+
 	// update golden files if necessary
 	if *update {
 		if err := ioutil.WriteFile(golden, res, 0644); err != nil {
@@ -133,7 +140,7 @@ type entry struct {
 	mode           checkMode
 }
 
-// Use gotest -update to create/update the respective golden files.
+// Use go test -update to create/update the respective golden files.
 var data = []entry{
 	{"empty.input", "empty.golden", 0},
 	{"comments.input", "comments.golden", 0},
@@ -223,7 +230,8 @@ func TestBadNodes(t *testing.T) {
 	}
 }
 
-// Print and parse f with 
+// testComment verifies that f can be parsed again after printing it
+// with its first comment set to comment at any possible source offset.
 func testComment(t *testing.T, f *ast.File, srclen int, comment *ast.Comment) {
 	f.Comments[0].List[0] = comment
 	var buf bytes.Buffer
@@ -280,3 +288,128 @@ func fibo(n int) {
 	testComment(t, f, len(src), &ast.Comment{pos, "/*-style \n comment */"})
 	testComment(t, f, len(src), &ast.Comment{pos, "/*-style comment \n\n\n */"})
 }
+
+type visitor chan *ast.Ident
+
+func (v visitor) Visit(n ast.Node) (w ast.Visitor) {
+	if ident, ok := n.(*ast.Ident); ok {
+		v <- ident
+	}
+	return v
+}
+
+// idents is an iterator that returns all idents in f via the result channel.
+func idents(f *ast.File) <-chan *ast.Ident {
+	v := make(visitor)
+	go func() {
+		ast.Walk(v, f)
+		close(v)
+	}()
+	return v
+}
+
+// identCount returns the number of identifiers found in f.
+func identCount(f *ast.File) int {
+	n := 0
+	for _ = range idents(f) {
+		n++
+	}
+	return n
+}
+
+// Verify that the SourcePos mode emits correct //line comments
+// by testing that position information for matching identifiers
+// is maintained.
+func TestSourcePos(t *testing.T) {
+	const src = `
+package p
+import ( "go/printer"; "math" )
+const pi = 3.14; var x = 0
+type t struct{ x, y, z int; u, v, w float32 }
+func (t *t) foo(a, b, c int) int {
+	return a*t.x + b*t.y +
+		// two extra lines here
+		// ...
+		c*t.z
+}
+`
+
+	// parse original
+	f1, err := parser.ParseFile(fset, "src", src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// pretty-print original
+	var buf bytes.Buffer
+	err = (&Config{Mode: UseSpaces | SourcePos, Tabwidth: 8}).Fprint(&buf, fset, f1)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// parse pretty printed original
+	// (//line comments must be interpreted even w/o parser.ParseComments set)
+	f2, err := parser.ParseFile(fset, "", buf.Bytes(), 0)
+	if err != nil {
+		t.Fatalf("%s\n%s", err, buf.Bytes())
+	}
+
+	// At this point the position information of identifiers in f2 should
+	// match the position information of corresponding identifiers in f1.
+
+	// number of identifiers must be > 0 (test should run) and must match
+	n1 := identCount(f1)
+	n2 := identCount(f2)
+	if n1 == 0 {
+		t.Fatal("got no idents")
+	}
+	if n2 != n1 {
+		t.Errorf("got %d idents; want %d", n2, n1)
+	}
+
+	// verify that all identifiers have correct line information
+	i2range := idents(f2)
+	for i1 := range idents(f1) {
+		i2 := <-i2range
+
+		if i2.Name != i1.Name {
+			t.Errorf("got ident %s; want %s", i2.Name, i1.Name)
+		}
+
+		l1 := fset.Position(i1.Pos()).Line
+		l2 := fset.Position(i2.Pos()).Line
+		if l2 != l1 {
+			t.Errorf("got line %d; want %d for %s", l2, l1, i1.Name)
+		}
+	}
+
+	if t.Failed() {
+		t.Logf("\n%s", buf.Bytes())
+	}
+}
+
+// TextX is a skeleton test that can be filled in for debugging one-off cases.
+// Do not remove.
+func TestX(t *testing.T) {
+	const src = `
+package p
+func _() {}
+`
+	// parse original
+	f, err := parser.ParseFile(fset, "src", src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// pretty-print original
+	var buf bytes.Buffer
+	if err = (&Config{Mode: UseSpaces, Tabwidth: 8}).Fprint(&buf, fset, f); err != nil {
+		t.Fatal(err)
+	}
+
+	// parse pretty printed original
+	if _, err := parser.ParseFile(fset, "", buf.Bytes(), 0); err != nil {
+		t.Fatalf("%s\n%s", err, buf.Bytes())
+	}
+
+}
diff --git a/libgo/go/go/printer/testdata/comments.golden b/libgo/go/go/printer/testdata/comments.golden
index d2ad9e3a2ff..e5826eecefe 100644
--- a/libgo/go/go/printer/testdata/comments.golden
+++ b/libgo/go/go/printer/testdata/comments.golden
@@ -404,7 +404,7 @@ func _() {
 	*/
 }
 
-// Some interesting interspersed comments
+// Some interesting interspersed comments.
 func _( /* this */ x /* is */ /* an */ int) {
 }
 
@@ -428,6 +428,26 @@ func _() {
 	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */ }
 }
 
+// Test cases from issue 1542:
+// Comments must not be placed before commas and cause invalid programs.
+func _() {
+	var a = []int{1, 2	/*jasldf*/}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2}/*jasldf
+	 */
+
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2}// jasldf 
+
+	_ = a
+}
+
 // Comments immediately adjacent to punctuation (for which the go/printer
 // may only have estimated position information) must remain after the punctuation.
 func _() {
@@ -459,6 +479,25 @@ func _() {
 	}
 }
 
+// Print line directives correctly.
+
+// The following is a legal line directive.
+//line foo:1
+func _() {
+	_ = 0
+	// The following is a legal line directive. It must not be indented:
+//line foo:2
+	_ = 1
+
+	// The following is not a legal line directive (it doesn't start in column 1):
+	//line foo:2
+	_ = 2
+
+	// The following is not a legal line directive (negative line number):
+	//line foo:-3
+	_ = 3
+}
+
 // Line comments with tabs
 func _() {
 	var finput *bufio.Reader	// input file
diff --git a/libgo/go/go/printer/testdata/comments.input b/libgo/go/go/printer/testdata/comments.input
index 222e0a713d4..55f6b61f21f 100644
--- a/libgo/go/go/printer/testdata/comments.input
+++ b/libgo/go/go/printer/testdata/comments.input
@@ -410,7 +410,7 @@ func _() {
 }
 
 
-// Some interesting interspersed comments
+// Some interesting interspersed comments.
 func _(/* this */x/* is *//* an */ int) {
 }
 
@@ -432,6 +432,26 @@ func _() {
 	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */}
 }
 
+// Test cases from issue 1542:
+// Comments must not be placed before commas and cause invalid programs.
+func _() {
+	var a = []int{1, 2, /*jasldf*/
+	}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2, /*jasldf
+						*/
+	}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2, // jasldf 
+	}
+	_ = a
+}
 
 // Comments immediately adjacent to punctuation (for which the go/printer
 // may only have estimated position information) must remain after the punctuation.
@@ -467,6 +487,25 @@ func _() {
 }
 
 
+// Print line directives correctly.
+
+// The following is a legal line directive.
+//line foo:1
+func _() {
+	_ = 0
+// The following is a legal line directive. It must not be indented:
+//line foo:2
+	_ = 1
+
+// The following is not a legal line directive (it doesn't start in column 1):
+	//line foo:2
+	_ = 2
+
+// The following is not a legal line directive (negative line number):
+//line foo:-3
+	_ = 3
+}
+
 // Line comments with tabs
 func _() {
 var	finput		*bufio.Reader			// input file
diff --git a/libgo/go/go/scanner/errors.go b/libgo/go/go/scanner/errors.go
index cd9620b878b..8a75a96508e 100644
--- a/libgo/go/go/scanner/errors.go
+++ b/libgo/go/go/scanner/errors.go
@@ -11,44 +11,18 @@ import (
 	"sort"
 )
 
-// An implementation of an ErrorHandler may be provided to the Scanner.
-// If a syntax error is encountered and a handler was installed, Error
-// is called with a position and an error message. The position points
-// to the beginning of the offending token.
-//
-type ErrorHandler interface {
-	Error(pos token.Position, msg string)
-}
-
-// ErrorVector implements the ErrorHandler interface. It maintains a list
-// of errors which can be retrieved with GetErrorList and GetError. The
-// zero value for an ErrorVector is an empty ErrorVector ready to use.
-//
-// A common usage pattern is to embed an ErrorVector alongside a
-// scanner in a data structure that uses the scanner. By passing a
-// reference to an ErrorVector to the scanner's Init call, default
-// error handling is obtained.
-//
-type ErrorVector struct {
-	errors []*Error
-}
-
-// Reset resets an ErrorVector to no errors.
-func (h *ErrorVector) Reset() { h.errors = h.errors[:0] }
-
-// ErrorCount returns the number of errors collected.
-func (h *ErrorVector) ErrorCount() int { return len(h.errors) }
-
-// Within ErrorVector, an error is represented by an Error node. The
-// position Pos, if valid, points to the beginning of the offending
-// token, and the error condition is described by Msg.
+// In an ErrorList, an error is represented by an *Error.
+// The position Pos, if valid, points to the beginning of
+// the offending token, and the error condition is described
+// by Msg.
 //
 type Error struct {
 	Pos token.Position
 	Msg string
 }
 
-func (e *Error) Error() string {
+// Error implements the error interface.
+func (e Error) Error() string {
 	if e.Pos.Filename != "" || e.Pos.IsValid() {
 		// don't print "<unknown position>"
 		// TODO(gri) reconsider the semantics of Position.IsValid
@@ -57,9 +31,19 @@ func (e *Error) Error() string {
 	return e.Msg
 }
 
-// An ErrorList is a (possibly sorted) list of Errors.
+// ErrorList is a list of *Errors.
+// The zero value for an ErrorList is an empty ErrorList ready to use.
+//
 type ErrorList []*Error
 
+// Add adds an Error with given position and error message to an ErrorList.
+func (p *ErrorList) Add(pos token.Position, msg string) {
+	*p = append(*p, &Error{pos, msg})
+}
+
+// Reset resets an ErrorList to no errors.
+func (p *ErrorList) Reset() { *p = (*p)[0:0] }
+
 // ErrorList implements the sort Interface.
 func (p ErrorList) Len() int      { return len(p) }
 func (p ErrorList) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
@@ -84,72 +68,47 @@ func (p ErrorList) Less(i, j int) bool {
 	return false
 }
 
+// Sort sorts an ErrorList. *Error entries are sorted by position,
+// other errors are sorted by error message, and before any *Error
+// entry.
+//
+func (p ErrorList) Sort() {
+	sort.Sort(p)
+}
+
+// RemoveMultiples sorts an ErrorList and removes all but the first error per line.
+func (p *ErrorList) RemoveMultiples() {
+	sort.Sort(p)
+	var last token.Position // initial last.Line is != any legal error line
+	i := 0
+	for _, e := range *p {
+		if e.Pos.Filename != last.Filename || e.Pos.Line != last.Line {
+			last = e.Pos
+			(*p)[i] = e
+			i++
+		}
+	}
+	(*p) = (*p)[0:i]
+}
+
+// An ErrorList implements the error interface.
 func (p ErrorList) Error() string {
 	switch len(p) {
 	case 0:
-		return "unspecified error"
+		return "no errors"
 	case 1:
 		return p[0].Error()
 	}
 	return fmt.Sprintf("%s (and %d more errors)", p[0], len(p)-1)
 }
 
-// These constants control the construction of the ErrorList
-// returned by GetErrors.
-//
-const (
-	Raw         = iota // leave error list unchanged
-	Sorted             // sort error list by file, line, and column number
-	NoMultiples        // sort error list and leave only the first error per line
-)
-
-// GetErrorList returns the list of errors collected by an ErrorVector.
-// The construction of the ErrorList returned is controlled by the mode
-// parameter. If there are no errors, the result is nil.
-//
-func (h *ErrorVector) GetErrorList(mode int) ErrorList {
-	if len(h.errors) == 0 {
-		return nil
-	}
-
-	list := make(ErrorList, len(h.errors))
-	copy(list, h.errors)
-
-	if mode >= Sorted {
-		sort.Sort(list)
-	}
-
-	if mode >= NoMultiples {
-		var last token.Position // initial last.Line is != any legal error line
-		i := 0
-		for _, e := range list {
-			if e.Pos.Filename != last.Filename || e.Pos.Line != last.Line {
-				last = e.Pos
-				list[i] = e
-				i++
-			}
-		}
-		list = list[0:i]
-	}
-
-	return list
-}
-
-// GetError is like GetErrorList, but it returns an error instead
-// so that a nil result can be assigned to an error variable and
-// remains nil.
-//
-func (h *ErrorVector) GetError(mode int) error {
-	if len(h.errors) == 0 {
+// Err returns an error equivalent to this error list.
+// If the list is empty, Err returns nil.
+func (p ErrorList) Err() error {
+	if len(p) == 0 {
 		return nil
 	}
-
-	return h.GetErrorList(mode)
-}
-
-// ErrorVector implements the ErrorHandler interface.
-func (h *ErrorVector) Error(pos token.Position, msg string) {
-	h.errors = append(h.errors, &Error{pos, msg})
+	return p
 }
 
 // PrintError is a utility function that prints a list of errors to w,
diff --git a/libgo/go/go/scanner/scanner.go b/libgo/go/go/scanner/scanner.go
index 0aabfe34c41..458e1f9f37a 100644
--- a/libgo/go/go/scanner/scanner.go
+++ b/libgo/go/go/scanner/scanner.go
@@ -30,6 +30,13 @@ import (
 	"unicode/utf8"
 )
 
+// An ErrorHandler may be provided to Scanner.Init. If a syntax error is
+// encountered and a handler was installed, the handler is called with a
+// position and an error message. The position points to the beginning of
+// the offending token.
+//
+type ErrorHandler func(pos token.Position, msg string)
+
 // A Scanner holds the scanner's internal state while processing
 // a given text.  It can be allocated as part of another data
 // structure but must be initialized via Init before use.
@@ -103,7 +110,7 @@ const (
 // line information which is already present is ignored. Init causes a
 // panic if the file size does not match the src size.
 //
-// Calls to Scan will use the error handler err if they encounter a
+// Calls to Scan will invoke the error handler err if they encounter a
 // syntax error and err is not nil. Also, for each error encountered,
 // the Scanner field ErrorCount is incremented by one. The mode parameter
 // determines how comments are handled.
@@ -134,7 +141,7 @@ func (s *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode Mode
 
 func (s *Scanner) error(offs int, msg string) {
 	if s.err != nil {
-		s.err.Error(s.file.Position(s.file.Pos(offs)), msg)
+		s.err(s.file.Position(s.file.Pos(offs)), msg)
 	}
 	s.ErrorCount++
 }
diff --git a/libgo/go/go/scanner/scanner_test.go b/libgo/go/go/scanner/scanner_test.go
index e7f7cd1c1e9..06223e23bd8 100644
--- a/libgo/go/go/scanner/scanner_test.go
+++ b/libgo/go/go/scanner/scanner_test.go
@@ -186,14 +186,6 @@ var source = func() []byte {
 	return src
 }()
 
-type testErrorHandler struct {
-	t *testing.T
-}
-
-func (h *testErrorHandler) Error(pos token.Position, msg string) {
-	h.t.Errorf("Error() called (msg = %s)", msg)
-}
-
 func newlineCount(s string) int {
 	n := 0
 	for i := 0; i < len(s); i++ {
@@ -226,9 +218,14 @@ func TestScan(t *testing.T) {
 	src_linecount := newlineCount(string(source))
 	whitespace_linecount := newlineCount(whitespace)
 
+	// error handler
+	eh := func(_ token.Position, msg string) {
+		t.Errorf("error handler called (msg = %s)", msg)
+	}
+
 	// verify scan
 	var s Scanner
-	s.Init(fset.AddFile("", fset.Base(), len(source)), source, &testErrorHandler{t}, ScanComments|dontInsertSemis)
+	s.Init(fset.AddFile("", fset.Base(), len(source)), source, eh, ScanComments|dontInsertSemis)
 	index := 0
 	// epos is the expected position
 	epos := token.Position{
@@ -569,36 +566,37 @@ func TestStdErrorHander(t *testing.T) {
 		"//line File1:1\n" +
 		"@ @ @" // original file, line 1 again
 
-	v := new(ErrorVector)
+	var list ErrorList
+	eh := func(pos token.Position, msg string) { list.Add(pos, msg) }
+
 	var s Scanner
-	s.Init(fset.AddFile("File1", fset.Base(), len(src)), []byte(src), v, dontInsertSemis)
+	s.Init(fset.AddFile("File1", fset.Base(), len(src)), []byte(src), eh, dontInsertSemis)
 	for {
 		if _, tok, _ := s.Scan(); tok == token.EOF {
 			break
 		}
 	}
 
-	list := v.GetErrorList(Raw)
+	if len(list) != s.ErrorCount {
+		t.Errorf("found %d errors, expected %d", len(list), s.ErrorCount)
+	}
+
 	if len(list) != 9 {
 		t.Errorf("found %d raw errors, expected 9", len(list))
 		PrintError(os.Stderr, list)
 	}
 
-	list = v.GetErrorList(Sorted)
+	list.Sort()
 	if len(list) != 9 {
 		t.Errorf("found %d sorted errors, expected 9", len(list))
 		PrintError(os.Stderr, list)
 	}
 
-	list = v.GetErrorList(NoMultiples)
+	list.RemoveMultiples()
 	if len(list) != 4 {
 		t.Errorf("found %d one-per-line errors, expected 4", len(list))
 		PrintError(os.Stderr, list)
 	}
-
-	if v.ErrorCount() != s.ErrorCount {
-		t.Errorf("found %d errors, expected %d", v.ErrorCount(), s.ErrorCount)
-	}
 }
 
 type errorCollector struct {
@@ -607,16 +605,15 @@ type errorCollector struct {
 	pos token.Position // last error position encountered
 }
 
-func (h *errorCollector) Error(pos token.Position, msg string) {
-	h.cnt++
-	h.msg = msg
-	h.pos = pos
-}
-
 func checkError(t *testing.T, src string, tok token.Token, pos int, err string) {
 	var s Scanner
 	var h errorCollector
-	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), &h, ScanComments|dontInsertSemis)
+	eh := func(pos token.Position, msg string) {
+		h.cnt++
+		h.msg = msg
+		h.pos = pos
+	}
+	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), eh, ScanComments|dontInsertSemis)
 	_, tok0, _ := s.Scan()
 	_, tok1, _ := s.Scan()
 	if tok0 != tok {