diff --git a/src/pkg/go/ast/filter.go b/src/pkg/go/ast/filter.go
index 4c96e71c037..d4b580e003a 100644
--- a/src/pkg/go/ast/filter.go
+++ b/src/pkg/go/ast/filter.go
@@ -20,24 +20,6 @@ func identListExports(list []*Ident) []*Ident {
 	return list[0:j]
 }
 
-// fieldName assumes that x is the type of an anonymous field and
-// returns the corresponding field name. If x is not an acceptable
-// anonymous field, the result is nil.
-//
-func fieldName(x Expr) *Ident {
-	switch t := x.(type) {
-	case *Ident:
-		return t
-	case *SelectorExpr:
-		if _, ok := t.X.(*Ident); ok {
-			return t.Sel
-		}
-	case *StarExpr:
-		return fieldName(t.X)
-	}
-	return nil
-}
-
 func fieldListExports(fields *FieldList) (removedFields bool) {
 	if fields == nil {
 		return
@@ -203,6 +185,24 @@ func filterIdentList(list []*Ident, f Filter) []*Ident {
 	return list[0:j]
 }
 
+// fieldName assumes that x is the type of an anonymous field and
+// returns the corresponding field name. If x is not an acceptable
+// anonymous field, the result is nil.
+//
+func fieldName(x Expr) *Ident {
+	switch t := x.(type) {
+	case *Ident:
+		return t
+	case *SelectorExpr:
+		if _, ok := t.X.(*Ident); ok {
+			return t.Sel
+		}
+	case *StarExpr:
+		return fieldName(t.X)
+	}
+	return nil
+}
+
 func filterFieldList(fields *FieldList, filter Filter) (removedFields bool) {
 	if fields == nil {
 		return false
@@ -224,6 +224,7 @@ func filterFieldList(fields *FieldList, filter Filter) (removedFields bool) {
 			keepField = len(f.Names) > 0
 		}
 		if keepField {
+			filterType(f.Type, filter)
 			list[j] = f
 			j++
 		}
@@ -235,26 +236,71 @@ func filterFieldList(fields *FieldList, filter Filter) (removedFields bool) {
 	return
 }
 
+func filterParamList(fields *FieldList, filter Filter) bool {
+	if fields == nil {
+		return false
+	}
+	var b bool
+	for _, f := range fields.List {
+		if filterType(f.Type, filter) {
+			b = true
+		}
+	}
+	return b
+}
+
+func filterType(typ Expr, f Filter) bool {
+	switch t := typ.(type) {
+	case *Ident:
+		return f(t.Name)
+	case *ParenExpr:
+		return filterType(t.X, f)
+	case *ArrayType:
+		return filterType(t.Elt, f)
+	case *StructType:
+		if filterFieldList(t.Fields, f) {
+			t.Incomplete = true
+		}
+		return len(t.Fields.List) > 0
+	case *FuncType:
+		b1 := filterParamList(t.Params, f)
+		b2 := filterParamList(t.Results, f)
+		return b1 || b2
+	case *InterfaceType:
+		if filterFieldList(t.Methods, f) {
+			t.Incomplete = true
+		}
+		return len(t.Methods.List) > 0
+	case *MapType:
+		b1 := filterType(t.Key, f)
+		b2 := filterType(t.Value, f)
+		return b1 || b2
+	case *ChanType:
+		return filterType(t.Value, f)
+	}
+	return false
+}
+
 func filterSpec(spec Spec, f Filter) bool {
 	switch s := spec.(type) {
 	case *ValueSpec:
 		s.Names = filterIdentList(s.Names, f)
-		return len(s.Names) > 0
-	case *TypeSpec:
-		if f(s.Name.Name) {
+		if len(s.Names) > 0 {
+			filterType(s.Type, f)
 			return true
 		}
-		switch t := s.Type.(type) {
-		case *StructType:
-			if filterFieldList(t.Fields, f) {
-				t.Incomplete = true
-			}
-			return len(t.Fields.List) > 0
-		case *InterfaceType:
-			if filterFieldList(t.Methods, f) {
-				t.Incomplete = true
-			}
-			return len(t.Methods.List) > 0
+	case *TypeSpec:
+		if f(s.Name.Name) {
+			filterType(s.Type, f)
+			return true
+		}
+		if f != IsExported {
+			// For general filtering (not just exports),
+			// filter type even if name is not filtered
+			// out.
+			// If the type contains filtered elements,
+			// keep the declaration.
+			return filterType(s.Type, f)
 		}
 	}
 	return false
@@ -284,6 +330,7 @@ func FilterDecl(decl Decl, f Filter) bool {
 		d.Specs = filterSpecList(d.Specs, f)
 		return len(d.Specs) > 0
 	case *FuncDecl:
+		d.Body = nil // strip body
 		return f(d.Name.Name)
 	}
 	return false
@@ -292,13 +339,16 @@ func FilterDecl(decl Decl, f Filter) bool {
 // FilterFile trims the AST for a Go file in place by removing all
 // names from top-level declarations (including struct field and
 // interface method names, but not from parameter lists) that don't
-// pass through the filter f. If the declaration is empty afterwards,
-// the declaration is removed from the AST.
-// The File.comments list is not changed.
+// pass through the filter f. Function bodies are set to nil.
+// If the declaration is empty afterwards, the declaration is
+// removed from the AST. The File.comments list is not changed.
 //
 // FilterFile returns true if there are any top-level declarations
 // left after filtering; it returns false otherwise.
 //
+// To trim an AST such that only exported nodes remain, call
+// FilterFile with IsExported as filter function.
+//
 func FilterFile(src *File, f Filter) bool {
 	j := 0
 	for _, d := range src.Decls {
@@ -314,14 +364,17 @@ func FilterFile(src *File, f Filter) bool {
 // FilterPackage trims the AST for a Go package in place by removing all
 // names from top-level declarations (including struct field and
 // interface method names, but not from parameter lists) that don't
-// pass through the filter f. If the declaration is empty afterwards,
-// the declaration is removed from the AST.
-// The pkg.Files list is not changed, so that file names and top-level
-// package comments don't get lost.
+// pass through the filter f. Function bodies are set to nil.
+// If the declaration is empty afterwards, the declaration is
+// removed from the AST. The pkg.Files list is not changed, so
+// that file names and top-level package comments don't get lost.
 //
 // FilterPackage returns true if there are any top-level declarations
 // left after filtering; it returns false otherwise.
 //
+// To trim an AST such that only exported nodes remain, call
+// FilterPackage with IsExported as filter function.
+//
 func FilterPackage(pkg *Package, f Filter) bool {
 	hasDecls := false
 	for _, src := range pkg.Files {
@@ -467,17 +520,16 @@ func MergePackageFiles(pkg *Package, mode MergeMode) *File {
 		seen := make(map[string]bool)
 		for _, f := range pkg.Files {
 			for _, imp := range f.Imports {
-				path := imp.Path.Value
-				if !seen[path] {
-					//TODO: consider handling cases where:
+				if path := imp.Path.Value; !seen[path] {
+					// TODO: consider handling cases where:
 					// - 2 imports exist with the same import path but
 					//   have different local names (one should probably 
 					//   keep both of them)
 					// - 2 imports exist but only one has a comment
 					// - 2 imports exist and they both have (possibly
 					//   different) comments
-					seen[path] = true
 					imports = append(imports, imp)
+					seen[path] = true
 				}
 			}
 		}
diff --git a/src/pkg/go/parser/filter_test.go b/src/pkg/go/parser/filter_test.go
new file mode 100644
index 00000000000..f1672a9dd8d
--- /dev/null
+++ b/src/pkg/go/parser/filter_test.go
@@ -0,0 +1,91 @@
+// Copyright 2011 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.
+
+// A test that ensures that ast.FileExports(file) and
+// ast.FilterFile(file, ast.IsExported) produce the
+// same trimmed AST given the same input file for all
+// files under runtime.GOROOT().
+//
+// The test is here because it requires parsing, and the
+// parser imports AST already (avoid import cycle).
+
+package parser
+
+import (
+	"bytes"
+	"go/ast"
+	"go/printer"
+	"go/token"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// For a short test run, limit the number of files to a few.
+// Set to a large value to test all files under GOROOT.
+const maxFiles = 10
+
+type visitor struct {
+	t *testing.T
+	n int
+}
+
+func (v *visitor) VisitDir(path string, f *os.FileInfo) bool {
+	return true
+}
+
+func str(f *ast.File, fset *token.FileSet) string {
+	var buf bytes.Buffer
+	printer.Fprint(&buf, fset, f)
+	return buf.String()
+}
+
+func (v *visitor) VisitFile(path string, f *os.FileInfo) {
+	// exclude files that clearly don't make it
+	if !f.IsRegular() || len(f.Name) > 0 && f.Name[0] == '.' || !strings.HasSuffix(f.Name, ".go") {
+		return
+	}
+
+	// should we stop early for quick test runs?
+	if v.n <= 0 {
+		return
+	}
+	v.n--
+
+	fset := token.NewFileSet()
+
+	// get two ASTs f1, f2 of identical structure;
+	// parsing twice is easiest
+	f1, err := ParseFile(fset, path, nil, ParseComments)
+	if err != nil {
+		v.t.Logf("parse error (1): %s", err)
+		return
+	}
+
+	f2, err := ParseFile(fset, path, nil, ParseComments)
+	if err != nil {
+		v.t.Logf("parse error (2): %s", err)
+		return
+	}
+
+	b1 := ast.FileExports(f1)
+	b2 := ast.FilterFile(f2, ast.IsExported)
+	if b1 != b2 {
+		v.t.Errorf("filtering failed (a): %s", path)
+		return
+	}
+
+	s1 := str(f1, fset)
+	s2 := str(f2, fset)
+	if s1 != s2 {
+		v.t.Errorf("filtering failed (b): %s", path)
+		return
+	}
+}
+
+func TestFilter(t *testing.T) {
+	filepath.Walk(runtime.GOROOT(), &visitor{t, maxFiles}, nil)
+}