[dev.link] all: merge branch 'master' into dev.linkdev.link

Clean merge.

Change-Id: Ia7b2808bc649790198d34c226a61d9e569084dc5

23 files changed, 1194 insertions, 592 deletions

diff --git a/src/go/build/build.go b/src/go/build/build.go
index 5c3d876130..80e9b9c739 100644
--- a/src/go/build/build.go
+++ b/src/go/build/build.go
@@ -10,11 +10,11 @@ import (
 	"fmt"
 	"go/ast"
 	"go/doc"
-	"go/parser"
 	"go/token"
 	"internal/goroot"
 	"internal/goversion"
 	"io"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -98,10 +98,10 @@ type Context struct {
 	// filepath.EvalSymlinks.
 	HasSubdir func(root, dir string) (rel string, ok bool)
 
-	// ReadDir returns a slice of os.FileInfo, sorted by Name,
+	// ReadDir returns a slice of fs.FileInfo, sorted by Name,
 	// describing the content of the named directory.
 	// If ReadDir is nil, Import uses ioutil.ReadDir.
-	ReadDir func(dir string) ([]os.FileInfo, error)
+	ReadDir func(dir string) ([]fs.FileInfo, error)
 
 	// OpenFile opens a file (not a directory) for reading.
 	// If OpenFile is nil, Import uses os.Open.
@@ -183,7 +183,7 @@ func hasSubdir(root, dir string) (rel string, ok bool) {
 }
 
 // readDir calls ctxt.ReadDir (if not nil) or else ioutil.ReadDir.
-func (ctxt *Context) readDir(path string) ([]os.FileInfo, error) {
+func (ctxt *Context) readDir(path string) ([]fs.FileInfo, error) {
 	if f := ctxt.ReadDir; f != nil {
 		return f(path)
 	}
@@ -409,19 +409,20 @@ type Package struct {
 	BinaryOnly    bool     // cannot be rebuilt from source (has //go:binary-only-package comment)
 
 	// Source files
-	GoFiles        []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
-	CgoFiles       []string // .go source files that import "C"
-	IgnoredGoFiles []string // .go source files ignored for this build
-	InvalidGoFiles []string // .go source files with detected problems (parse error, wrong package name, and so on)
-	CFiles         []string // .c source files
-	CXXFiles       []string // .cc, .cpp and .cxx source files
-	MFiles         []string // .m (Objective-C) source files
-	HFiles         []string // .h, .hh, .hpp and .hxx source files
-	FFiles         []string // .f, .F, .for and .f90 Fortran source files
-	SFiles         []string // .s source files
-	SwigFiles      []string // .swig files
-	SwigCXXFiles   []string // .swigcxx files
-	SysoFiles      []string // .syso system object files to add to archive
+	GoFiles           []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
+	CgoFiles          []string // .go source files that import "C"
+	IgnoredGoFiles    []string // .go source files ignored for this build (including ignored _test.go files)
+	InvalidGoFiles    []string // .go source files with detected problems (parse error, wrong package name, and so on)
+	IgnoredOtherFiles []string // non-.go source files ignored for this build
+	CFiles            []string // .c source files
+	CXXFiles          []string // .cc, .cpp and .cxx source files
+	MFiles            []string // .m (Objective-C) source files
+	HFiles            []string // .h, .hh, .hpp and .hxx source files
+	FFiles            []string // .f, .F, .for and .f90 Fortran source files
+	SFiles            []string // .s source files
+	SwigFiles         []string // .swig files
+	SwigCXXFiles      []string // .swigcxx files
+	SysoFiles         []string // .syso system object files to add to archive
 
 	// Cgo directives
 	CgoCFLAGS    []string // Cgo CFLAGS directives
@@ -431,17 +432,26 @@ type Package struct {
 	CgoLDFLAGS   []string // Cgo LDFLAGS directives
 	CgoPkgConfig []string // Cgo pkg-config directives
 
-	// Dependency information
-	Imports   []string                    // import paths from GoFiles, CgoFiles
-	ImportPos map[string][]token.Position // line information for Imports
-
 	// Test information
-	TestGoFiles    []string                    // _test.go files in package
+	TestGoFiles  []string // _test.go files in package
+	XTestGoFiles []string // _test.go files outside package
+
+	// Dependency information
+	Imports        []string                    // import paths from GoFiles, CgoFiles
+	ImportPos      map[string][]token.Position // line information for Imports
 	TestImports    []string                    // import paths from TestGoFiles
 	TestImportPos  map[string][]token.Position // line information for TestImports
-	XTestGoFiles   []string                    // _test.go files outside package
 	XTestImports   []string                    // import paths from XTestGoFiles
 	XTestImportPos map[string][]token.Position // line information for XTestImports
+
+	// //go:embed patterns found in Go source files
+	// For example, if a source file says
+	//	//go:embed a* b.c
+	// then the list will contain those two strings as separate entries.
+	// (See package embed for more details about //go:embed.)
+	EmbedPatterns      []string // patterns from GoFiles, CgoFiles
+	TestEmbedPatterns  []string // patterns from TestGoFiles
+	XTestEmbedPatterns []string // patterns from XTestGoFiles
 }
 
 // IsCommand reports whether the package is considered a
@@ -784,6 +794,7 @@ Found:
 	var badGoError error
 	var Sfiles []string // files with ".S"(capital S)/.sx(capital s equivalent for case insensitive filesystems)
 	var firstFile, firstCommentFile string
+	var embeds, testEmbeds, xTestEmbeds []string
 	imported := make(map[string][]token.Position)
 	testImported := make(map[string][]token.Position)
 	xTestImported := make(map[string][]token.Position)
@@ -793,7 +804,7 @@ Found:
 		if d.IsDir() {
 			continue
 		}
-		if (d.Mode() & os.ModeSymlink) != 0 {
+		if d.Mode()&fs.ModeSymlink != 0 {
 			if fi, err := os.Stat(filepath.Join(p.Dir, d.Name())); err == nil && fi.IsDir() {
 				// Symlinks to directories are not source files.
 				continue
@@ -810,60 +821,43 @@ Found:
 			p.InvalidGoFiles = append(p.InvalidGoFiles, name)
 		}
 
-		match, data, filename, err := ctxt.matchFile(p.Dir, name, allTags, &p.BinaryOnly)
+		info, err := ctxt.matchFile(p.Dir, name, allTags, &p.BinaryOnly, fset)
 		if err != nil {
 			badFile(err)
 			continue
 		}
-		if !match {
-			if ext == ".go" {
+		if info == nil {
+			if strings.HasPrefix(name, "_") || strings.HasPrefix(name, ".") {
+				// not due to build constraints - don't report
+			} else if ext == ".go" {
 				p.IgnoredGoFiles = append(p.IgnoredGoFiles, name)
+			} else if fileListForExt(p, ext) != nil {
+				p.IgnoredOtherFiles = append(p.IgnoredOtherFiles, name)
 			}
 			continue
 		}
+		data, filename := info.header, info.name
 
 		// Going to save the file. For non-Go files, can stop here.
 		switch ext {
-		case ".c":
-			p.CFiles = append(p.CFiles, name)
-			continue
-		case ".cc", ".cpp", ".cxx":
-			p.CXXFiles = append(p.CXXFiles, name)
-			continue
-		case ".m":
-			p.MFiles = append(p.MFiles, name)
-			continue
-		case ".h", ".hh", ".hpp", ".hxx":
-			p.HFiles = append(p.HFiles, name)
-			continue
-		case ".f", ".F", ".for", ".f90":
-			p.FFiles = append(p.FFiles, name)
-			continue
-		case ".s":
-			p.SFiles = append(p.SFiles, name)
-			continue
+		case ".go":
+			// keep going
 		case ".S", ".sx":
+			// special case for cgo, handled at end
 			Sfiles = append(Sfiles, name)
 			continue
-		case ".swig":
-			p.SwigFiles = append(p.SwigFiles, name)
-			continue
-		case ".swigcxx":
-			p.SwigCXXFiles = append(p.SwigCXXFiles, name)
-			continue
-		case ".syso":
-			// binary objects to add to package archive
-			// Likely of the form foo_windows.syso, but
-			// the name was vetted above with goodOSArchFile.
-			p.SysoFiles = append(p.SysoFiles, name)
+		default:
+			if list := fileListForExt(p, ext); list != nil {
+				*list = append(*list, name)
+			}
 			continue
 		}
 
-		pf, err := parser.ParseFile(fset, filename, data, parser.ImportsOnly|parser.ParseComments)
-		if err != nil {
-			badFile(err)
+		if info.parseErr != nil {
+			badFile(info.parseErr)
 			continue
 		}
+		pf := info.parsed
 
 		pkg := pf.Name.Name
 		if pkg == "documentation" {
@@ -910,48 +904,23 @@ Found:
 		}
 
 		// Record imports and information about cgo.
-		type importPos struct {
-			path string
-			pos  token.Pos
-		}
-		var fileImports []importPos
 		isCgo := false
-		for _, decl := range pf.Decls {
-			d, ok := decl.(*ast.GenDecl)
-			if !ok {
-				continue
-			}
-			for _, dspec := range d.Specs {
-				spec, ok := dspec.(*ast.ImportSpec)
-				if !ok {
+		for _, imp := range info.imports {
+			if imp.path == "C" {
+				if isTest {
+					badFile(fmt.Errorf("use of cgo in test %s not supported", filename))
 					continue
 				}
-				quoted := spec.Path.Value
-				path, err := strconv.Unquote(quoted)
-				if err != nil {
-					panic(fmt.Sprintf("%s: parser returned invalid quoted string: <%s>", filename, quoted))
-				}
-				fileImports = append(fileImports, importPos{path, spec.Pos()})
-				if path == "C" {
-					if isTest {
-						badFile(fmt.Errorf("use of cgo in test %s not supported", filename))
-					} else {
-						cg := spec.Doc
-						if cg == nil && len(d.Specs) == 1 {
-							cg = d.Doc
-						}
-						if cg != nil {
-							if err := ctxt.saveCgo(filename, p, cg); err != nil {
-								badFile(err)
-							}
-						}
-						isCgo = true
+				isCgo = true
+				if imp.doc != nil {
+					if err := ctxt.saveCgo(filename, p, imp.doc); err != nil {
+						badFile(err)
 					}
 				}
 			}
 		}
 
-		var fileList *[]string
+		var fileList, embedList *[]string
 		var importMap map[string][]token.Position
 		switch {
 		case isCgo:
@@ -959,6 +928,7 @@ Found:
 			if ctxt.CgoEnabled {
 				fileList = &p.CgoFiles
 				importMap = imported
+				embedList = &embeds
 			} else {
 				// Ignore imports from cgo files if cgo is disabled.
 				fileList = &p.IgnoredGoFiles
@@ -966,19 +936,25 @@ Found:
 		case isXTest:
 			fileList = &p.XTestGoFiles
 			importMap = xTestImported
+			embedList = &xTestEmbeds
 		case isTest:
 			fileList = &p.TestGoFiles
 			importMap = testImported
+			embedList = &testEmbeds
 		default:
 			fileList = &p.GoFiles
 			importMap = imported
+			embedList = &embeds
 		}
 		*fileList = append(*fileList, name)
 		if importMap != nil {
-			for _, imp := range fileImports {
+			for _, imp := range info.imports {
 				importMap[imp.path] = append(importMap[imp.path], fset.Position(imp.pos))
 			}
 		}
+		if embedList != nil {
+			*embedList = append(*embedList, info.embeds...)
+		}
 	}
 
 	for tag := range allTags {
@@ -986,6 +962,10 @@ Found:
 	}
 	sort.Strings(p.AllTags)
 
+	p.EmbedPatterns = uniq(embeds)
+	p.TestEmbedPatterns = uniq(testEmbeds)
+	p.XTestEmbedPatterns = uniq(xTestEmbeds)
+
 	p.Imports, p.ImportPos = cleanImports(imported)
 	p.TestImports, p.TestImportPos = cleanImports(testImported)
 	p.XTestImports, p.XTestImportPos = cleanImports(xTestImported)
@@ -996,6 +976,9 @@ Found:
 	if len(p.CgoFiles) > 0 {
 		p.SFiles = append(p.SFiles, Sfiles...)
 		sort.Strings(p.SFiles)
+	} else {
+		p.IgnoredOtherFiles = append(p.IgnoredOtherFiles, Sfiles...)
+		sort.Strings(p.IgnoredOtherFiles)
 	}
 
 	if badGoError != nil {
@@ -1007,6 +990,46 @@ Found:
 	return p, pkgerr
 }
 
+func fileListForExt(p *Package, ext string) *[]string {
+	switch ext {
+	case ".c":
+		return &p.CFiles
+	case ".cc", ".cpp", ".cxx":
+		return &p.CXXFiles
+	case ".m":
+		return &p.MFiles
+	case ".h", ".hh", ".hpp", ".hxx":
+		return &p.HFiles
+	case ".f", ".F", ".for", ".f90":
+		return &p.FFiles
+	case ".s", ".S", ".sx":
+		return &p.SFiles
+	case ".swig":
+		return &p.SwigFiles
+	case ".swigcxx":
+		return &p.SwigCXXFiles
+	case ".syso":
+		return &p.SysoFiles
+	}
+	return nil
+}
+
+func uniq(list []string) []string {
+	if list == nil {
+		return nil
+	}
+	out := make([]string, len(list))
+	copy(out, list)
+	sort.Strings(out)
+	uniq := out[:0]
+	for _, x := range out {
+		if len(uniq) == 0 || uniq[len(uniq)-1] != x {
+			uniq = append(uniq, x)
+		}
+	}
+	return uniq
+}
+
 var errNoModules = errors.New("not using modules")
 
 // importGo checks whether it can use the go command to find the directory for path.
@@ -1298,22 +1321,46 @@ func parseWord(data []byte) (word, rest []byte) {
 // MatchFile considers the name of the file and may use ctxt.OpenFile to
 // read some or all of the file's content.
 func (ctxt *Context) MatchFile(dir, name string) (match bool, err error) {
-	match, _, _, err = ctxt.matchFile(dir, name, nil, nil)
-	return
+	info, err := ctxt.matchFile(dir, name, nil, nil, nil)
+	return info != nil, err
+}
+
+var dummyPkg Package
+
+// fileInfo records information learned about a file included in a build.
+type fileInfo struct {
+	name     string // full name including dir
+	header   []byte
+	fset     *token.FileSet
+	parsed   *ast.File
+	parseErr error
+	imports  []fileImport
+	embeds   []string
+	embedErr error
+}
+
+type fileImport struct {
+	path string
+	pos  token.Pos
+	doc  *ast.CommentGroup
 }
 
 // matchFile determines whether the file with the given name in the given directory
 // should be included in the package being constructed.
-// It returns the data read from the file.
+// If the file should be included, matchFile returns a non-nil *fileInfo (and a nil error).
+// Non-nil errors are reserved for unexpected problems.
+//
 // If name denotes a Go program, matchFile reads until the end of the
-// imports (and returns that data) even though it only considers text
-// until the first non-comment.
+// imports and returns that section of the file in the fileInfo's header field,
+// even though it only considers text until the first non-comment
+// for +build lines.
+//
 // If allTags is non-nil, matchFile records any encountered build tag
 // by setting allTags[tag] = true.
-func (ctxt *Context) matchFile(dir, name string, allTags map[string]bool, binaryOnly *bool) (match bool, data []byte, filename string, err error) {
+func (ctxt *Context) matchFile(dir, name string, allTags map[string]bool, binaryOnly *bool, fset *token.FileSet) (*fileInfo, error) {
 	if strings.HasPrefix(name, "_") ||
 		strings.HasPrefix(name, ".") {
-		return
+		return nil, nil
 	}
 
 	i := strings.LastIndex(name, ".")
@@ -1323,53 +1370,53 @@ func (ctxt *Context) matchFile(dir, name string, allTags map[string]bool, binary
 	ext := name[i:]
 
 	if !ctxt.goodOSArchFile(name, allTags) && !ctxt.UseAllFiles {
-		return
+		return nil, nil
 	}
 
-	switch ext {
-	case ".go", ".c", ".cc", ".cxx", ".cpp", ".m", ".s", ".h", ".hh", ".hpp", ".hxx", ".f", ".F", ".f90", ".S", ".sx", ".swig", ".swigcxx":
-		// tentatively okay - read to make sure
-	case ".syso":
-		// binary, no reading
-		match = true
-		return
-	default:
+	if ext != ".go" && fileListForExt(&dummyPkg, ext) == nil {
 		// skip
-		return
+		return nil, nil
+	}
+
+	info := &fileInfo{name: ctxt.joinPath(dir, name), fset: fset}
+	if ext == ".syso" {
+		// binary, no reading
+		return info, nil
 	}
 
-	filename = ctxt.joinPath(dir, name)
-	f, err := ctxt.openFile(filename)
+	f, err := ctxt.openFile(info.name)
 	if err != nil {
-		return
+		return nil, err
 	}
 
-	if strings.HasSuffix(filename, ".go") {
-		data, err = readImports(f, false, nil)
-		if strings.HasSuffix(filename, "_test.go") {
+	if strings.HasSuffix(name, ".go") {
+		err = readGoInfo(f, info)
+		if strings.HasSuffix(name, "_test.go") {
 			binaryOnly = nil // ignore //go:binary-only-package comments in _test.go files
 		}
 	} else {
 		binaryOnly = nil // ignore //go:binary-only-package comments in non-Go sources
-		data, err = readComments(f)
+		info.header, err = readComments(f)
 	}
 	f.Close()
 	if err != nil {
-		err = fmt.Errorf("read %s: %v", filename, err)
-		return
+		return nil, fmt.Errorf("read %s: %v", info.name, err)
 	}
 
 	// Look for +build comments to accept or reject the file.
-	var sawBinaryOnly bool
-	if !ctxt.shouldBuild(data, allTags, &sawBinaryOnly) && !ctxt.UseAllFiles {
-		return
+	ok, sawBinaryOnly, err := ctxt.shouldBuild(info.header, allTags)
+	if err != nil {
+		return nil, err
+	}
+	if !ok && !ctxt.UseAllFiles {
+		return nil, nil
 	}
 
 	if binaryOnly != nil && sawBinaryOnly {
 		*binaryOnly = true
 	}
-	match = true
-	return
+
+	return info, nil
 }
 
 func cleanImports(m map[string][]token.Position) ([]string, map[string][]token.Position) {
@@ -1391,7 +1438,25 @@ func ImportDir(dir string, mode ImportMode) (*Package, error) {
 	return Default.ImportDir(dir, mode)
 }
 
-var slashslash = []byte("//")
+var (
+	bSlashSlash = []byte(slashSlash)
+	bStarSlash  = []byte(starSlash)
+	bSlashStar  = []byte(slashStar)
+
+	goBuildComment = []byte("//go:build")
+
+	errGoBuildWithoutBuild = errors.New("//go:build comment without // +build comment")
+	errMultipleGoBuild     = errors.New("multiple //go:build comments") // unused in Go 1.(N-1)
+)
+
+func isGoBuildComment(line []byte) bool {
+	if !bytes.HasPrefix(line, goBuildComment) {
+		return false
+	}
+	line = bytes.TrimSpace(line)
+	rest := line[len(goBuildComment):]
+	return len(rest) == 0 || len(bytes.TrimSpace(rest)) < len(rest)
+}
 
 // Special comment denoting a binary-only package.
 // See https://golang.org/design/2775-binary-only-packages
@@ -1411,37 +1476,24 @@ var binaryOnlyComment = []byte("//go:binary-only-package")
 //
 // marks the file as applicable only on Windows and Linux.
 //
-// If shouldBuild finds a //go:binary-only-package comment in the file,
-// it sets *binaryOnly to true. Otherwise it does not change *binaryOnly.
+// For each build tag it consults, shouldBuild sets allTags[tag] = true.
 //
-func (ctxt *Context) shouldBuild(content []byte, allTags map[string]bool, binaryOnly *bool) bool {
-	sawBinaryOnly := false
+// shouldBuild reports whether the file should be built
+// and whether a //go:binary-only-package comment was found.
+func (ctxt *Context) shouldBuild(content []byte, allTags map[string]bool) (shouldBuild, binaryOnly bool, err error) {
 
 	// Pass 1. Identify leading run of // comments and blank lines,
 	// which must be followed by a blank line.
-	end := 0
-	p := content
-	for len(p) > 0 {
-		line := p
-		if i := bytes.IndexByte(line, '\n'); i >= 0 {
-			line, p = line[:i], p[i+1:]
-		} else {
-			p = p[len(p):]
-		}
-		line = bytes.TrimSpace(line)
-		if len(line) == 0 { // Blank line
-			end = len(content) - len(p)
-			continue
-		}
-		if !bytes.HasPrefix(line, slashslash) { // Not comment line
-			break
-		}
+	// Also identify any //go:build comments.
+	content, goBuild, sawBinaryOnly, err := parseFileHeader(content)
+	if err != nil {
+		return false, false, err
 	}
-	content = content[:end]
 
-	// Pass 2.  Process each line in the run.
-	p = content
-	allok := true
+	// Pass 2.  Process each +build line in the run.
+	p := content
+	shouldBuild = true
+	sawBuild := false
 	for len(p) > 0 {
 		line := p
 		if i := bytes.IndexByte(line, '\n'); i >= 0 {
@@ -1450,17 +1502,15 @@ func (ctxt *Context) shouldBuild(content []byte, allTags map[string]bool, binary
 			p = p[len(p):]
 		}
 		line = bytes.TrimSpace(line)
-		if !bytes.HasPrefix(line, slashslash) {
+		if !bytes.HasPrefix(line, bSlashSlash) {
 			continue
 		}
-		if bytes.Equal(line, binaryOnlyComment) {
-			sawBinaryOnly = true
-		}
-		line = bytes.TrimSpace(line[len(slashslash):])
+		line = bytes.TrimSpace(line[len(bSlashSlash):])
 		if len(line) > 0 && line[0] == '+' {
 			// Looks like a comment +line.
 			f := strings.Fields(string(line))
 			if f[0] == "+build" {
+				sawBuild = true
 				ok := false
 				for _, tok := range f[1:] {
 					if ctxt.match(tok, allTags) {
@@ -1468,17 +1518,84 @@ func (ctxt *Context) shouldBuild(content []byte, allTags map[string]bool, binary
 					}
 				}
 				if !ok {
-					allok = false
+					shouldBuild = false
 				}
 			}
 		}
 	}
 
-	if binaryOnly != nil && sawBinaryOnly {
-		*binaryOnly = true
+	if goBuild != nil && !sawBuild {
+		return false, false, errGoBuildWithoutBuild
+	}
+
+	return shouldBuild, sawBinaryOnly, nil
+}
+
+func parseFileHeader(content []byte) (trimmed, goBuild []byte, sawBinaryOnly bool, err error) {
+	end := 0
+	p := content
+	ended := false       // found non-blank, non-// line, so stopped accepting // +build lines
+	inSlashStar := false // in /* */ comment
+
+Lines:
+	for len(p) > 0 {
+		line := p
+		if i := bytes.IndexByte(line, '\n'); i >= 0 {
+			line, p = line[:i], p[i+1:]
+		} else {
+			p = p[len(p):]
+		}
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 && !ended { // Blank line
+			// Remember position of most recent blank line.
+			// When we find the first non-blank, non-// line,
+			// this "end" position marks the latest file position
+			// where a // +build line can appear.
+			// (It must appear _before_ a blank line before the non-blank, non-// line.
+			// Yes, that's confusing, which is part of why we moved to //go:build lines.)
+			// Note that ended==false here means that inSlashStar==false,
+			// since seeing a /* would have set ended==true.
+			end = len(content) - len(p)
+			continue Lines
+		}
+		if !bytes.HasPrefix(line, slashSlash) { // Not comment line
+			ended = true
+		}
+
+		if !inSlashStar && isGoBuildComment(line) {
+			if false && goBuild != nil { // enabled in Go 1.N
+				return nil, nil, false, errMultipleGoBuild
+			}
+			goBuild = line
+		}
+		if !inSlashStar && bytes.Equal(line, binaryOnlyComment) {
+			sawBinaryOnly = true
+		}
+
+	Comments:
+		for len(line) > 0 {
+			if inSlashStar {
+				if i := bytes.Index(line, starSlash); i >= 0 {
+					inSlashStar = false
+					line = bytes.TrimSpace(line[i+len(starSlash):])
+					continue Comments
+				}
+				continue Lines
+			}
+			if bytes.HasPrefix(line, bSlashSlash) {
+				continue Lines
+			}
+			if bytes.HasPrefix(line, bSlashStar) {
+				inSlashStar = true
+				line = bytes.TrimSpace(line[len(bSlashStar):])
+				continue Comments
+			}
+			// Found non-comment text.
+			break Lines
+		}
 	}
 
-	return allok
+	return content[:end], goBuild, sawBinaryOnly, nil
 }
 
 // saveCgo saves the information from the #cgo lines in the import "C" comment.
diff --git a/src/go/build/build_test.go b/src/go/build/build_test.go
index 22c62ce87d..5a4a2d62f5 100644
--- a/src/go/build/build_test.go
+++ b/src/go/build/build_test.go
@@ -120,7 +120,7 @@ func TestMultiplePackageImport(t *testing.T) {
 }
 
 func TestLocalDirectory(t *testing.T) {
-	if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && runtime.GOARCH == "arm64" {
+	if runtime.GOOS == "ios" {
 		t.Skipf("skipping on %s/%s, no valid GOROOT", runtime.GOOS, runtime.GOARCH)
 	}
 
@@ -138,48 +138,178 @@ func TestLocalDirectory(t *testing.T) {
 	}
 }
 
-func TestShouldBuild(t *testing.T) {
-	const file1 = "// +build tag1\n\n" +
-		"package main\n"
-	want1 := map[string]bool{"tag1": true}
-
-	const file2 = "// +build cgo\n\n" +
-		"// This package implements parsing of tags like\n" +
-		"// +build tag1\n" +
-		"package build"
-	want2 := map[string]bool{"cgo": true}
-
-	const file3 = "// Copyright The Go Authors.\n\n" +
-		"package build\n\n" +
-		"// shouldBuild checks tags given by lines of the form\n" +
-		"// +build tag\n" +
-		"func shouldBuild(content []byte)\n"
-	want3 := map[string]bool{}
-
-	ctx := &Context{BuildTags: []string{"tag1"}}
-	m := map[string]bool{}
-	if !ctx.shouldBuild([]byte(file1), m, nil) {
-		t.Errorf("shouldBuild(file1) = false, want true")
-	}
-	if !reflect.DeepEqual(m, want1) {
-		t.Errorf("shouldBuild(file1) tags = %v, want %v", m, want1)
-	}
-
-	m = map[string]bool{}
-	if ctx.shouldBuild([]byte(file2), m, nil) {
-		t.Errorf("shouldBuild(file2) = true, want false")
-	}
-	if !reflect.DeepEqual(m, want2) {
-		t.Errorf("shouldBuild(file2) tags = %v, want %v", m, want2)
-	}
+var shouldBuildTests = []struct {
+	name        string
+	content     string
+	tags        map[string]bool
+	binaryOnly  bool
+	shouldBuild bool
+	err         error
+}{
+	{
+		name: "Yes",
+		content: "// +build yes\n\n" +
+			"package main\n",
+		tags:        map[string]bool{"yes": true},
+		shouldBuild: true,
+	},
+	{
+		name: "Or",
+		content: "// +build no yes\n\n" +
+			"package main\n",
+		tags:        map[string]bool{"yes": true, "no": true},
+		shouldBuild: true,
+	},
+	{
+		name: "And",
+		content: "// +build no,yes\n\n" +
+			"package main\n",
+		tags:        map[string]bool{"yes": true, "no": true},
+		shouldBuild: false,
+	},
+	{
+		name: "Cgo",
+		content: "// +build cgo\n\n" +
+			"// Copyright The Go Authors.\n\n" +
+			"// This package implements parsing of tags like\n" +
+			"// +build tag1\n" +
+			"package build",
+		tags:        map[string]bool{"cgo": true},
+		shouldBuild: false,
+	},
+	{
+		name: "AfterPackage",
+		content: "// Copyright The Go Authors.\n\n" +
+			"package build\n\n" +
+			"// shouldBuild checks tags given by lines of the form\n" +
+			"// +build tag\n" +
+			"func shouldBuild(content []byte)\n",
+		tags:        map[string]bool{},
+		shouldBuild: true,
+	},
+	{
+		name: "TooClose",
+		content: "// +build yes\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: true,
+	},
+	{
+		name: "TooCloseNo",
+		content: "// +build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: true,
+	},
+	{
+		name: "BinaryOnly",
+		content: "//go:binary-only-package\n" +
+			"// +build yes\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		binaryOnly:  true,
+		shouldBuild: true,
+	},
+	{
+		name: "ValidGoBuild",
+		content: "// +build yes\n\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{"yes": true},
+		shouldBuild: true,
+	},
+	{
+		name: "MissingBuild",
+		content: "//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+	{
+		name: "MissingBuild2",
+		content: "/* */\n" +
+			"// +build yes\n\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+	{
+		name: "MissingBuild2",
+		content: "/*\n" +
+			"// +build yes\n\n" +
+			"*/\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+	{
+		name: "Comment1",
+		content: "/*\n" +
+			"//go:build no\n" +
+			"*/\n\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: true,
+	},
+	{
+		name: "Comment2",
+		content: "/*\n" +
+			"text\n" +
+			"*/\n\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+	{
+		name: "Comment3",
+		content: "/*/*/ /* hi *//* \n" +
+			"text\n" +
+			"*/\n\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+	{
+		name: "Comment4",
+		content: "/**///go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: true,
+	},
+	{
+		name: "Comment5",
+		content: "/**/\n" +
+			"//go:build no\n" +
+			"package main\n",
+		tags:        map[string]bool{},
+		shouldBuild: false,
+		err:         errGoBuildWithoutBuild,
+	},
+}
 
-	m = map[string]bool{}
-	ctx = &Context{BuildTags: nil}
-	if !ctx.shouldBuild([]byte(file3), m, nil) {
-		t.Errorf("shouldBuild(file3) = false, want true")
-	}
-	if !reflect.DeepEqual(m, want3) {
-		t.Errorf("shouldBuild(file3) tags = %v, want %v", m, want3)
+func TestShouldBuild(t *testing.T) {
+	for _, tt := range shouldBuildTests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := &Context{BuildTags: []string{"yes"}}
+			tags := map[string]bool{}
+			shouldBuild, binaryOnly, err := ctx.shouldBuild([]byte(tt.content), tags)
+			if shouldBuild != tt.shouldBuild || binaryOnly != tt.binaryOnly || !reflect.DeepEqual(tags, tt.tags) || err != tt.err {
+				t.Errorf("mismatch:\n"+
+					"have shouldBuild=%v, binaryOnly=%v, tags=%v, err=%v\n"+
+					"want shouldBuild=%v, binaryOnly=%v, tags=%v, err=%v",
+					shouldBuild, binaryOnly, tags, err,
+					tt.shouldBuild, tt.binaryOnly, tt.tags, tt.err)
+			}
+		})
 	}
 }
 
@@ -250,7 +380,7 @@ func TestMatchFile(t *testing.T) {
 }
 
 func TestImportCmd(t *testing.T) {
-	if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && runtime.GOARCH == "arm64" {
+	if runtime.GOOS == "ios" {
 		t.Skipf("skipping on %s/%s, no valid GOROOT", runtime.GOOS, runtime.GOARCH)
 	}
 
@@ -482,11 +612,13 @@ func TestImportPackageOutsideModule(t *testing.T) {
 	ctxt.GOPATH = gopath
 	ctxt.Dir = filepath.Join(gopath, "src/example.com/p")
 
-	want := "cannot find module providing package"
+	want := "working directory is not part of a module"
 	if _, err := ctxt.Import("example.com/p", gopath, FindOnly); err == nil {
 		t.Fatal("importing package when no go.mod is present succeeded unexpectedly")
 	} else if errStr := err.Error(); !strings.Contains(errStr, want) {
 		t.Fatalf("error when importing package when no go.mod is present: got %q; want %q", errStr, want)
+	} else {
+		t.Logf(`ctxt.Import("example.com/p", _, FindOnly): %v`, err)
 	}
 }
 
@@ -547,9 +679,16 @@ func TestMissingImportErrorRepetition(t *testing.T) {
 	if err == nil {
 		t.Fatal("unexpected success")
 	}
+
 	// Don't count the package path with a URL like https://...?go-get=1.
 	// See golang.org/issue/35986.
 	errStr := strings.ReplaceAll(err.Error(), "://"+pkgPath+"?go-get=1", "://...?go-get=1")
+
+	// Also don't count instances in suggested "go get" or similar commands
+	// (see https://golang.org/issue/41576). The suggested command typically
+	// follows a semicolon.
+	errStr = strings.SplitN(errStr, ";", 2)[0]
+
 	if n := strings.Count(errStr, pkgPath); n != 1 {
 		t.Fatalf("package path %q appears in error %d times; should appear once\nerror: %v", pkgPath, n, err)
 	}
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index fa8ecf10f4..b26b2bd199 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -11,12 +11,12 @@ import (
 	"bytes"
 	"fmt"
 	"internal/testenv"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
 	"sort"
-	"strconv"
 	"strings"
 	"testing"
 )
@@ -99,10 +99,16 @@ var depsRules = `
 	RUNTIME
 	< io;
 
+	syscall !< io;
 	reflect !< sort;
 
+	RUNTIME, unicode/utf8
+	< path;
+
+	unicode !< path;
+
 	# SYSCALL is RUNTIME plus the packages necessary for basic system calls.
-	RUNTIME, unicode/utf8, unicode/utf16, io
+	RUNTIME, unicode/utf8, unicode/utf16
 	< internal/syscall/windows/sysdll, syscall/js
 	< syscall
 	< internal/syscall/unix, internal/syscall/windows, internal/syscall/windows/registry
@@ -116,6 +122,9 @@ var depsRules = `
 	< context
 	< TIME;
 
+	TIME, io, path, sort
+	< io/fs;
+
 	# MATH is RUNTIME plus the basic math packages.
 	RUNTIME
 	< math
@@ -129,6 +138,9 @@ var depsRules = `
 	MATH
 	< math/rand;
 
+	MATH
+	< runtime/metrics;
+
 	MATH, unicode/utf8
 	< strconv;
 
@@ -137,7 +149,7 @@ var depsRules = `
 	# STR is basic string and buffer manipulation.
 	RUNTIME, io, unicode/utf8, unicode/utf16, unicode
 	< bytes, strings
-	< bufio, path;
+	< bufio;
 
 	bufio, path, strconv
 	< STR;
@@ -145,7 +157,7 @@ var depsRules = `
 	# OS is basic OS access, including helpers (path/filepath, os/exec, etc).
 	# OS includes string routines, but those must be layered above package os.
 	# OS does not include reflection.
-	TIME, io, sort
+	io/fs
 	< internal/testlog
 	< internal/poll
 	< os
@@ -155,7 +167,9 @@ var depsRules = `
 
 	os/signal, STR
 	< path/filepath
-	< io/ioutil, os/exec
+	< io/ioutil, os/exec;
+
+	io/ioutil, os/exec, os/signal
 	< OS;
 
 	reflect !< OS;
@@ -318,7 +332,6 @@ var depsRules = `
 	# so large dependencies must be kept out.
 	# This is a long-looking list but most of these
 	# are small with few dependencies.
-	# math/rand should probably be removed at some point.
 	CGO,
 	golang.org/x/net/dns/dnsmessage,
 	golang.org/x/net/lif,
@@ -327,11 +340,11 @@ var depsRules = `
 	internal/poll,
 	internal/singleflight,
 	internal/race,
-	math/rand,
 	os
 	< net;
 
 	fmt, unicode !< net;
+	math/rand !< net; # net uses runtime instead
 
 	# NET is net plus net-helper packages.
 	FMT, net
@@ -449,7 +462,7 @@ var depsRules = `
 	OS, compress/gzip, regexp
 	< internal/profile;
 
-	html/template, internal/profile, net/http, runtime/pprof, runtime/trace
+	html, internal/profile, net/http, runtime/pprof, runtime/trace
 	< net/http/pprof;
 
 	# RPC
@@ -457,14 +470,19 @@ var depsRules = `
 	< net/rpc
 	< net/rpc/jsonrpc;
 
+	# System Information
+	internal/cpu, sync
+	< internal/sysinfo;
+
 	# Test-only
 	log
-	< testing/iotest;
+	< testing/iotest
+	< testing/fstest;
 
 	FMT, flag, math/rand
 	< testing/quick;
 
-	FMT, flag, runtime/debug, runtime/trace
+	FMT, flag, runtime/debug, runtime/trace, internal/sysinfo
 	< testing;
 
 	internal/testlog, runtime/pprof, regexp
@@ -479,7 +497,7 @@ var depsRules = `
 	CGO, OS, fmt
 	< os/signal/internal/pty;
 
-	NET, testing
+	NET, testing, math/rand
 	< golang.org/x/net/nettest;
 
 	FMT, container/heap, math/rand
@@ -492,7 +510,7 @@ func listStdPkgs(goroot string) ([]string, error) {
 	var pkgs []string
 
 	src := filepath.Join(goroot, "src") + string(filepath.Separator)
-	walkFn := func(path string, fi os.FileInfo, err error) error {
+	walkFn := func(path string, fi fs.FileInfo, err error) error {
 		if err != nil || !fi.IsDir() || path == src {
 			return nil
 		}
@@ -594,24 +612,22 @@ func findImports(pkg string) ([]string, error) {
 		if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
 			continue
 		}
-		f, err := os.Open(filepath.Join(dir, name))
+		var info fileInfo
+		info.name = filepath.Join(dir, name)
+		f, err := os.Open(info.name)
 		if err != nil {
 			return nil, err
 		}
-		var imp []string
-		data, err := readImports(f, false, &imp)
+		err = readGoInfo(f, &info)
 		f.Close()
 		if err != nil {
 			return nil, fmt.Errorf("reading %v: %v", name, err)
 		}
-		if bytes.Contains(data, buildIgnore) {
+		if bytes.Contains(info.header, buildIgnore) {
 			continue
 		}
-		for _, quoted := range imp {
-			path, err := strconv.Unquote(quoted)
-			if err != nil {
-				continue
-			}
+		for _, imp := range info.imports {
+			path := imp.path
 			if !haveImport[path] {
 				haveImport[path] = true
 				imports = append(imports, path)
diff --git a/src/go/build/read.go b/src/go/build/read.go
index 29b8cdc786..6806a51c24 100644
--- a/src/go/build/read.go
+++ b/src/go/build/read.go
@@ -7,7 +7,13 @@ package build
 import (
 	"bufio"
 	"errors"
+	"fmt"
+	"go/ast"
+	"go/parser"
 	"io"
+	"strconv"
+	"strings"
+	"unicode"
 	"unicode/utf8"
 )
 
@@ -57,6 +63,29 @@ func (r *importReader) readByte() byte {
 	return c
 }
 
+// readByteNoBuf is like readByte but doesn't buffer the byte.
+// It exhausts r.buf before reading from r.b.
+func (r *importReader) readByteNoBuf() byte {
+	if len(r.buf) > 0 {
+		c := r.buf[0]
+		r.buf = r.buf[1:]
+		return c
+	}
+	c, err := r.b.ReadByte()
+	if err == nil && c == 0 {
+		err = errNUL
+	}
+	if err != nil {
+		if err == io.EOF {
+			r.eof = true
+		} else if r.err == nil {
+			r.err = err
+		}
+		c = 0
+	}
+	return c
+}
+
 // peekByte returns the next byte from the input reader but does not advance beyond it.
 // If skipSpace is set, peekByte skips leading spaces and comments.
 func (r *importReader) peekByte(skipSpace bool) byte {
@@ -117,6 +146,74 @@ func (r *importReader) nextByte(skipSpace bool) byte {
 	return c
 }
 
+var goEmbed = []byte("go:embed")
+
+// findEmbed advances the input reader to the next //go:embed comment.
+// It reports whether it found a comment.
+// (Otherwise it found an error or EOF.)
+func (r *importReader) findEmbed(first bool) bool {
+	// The import block scan stopped after a non-space character,
+	// so the reader is not at the start of a line on the first call.
+	// After that, each //go:embed extraction leaves the reader
+	// at the end of a line.
+	startLine := !first
+	var c byte
+	for r.err == nil && !r.eof {
+		c = r.readByteNoBuf()
+	Reswitch:
+		switch c {
+		default:
+			startLine = false
+
+		case '\n':
+			startLine = true
+
+		case ' ', '\t':
+			// leave startLine alone
+
+		case '/':
+			c = r.readByteNoBuf()
+			switch c {
+			default:
+				startLine = false
+				goto Reswitch
+
+			case '*':
+				var c1 byte
+				for (c != '*' || c1 != '/') && r.err == nil {
+					if r.eof {
+						r.syntaxError()
+					}
+					c, c1 = c1, r.readByteNoBuf()
+				}
+				startLine = false
+
+			case '/':
+				if startLine {
+					// Try to read this as a //go:embed comment.
+					for i := range goEmbed {
+						c = r.readByteNoBuf()
+						if c != goEmbed[i] {
+							goto SkipSlashSlash
+						}
+					}
+					c = r.readByteNoBuf()
+					if c == ' ' || c == '\t' {
+						// Found one!
+						return true
+					}
+				}
+			SkipSlashSlash:
+				for c != '\n' && r.err == nil && !r.eof {
+					c = r.readByteNoBuf()
+				}
+				startLine = true
+			}
+		}
+	}
+	return false
+}
+
 // readKeyword reads the given keyword from the input.
 // If the keyword is not present, readKeyword records a syntax error.
 func (r *importReader) readKeyword(kw string) {
@@ -147,15 +244,11 @@ func (r *importReader) readIdent() {
 
 // readString reads a quoted string literal from the input.
 // If an identifier is not present, readString records a syntax error.
-func (r *importReader) readString(save *[]string) {
+func (r *importReader) readString() {
 	switch r.nextByte(true) {
 	case '`':
-		start := len(r.buf) - 1
 		for r.err == nil {
 			if r.nextByte(false) == '`' {
-				if save != nil {
-					*save = append(*save, string(r.buf[start:]))
-				}
 				break
 			}
 			if r.eof {
@@ -163,13 +256,9 @@ func (r *importReader) readString(save *[]string) {
 			}
 		}
 	case '"':
-		start := len(r.buf) - 1
 		for r.err == nil {
 			c := r.nextByte(false)
 			if c == '"' {
-				if save != nil {
-					*save = append(*save, string(r.buf[start:]))
-				}
 				break
 			}
 			if r.eof || c == '\n' {
@@ -186,17 +275,17 @@ func (r *importReader) readString(save *[]string) {
 
 // readImport reads an import clause - optional identifier followed by quoted string -
 // from the input.
-func (r *importReader) readImport(imports *[]string) {
+func (r *importReader) readImport() {
 	c := r.peekByte(true)
 	if c == '.' {
 		r.peek = 0
 	} else if isIdent(c) {
 		r.readIdent()
 	}
-	r.readString(imports)
+	r.readString()
 }
 
-// readComments is like ioutil.ReadAll, except that it only reads the leading
+// readComments is like io.ReadAll, except that it only reads the leading
 // block of comments in the file.
 func readComments(f io.Reader) ([]byte, error) {
 	r := &importReader{b: bufio.NewReader(f)}
@@ -208,9 +297,14 @@ func readComments(f io.Reader) ([]byte, error) {
 	return r.buf, r.err
 }
 
-// readImports is like ioutil.ReadAll, except that it expects a Go file as input
-// and stops reading the input once the imports have completed.
-func readImports(f io.Reader, reportSyntaxError bool, imports *[]string) ([]byte, error) {
+// readGoInfo expects a Go file as input and reads the file up to and including the import section.
+// It records what it learned in *info.
+// If info.fset is non-nil, readGoInfo parses the file and sets info.parsed, info.parseErr,
+// info.imports, info.embeds, and info.embedErr.
+//
+// It only returns an error if there are problems reading the file,
+// not for syntax errors in the file itself.
+func readGoInfo(f io.Reader, info *fileInfo) error {
 	r := &importReader{b: bufio.NewReader(f)}
 
 	r.readKeyword("package")
@@ -220,28 +314,162 @@ func readImports(f io.Reader, reportSyntaxError bool, imports *[]string) ([]byte
 		if r.peekByte(true) == '(' {
 			r.nextByte(false)
 			for r.peekByte(true) != ')' && r.err == nil {
-				r.readImport(imports)
+				r.readImport()
 			}
 			r.nextByte(false)
 		} else {
-			r.readImport(imports)
+			r.readImport()
 		}
 	}
 
+	info.header = r.buf
+
 	// If we stopped successfully before EOF, we read a byte that told us we were done.
 	// Return all but that last byte, which would cause a syntax error if we let it through.
 	if r.err == nil && !r.eof {
-		return r.buf[:len(r.buf)-1], nil
+		info.header = r.buf[:len(r.buf)-1]
 	}
 
 	// If we stopped for a syntax error, consume the whole file so that
 	// we are sure we don't change the errors that go/parser returns.
-	if r.err == errSyntax && !reportSyntaxError {
+	if r.err == errSyntax {
 		r.err = nil
 		for r.err == nil && !r.eof {
 			r.readByte()
 		}
+		info.header = r.buf
+	}
+	if r.err != nil {
+		return r.err
+	}
+
+	if info.fset == nil {
+		return nil
+	}
+
+	// Parse file header & record imports.
+	info.parsed, info.parseErr = parser.ParseFile(info.fset, info.name, info.header, parser.ImportsOnly|parser.ParseComments)
+	if info.parseErr != nil {
+		return nil
+	}
+
+	hasEmbed := false
+	for _, decl := range info.parsed.Decls {
+		d, ok := decl.(*ast.GenDecl)
+		if !ok {
+			continue
+		}
+		for _, dspec := range d.Specs {
+			spec, ok := dspec.(*ast.ImportSpec)
+			if !ok {
+				continue
+			}
+			quoted := spec.Path.Value
+			path, err := strconv.Unquote(quoted)
+			if err != nil {
+				return fmt.Errorf("parser returned invalid quoted string: <%s>", quoted)
+			}
+			if path == "embed" {
+				hasEmbed = true
+			}
+
+			doc := spec.Doc
+			if doc == nil && len(d.Specs) == 1 {
+				doc = d.Doc
+			}
+			info.imports = append(info.imports, fileImport{path, spec.Pos(), doc})
+		}
 	}
 
-	return r.buf, r.err
+	// If the file imports "embed",
+	// we have to look for //go:embed comments
+	// in the remainder of the file.
+	// The compiler will enforce the mapping of comments to
+	// declared variables. We just need to know the patterns.
+	// If there were //go:embed comments earlier in the file
+	// (near the package statement or imports), the compiler
+	// will reject them. They can be (and have already been) ignored.
+	if hasEmbed {
+		var line []byte
+		for first := true; r.findEmbed(first); first = false {
+			line = line[:0]
+			for {
+				c := r.readByteNoBuf()
+				if c == '\n' || r.err != nil || r.eof {
+					break
+				}
+				line = append(line, c)
+			}
+			// Add args if line is well-formed.
+			// Ignore badly-formed lines - the compiler will report them when it finds them,
+			// and we can pretend they are not there to help go list succeed with what it knows.
+			args, err := parseGoEmbed(string(line))
+			if err == nil {
+				info.embeds = append(info.embeds, args...)
+			}
+		}
+	}
+
+	return nil
+}
+
+// parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
+// It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.
+// There is a copy of this code in cmd/compile/internal/gc/noder.go as well.
+func parseGoEmbed(args string) ([]string, error) {
+	var list []string
+	for args = strings.TrimSpace(args); args != ""; args = strings.TrimSpace(args) {
+		var path string
+	Switch:
+		switch args[0] {
+		default:
+			i := len(args)
+			for j, c := range args {
+				if unicode.IsSpace(c) {
+					i = j
+					break
+				}
+			}
+			path = args[:i]
+			args = args[i:]
+
+		case '`':
+			i := strings.Index(args[1:], "`")
+			if i < 0 {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+			path = args[1 : 1+i]
+			args = args[1+i+1:]
+
+		case '"':
+			i := 1
+			for ; i < len(args); i++ {
+				if args[i] == '\\' {
+					i++
+					continue
+				}
+				if args[i] == '"' {
+					q, err := strconv.Unquote(args[:i+1])
+					if err != nil {
+						return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args[:i+1])
+					}
+					path = q
+					args = args[i+1:]
+					break Switch
+				}
+			}
+			if i >= len(args) {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+		}
+
+		if args != "" {
+			r, _ := utf8.DecodeRuneInString(args)
+			if !unicode.IsSpace(r) {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+		}
+		list = append(list, path)
+	}
+	return list, nil
 }
diff --git a/src/go/build/read_test.go b/src/go/build/read_test.go
index 8636533f69..9264d2606f 100644
--- a/src/go/build/read_test.go
+++ b/src/go/build/read_test.go
@@ -5,7 +5,9 @@
 package build
 
 import (
+	"go/token"
 	"io"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -13,12 +15,12 @@ import (
 const quote = "`"
 
 type readTest struct {
-	// Test input contains ℙ where readImports should stop.
+	// Test input contains ℙ where readGoInfo should stop.
 	in  string
 	err string
 }
 
-var readImportsTests = []readTest{
+var readGoInfoTests = []readTest{
 	{
 		`package p`,
 		"",
@@ -37,15 +39,15 @@ var readImportsTests = []readTest{
 	},
 	{
 		`package p
-		
+
 		// comment
-		
+
 		import "x"
 		import _ "x"
 		import a "x"
-		
+
 		/* comment */
-		
+
 		import (
 			"x" /* comment */
 			_ "x"
@@ -59,7 +61,7 @@ var readImportsTests = []readTest{
 		import ()
 		import()import()import()
 		import();import();import()
-		
+
 		ℙvar x = 1
 		`,
 		"",
@@ -85,7 +87,7 @@ var readCommentsTests = []readTest{
 		/* bar */
 
 		/* quux */ // baz
-		
+
 		/*/ zot */
 
 		// asdf
@@ -127,8 +129,12 @@ func testRead(t *testing.T, tests []readTest, read func(io.Reader) ([]byte, erro
 	}
 }
 
-func TestReadImports(t *testing.T) {
-	testRead(t, readImportsTests, func(r io.Reader) ([]byte, error) { return readImports(r, true, nil) })
+func TestReadGoInfo(t *testing.T) {
+	testRead(t, readGoInfoTests, func(r io.Reader) ([]byte, error) {
+		var info fileInfo
+		err := readGoInfo(r, &info)
+		return info.header, err
+	})
 }
 
 func TestReadComments(t *testing.T) {
@@ -202,11 +208,6 @@ var readFailuresTests = []readTest{
 	},
 }
 
-func TestReadFailures(t *testing.T) {
-	// Errors should be reported (true arg to readImports).
-	testRead(t, readFailuresTests, func(r io.Reader) ([]byte, error) { return readImports(r, true, nil) })
-}
-
 func TestReadFailuresIgnored(t *testing.T) {
 	// Syntax errors should not be reported (false arg to readImports).
 	// Instead, entire file should be the output and no error.
@@ -219,5 +220,63 @@ func TestReadFailuresIgnored(t *testing.T) {
 			tt.err = ""
 		}
 	}
-	testRead(t, tests, func(r io.Reader) ([]byte, error) { return readImports(r, false, nil) })
+	testRead(t, tests, func(r io.Reader) ([]byte, error) {
+		var info fileInfo
+		err := readGoInfo(r, &info)
+		return info.header, err
+	})
+}
+
+var readEmbedTests = []struct {
+	in  string
+	out []string
+}{
+	{
+		"package p\n",
+		nil,
+	},
+	{
+		"package p\nimport \"embed\"\nvar i int\n//go:embed x y z\nvar files embed.FS",
+		[]string{"x", "y", "z"},
+	},
+	{
+		"package p\nimport \"embed\"\nvar i int\n//go:embed x \"\\x79\" `z`\nvar files embed.FS",
+		[]string{"x", "y", "z"},
+	},
+	{
+		"package p\nimport \"embed\"\nvar i int\n//go:embed x y\n//go:embed z\nvar files embed.FS",
+		[]string{"x", "y", "z"},
+	},
+	{
+		"package p\nimport \"embed\"\nvar i int\n\t //go:embed x y\n\t //go:embed z\n\t var files embed.FS",
+		[]string{"x", "y", "z"},
+	},
+	{
+		"package p\nimport \"embed\"\n//go:embed x y z\nvar files embed.FS",
+		[]string{"x", "y", "z"},
+	},
+	{
+		"package p\n//go:embed x y z\n", // no import, no scan
+		nil,
+	},
+	{
+		"package p\n//go:embed x y z\nvar files embed.FS", // no import, no scan
+		nil,
+	},
+}
+
+func TestReadEmbed(t *testing.T) {
+	fset := token.NewFileSet()
+	for i, tt := range readEmbedTests {
+		var info fileInfo
+		info.fset = fset
+		err := readGoInfo(strings.NewReader(tt.in), &info)
+		if err != nil {
+			t.Errorf("#%d: %v", i, err)
+			continue
+		}
+		if !reflect.DeepEqual(info.embeds, tt.out) {
+			t.Errorf("#%d: embeds=%v, want %v", i, info.embeds, tt.out)
+		}
+	}
 }
diff --git a/src/go/doc/doc_test.go b/src/go/doc/doc_test.go
index f1e612c18b..ab98bed62b 100644
--- a/src/go/doc/doc_test.go
+++ b/src/go/doc/doc_test.go
@@ -12,8 +12,8 @@ import (
 	"go/parser"
 	"go/printer"
 	"go/token"
+	"io/fs"
 	"io/ioutil"
-	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
@@ -66,7 +66,7 @@ func indentFmt(indent, s string) string {
 	return indent + strings.ReplaceAll(s, "\n", "\n"+indent) + end
 }
 
-func isGoFile(fi os.FileInfo) bool {
+func isGoFile(fi fs.FileInfo) bool {
 	name := fi.Name()
 	return !fi.IsDir() &&
 		len(name) > 0 && name[0] != '.' && // ignore .files
@@ -86,7 +86,7 @@ func test(t *testing.T, mode Mode) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		filter = func(fi os.FileInfo) bool {
+		filter = func(fi fs.FileInfo) bool {
 			return isGoFile(fi) && rx.MatchString(fi.Name())
 		}
 	}
diff --git a/src/go/doc/headscan.go b/src/go/doc/headscan.go
index 3f782cc1b4..8ea462366e 100644
--- a/src/go/doc/headscan.go
+++ b/src/go/doc/headscan.go
@@ -23,6 +23,7 @@ import (
 	"go/parser"
 	"go/token"
 	"internal/lazyregexp"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -39,7 +40,7 @@ var html_h = lazyregexp.New(`<h3 id="[^"]*">`)
 
 const html_endh = "</h3>\n"
 
-func isGoFile(fi os.FileInfo) bool {
+func isGoFile(fi fs.FileInfo) bool {
 	return strings.HasSuffix(fi.Name(), ".go") &&
 		!strings.HasSuffix(fi.Name(), "_test.go")
 }
@@ -68,7 +69,7 @@ func main() {
 	flag.Parse()
 	fset := token.NewFileSet()
 	nheadings := 0
-	err := filepath.Walk(*root, func(path string, fi os.FileInfo, err error) error {
+	err := filepath.Walk(*root, func(path string, fi fs.FileInfo, err error) error {
 		if !fi.IsDir() {
 			return nil
 		}
diff --git a/src/go/internal/gccgoimporter/importer.go b/src/go/internal/gccgoimporter/importer.go
index 2494fd7b2a..94f2defd8d 100644
--- a/src/go/internal/gccgoimporter/importer.go
+++ b/src/go/internal/gccgoimporter/importer.go
@@ -221,7 +221,7 @@ func GetImporter(searchpaths []string, initmap map[*types.Package]InitData) Impo
 		// Excluded for now: Standard gccgo doesn't support this import format currently.
 		// case goimporterMagic:
 		// 	var data []byte
-		// 	data, err = ioutil.ReadAll(reader)
+		// 	data, err = io.ReadAll(reader)
 		// 	if err != nil {
 		// 		return
 		// 	}
diff --git a/src/go/internal/gccgoimporter/importer_test.go b/src/go/internal/gccgoimporter/importer_test.go
index a74a456868..e4236a5867 100644
--- a/src/go/internal/gccgoimporter/importer_test.go
+++ b/src/go/internal/gccgoimporter/importer_test.go
@@ -97,6 +97,7 @@ var importerTests = [...]importerTest{
 	{pkgpath: "issue30628", name: "Apple", want: "type Apple struct{hey sync.RWMutex; x int; RQ [517]struct{Count uintptr; NumBytes uintptr; Last uintptr}}"},
 	{pkgpath: "issue31540", name: "S", gccgoVersion: 7, want: "type S struct{b int; map[Y]Z}"},
 	{pkgpath: "issue34182", name: "T1", want: "type T1 struct{f *T2}"},
+	{pkgpath: "notinheap", name: "S", want: "type S struct{}"},
 }
 
 func TestGoxImporter(t *testing.T) {
diff --git a/src/go/internal/gccgoimporter/parser.go b/src/go/internal/gccgoimporter/parser.go
index e2ef33f7ae..1b1d07d3f6 100644
--- a/src/go/internal/gccgoimporter/parser.go
+++ b/src/go/internal/gccgoimporter/parser.go
@@ -517,6 +517,13 @@ func (p *parser) parseNamedType(nlist []interface{}) types.Type {
 		p.errorf("%v has nil type", obj)
 	}
 
+	if p.tok == scanner.Ident && p.lit == "notinheap" {
+		p.next()
+		// The go/types package has no way of recording that
+		// this type is marked notinheap. Presumably no user
+		// of this package actually cares.
+	}
+
 	// type alias
 	if p.tok == '=' {
 		p.next()
diff --git a/src/go/internal/gccgoimporter/testdata/notinheap.go b/src/go/internal/gccgoimporter/testdata/notinheap.go
new file mode 100644
index 0000000000..b1ac967227
--- /dev/null
+++ b/src/go/internal/gccgoimporter/testdata/notinheap.go
@@ -0,0 +1,4 @@
+package notinheap
+
+//go:notinheap
+type S struct{}
diff --git a/src/go/internal/gccgoimporter/testdata/notinheap.gox b/src/go/internal/gccgoimporter/testdata/notinheap.gox
new file mode 100644
index 0000000000..cc438e75e0
--- /dev/null
+++ b/src/go/internal/gccgoimporter/testdata/notinheap.gox
@@ -0,0 +1,7 @@
+v3;
+package notinheap
+pkgpath notinheap
+init notinheap ~notinheap
+types 3 2 30 18
+type 1 "S" notinheap <type 2>
+type 2 struct { }
diff --git a/src/go/internal/gcimporter/gcimporter.go b/src/go/internal/gcimporter/gcimporter.go
index fda15eaaae..b74daca246 100644
--- a/src/go/internal/gcimporter/gcimporter.go
+++ b/src/go/internal/gcimporter/gcimporter.go
@@ -12,7 +12,6 @@ import (
 	"go/token"
 	"go/types"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -147,7 +146,7 @@ func Import(fset *token.FileSet, packages map[string]*types.Package, path, srcDi
 
 	case "$$B\n":
 		var data []byte
-		data, err = ioutil.ReadAll(buf)
+		data, err = io.ReadAll(buf)
 		if err != nil {
 			break
 		}
diff --git a/src/go/internal/gcimporter/support.go b/src/go/internal/gcimporter/support.go
index 2de7cacd2d..b8bb14dc49 100644
--- a/src/go/internal/gcimporter/support.go
+++ b/src/go/internal/gcimporter/support.go
@@ -17,7 +17,10 @@ func errorf(format string, args ...interface{}) {
 	panic(fmt.Sprintf(format, args...))
 }
 
-const deltaNewFile = -64 // see cmd/compile/internal/gc/bexport.go
+// deltaNewFile is a magic line delta offset indicating a new file.
+// We use -64 because it is rare; see issue 20080 and CL 41619.
+// -64 is the smallest int that fits in a single byte as a varint.
+const deltaNewFile = -64
 
 // Synthesize a token.Pos
 type fakeFileSet struct {
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
index 54f9d7b80a..cc7e455c4d 100644
--- a/src/go/parser/interface.go
+++ b/src/go/parser/interface.go
@@ -12,8 +12,8 @@ import (
 	"go/ast"
 	"go/token"
 	"io"
+	"io/fs"
 	"io/ioutil"
-	"os"
 	"path/filepath"
 	"strings"
 )
@@ -35,7 +35,7 @@ func readSource(filename string, src interface{}) ([]byte, error) {
 				return s.Bytes(), nil
 			}
 		case io.Reader:
-			return ioutil.ReadAll(s)
+			return io.ReadAll(s)
 		}
 		return nil, errors.New("invalid source")
 	}
@@ -123,7 +123,7 @@ func ParseFile(fset *token.FileSet, filename string, src interface{}, mode Mode)
 // directory specified by path and returns a map of package name -> package
 // AST with all the packages found.
 //
-// If filter != nil, only the files with os.FileInfo entries passing through
+// If filter != nil, only the files with fs.FileInfo entries passing through
 // the filter (and ending in ".go") are considered. The mode bits are passed
 // to ParseFile unchanged. Position information is recorded in fset, which
 // must not be nil.
@@ -132,7 +132,7 @@ func ParseFile(fset *token.FileSet, filename string, src interface{}, mode Mode)
 // returned. If a parse error occurred, a non-nil but incomplete map and the
 // first error encountered are returned.
 //
-func ParseDir(fset *token.FileSet, path string, filter func(os.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
+func ParseDir(fset *token.FileSet, path string, filter func(fs.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
 	list, err := ioutil.ReadDir(path)
 	if err != nil {
 		return nil, err
diff --git a/src/go/parser/parser_test.go b/src/go/parser/parser_test.go
index 25a374eeef..7193a329fe 100644
--- a/src/go/parser/parser_test.go
+++ b/src/go/parser/parser_test.go
@@ -9,7 +9,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/token"
-	"os"
+	"io/fs"
 	"strings"
 	"testing"
 )
@@ -40,7 +40,7 @@ func nameFilter(filename string) bool {
 	return false
 }
 
-func dirFilter(f os.FileInfo) bool { return nameFilter(f.Name()) }
+func dirFilter(f fs.FileInfo) bool { return nameFilter(f.Name()) }
 
 func TestParseFile(t *testing.T) {
 	src := "package p\nvar _=s[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]"
diff --git a/src/go/printer/performance_test.go b/src/go/printer/performance_test.go
index 2e67154e6b..e23de3fbae 100644
--- a/src/go/printer/performance_test.go
+++ b/src/go/printer/performance_test.go
@@ -53,6 +53,6 @@ func BenchmarkPrint(b *testing.B) {
 		initialize()
 	}
 	for i := 0; i < b.N; i++ {
-		testprint(ioutil.Discard, testfile)
+		testprint(io.Discard, testfile)
 	}
 }
diff --git a/src/go/token/position.go b/src/go/token/position.go
index d0dbc2998f..a21f5fd056 100644
--- a/src/go/token/position.go
+++ b/src/go/token/position.go
@@ -150,12 +150,12 @@ func (f *File) AddLine(offset int) {
 //
 func (f *File) MergeLine(line int) {
 	if line < 1 {
-		panic("illegal line number (line numbering starts at 1)")
+		panic(fmt.Sprintf("invalid line number %d (should be >= 1)", line))
 	}
 	f.mutex.Lock()
 	defer f.mutex.Unlock()
 	if line >= len(f.lines) {
-		panic("illegal line number")
+		panic(fmt.Sprintf("invalid line number %d (should be < %d)", line, len(f.lines)))
 	}
 	// To merge the line numbered <line> with the line numbered <line+1>,
 	// we need to remove the entry in lines corresponding to the line
@@ -217,12 +217,12 @@ func (f *File) SetLinesForContent(content []byte) {
 // LineStart panics if the 1-based line number is invalid.
 func (f *File) LineStart(line int) Pos {
 	if line < 1 {
-		panic("illegal line number (line numbering starts at 1)")
+		panic(fmt.Sprintf("invalid line number %d (should be >= 1)", line))
 	}
 	f.mutex.Lock()
 	defer f.mutex.Unlock()
 	if line > len(f.lines) {
-		panic("illegal line number")
+		panic(fmt.Sprintf("invalid line number %d (should be < %d)", line, len(f.lines)))
 	}
 	return Pos(f.base + f.lines[line-1])
 }
@@ -267,7 +267,7 @@ func (f *File) AddLineColumnInfo(offset int, filename string, line, column int)
 //
 func (f *File) Pos(offset int) Pos {
 	if offset > f.size {
-		panic("illegal file offset")
+		panic(fmt.Sprintf("invalid file offset %d (should be <= %d)", offset, f.size))
 	}
 	return Pos(f.base + offset)
 }
@@ -278,7 +278,7 @@ func (f *File) Pos(offset int) Pos {
 //
 func (f *File) Offset(p Pos) int {
 	if int(p) < f.base || int(p) > f.base+f.size {
-		panic("illegal Pos value")
+		panic(fmt.Sprintf("invalid Pos value %d (should be in [%d, %d[)", p, f.base, f.base+f.size))
 	}
 	return int(p) - f.base
 }
@@ -346,7 +346,7 @@ func (f *File) position(p Pos, adjusted bool) (pos Position) {
 func (f *File) PositionFor(p Pos, adjusted bool) (pos Position) {
 	if p != NoPos {
 		if int(p) < f.base || int(p) > f.base+f.size {
-			panic("illegal Pos value")
+			panic(fmt.Sprintf("invalid Pos value %d (should be in [%d, %d[)", p, f.base, f.base+f.size))
 		}
 		pos = f.position(p, adjusted)
 	}
@@ -430,8 +430,11 @@ func (s *FileSet) AddFile(filename string, base, size int) *File {
 	if base < 0 {
 		base = s.base
 	}
-	if base < s.base || size < 0 {
-		panic("illegal base or size")
+	if base < s.base {
+		panic(fmt.Sprintf("invalid base %d (should be >= %d)", base, s.base))
+	}
+	if size < 0 {
+		panic(fmt.Sprintf("invalid size %d (should be >= 0)", size))
 	}
 	// base >= s.base && size >= 0
 	f := &File{set: s, name: filename, base: base, size: size, lines: []int{0}}
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 5c0e611c51..a022ec5678 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -381,6 +381,76 @@ func firstInSrc(path []Object) int {
 	return fst
 }
 
+type (
+	decl interface {
+		node() ast.Node
+	}
+
+	importDecl struct{ spec *ast.ImportSpec }
+	constDecl  struct {
+		spec *ast.ValueSpec
+		iota int
+		typ  ast.Expr
+		init []ast.Expr
+	}
+	varDecl  struct{ spec *ast.ValueSpec }
+	typeDecl struct{ spec *ast.TypeSpec }
+	funcDecl struct{ decl *ast.FuncDecl }
+)
+
+func (d importDecl) node() ast.Node { return d.spec }
+func (d constDecl) node() ast.Node  { return d.spec }
+func (d varDecl) node() ast.Node    { return d.spec }
+func (d typeDecl) node() ast.Node   { return d.spec }
+func (d funcDecl) node() ast.Node   { return d.decl }
+
+func (check *Checker) walkDecls(decls []ast.Decl, f func(decl)) {
+	for _, d := range decls {
+		check.walkDecl(d, f)
+	}
+}
+
+func (check *Checker) walkDecl(d ast.Decl, f func(decl)) {
+	switch d := d.(type) {
+	case *ast.BadDecl:
+		// ignore
+	case *ast.GenDecl:
+		var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
+		for iota, s := range d.Specs {
+			switch s := s.(type) {
+			case *ast.ImportSpec:
+				f(importDecl{s})
+			case *ast.ValueSpec:
+				switch d.Tok {
+				case token.CONST:
+					// determine which initialization expressions to use
+					switch {
+					case s.Type != nil || len(s.Values) > 0:
+						last = s
+					case last == nil:
+						last = new(ast.ValueSpec) // make sure last exists
+					}
+					check.arityMatch(s, last)
+					f(constDecl{spec: s, iota: iota, init: last.Values, typ: last.Type})
+				case token.VAR:
+					check.arityMatch(s, nil)
+					f(varDecl{s})
+				default:
+					check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
+				}
+			case *ast.TypeSpec:
+				f(typeDecl{s})
+			default:
+				check.invalidAST(s.Pos(), "unknown ast.Spec node %T", s)
+			}
+		}
+	case *ast.FuncDecl:
+		f(funcDecl{d})
+	default:
+		check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
+	}
+}
+
 func (check *Checker) constDecl(obj *Const, typ, init ast.Expr) {
 	assert(obj.typ == nil)
 
@@ -664,133 +734,105 @@ func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
 	}
 }
 
-func (check *Checker) declStmt(decl ast.Decl) {
+func (check *Checker) declStmt(d ast.Decl) {
 	pkg := check.pkg
 
-	switch d := decl.(type) {
-	case *ast.BadDecl:
-		// ignore
+	check.walkDecl(d, func(d decl) {
+		switch d := d.(type) {
+		case constDecl:
+			top := len(check.delayed)
 
-	case *ast.GenDecl:
-		var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
-		for iota, spec := range d.Specs {
-			switch s := spec.(type) {
-			case *ast.ValueSpec:
-				switch d.Tok {
-				case token.CONST:
-					top := len(check.delayed)
+			// declare all constants
+			lhs := make([]*Const, len(d.spec.Names))
+			for i, name := range d.spec.Names {
+				obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
+				lhs[i] = obj
 
-					// determine which init exprs to use
-					switch {
-					case s.Type != nil || len(s.Values) > 0:
-						last = s
-					case last == nil:
-						last = new(ast.ValueSpec) // make sure last exists
-					}
-
-					// declare all constants
-					lhs := make([]*Const, len(s.Names))
-					for i, name := range s.Names {
-						obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(iota)))
-						lhs[i] = obj
-
-						var init ast.Expr
-						if i < len(last.Values) {
-							init = last.Values[i]
-						}
+				var init ast.Expr
+				if i < len(d.init) {
+					init = d.init[i]
+				}
 
-						check.constDecl(obj, last.Type, init)
-					}
+				check.constDecl(obj, d.typ, init)
+			}
 
-					check.arityMatch(s, last)
+			// process function literals in init expressions before scope changes
+			check.processDelayed(top)
 
-					// process function literals in init expressions before scope changes
-					check.processDelayed(top)
+			// spec: "The scope of a constant or variable identifier declared
+			// inside a function begins at the end of the ConstSpec or VarSpec
+			// (ShortVarDecl for short variable declarations) and ends at the
+			// end of the innermost containing block."
+			scopePos := d.spec.End()
+			for i, name := range d.spec.Names {
+				check.declare(check.scope, name, lhs[i], scopePos)
+			}
 
-					// spec: "The scope of a constant or variable identifier declared
-					// inside a function begins at the end of the ConstSpec or VarSpec
-					// (ShortVarDecl for short variable declarations) and ends at the
-					// end of the innermost containing block."
-					scopePos := s.End()
-					for i, name := range s.Names {
-						check.declare(check.scope, name, lhs[i], scopePos)
-					}
+		case varDecl:
+			top := len(check.delayed)
 
-				case token.VAR:
-					top := len(check.delayed)
+			lhs0 := make([]*Var, len(d.spec.Names))
+			for i, name := range d.spec.Names {
+				lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
+			}
 
-					lhs0 := make([]*Var, len(s.Names))
-					for i, name := range s.Names {
-						lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
+			// initialize all variables
+			for i, obj := range lhs0 {
+				var lhs []*Var
+				var init ast.Expr
+				switch len(d.spec.Values) {
+				case len(d.spec.Names):
+					// lhs and rhs match
+					init = d.spec.Values[i]
+				case 1:
+					// rhs is expected to be a multi-valued expression
+					lhs = lhs0
+					init = d.spec.Values[0]
+				default:
+					if i < len(d.spec.Values) {
+						init = d.spec.Values[i]
 					}
-
-					// initialize all variables
-					for i, obj := range lhs0 {
-						var lhs []*Var
-						var init ast.Expr
-						switch len(s.Values) {
-						case len(s.Names):
-							// lhs and rhs match
-							init = s.Values[i]
-						case 1:
-							// rhs is expected to be a multi-valued expression
-							lhs = lhs0
-							init = s.Values[0]
-						default:
-							if i < len(s.Values) {
-								init = s.Values[i]
-							}
-						}
-						check.varDecl(obj, lhs, s.Type, init)
-						if len(s.Values) == 1 {
-							// If we have a single lhs variable we are done either way.
-							// If we have a single rhs expression, it must be a multi-
-							// valued expression, in which case handling the first lhs
-							// variable will cause all lhs variables to have a type
-							// assigned, and we are done as well.
-							if debug {
-								for _, obj := range lhs0 {
-									assert(obj.typ != nil)
-								}
-							}
-							break
+				}
+				check.varDecl(obj, lhs, d.spec.Type, init)
+				if len(d.spec.Values) == 1 {
+					// If we have a single lhs variable we are done either way.
+					// If we have a single rhs expression, it must be a multi-
+					// valued expression, in which case handling the first lhs
+					// variable will cause all lhs variables to have a type
+					// assigned, and we are done as well.
+					if debug {
+						for _, obj := range lhs0 {
+							assert(obj.typ != nil)
 						}
 					}
-
-					check.arityMatch(s, nil)
-
-					// process function literals in init expressions before scope changes
-					check.processDelayed(top)
-
-					// declare all variables
-					// (only at this point are the variable scopes (parents) set)
-					scopePos := s.End() // see constant declarations
-					for i, name := range s.Names {
-						// see constant declarations
-						check.declare(check.scope, name, lhs0[i], scopePos)
-					}
-
-				default:
-					check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
+					break
 				}
+			}
 
-			case *ast.TypeSpec:
-				obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Name, nil)
-				// spec: "The scope of a type identifier declared inside a function
-				// begins at the identifier in the TypeSpec and ends at the end of
-				// the innermost containing block."
-				scopePos := s.Name.Pos()
-				check.declare(check.scope, s.Name, obj, scopePos)
-				// mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
-				obj.setColor(grey + color(check.push(obj)))
-				check.typeDecl(obj, s.Type, nil, s.Assign.IsValid())
-				check.pop().setColor(black)
-			default:
-				check.invalidAST(s.Pos(), "const, type, or var declaration expected")
+			// process function literals in init expressions before scope changes
+			check.processDelayed(top)
+
+			// declare all variables
+			// (only at this point are the variable scopes (parents) set)
+			scopePos := d.spec.End() // see constant declarations
+			for i, name := range d.spec.Names {
+				// see constant declarations
+				check.declare(check.scope, name, lhs0[i], scopePos)
 			}
-		}
 
-	default:
-		check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
-	}
+		case typeDecl:
+			obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
+			// spec: "The scope of a type identifier declared inside a function
+			// begins at the identifier in the TypeSpec and ends at the end of
+			// the innermost containing block."
+			scopePos := d.spec.Name.Pos()
+			check.declare(check.scope, d.spec.Name, obj, scopePos)
+			// mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
+			obj.setColor(grey + color(check.push(obj)))
+			check.typeDecl(obj, d.spec.Type, nil, d.spec.Assign.IsValid())
+			check.pop().setColor(black)
+		default:
+			check.invalidAST(d.node().Pos(), "unknown ast.Decl node %T", d.node())
+		}
+	})
 }
diff --git a/src/go/types/gotype.go b/src/go/types/gotype.go
index eacf68f52f..52709df17b 100644
--- a/src/go/types/gotype.go
+++ b/src/go/types/gotype.go
@@ -88,7 +88,7 @@ import (
 	"go/scanner"
 	"go/token"
 	"go/types"
-	"io/ioutil"
+	"io"
 	"os"
 	"path/filepath"
 	"sync"
@@ -191,7 +191,7 @@ func parse(filename string, src interface{}) (*ast.File, error) {
 }
 
 func parseStdin() (*ast.File, error) {
-	src, err := ioutil.ReadAll(os.Stdin)
+	src, err := io.ReadAll(os.Stdin)
 	if err != nil {
 		return nil, err
 	}
diff --git a/src/go/types/resolver.go b/src/go/types/resolver.go
index 078adc5ec7..cce222cbc5 100644
--- a/src/go/types/resolver.go
+++ b/src/go/types/resolver.go
@@ -235,179 +235,147 @@ func (check *Checker) collectObjects() {
 		// we get "." as the directory which is what we would want.
 		fileDir := dir(check.fset.Position(file.Name.Pos()).Filename)
 
-		for _, decl := range file.Decls {
-			switch d := decl.(type) {
-			case *ast.BadDecl:
-				// ignore
-
-			case *ast.GenDecl:
-				var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
-				for iota, spec := range d.Specs {
-					switch s := spec.(type) {
-					case *ast.ImportSpec:
-						// import package
-						path, err := validatedImportPath(s.Path.Value)
-						if err != nil {
-							check.errorf(s.Path.Pos(), "invalid import path (%s)", err)
-							continue
-						}
+		check.walkDecls(file.Decls, func(d decl) {
+			switch d := d.(type) {
+			case importDecl:
+				// import package
+				path, err := validatedImportPath(d.spec.Path.Value)
+				if err != nil {
+					check.errorf(d.spec.Path.Pos(), "invalid import path (%s)", err)
+					return
+				}
 
-						imp := check.importPackage(s.Path.Pos(), path, fileDir)
-						if imp == nil {
-							continue
-						}
+				imp := check.importPackage(d.spec.Path.Pos(), path, fileDir)
+				if imp == nil {
+					return
+				}
 
-						// add package to list of explicit imports
-						// (this functionality is provided as a convenience
-						// for clients; it is not needed for type-checking)
-						if !pkgImports[imp] {
-							pkgImports[imp] = true
-							pkg.imports = append(pkg.imports, imp)
-						}
+				// add package to list of explicit imports
+				// (this functionality is provided as a convenience
+				// for clients; it is not needed for type-checking)
+				if !pkgImports[imp] {
+					pkgImports[imp] = true
+					pkg.imports = append(pkg.imports, imp)
+				}
 
-						// local name overrides imported package name
-						name := imp.name
-						if s.Name != nil {
-							name = s.Name.Name
-							if path == "C" {
-								// match cmd/compile (not prescribed by spec)
-								check.errorf(s.Name.Pos(), `cannot rename import "C"`)
-								continue
-							}
-							if name == "init" {
-								check.errorf(s.Name.Pos(), "cannot declare init - must be func")
-								continue
-							}
-						}
+				// local name overrides imported package name
+				name := imp.name
+				if d.spec.Name != nil {
+					name = d.spec.Name.Name
+					if path == "C" {
+						// match cmd/compile (not prescribed by spec)
+						check.errorf(d.spec.Name.Pos(), `cannot rename import "C"`)
+						return
+					}
+					if name == "init" {
+						check.errorf(d.spec.Name.Pos(), "cannot declare init - must be func")
+						return
+					}
+				}
 
-						obj := NewPkgName(s.Pos(), pkg, name, imp)
-						if s.Name != nil {
-							// in a dot-import, the dot represents the package
-							check.recordDef(s.Name, obj)
-						} else {
-							check.recordImplicit(s, obj)
-						}
+				obj := NewPkgName(d.spec.Pos(), pkg, name, imp)
+				if d.spec.Name != nil {
+					// in a dot-import, the dot represents the package
+					check.recordDef(d.spec.Name, obj)
+				} else {
+					check.recordImplicit(d.spec, obj)
+				}
 
-						if path == "C" {
-							// match cmd/compile (not prescribed by spec)
-							obj.used = true
-						}
+				if path == "C" {
+					// match cmd/compile (not prescribed by spec)
+					obj.used = true
+				}
 
-						// add import to file scope
-						if name == "." {
-							// merge imported scope with file scope
-							for _, obj := range imp.scope.elems {
-								// A package scope may contain non-exported objects,
-								// do not import them!
-								if obj.Exported() {
-									// declare dot-imported object
-									// (Do not use check.declare because it modifies the object
-									// via Object.setScopePos, which leads to a race condition;
-									// the object may be imported into more than one file scope
-									// concurrently. See issue #32154.)
-									if alt := fileScope.Insert(obj); alt != nil {
-										check.errorf(s.Name.Pos(), "%s redeclared in this block", obj.Name())
-										check.reportAltDecl(alt)
-									}
-								}
+				// add import to file scope
+				if name == "." {
+					// merge imported scope with file scope
+					for _, obj := range imp.scope.elems {
+						// A package scope may contain non-exported objects,
+						// do not import them!
+						if obj.Exported() {
+							// declare dot-imported object
+							// (Do not use check.declare because it modifies the object
+							// via Object.setScopePos, which leads to a race condition;
+							// the object may be imported into more than one file scope
+							// concurrently. See issue #32154.)
+							if alt := fileScope.Insert(obj); alt != nil {
+								check.errorf(d.spec.Name.Pos(), "%s redeclared in this block", obj.Name())
+								check.reportAltDecl(alt)
 							}
-							// add position to set of dot-import positions for this file
-							// (this is only needed for "imported but not used" errors)
-							check.addUnusedDotImport(fileScope, imp, s.Pos())
-						} else {
-							// declare imported package object in file scope
-							// (no need to provide s.Name since we called check.recordDef earlier)
-							check.declare(fileScope, nil, obj, token.NoPos)
 						}
+					}
+					// add position to set of dot-import positions for this file
+					// (this is only needed for "imported but not used" errors)
+					check.addUnusedDotImport(fileScope, imp, d.spec.Pos())
+				} else {
+					// declare imported package object in file scope
+					// (no need to provide s.Name since we called check.recordDef earlier)
+					check.declare(fileScope, nil, obj, token.NoPos)
+				}
+			case constDecl:
+				// declare all constants
+				for i, name := range d.spec.Names {
+					obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
+
+					var init ast.Expr
+					if i < len(d.init) {
+						init = d.init[i]
+					}
 
-					case *ast.ValueSpec:
-						switch d.Tok {
-						case token.CONST:
-							// determine which initialization expressions to use
-							switch {
-							case s.Type != nil || len(s.Values) > 0:
-								last = s
-							case last == nil:
-								last = new(ast.ValueSpec) // make sure last exists
-							}
-
-							// declare all constants
-							for i, name := range s.Names {
-								obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(iota)))
-
-								var init ast.Expr
-								if i < len(last.Values) {
-									init = last.Values[i]
-								}
-
-								d := &declInfo{file: fileScope, typ: last.Type, init: init}
-								check.declarePkgObj(name, obj, d)
-							}
-
-							check.arityMatch(s, last)
-
-						case token.VAR:
-							lhs := make([]*Var, len(s.Names))
-							// If there's exactly one rhs initializer, use
-							// the same declInfo d1 for all lhs variables
-							// so that each lhs variable depends on the same
-							// rhs initializer (n:1 var declaration).
-							var d1 *declInfo
-							if len(s.Values) == 1 {
-								// The lhs elements are only set up after the for loop below,
-								// but that's ok because declareVar only collects the declInfo
-								// for a later phase.
-								d1 = &declInfo{file: fileScope, lhs: lhs, typ: s.Type, init: s.Values[0]}
-							}
-
-							// declare all variables
-							for i, name := range s.Names {
-								obj := NewVar(name.Pos(), pkg, name.Name, nil)
-								lhs[i] = obj
-
-								d := d1
-								if d == nil {
-									// individual assignments
-									var init ast.Expr
-									if i < len(s.Values) {
-										init = s.Values[i]
-									}
-									d = &declInfo{file: fileScope, typ: s.Type, init: init}
-								}
-
-								check.declarePkgObj(name, obj, d)
-							}
+					d := &declInfo{file: fileScope, typ: d.typ, init: init}
+					check.declarePkgObj(name, obj, d)
+				}
 
-							check.arityMatch(s, nil)
+			case varDecl:
+				lhs := make([]*Var, len(d.spec.Names))
+				// If there's exactly one rhs initializer, use
+				// the same declInfo d1 for all lhs variables
+				// so that each lhs variable depends on the same
+				// rhs initializer (n:1 var declaration).
+				var d1 *declInfo
+				if len(d.spec.Values) == 1 {
+					// The lhs elements are only set up after the for loop below,
+					// but that's ok because declareVar only collects the declInfo
+					// for a later phase.
+					d1 = &declInfo{file: fileScope, lhs: lhs, typ: d.spec.Type, init: d.spec.Values[0]}
+				}
 
-						default:
-							check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
+				// declare all variables
+				for i, name := range d.spec.Names {
+					obj := NewVar(name.Pos(), pkg, name.Name, nil)
+					lhs[i] = obj
+
+					di := d1
+					if di == nil {
+						// individual assignments
+						var init ast.Expr
+						if i < len(d.spec.Values) {
+							init = d.spec.Values[i]
 						}
-
-					case *ast.TypeSpec:
-						obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Name, nil)
-						check.declarePkgObj(s.Name, obj, &declInfo{file: fileScope, typ: s.Type, alias: s.Assign.IsValid()})
-
-					default:
-						check.invalidAST(s.Pos(), "unknown ast.Spec node %T", s)
+						di = &declInfo{file: fileScope, typ: d.spec.Type, init: init}
 					}
-				}
 
-			case *ast.FuncDecl:
-				name := d.Name.Name
-				obj := NewFunc(d.Name.Pos(), pkg, name, nil)
-				if d.Recv == nil {
+					check.declarePkgObj(name, obj, di)
+				}
+			case typeDecl:
+				obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
+				check.declarePkgObj(d.spec.Name, obj, &declInfo{file: fileScope, typ: d.spec.Type, alias: d.spec.Assign.IsValid()})
+			case funcDecl:
+				info := &declInfo{file: fileScope, fdecl: d.decl}
+				name := d.decl.Name.Name
+				obj := NewFunc(d.decl.Name.Pos(), pkg, name, nil)
+				if d.decl.Recv == nil {
 					// regular function
 					if name == "init" {
 						// don't declare init functions in the package scope - they are invisible
 						obj.parent = pkg.scope
-						check.recordDef(d.Name, obj)
+						check.recordDef(d.decl.Name, obj)
 						// init functions must have a body
-						if d.Body == nil {
+						if d.decl.Body == nil {
 							check.softErrorf(obj.pos, "missing function body")
 						}
 					} else {
-						check.declare(pkg.scope, d.Name, obj, token.NoPos)
+						check.declare(pkg.scope, d.decl.Name, obj, token.NoPos)
 					}
 				} else {
 					// method
@@ -417,20 +385,16 @@ func (check *Checker) collectObjects() {
 					if name != "_" {
 						methods = append(methods, obj)
 					}
-					check.recordDef(d.Name, obj)
+					check.recordDef(d.decl.Name, obj)
 				}
-				info := &declInfo{file: fileScope, fdecl: d}
 				// Methods are not package-level objects but we still track them in the
 				// object map so that we can handle them like regular functions (if the
 				// receiver is invalid); also we need their fdecl info when associating
 				// them with their receiver base type, below.
 				check.objMap[obj] = info
 				obj.setOrder(uint32(len(check.objMap)))
-
-			default:
-				check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
 			}
-		}
+		})
 	}
 
 	// verify that objects in package and file scopes have different names
diff --git a/src/go/types/self_test.go b/src/go/types/self_test.go
index 04c9cd3458..b5f6bfe532 100644
--- a/src/go/types/self_test.go
+++ b/src/go/types/self_test.go
@@ -5,12 +5,11 @@
 package types_test
 
 import (
-	"flag"
-	"fmt"
 	"go/ast"
 	"go/importer"
 	"go/parser"
 	"go/token"
+	"path"
 	"path/filepath"
 	"testing"
 	"time"
@@ -18,8 +17,6 @@ import (
 	. "go/types"
 )
 
-var benchmark = flag.Bool("b", false, "run benchmarks")
-
 func TestSelf(t *testing.T) {
 	fset := token.NewFileSet()
 	files, err := pkgFiles(fset, ".")
@@ -39,46 +36,39 @@ func TestSelf(t *testing.T) {
 	}
 }
 
-func TestBenchmark(t *testing.T) {
-	if !*benchmark {
-		return
-	}
-
-	// We're not using testing's benchmarking mechanism directly
-	// because we want custom output.
-
+func BenchmarkCheck(b *testing.B) {
 	for _, p := range []string{
 		"net/http",
 		"go/parser",
 		"go/constant",
 		filepath.Join("go", "internal", "gcimporter"),
 	} {
-		path := filepath.Join("..", "..", p)
-		runbench(t, path, false)
-		runbench(t, path, true)
-		fmt.Println()
+		b.Run(path.Base(p), func(b *testing.B) {
+			path := filepath.Join("..", "..", p)
+			for _, ignoreFuncBodies := range []bool{false, true} {
+				name := "funcbodies"
+				if ignoreFuncBodies {
+					name = "nofuncbodies"
+				}
+				b.Run(name, func(b *testing.B) {
+					b.Run("info", func(b *testing.B) {
+						runbench(b, path, ignoreFuncBodies, true)
+					})
+					b.Run("noinfo", func(b *testing.B) {
+						runbench(b, path, ignoreFuncBodies, false)
+					})
+				})
+			}
+		})
 	}
 }
 
-func runbench(t *testing.T, path string, ignoreFuncBodies bool) {
+func runbench(b *testing.B, path string, ignoreFuncBodies, writeInfo bool) {
 	fset := token.NewFileSet()
 	files, err := pkgFiles(fset, path)
 	if err != nil {
-		t.Fatal(err)
+		b.Fatal(err)
 	}
-
-	b := testing.Benchmark(func(b *testing.B) {
-		for i := 0; i < b.N; i++ {
-			conf := Config{
-				IgnoreFuncBodies: ignoreFuncBodies,
-				Importer:         importer.Default(),
-			}
-			if _, err := conf.Check(path, fset, files, nil); err != nil {
-				t.Fatal(err)
-			}
-		}
-	})
-
 	// determine line count
 	lines := 0
 	fset.Iterate(func(f *token.File) bool {
@@ -86,10 +76,30 @@ func runbench(t *testing.T, path string, ignoreFuncBodies bool) {
 		return true
 	})
 
-	d := time.Duration(b.NsPerOp())
-	fmt.Printf("%s (ignoreFuncBodies = %v):\n", filepath.Base(path), ignoreFuncBodies)
-	fmt.Printf("\t%s for %d lines (%.0f lines/s)\n", d, lines, float64(lines)/d.Seconds())
-	fmt.Printf("\t%s\n", b.MemString())
+	b.ResetTimer()
+	start := time.Now()
+	for i := 0; i < b.N; i++ {
+		conf := Config{
+			IgnoreFuncBodies: ignoreFuncBodies,
+			Importer:         importer.Default(),
+		}
+		var info *Info
+		if writeInfo {
+			info = &Info{
+				Types:      make(map[ast.Expr]TypeAndValue),
+				Defs:       make(map[*ast.Ident]Object),
+				Uses:       make(map[*ast.Ident]Object),
+				Implicits:  make(map[ast.Node]Object),
+				Selections: make(map[*ast.SelectorExpr]*Selection),
+				Scopes:     make(map[ast.Node]*Scope),
+			}
+		}
+		if _, err := conf.Check(path, fset, files, info); err != nil {
+			b.Fatal(err)
+		}
+	}
+	b.StopTimer()
+	b.ReportMetric(float64(lines)*float64(b.N)/time.Since(start).Seconds(), "lines/s")
 }
 
 func pkgFiles(fset *token.FileSet, path string) ([]*ast.File, error) {
diff --git a/src/go/types/stdlib_test.go b/src/go/types/stdlib_test.go
index f5a3273fa1..669e7bec20 100644
--- a/src/go/types/stdlib_test.go
+++ b/src/go/types/stdlib_test.go
@@ -183,6 +183,8 @@ func TestStdFixed(t *testing.T) {
 		"issue31747.go",  // go/types does not have constraints on language level (-lang=go1.12) (see #31793)
 		"issue34329.go",  // go/types does not have constraints on language level (-lang=go1.13) (see #31793)
 		"bug251.go",      // issue #34333 which was exposed with fix for #34151
+		"issue42058a.go", // go/types does not have constraints on channel element size
+		"issue42058b.go", // go/types does not have constraints on channel element size
 	)
 }