cmd/cover/cover.go - tools - Git at Google

 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 import (
 	"bytes"
 	"flag"
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"go/printer"
 	"go/token"
 	"io"
 	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
 )

 const usageMessage = "" +
 	`Usage of 'go tool cover':
 Given a coverage profile produced by 'go test':
 	go test -coverprofile=c.out

 Open a web browser displaying annotated source code:
 	go tool cover -html=c.out

 Write out an HTML file instead of launching a web browser:
 	go tool cover -html=c.out -o coverage.html

 Display coverage percentages to stdout for each function:
 	go tool cover -func=c.out

 Finally, to generate modified source code with coverage annotations
 (what go test -cover does):
 	go tool cover -mode=set -var=CoverageVariableName program.go
 `

 func usage() {
 	fmt.Fprintln(os.Stderr, usageMessage)
 	fmt.Fprintln(os.Stderr, "Flags:")
 	flag.PrintDefaults()
 	fmt.Fprintln(os.Stderr, "\n  Only one of -html, -func, or -mode may be set.")
 	os.Exit(2)
 }

 var (
 	mode    = flag.String("mode", "", "coverage mode: set, count, atomic")
 	varVar  = flag.String("var", "GoCover", "name of coverage variable to generate")
 	output  = flag.String("o", "", "file for output; default: stdout")
 	htmlOut = flag.String("html", "", "generate HTML representation of coverage profile")
 	funcOut = flag.String("func", "", "output coverage profile information for each function")
 )

 var profile string // The profile to read; the value of -html or -func

 var counterStmt func(*File, ast.Expr) ast.Stmt

 const (
 	atomicPackagePath = "sync/atomic"
 	atomicPackageName = "_cover_atomic_"
 )

 func main() {
 	flag.Usage = usage
 	flag.Parse()

 	// Usage information when no arguments.
 	if flag.NFlag() == 0 && flag.NArg() == 0 {
 		flag.Usage()
 	}

 	err := parseFlags()
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		fmt.Fprintln(os.Stderr, `For usage information, run "go tool cover -help"`)
 		os.Exit(2)
 	}

 	// Generate coverage-annotated source.
 	if *mode != "" {
 		annotate(flag.Arg(0))
 		return
 	}

 	// Output HTML or function coverage information.
 	if *htmlOut != "" {
 		err = htmlOutput(profile, *output)
 	} else {
 		err = funcOutput(profile, *output)
 	}

 	if err != nil {
 		fmt.Fprintf(os.Stderr, "cover: %v\n", err)
 		os.Exit(2)
 	}
 }

 // parseFlags sets the profile and counterStmt globals and performs validations.
 func parseFlags() error {
 	profile = *htmlOut
 	if *funcOut != "" {
 		if profile != "" {
 			return fmt.Errorf("too many options")
 		}
 		profile = *funcOut
 	}

 	// Must either display a profile or rewrite Go source.
 	if (profile == "") == (*mode == "") {
 		return fmt.Errorf("too many options")
 	}

 	if *mode != "" {
 		switch *mode {
 		case "set":
 			counterStmt = setCounterStmt
 		case "count":
 			counterStmt = incCounterStmt
 		case "atomic":
 			counterStmt = atomicCounterStmt
 		default:
 			return fmt.Errorf("unknown -mode %v", *mode)
 		}

 		if flag.NArg() == 0 {
 			return fmt.Errorf("missing source file")
 		} else if flag.NArg() == 1 {
 			return nil
 		}
 	} else if flag.NArg() == 0 {
 		return nil
 	}
 	return fmt.Errorf("too many arguments")
 }

 // Block represents the information about a basic block to be recorded in the analysis.
 // Note: Our definition of basic block is based on control structures; we don't break
 // apart && and ||. We could but it doesn't seem important enough to bother.
 type Block struct {
 	startByte token.Pos
 	endByte   token.Pos
 	numStmt   int
 }

 // File is a wrapper for the state of a file used in the parser.
 // The basic parse tree walker is a method of this type.
 type File struct {
 	fset      *token.FileSet
 	name      string // Name of file.
 	astFile   *ast.File
 	blocks    []Block
 	atomicPkg string // Package name for "sync/atomic" in this file.
 }

 // Visit implements the ast.Visitor interface.
 func (f *File) Visit(node ast.Node) ast.Visitor {
 	switch n := node.(type) {
 	case *ast.BlockStmt:
 		// If it's a switch or select, the body is a list of case clauses; don't tag the block itself.
 		if len(n.List) > 0 {
 			switch n.List[0].(type) {
 			case *ast.CaseClause: // switch
 				for _, n := range n.List {
 					clause := n.(*ast.CaseClause)
 					clause.Body = f.addCounters(clause.Pos(), clause.End(), clause.Body, false)
 				}
 				return f
 			case *ast.CommClause: // select
 				for _, n := range n.List {
 					clause := n.(*ast.CommClause)
 					clause.Body = f.addCounters(clause.Pos(), clause.End(), clause.Body, false)
 				}
 				return f
 			}
 		}
 		n.List = f.addCounters(n.Lbrace, n.Rbrace+1, n.List, true) // +1 to step past closing brace.
 	case *ast.IfStmt:
 		ast.Walk(f, n.Body)
 		if n.Else == nil {
 			return nil
 		}
 		// The elses are special, because if we have
 		//	if x {
 		//	} else if y {
 		//	}
 		// we want to cover the "if y". To do this, we need a place to drop the counter,
 		// so we add a hidden block:
 		//	if x {
 		//	} else {
 		//		if y {
 		//		}
 		//	}
 		switch stmt := n.Else.(type) {
 		case *ast.IfStmt:
 			block := &ast.BlockStmt{
 				Lbrace: n.Body.End(), // Start at end of the "if" block so the covered part looks like it starts at the "else".
 				List:   []ast.Stmt{stmt},
 				Rbrace: stmt.End(),
 			}
 			n.Else = block
 		case *ast.BlockStmt:
 			stmt.Lbrace = n.Body.End() // Start at end of the "if" block so the covered part looks like it starts at the "else".
 		default:
 			panic("unexpected node type in if")
 		}
 		ast.Walk(f, n.Else)
 		return nil
 	case *ast.SelectStmt:
 		// Don't annotate an empty select - creates a syntax error.
 		if n.Body == nil || len(n.Body.List) == 0 {
 			return nil
 		}
 	case *ast.SwitchStmt:
 		// Don't annotate an empty switch - creates a syntax error.
 		if n.Body == nil || len(n.Body.List) == 0 {
 			return nil
 		}
 	case *ast.TypeSwitchStmt:
 		// Don't annotate an empty type switch - creates a syntax error.
 		if n.Body == nil || len(n.Body.List) == 0 {
 			return nil
 		}
 	}
 	return f
 }

 // unquote returns the unquoted string.
 func unquote(s string) string {
 	t, err := strconv.Unquote(s)
 	if err != nil {
 		log.Fatalf("cover: improperly quoted string %q\n", s)
 	}
 	return t
 }

 // addImport adds an import for the specified path, if one does not already exist, and returns
 // the local package name.
 func (f *File) addImport(path string) string {
 	// Does the package already import it?
 	for _, s := range f.astFile.Imports {
 		if unquote(s.Path.Value) == path {
 			if s.Name != nil {
 				return s.Name.Name
 			}
 			return filepath.Base(path)
 		}
 	}
 	newImport := &ast.ImportSpec{
 		Name: ast.NewIdent(atomicPackageName),
 		Path: &ast.BasicLit{
 			Kind:  token.STRING,
 			Value: fmt.Sprintf("%q", path),
 		},
 	}
 	impDecl := &ast.GenDecl{
 		Tok: token.IMPORT,
 		Specs: []ast.Spec{
 			newImport,
 		},
 	}
 	// Make the new import the first Decl in the file.
 	astFile := f.astFile
 	astFile.Decls = append(astFile.Decls, nil)
 	copy(astFile.Decls[1:], astFile.Decls[0:])
 	astFile.Decls[0] = impDecl
 	astFile.Imports = append(astFile.Imports, newImport)

 	// Now refer to the package, just in case it ends up unused.
 	// That is, append to the end of the file the declaration
 	//	var _ = _cover_atomic_.AddUint32
 	reference := &ast.GenDecl{
 		Tok: token.VAR,
 		Specs: []ast.Spec{
 			&ast.ValueSpec{
 				Names: []*ast.Ident{
 					ast.NewIdent("_"),
 				},
 				Values: []ast.Expr{
 					&ast.SelectorExpr{
 						X:   ast.NewIdent(atomicPackageName),
 						Sel: ast.NewIdent("AddUint32"),
 					},
 				},
 			},
 		},
 	}
 	astFile.Decls = append(astFile.Decls, reference)
 	return atomicPackageName
 }

 var slashslash = []byte("//")

 // initialComments returns the prefix of content containing only
 // whitespace and line comments.  Any +build directives must appear
 // within this region.  This approach is more reliable than using
 // go/printer to print a modified AST containing comments.
 //
 func initialComments(content []byte) []byte {
 	// Derived from go/build.Context.shouldBuild.
 	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
 		}
 	}
 	return content[:end]
 }

 func annotate(name string) {
 	fset := token.NewFileSet()
 	content, err := ioutil.ReadFile(name)
 	if err != nil {
 		log.Fatalf("cover: %s: %s", name, err)
 	}
 	parsedFile, err := parser.ParseFile(fset, name, content, parser.ParseComments)
 	if err != nil {
 		log.Fatalf("cover: %s: %s", name, err)
 	}
 	parsedFile.Comments = trimComments(parsedFile, fset)

 	file := &File{
 		fset:    fset,
 		name:    name,
 		astFile: parsedFile,
 	}
 	if *mode == "atomic" {
 		file.atomicPkg = file.addImport(atomicPackagePath)
 	}
 	ast.Walk(file, file.astFile)
 	fd := os.Stdout
 	if *output != "" {
 		var err error
 		fd, err = os.Create(*output)
 		if err != nil {
 			log.Fatalf("cover: %s", err)
 		}
 	}
 	fd.Write(initialComments(content)) // Retain '// +build' directives.
 	file.print(fd)
 	// After printing the source tree, add some declarations for the counters etc.
 	// We could do this by adding to the tree, but it's easier just to print the text.
 	file.addVariables(fd)
 }

 // trimComments drops all but the //go: comments, some of which are semantically important.
 // We drop all others because they can appear in places that cause our counters
 // to appear in syntactically incorrect places. //go: appears at the beginning of
 // the line and is syntactically safe.
 func trimComments(file *ast.File, fset *token.FileSet) []*ast.CommentGroup {
 	var comments []*ast.CommentGroup
 	for _, group := range file.Comments {
 		var list []*ast.Comment
 		for _, comment := range group.List {
 			if strings.HasPrefix(comment.Text, "//go:") && fset.Position(comment.Slash).Column == 1 {
 				list = append(list, comment)
 			}
 		}
 		if list != nil {
 			comments = append(comments, &ast.CommentGroup{List: list})
 		}
 	}
 	return comments
 }

 func (f *File) print(w io.Writer) {
 	printer.Fprint(w, f.fset, f.astFile)
 }

 // intLiteral returns an ast.BasicLit representing the integer value.
 func (f *File) intLiteral(i int) *ast.BasicLit {
 	node := &ast.BasicLit{
 		Kind:  token.INT,
 		Value: fmt.Sprint(i),
 	}
 	return node
 }

 // index returns an ast.BasicLit representing the number of counters present.
 func (f *File) index() *ast.BasicLit {
 	return f.intLiteral(len(f.blocks))
 }

 // setCounterStmt returns the expression: __count[23] = 1.
 func setCounterStmt(f *File, counter ast.Expr) ast.Stmt {
 	return &ast.AssignStmt{
 		Lhs: []ast.Expr{counter},
 		Tok: token.ASSIGN,
 		Rhs: []ast.Expr{f.intLiteral(1)},
 	}
 }

 // incCounterStmt returns the expression: __count[23]++.
 func incCounterStmt(f *File, counter ast.Expr) ast.Stmt {
 	return &ast.IncDecStmt{
 		X:   counter,
 		Tok: token.INC,
 	}
 }

 // atomicCounterStmt returns the expression: atomic.AddUint32(&__count[23], 1)
 func atomicCounterStmt(f *File, counter ast.Expr) ast.Stmt {
 	return &ast.ExprStmt{
 		X: &ast.CallExpr{
 			Fun: &ast.SelectorExpr{
 				X:   ast.NewIdent(f.atomicPkg),
 				Sel: ast.NewIdent("AddUint32"),
 			},
 			Args: []ast.Expr{&ast.UnaryExpr{
 				Op: token.AND,
 				X:  counter,
 			},
 				f.intLiteral(1),
 			},
 		},
 	}
 }

 // newCounter creates a new counter expression of the appropriate form.
 func (f *File) newCounter(start, end token.Pos, numStmt int) ast.Stmt {
 	counter := &ast.IndexExpr{
 		X: &ast.SelectorExpr{
 			X:   ast.NewIdent(*varVar),
 			Sel: ast.NewIdent("Count"),
 		},
 		Index: f.index(),
 	}
 	stmt := counterStmt(f, counter)
 	f.blocks = append(f.blocks, Block{start, end, numStmt})
 	return stmt
 }

 // addCounters takes a list of statements and adds counters to the beginning of
 // each basic block at the top level of that list. For instance, given
 //
 //	S1
 //	if cond {
 //		S2
 // 	}
 //	S3
 //
 // counters will be added before S1 and before S3. The block containing S2
 // will be visited in a separate call.
 // TODO: Nested simple blocks get unnecessary (but correct) counters
 func (f *File) addCounters(pos, blockEnd token.Pos, list []ast.Stmt, extendToClosingBrace bool) []ast.Stmt {
 	// Special case: make sure we add a counter to an empty block. Can't do this below
 	// or we will add a counter to an empty statement list after, say, a return statement.
 	if len(list) == 0 {
 		return []ast.Stmt{f.newCounter(pos, blockEnd, 0)}
 	}
 	// We have a block (statement list), but it may have several basic blocks due to the
 	// appearance of statements that affect the flow of control.
 	var newList []ast.Stmt
 	for {
 		// Find first statement that affects flow of control (break, continue, if, etc.).
 		// It will be the last statement of this basic block.
 		var last int
 		end := blockEnd
 		for last = 0; last < len(list); last++ {
 			end = f.statementBoundary(list[last])
 			if f.endsBasicSourceBlock(list[last]) {
 				extendToClosingBrace = false // Block is broken up now.
 				last++
 				break
 			}
 		}
 		if extendToClosingBrace {
 			end = blockEnd
 		}
 		if pos != end { // Can have no source to cover if e.g. blocks abut.
 			newList = append(newList, f.newCounter(pos, end, last))
 		}
 		newList = append(newList, list[0:last]...)
 		list = list[last:]
 		if len(list) == 0 {
 			break
 		}
 		pos = list[0].Pos()
 	}
 	return newList
 }

 // hasFuncLiteral reports the existence and position of the first func literal
 // in the node, if any. If a func literal appears, it usually marks the termination
 // of a basic block because the function body is itself a block.
 // Therefore we draw a line at the start of the body of the first function literal we find.
 // TODO: what if there's more than one? Probably doesn't matter much.
 func hasFuncLiteral(n ast.Node) (bool, token.Pos) {
 	if n == nil {
 		return false, 0
 	}
 	var literal funcLitFinder
 	ast.Walk(&literal, n)
 	return literal.found(), token.Pos(literal)
 }

 // statementBoundary finds the location in s that terminates the current basic
 // block in the source.
 func (f *File) statementBoundary(s ast.Stmt) token.Pos {
 	// Control flow statements are easy.
 	switch s := s.(type) {
 	case *ast.BlockStmt:
 		// Treat blocks like basic blocks to avoid overlapping counters.
 		return s.Lbrace
 	case *ast.IfStmt:
 		found, pos := hasFuncLiteral(s.Init)
 		if found {
 			return pos
 		}
 		found, pos = hasFuncLiteral(s.Cond)
 		if found {
 			return pos
 		}
 		return s.Body.Lbrace
 	case *ast.ForStmt:
 		found, pos := hasFuncLiteral(s.Init)
 		if found {
 			return pos
 		}
 		found, pos = hasFuncLiteral(s.Cond)
 		if found {
 			return pos
 		}
 		found, pos = hasFuncLiteral(s.Post)
 		if found {
 			return pos
 		}
 		return s.Body.Lbrace
 	case *ast.LabeledStmt:
 		return f.statementBoundary(s.Stmt)
 	case *ast.RangeStmt:
 		found, pos := hasFuncLiteral(s.X)
 		if found {
 			return pos
 		}
 		return s.Body.Lbrace
 	case *ast.SwitchStmt:
 		found, pos := hasFuncLiteral(s.Init)
 		if found {
 			return pos
 		}
 		found, pos = hasFuncLiteral(s.Tag)
 		if found {
 			return pos
 		}
 		return s.Body.Lbrace
 	case *ast.SelectStmt:
 		return s.Body.Lbrace
 	case *ast.TypeSwitchStmt:
 		found, pos := hasFuncLiteral(s.Init)
 		if found {
 			return pos
 		}
 		return s.Body.Lbrace
 	}
 	// If not a control flow statement, it is a declaration, expression, call, etc. and it may have a function literal.
 	// If it does, that's tricky because we want to exclude the body of the function from this block.
 	// Draw a line at the start of the body of the first function literal we find.
 	// TODO: what if there's more than one? Probably doesn't matter much.
 	found, pos := hasFuncLiteral(s)
 	if found {
 		return pos
 	}
 	return s.End()
 }

 // endsBasicSourceBlock reports whether s changes the flow of control: break, if, etc.,
 // or if it's just problematic, for instance contains a function literal, which will complicate
 // accounting due to the block-within-an expression.
 func (f *File) endsBasicSourceBlock(s ast.Stmt) bool {
 	switch s := s.(type) {
 	case *ast.BlockStmt:
 		// Treat blocks like basic blocks to avoid overlapping counters.
 		return true
 	case *ast.BranchStmt:
 		return true
 	case *ast.ForStmt:
 		return true
 	case *ast.IfStmt:
 		return true
 	case *ast.LabeledStmt:
 		return f.endsBasicSourceBlock(s.Stmt)
 	case *ast.RangeStmt:
 		return true
 	case *ast.SwitchStmt:
 		return true
 	case *ast.SelectStmt:
 		return true
 	case *ast.TypeSwitchStmt:
 		return true
 	case *ast.ExprStmt:
 		// Calls to panic change the flow.
 		// We really should verify that "panic" is the predefined function,
 		// but without type checking we can't and the likelihood of it being
 		// an actual problem is vanishingly small.
 		if call, ok := s.X.(*ast.CallExpr); ok {
 			if ident, ok := call.Fun.(*ast.Ident); ok && ident.Name == "panic" && len(call.Args) == 1 {
 				return true
 			}
 		}
 	}
 	found, _ := hasFuncLiteral(s)
 	return found
 }

 // funcLitFinder implements the ast.Visitor pattern to find the location of any
 // function literal in a subtree.
 type funcLitFinder token.Pos

 func (f *funcLitFinder) Visit(node ast.Node) (w ast.Visitor) {
 	if f.found() {
 		return nil // Prune search.
 	}
 	switch n := node.(type) {
 	case *ast.FuncLit:
 		*f = funcLitFinder(n.Body.Lbrace)
 		return nil // Prune search.
 	}
 	return f
 }

 func (f *funcLitFinder) found() bool {
 	return token.Pos(*f) != token.NoPos
 }

 // Sort interface for []block1; used for self-check in addVariables.

 type block1 struct {
 	Block
 	index int
 }

 type blockSlice []block1

 func (b blockSlice) Len() int           { return len(b) }
 func (b blockSlice) Less(i, j int) bool { return b[i].startByte < b[j].startByte }
 func (b blockSlice) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }

 // offset translates a token position into a 0-indexed byte offset.
 func (f *File) offset(pos token.Pos) int {
 	return f.fset.Position(pos).Offset
 }

 // addVariables adds to the end of the file the declarations to set up the counter and position variables.
 func (f *File) addVariables(w io.Writer) {
 	// Self-check: Verify that the instrumented basic blocks are disjoint.
 	t := make([]block1, len(f.blocks))
 	for i := range f.blocks {
 		t[i].Block = f.blocks[i]
 		t[i].index = i
 	}
 	sort.Sort(blockSlice(t))
 	for i := 1; i < len(t); i++ {
 		if t[i-1].endByte > t[i].startByte {
 			fmt.Fprintf(os.Stderr, "cover: internal error: block %d overlaps block %d\n", t[i-1].index, t[i].index)
 			// Note: error message is in byte positions, not token positions.
 			fmt.Fprintf(os.Stderr, "\t%s:#%d,#%d %s:#%d,#%d\n",
 				f.name, f.offset(t[i-1].startByte), f.offset(t[i-1].endByte),
 				f.name, f.offset(t[i].startByte), f.offset(t[i].endByte))
 		}
 	}

 	// Declare the coverage struct as a package-level variable.
 	fmt.Fprintf(w, "\nvar %s = struct {\n", *varVar)
 	fmt.Fprintf(w, "\tCount     [%d]uint32\n", len(f.blocks))
 	fmt.Fprintf(w, "\tPos       [3 * %d]uint32\n", len(f.blocks))
 	fmt.Fprintf(w, "\tNumStmt   [%d]uint16\n", len(f.blocks))
 	fmt.Fprintf(w, "} {\n")

 	// Initialize the position array field.
 	fmt.Fprintf(w, "\tPos: [3 * %d]uint32{\n", len(f.blocks))

 	// A nice long list of positions. Each position is encoded as follows to reduce size:
 	// - 32-bit starting line number
 	// - 32-bit ending line number
 	// - (16 bit ending column number << 16) | (16-bit starting column number).
 	for i, block := range f.blocks {
 		start := f.fset.Position(block.startByte)
 		end := f.fset.Position(block.endByte)
 		fmt.Fprintf(w, "\t\t%d, %d, %#x, // [%d]\n", start.Line, end.Line, (end.Column&0xFFFF)<<16|(start.Column&0xFFFF), i)
 	}

 	// Close the position array.
 	fmt.Fprintf(w, "\t},\n")

 	// Initialize the position array field.
 	fmt.Fprintf(w, "\tNumStmt: [%d]uint16{\n", len(f.blocks))

 	// A nice long list of statements-per-block, so we can give a conventional
 	// valuation of "percent covered". To save space, it's a 16-bit number, so we
 	// clamp it if it overflows - won't matter in practice.
 	for i, block := range f.blocks {
 		n := block.numStmt
 		if n > 1<<16-1 {
 			n = 1<<16 - 1
 		}
 		fmt.Fprintf(w, "\t\t%d, // %d\n", n, i)
 	}

 	// Close the statements-per-block array.
 	fmt.Fprintf(w, "\t},\n")

 	// Close the struct initialization.
 	fmt.Fprintf(w, "}\n")
 }
	// Copyright 2013 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	import (
	"bytes"
	"flag"
	"fmt"
	"go/ast"
	"go/parser"
	"go/printer"
	"go/token"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	)

	const usageMessage = "" +
	`Usage of 'go tool cover':
	Given a coverage profile produced by 'go test':
	go test -coverprofile=c.out

	Open a web browser displaying annotated source code:
	go tool cover -html=c.out

	Write out an HTML file instead of launching a web browser:
	go tool cover -html=c.out -o coverage.html

	Display coverage percentages to stdout for each function:
	go tool cover -func=c.out

	Finally, to generate modified source code with coverage annotations
	(what go test -cover does):
	go tool cover -mode=set -var=CoverageVariableName program.go
	`

	func usage() {
	fmt.Fprintln(os.Stderr, usageMessage)
	fmt.Fprintln(os.Stderr, "Flags:")
	flag.PrintDefaults()
	fmt.Fprintln(os.Stderr, "\n Only one of -html, -func, or -mode may be set.")
	os.Exit(2)
	}

	var (
	mode = flag.String("mode", "", "coverage mode: set, count, atomic")
	varVar = flag.String("var", "GoCover", "name of coverage variable to generate")
	output = flag.String("o", "", "file for output; default: stdout")
	htmlOut = flag.String("html", "", "generate HTML representation of coverage profile")
	funcOut = flag.String("func", "", "output coverage profile information for each function")
	)

	var profile string // The profile to read; the value of -html or -func

	var counterStmt func(*File, ast.Expr) ast.Stmt

	const (
	atomicPackagePath = "sync/atomic"
	atomicPackageName = "_cover_atomic_"
	)

	func main() {
	flag.Usage = usage
	flag.Parse()

	// Usage information when no arguments.
	if flag.NFlag() == 0 && flag.NArg() == 0 {
	flag.Usage()
	}

	err := parseFlags()
	if err != nil {
	fmt.Fprintln(os.Stderr, err)
	fmt.Fprintln(os.Stderr, `For usage information, run "go tool cover -help"`)
	os.Exit(2)
	}

	// Generate coverage-annotated source.
	if *mode != "" {
	annotate(flag.Arg(0))
	return
	}

	// Output HTML or function coverage information.
	if *htmlOut != "" {
	err = htmlOutput(profile, *output)
	} else {
	err = funcOutput(profile, *output)
	}

	if err != nil {
	fmt.Fprintf(os.Stderr, "cover: %v\n", err)
	os.Exit(2)
	}
	}

	// parseFlags sets the profile and counterStmt globals and performs validations.
	func parseFlags() error {
	profile = *htmlOut
	if *funcOut != "" {
	if profile != "" {
	return fmt.Errorf("too many options")
	}
	profile = *funcOut
	}

	// Must either display a profile or rewrite Go source.
	if (profile == "") == (*mode == "") {
	return fmt.Errorf("too many options")
	}

	if *mode != "" {
	switch *mode {
	case "set":
	counterStmt = setCounterStmt
	case "count":
	counterStmt = incCounterStmt
	case "atomic":
	counterStmt = atomicCounterStmt
	default:
	return fmt.Errorf("unknown -mode %v", *mode)
	}

	if flag.NArg() == 0 {
	return fmt.Errorf("missing source file")
	} else if flag.NArg() == 1 {
	return nil
	}
	} else if flag.NArg() == 0 {
	return nil
	}
	return fmt.Errorf("too many arguments")
	}

	// Block represents the information about a basic block to be recorded in the analysis.
	// Note: Our definition of basic block is based on control structures; we don't break
	// apart && and \|\|. We could but it doesn't seem important enough to bother.
	type Block struct {
	startByte token.Pos
	endByte token.Pos
	numStmt int
	}

	// File is a wrapper for the state of a file used in the parser.
	// The basic parse tree walker is a method of this type.
	type File struct {
	fset *token.FileSet
	name string // Name of file.
	astFile *ast.File
	blocks []Block
	atomicPkg string // Package name for "sync/atomic" in this file.
	}

	// Visit implements the ast.Visitor interface.
	func (f *File) Visit(node ast.Node) ast.Visitor {
	switch n := node.(type) {
	case *ast.BlockStmt:
	// If it's a switch or select, the body is a list of case clauses; don't tag the block itself.
	if len(n.List) > 0 {
	switch n.List[0].(type) {
	case *ast.CaseClause: // switch
	for _, n := range n.List {
	clause := n.(*ast.CaseClause)
	clause.Body = f.addCounters(clause.Pos(), clause.End(), clause.Body, false)
	}
	return f
	case *ast.CommClause: // select
	for _, n := range n.List {
	clause := n.(*ast.CommClause)
	clause.Body = f.addCounters(clause.Pos(), clause.End(), clause.Body, false)
	}
	return f
	}
	}
	n.List = f.addCounters(n.Lbrace, n.Rbrace+1, n.List, true) // +1 to step past closing brace.
	case *ast.IfStmt:
	ast.Walk(f, n.Body)
	if n.Else == nil {
	return nil
	}
	// The elses are special, because if we have
	// if x {
	// } else if y {
	// }
	// we want to cover the "if y". To do this, we need a place to drop the counter,
	// so we add a hidden block:
	// if x {
	// } else {
	// if y {
	// }
	// }
	switch stmt := n.Else.(type) {
	case *ast.IfStmt:
	block := &ast.BlockStmt{
	Lbrace: n.Body.End(), // Start at end of the "if" block so the covered part looks like it starts at the "else".
	List: []ast.Stmt{stmt},
	Rbrace: stmt.End(),
	}
	n.Else = block
	case *ast.BlockStmt:
	stmt.Lbrace = n.Body.End() // Start at end of the "if" block so the covered part looks like it starts at the "else".
	default:
	panic("unexpected node type in if")
	}
	ast.Walk(f, n.Else)
	return nil
	case *ast.SelectStmt:
	// Don't annotate an empty select - creates a syntax error.
	if n.Body == nil \|\| len(n.Body.List) == 0 {
	return nil
	}
	case *ast.SwitchStmt:
	// Don't annotate an empty switch - creates a syntax error.
	if n.Body == nil \|\| len(n.Body.List) == 0 {
	return nil
	}
	case *ast.TypeSwitchStmt:
	// Don't annotate an empty type switch - creates a syntax error.
	if n.Body == nil \|\| len(n.Body.List) == 0 {
	return nil
	}
	}
	return f
	}

	// unquote returns the unquoted string.
	func unquote(s string) string {
	t, err := strconv.Unquote(s)
	if err != nil {
	log.Fatalf("cover: improperly quoted string %q\n", s)
	}
	return t
	}

	// addImport adds an import for the specified path, if one does not already exist, and returns
	// the local package name.
	func (f *File) addImport(path string) string {
	// Does the package already import it?
	for _, s := range f.astFile.Imports {
	if unquote(s.Path.Value) == path {
	if s.Name != nil {
	return s.Name.Name
	}
	return filepath.Base(path)
	}
	}
	newImport := &ast.ImportSpec{
	Name: ast.NewIdent(atomicPackageName),
	Path: &ast.BasicLit{
	Kind: token.STRING,
	Value: fmt.Sprintf("%q", path),
	},
	}
	impDecl := &ast.GenDecl{
	Tok: token.IMPORT,
	Specs: []ast.Spec{
	newImport,
	},
	}
	// Make the new import the first Decl in the file.
	astFile := f.astFile
	astFile.Decls = append(astFile.Decls, nil)
	copy(astFile.Decls[1:], astFile.Decls[0:])
	astFile.Decls[0] = impDecl
	astFile.Imports = append(astFile.Imports, newImport)

	// Now refer to the package, just in case it ends up unused.
	// That is, append to the end of the file the declaration
	// var _ = _cover_atomic_.AddUint32
	reference := &ast.GenDecl{
	Tok: token.VAR,
	Specs: []ast.Spec{
	&ast.ValueSpec{
	Names: []*ast.Ident{
	ast.NewIdent("_"),
	},
	Values: []ast.Expr{
	&ast.SelectorExpr{
	X: ast.NewIdent(atomicPackageName),
	Sel: ast.NewIdent("AddUint32"),
	},
	},
	},
	},
	}
	astFile.Decls = append(astFile.Decls, reference)
	return atomicPackageName
	}

	var slashslash = []byte("//")

	// initialComments returns the prefix of content containing only
	// whitespace and line comments. Any +build directives must appear
	// within this region. This approach is more reliable than using
	// go/printer to print a modified AST containing comments.
	//
	func initialComments(content []byte) []byte {
	// Derived from go/build.Context.shouldBuild.
	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
	}
	}
	return content[:end]
	}

	func annotate(name string) {
	fset := token.NewFileSet()
	content, err := ioutil.ReadFile(name)
	if err != nil {
	log.Fatalf("cover: %s: %s", name, err)
	}
	parsedFile, err := parser.ParseFile(fset, name, content, parser.ParseComments)
	if err != nil {
	log.Fatalf("cover: %s: %s", name, err)
	}
	parsedFile.Comments = trimComments(parsedFile, fset)

	file := &File{
	fset: fset,
	name: name,
	astFile: parsedFile,
	}
	if *mode == "atomic" {
	file.atomicPkg = file.addImport(atomicPackagePath)
	}
	ast.Walk(file, file.astFile)
	fd := os.Stdout
	if *output != "" {
	var err error
	fd, err = os.Create(*output)
	if err != nil {
	log.Fatalf("cover: %s", err)
	}
	}
	fd.Write(initialComments(content)) // Retain '// +build' directives.
	file.print(fd)
	// After printing the source tree, add some declarations for the counters etc.
	// We could do this by adding to the tree, but it's easier just to print the text.
	file.addVariables(fd)
	}

	// trimComments drops all but the //go: comments, some of which are semantically important.
	// We drop all others because they can appear in places that cause our counters
	// to appear in syntactically incorrect places. //go: appears at the beginning of
	// the line and is syntactically safe.
	func trimComments(file ast.File, fset token.FileSet) []*ast.CommentGroup {
	var comments []*ast.CommentGroup
	for _, group := range file.Comments {
	var list []*ast.Comment
	for _, comment := range group.List {
	if strings.HasPrefix(comment.Text, "//go:") && fset.Position(comment.Slash).Column == 1 {
	list = append(list, comment)
	}
	}
	if list != nil {
	comments = append(comments, &ast.CommentGroup{List: list})
	}
	}
	return comments
	}

	func (f *File) print(w io.Writer) {
	printer.Fprint(w, f.fset, f.astFile)
	}

	// intLiteral returns an ast.BasicLit representing the integer value.
	func (f File) intLiteral(i int) ast.BasicLit {
	node := &ast.BasicLit{
	Kind: token.INT,
	Value: fmt.Sprint(i),
	}
	return node
	}

	// index returns an ast.BasicLit representing the number of counters present.
	func (f File) index() ast.BasicLit {
	return f.intLiteral(len(f.blocks))
	}

	// setCounterStmt returns the expression: __count[23] = 1.
	func setCounterStmt(f *File, counter ast.Expr) ast.Stmt {
	return &ast.AssignStmt{
	Lhs: []ast.Expr{counter},
	Tok: token.ASSIGN,
	Rhs: []ast.Expr{f.intLiteral(1)},
	}
	}

	// incCounterStmt returns the expression: __count[23]++.
	func incCounterStmt(f *File, counter ast.Expr) ast.Stmt {
	return &ast.IncDecStmt{
	X: counter,
	Tok: token.INC,
	}
	}

	// atomicCounterStmt returns the expression: atomic.AddUint32(&__count[23], 1)
	func atomicCounterStmt(f *File, counter ast.Expr) ast.Stmt {
	return &ast.ExprStmt{
	X: &ast.CallExpr{
	Fun: &ast.SelectorExpr{
	X: ast.NewIdent(f.atomicPkg),
	Sel: ast.NewIdent("AddUint32"),
	},
	Args: []ast.Expr{&ast.UnaryExpr{
	Op: token.AND,
	X: counter,
	},
	f.intLiteral(1),
	},
	},
	}
	}

	// newCounter creates a new counter expression of the appropriate form.
	func (f *File) newCounter(start, end token.Pos, numStmt int) ast.Stmt {
	counter := &ast.IndexExpr{
	X: &ast.SelectorExpr{
	X: ast.NewIdent(*varVar),
	Sel: ast.NewIdent("Count"),
	},
	Index: f.index(),
	}
	stmt := counterStmt(f, counter)
	f.blocks = append(f.blocks, Block{start, end, numStmt})
	return stmt
	}

	// addCounters takes a list of statements and adds counters to the beginning of
	// each basic block at the top level of that list. For instance, given
	//
	// S1
	// if cond {
	// S2
	// }
	// S3
	//
	// counters will be added before S1 and before S3. The block containing S2
	// will be visited in a separate call.
	// TODO: Nested simple blocks get unnecessary (but correct) counters
	func (f *File) addCounters(pos, blockEnd token.Pos, list []ast.Stmt, extendToClosingBrace bool) []ast.Stmt {
	// Special case: make sure we add a counter to an empty block. Can't do this below
	// or we will add a counter to an empty statement list after, say, a return statement.
	if len(list) == 0 {
	return []ast.Stmt{f.newCounter(pos, blockEnd, 0)}
	}
	// We have a block (statement list), but it may have several basic blocks due to the
	// appearance of statements that affect the flow of control.
	var newList []ast.Stmt
	for {
	// Find first statement that affects flow of control (break, continue, if, etc.).
	// It will be the last statement of this basic block.
	var last int
	end := blockEnd
	for last = 0; last < len(list); last++ {
	end = f.statementBoundary(list[last])
	if f.endsBasicSourceBlock(list[last]) {
	extendToClosingBrace = false // Block is broken up now.
	last++
	break
	}
	}
	if extendToClosingBrace {
	end = blockEnd
	}
	if pos != end { // Can have no source to cover if e.g. blocks abut.
	newList = append(newList, f.newCounter(pos, end, last))
	}
	newList = append(newList, list[0:last]...)
	list = list[last:]
	if len(list) == 0 {
	break
	}
	pos = list[0].Pos()
	}
	return newList
	}

	// hasFuncLiteral reports the existence and position of the first func literal
	// in the node, if any. If a func literal appears, it usually marks the termination
	// of a basic block because the function body is itself a block.
	// Therefore we draw a line at the start of the body of the first function literal we find.
	// TODO: what if there's more than one? Probably doesn't matter much.
	func hasFuncLiteral(n ast.Node) (bool, token.Pos) {
	if n == nil {
	return false, 0
	}
	var literal funcLitFinder
	ast.Walk(&literal, n)
	return literal.found(), token.Pos(literal)
	}

	// statementBoundary finds the location in s that terminates the current basic
	// block in the source.
	func (f *File) statementBoundary(s ast.Stmt) token.Pos {
	// Control flow statements are easy.
	switch s := s.(type) {
	case *ast.BlockStmt:
	// Treat blocks like basic blocks to avoid overlapping counters.
	return s.Lbrace
	case *ast.IfStmt:
	found, pos := hasFuncLiteral(s.Init)
	if found {
	return pos
	}
	found, pos = hasFuncLiteral(s.Cond)
	if found {
	return pos
	}
	return s.Body.Lbrace
	case *ast.ForStmt:
	found, pos := hasFuncLiteral(s.Init)
	if found {
	return pos
	}
	found, pos = hasFuncLiteral(s.Cond)
	if found {
	return pos
	}
	found, pos = hasFuncLiteral(s.Post)
	if found {
	return pos
	}
	return s.Body.Lbrace
	case *ast.LabeledStmt:
	return f.statementBoundary(s.Stmt)
	case *ast.RangeStmt:
	found, pos := hasFuncLiteral(s.X)
	if found {
	return pos
	}
	return s.Body.Lbrace
	case *ast.SwitchStmt:
	found, pos := hasFuncLiteral(s.Init)
	if found {
	return pos
	}
	found, pos = hasFuncLiteral(s.Tag)
	if found {
	return pos
	}
	return s.Body.Lbrace
	case *ast.SelectStmt:
	return s.Body.Lbrace
	case *ast.TypeSwitchStmt:
	found, pos := hasFuncLiteral(s.Init)
	if found {
	return pos
	}
	return s.Body.Lbrace
	}
	// If not a control flow statement, it is a declaration, expression, call, etc. and it may have a function literal.
	// If it does, that's tricky because we want to exclude the body of the function from this block.
	// Draw a line at the start of the body of the first function literal we find.
	// TODO: what if there's more than one? Probably doesn't matter much.
	found, pos := hasFuncLiteral(s)
	if found {
	return pos
	}
	return s.End()
	}

	// endsBasicSourceBlock reports whether s changes the flow of control: break, if, etc.,
	// or if it's just problematic, for instance contains a function literal, which will complicate
	// accounting due to the block-within-an expression.
	func (f *File) endsBasicSourceBlock(s ast.Stmt) bool {
	switch s := s.(type) {
	case *ast.BlockStmt:
	// Treat blocks like basic blocks to avoid overlapping counters.
	return true
	case *ast.BranchStmt:
	return true
	case *ast.ForStmt:
	return true
	case *ast.IfStmt:
	return true
	case *ast.LabeledStmt:
	return f.endsBasicSourceBlock(s.Stmt)
	case *ast.RangeStmt:
	return true
	case *ast.SwitchStmt:
	return true
	case *ast.SelectStmt:
	return true
	case *ast.TypeSwitchStmt:
	return true
	case *ast.ExprStmt:
	// Calls to panic change the flow.
	// We really should verify that "panic" is the predefined function,
	// but without type checking we can't and the likelihood of it being
	// an actual problem is vanishingly small.
	if call, ok := s.X.(*ast.CallExpr); ok {
	if ident, ok := call.Fun.(*ast.Ident); ok && ident.Name == "panic" && len(call.Args) == 1 {
	return true
	}
	}
	}
	found, _ := hasFuncLiteral(s)
	return found
	}

	// funcLitFinder implements the ast.Visitor pattern to find the location of any
	// function literal in a subtree.
	type funcLitFinder token.Pos

	func (f *funcLitFinder) Visit(node ast.Node) (w ast.Visitor) {
	if f.found() {
	return nil // Prune search.
	}
	switch n := node.(type) {
	case *ast.FuncLit:
	*f = funcLitFinder(n.Body.Lbrace)
	return nil // Prune search.
	}
	return f
	}

	func (f *funcLitFinder) found() bool {
	return token.Pos(*f) != token.NoPos
	}

	// Sort interface for []block1; used for self-check in addVariables.

	type block1 struct {
	Block
	index int
	}

	type blockSlice []block1

	func (b blockSlice) Len() int { return len(b) }
	func (b blockSlice) Less(i, j int) bool { return b[i].startByte < b[j].startByte }
	func (b blockSlice) Swap(i, j int) { b[i], b[j] = b[j], b[i] }

	// offset translates a token position into a 0-indexed byte offset.
	func (f *File) offset(pos token.Pos) int {
	return f.fset.Position(pos).Offset
	}

	// addVariables adds to the end of the file the declarations to set up the counter and position variables.
	func (f *File) addVariables(w io.Writer) {
	// Self-check: Verify that the instrumented basic blocks are disjoint.
	t := make([]block1, len(f.blocks))
	for i := range f.blocks {
	t[i].Block = f.blocks[i]
	t[i].index = i
	}
	sort.Sort(blockSlice(t))
	for i := 1; i < len(t); i++ {
	if t[i-1].endByte > t[i].startByte {
	fmt.Fprintf(os.Stderr, "cover: internal error: block %d overlaps block %d\n", t[i-1].index, t[i].index)
	// Note: error message is in byte positions, not token positions.
	fmt.Fprintf(os.Stderr, "\t%s:#%d,#%d %s:#%d,#%d\n",
	f.name, f.offset(t[i-1].startByte), f.offset(t[i-1].endByte),
	f.name, f.offset(t[i].startByte), f.offset(t[i].endByte))
	}
	}

	// Declare the coverage struct as a package-level variable.
	fmt.Fprintf(w, "\nvar %s = struct {\n", *varVar)
	fmt.Fprintf(w, "\tCount [%d]uint32\n", len(f.blocks))
	fmt.Fprintf(w, "\tPos [3 * %d]uint32\n", len(f.blocks))
	fmt.Fprintf(w, "\tNumStmt [%d]uint16\n", len(f.blocks))
	fmt.Fprintf(w, "} {\n")

	// Initialize the position array field.
	fmt.Fprintf(w, "\tPos: [3 * %d]uint32{\n", len(f.blocks))

	// A nice long list of positions. Each position is encoded as follows to reduce size:
	// - 32-bit starting line number
	// - 32-bit ending line number
	// - (16 bit ending column number << 16) \| (16-bit starting column number).
	for i, block := range f.blocks {
	start := f.fset.Position(block.startByte)
	end := f.fset.Position(block.endByte)
	fmt.Fprintf(w, "\t\t%d, %d, %#x, // [%d]\n", start.Line, end.Line, (end.Column&0xFFFF)<<16\|(start.Column&0xFFFF), i)
	}

	// Close the position array.
	fmt.Fprintf(w, "\t},\n")

	// Initialize the position array field.
	fmt.Fprintf(w, "\tNumStmt: [%d]uint16{\n", len(f.blocks))

	// A nice long list of statements-per-block, so we can give a conventional
	// valuation of "percent covered". To save space, it's a 16-bit number, so we
	// clamp it if it overflows - won't matter in practice.
	for i, block := range f.blocks {
	n := block.numStmt
	if n > 1<<16-1 {
	n = 1<<16 - 1
	}
	fmt.Fprintf(w, "\t\t%d, // %d\n", n, i)
	}

	// Close the statements-per-block array.
	fmt.Fprintf(w, "\t},\n")

	// Close the struct initialization.
	fmt.Fprintf(w, "}\n")
	}