cmd/vet: move cmd/vet into std repo

cp -r x/tools/cmd/vet cmd/vet without any changes.
The next change will adjust the source to use std
repo go/types and friends.

This may (temporarily) break the build; the next
commit (immediately following) will fix it. We do
it in two commits so that we can see the manual
changes.

Change-Id: Ic45dab7066f13923e21f8c61200c8c3fd447b171
Reviewed-on: https://go-review.googlesource.com/10694Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/assign.go

+// 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.
+
+/*
+This file contains the code to check for useless assignments.
+*/
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+	"reflect"
+)
+
+func init() {
+	register("assign",
+		"check for useless assignments",
+		checkAssignStmt,
+		assignStmt)
+}
+
+// TODO: should also check for assignments to struct fields inside methods
+// that are on T instead of *T.
+
+// checkAssignStmt checks for assignments of the form "<expr> = <expr>".
+// These are almost always useless, and even when they aren't they are usually a mistake.
+func checkAssignStmt(f *File, node ast.Node) {
+	stmt := node.(*ast.AssignStmt)
+	if stmt.Tok != token.ASSIGN {
+		return // ignore :=
+	}
+	if len(stmt.Lhs) != len(stmt.Rhs) {
+		// If LHS and RHS have different cardinality, they can't be the same.
+		return
+	}
+	for i, lhs := range stmt.Lhs {
+		rhs := stmt.Rhs[i]
+		if reflect.TypeOf(lhs) != reflect.TypeOf(rhs) {
+			continue // short-circuit the heavy-weight gofmt check
+		}
+		le := f.gofmt(lhs)
+		re := f.gofmt(rhs)
+		if le == re {
+			f.Badf(stmt.Pos(), "self-assignment of %s to %s", re, le)
+		}
+	}
+}

src/cmd/vet/atomic.go

+// 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 (
+	"go/ast"
+	"go/token"
+)
+
+func init() {
+	register("atomic",
+		"check for common mistaken usages of the sync/atomic package",
+		checkAtomicAssignment,
+		assignStmt)
+}
+
+// checkAtomicAssignment walks the assignment statement checking for common
+// mistaken usage of atomic package, such as: x = atomic.AddUint64(&x, 1)
+func checkAtomicAssignment(f *File, node ast.Node) {
+	n := node.(*ast.AssignStmt)
+	if len(n.Lhs) != len(n.Rhs) {
+		return
+	}
+
+	for i, right := range n.Rhs {
+		call, ok := right.(*ast.CallExpr)
+		if !ok {
+			continue
+		}
+		sel, ok := call.Fun.(*ast.SelectorExpr)
+		if !ok {
+			continue
+		}
+		pkg, ok := sel.X.(*ast.Ident)
+		if !ok || pkg.Name != "atomic" {
+			continue
+		}
+
+		switch sel.Sel.Name {
+		case "AddInt32", "AddInt64", "AddUint32", "AddUint64", "AddUintptr":
+			f.checkAtomicAddAssignment(n.Lhs[i], call)
+		}
+	}
+}
+
+// checkAtomicAddAssignment walks the atomic.Add* method calls checking for assigning the return value
+// to the same variable being used in the operation
+func (f *File) checkAtomicAddAssignment(left ast.Expr, call *ast.CallExpr) {
+	if len(call.Args) != 2 {
+		return
+	}
+	arg := call.Args[0]
+	broken := false
+
+	if uarg, ok := arg.(*ast.UnaryExpr); ok && uarg.Op == token.AND {
+		broken = f.gofmt(left) == f.gofmt(uarg.X)
+	} else if star, ok := left.(*ast.StarExpr); ok {
+		broken = f.gofmt(star.X) == f.gofmt(arg)
+	}
+
+	if broken {
+		f.Bad(left.Pos(), "direct assignment to atomic value")
+	}
+}

src/cmd/vet/bool.go

+// Copyright 2014 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.
+
+// This file contains boolean condition tests.
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+func init() {
+	register("bool",
+		"check for mistakes involving boolean operators",
+		checkBool,
+		binaryExpr)
+}
+
+func checkBool(f *File, n ast.Node) {
+	e := n.(*ast.BinaryExpr)
+
+	var op boolOp
+	switch e.Op {
+	case token.LOR:
+		op = or
+	case token.LAND:
+		op = and
+	default:
+		return
+	}
+
+	comm := op.commutativeSets(e)
+	for _, exprs := range comm {
+		op.checkRedundant(f, exprs)
+		op.checkSuspect(f, exprs)
+	}
+}
+
+type boolOp struct {
+	name  string
+	tok   token.Token // token corresponding to this operator
+	badEq token.Token // token corresponding to the equality test that should not be used with this operator
+}
+
+var (
+	or  = boolOp{"or", token.LOR, token.NEQ}
+	and = boolOp{"and", token.LAND, token.EQL}
+)
+
+// commutativeSets returns all side effect free sets of
+// expressions in e that are connected by op.
+// For example, given 'a || b || f() || c || d' with the or op,
+// commutativeSets returns {{b, a}, {d, c}}.
+func (op boolOp) commutativeSets(e *ast.BinaryExpr) [][]ast.Expr {
+	exprs := op.split(e)
+
+	// Partition the slice of expressions into commutative sets.
+	i := 0
+	var sets [][]ast.Expr
+	for j := 0; j <= len(exprs); j++ {
+		if j == len(exprs) || hasSideEffects(exprs[j]) {
+			if i < j {
+				sets = append(sets, exprs[i:j])
+			}
+			i = j + 1
+		}
+	}
+
+	return sets
+}
+
+// checkRedundant checks for expressions of the form
+//   e && e
+//   e || e
+// Exprs must contain only side effect free expressions.
+func (op boolOp) checkRedundant(f *File, exprs []ast.Expr) {
+	seen := make(map[string]bool)
+	for _, e := range exprs {
+		efmt := f.gofmt(e)
+		if seen[efmt] {
+			f.Badf(e.Pos(), "redundant %s: %s %s %s", op.name, efmt, op.tok, efmt)
+		} else {
+			seen[efmt] = true
+		}
+	}
+}
+
+// checkSuspect checks for expressions of the form
+//   x != c1 || x != c2
+//   x == c1 && x == c2
+// where c1 and c2 are constant expressions.
+// If c1 and c2 are the same then it's redundant;
+// if c1 and c2 are different then it's always true or always false.
+// Exprs must contain only side effect free expressions.
+func (op boolOp) checkSuspect(f *File, exprs []ast.Expr) {
+	// seen maps from expressions 'x' to equality expressions 'x != c'.
+	seen := make(map[string]string)
+
+	for _, e := range exprs {
+		bin, ok := e.(*ast.BinaryExpr)
+		if !ok || bin.Op != op.badEq {
+			continue
+		}
+
+		// In order to avoid false positives, restrict to cases
+		// in which one of the operands is constant. We're then
+		// interested in the other operand.
+		// In the rare case in which both operands are constant
+		// (e.g. runtime.GOOS and "windows"), we'll only catch
+		// mistakes if the LHS is repeated, which is how most
+		// code is written.
+		var x ast.Expr
+		switch {
+		case f.pkg.types[bin.Y].Value != nil:
+			x = bin.X
+		case f.pkg.types[bin.X].Value != nil:
+			x = bin.Y
+		default:
+			continue
+		}
+
+		// e is of the form 'x != c' or 'x == c'.
+		xfmt := f.gofmt(x)
+		efmt := f.gofmt(e)
+		if prev, found := seen[xfmt]; found {
+			// checkRedundant handles the case in which efmt == prev.
+			if efmt != prev {
+				f.Badf(e.Pos(), "suspect %s: %s %s %s", op.name, efmt, op.tok, prev)
+			}
+		} else {
+			seen[xfmt] = efmt
+		}
+	}
+}
+
+// hasSideEffects reports whether evaluation of e has side effects.
+func hasSideEffects(e ast.Expr) bool {
+	safe := true
+	ast.Inspect(e, func(node ast.Node) bool {
+		switch n := node.(type) {
+		// Using CallExpr here will catch conversions
+		// as well as function and method invocations.
+		// We'll live with the false negatives for now.
+		case *ast.CallExpr:
+			safe = false
+			return false
+		case *ast.UnaryExpr:
+			if n.Op == token.ARROW {
+				safe = false
+				return false
+			}
+		}
+		return true
+	})
+	return !safe
+}
+
+// split returns a slice of all subexpressions in e that are connected by op.
+// For example, given 'a || (b || c) || d' with the or op,
+// split returns []{d, c, b, a}.
+func (op boolOp) split(e ast.Expr) (exprs []ast.Expr) {
+	for {
+		e = unparen(e)
+		if b, ok := e.(*ast.BinaryExpr); ok && b.Op == op.tok {
+			exprs = append(exprs, op.split(b.Y)...)
+			e = b.X
+		} else {
+			exprs = append(exprs, e)
+			break
+		}
+	}
+	return
+}
+
+// unparen returns e with any enclosing parentheses stripped.
+func unparen(e ast.Expr) ast.Expr {
+	for {
+		p, ok := e.(*ast.ParenExpr)
+		if !ok {
+			return e
+		}
+		e = p.X
+	}
+}

src/cmd/vet/buildtag.go

+// 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"
+	"fmt"
+	"os"
+	"strings"
+	"unicode"
+)
+
+var (
+	nl         = []byte("\n")
+	slashSlash = []byte("//")
+	plusBuild  = []byte("+build")
+)
+
+// checkBuildTag checks that build tags are in the correct location and well-formed.
+func checkBuildTag(name string, data []byte) {
+	if !vet("buildtags") {
+		return
+	}
+	lines := bytes.SplitAfter(data, nl)
+
+	// Determine cutpoint where +build comments are no longer valid.
+	// They are valid in leading // comments in the file followed by
+	// a blank line.
+	var cutoff int
+	for i, line := range lines {
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 {
+			cutoff = i
+			continue
+		}
+		if bytes.HasPrefix(line, slashSlash) {
+			continue
+		}
+		break
+	}
+
+	for i, line := range lines {
+		line = bytes.TrimSpace(line)
+		if !bytes.HasPrefix(line, slashSlash) {
+			continue
+		}
+		text := bytes.TrimSpace(line[2:])
+		if bytes.HasPrefix(text, plusBuild) {
+			fields := bytes.Fields(text)
+			if !bytes.Equal(fields[0], plusBuild) {
+				// Comment is something like +buildasdf not +build.
+				fmt.Fprintf(os.Stderr, "%s:%d: possible malformed +build comment\n", name, i+1)
+				continue
+			}
+			if i >= cutoff {
+				fmt.Fprintf(os.Stderr, "%s:%d: +build comment must appear before package clause and be followed by a blank line\n", name, i+1)
+				setExit(1)
+				continue
+			}
+			// Check arguments.
+		Args:
+			for _, arg := range fields[1:] {
+				for _, elem := range strings.Split(string(arg), ",") {
+					if strings.HasPrefix(elem, "!!") {
+						fmt.Fprintf(os.Stderr, "%s:%d: invalid double negative in build constraint: %s\n", name, i+1, arg)
+						setExit(1)
+						break Args
+					}
+					if strings.HasPrefix(elem, "!") {
+						elem = elem[1:]
+					}
+					for _, c := range elem {
+						if !unicode.IsLetter(c) && !unicode.IsDigit(c) && c != '_' && c != '.' {
+							fmt.Fprintf(os.Stderr, "%s:%d: invalid non-alphanumeric build constraint: %s\n", name, i+1, arg)
+							setExit(1)
+							break Args
+						}
+					}
+				}
+			}
+			continue
+		}
+		// Comment with +build but not at beginning.
+		if bytes.Contains(line, plusBuild) && i < cutoff {
+			fmt.Fprintf(os.Stderr, "%s:%d: possible malformed +build comment\n", name, i+1)
+			continue
+		}
+	}
+}

src/cmd/vet/composite.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains the test for unkeyed struct literals.
+
+package main
+
+import (
+	"flag"
+	"go/ast"
+	"strings"
+
+	"golang.org/x/tools/cmd/vet/whitelist"
+)
+
+var compositeWhiteList = flag.Bool("compositewhitelist", true, "use composite white list; for testing only")
+
+func init() {
+	register("composites",
+		"check that composite literals used field-keyed elements",
+		checkUnkeyedLiteral,
+		compositeLit)
+}
+
+// checkUnkeyedLiteral checks if a composite literal is a struct literal with
+// unkeyed fields.
+func checkUnkeyedLiteral(f *File, node ast.Node) {
+	c := node.(*ast.CompositeLit)
+	typ := c.Type
+	for {
+		if typ1, ok := c.Type.(*ast.ParenExpr); ok {
+			typ = typ1
+			continue
+		}
+		break
+	}
+
+	switch typ.(type) {
+	case *ast.ArrayType:
+		return
+	case *ast.MapType:
+		return
+	case *ast.StructType:
+		return // a literal struct type does not need to use keys
+	case *ast.Ident:
+		// A simple type name like t or T does not need keys either,
+		// since it is almost certainly declared in the current package.
+		// (The exception is names being used via import . "pkg", but
+		// those are already breaking the Go 1 compatibility promise,
+		// so not reporting potential additional breakage seems okay.)
+		return
+	}
+
+	// Otherwise the type is a selector like pkg.Name.
+	// We only care if pkg.Name is a struct, not if it's a map, array, or slice.
+	isStruct, typeString := f.pkg.isStruct(c)
+	if !isStruct {
+		return
+	}
+
+	if typeString == "" { // isStruct doesn't know
+		typeString = f.gofmt(typ)
+	}
+
+	// It's a struct, or we can't tell it's not a struct because we don't have types.
+
+	// Check if the CompositeLit contains an unkeyed field.
+	allKeyValue := true
+	for _, e := range c.Elts {
+		if _, ok := e.(*ast.KeyValueExpr); !ok {
+			allKeyValue = false
+			break
+		}
+	}
+	if allKeyValue {
+		return
+	}
+
+	// Check that the CompositeLit's type has the form pkg.Typ.
+	s, ok := c.Type.(*ast.SelectorExpr)
+	if !ok {
+		return
+	}
+	pkg, ok := s.X.(*ast.Ident)
+	if !ok {
+		return
+	}
+
+	// Convert the package name to an import path, and compare to a whitelist.
+	path := pkgPath(f, pkg.Name)
+	if path == "" {
+		f.Badf(c.Pos(), "unresolvable package for %s.%s literal", pkg.Name, s.Sel.Name)
+		return
+	}
+	typeName := path + "." + s.Sel.Name
+	if *compositeWhiteList && whitelist.UnkeyedLiteral[typeName] {
+		return
+	}
+
+	f.Bad(c.Pos(), typeString+" composite literal uses unkeyed fields")
+}
+
+// pkgPath returns the import path "image/png" for the package name "png".
+//
+// This is based purely on syntax and convention, and not on the imported
+// package's contents. It will be incorrect if a package name differs from the
+// leaf element of the import path, or if the package was a dot import.
+func pkgPath(f *File, pkgName string) (path string) {
+	for _, x := range f.file.Imports {
+		s := strings.Trim(x.Path.Value, `"`)
+		if x.Name != nil {
+			// Catch `import pkgName "foo/bar"`.
+			if x.Name.Name == pkgName {
+				return s
+			}
+		} else {
+			// Catch `import "pkgName"` or `import "foo/bar/pkgName"`.
+			if s == pkgName || strings.HasSuffix(s, "/"+pkgName) {
+				return s
+			}
+		}
+	}
+	return ""
+}

src/cmd/vet/copylock.go

+// 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.
+
+// This file contains the code to check that locks are not passed by value.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/token"
+
+	"golang.org/x/tools/go/types"
+)
+
+func init() {
+	register("copylocks",
+		"check that locks are not passed by value",
+		checkCopyLocks,
+		funcDecl, rangeStmt)
+}
+
+// checkCopyLocks checks whether node might
+// inadvertently copy a lock.
+func checkCopyLocks(f *File, node ast.Node) {
+	switch node := node.(type) {
+	case *ast.RangeStmt:
+		checkCopyLocksRange(f, node)
+	case *ast.FuncDecl:
+		checkCopyLocksFunc(f, node)
+	}
+}
+
+// checkCopyLocksFunc checks whether a function might
+// inadvertently copy a lock, by checking whether
+// its receiver, parameters, or return values
+// are locks.
+func checkCopyLocksFunc(f *File, d *ast.FuncDecl) {
+	if d.Recv != nil && len(d.Recv.List) > 0 {
+		expr := d.Recv.List[0].Type
+		if path := lockPath(f.pkg.typesPkg, f.pkg.types[expr].Type); path != nil {
+			f.Badf(expr.Pos(), "%s passes Lock by value: %v", d.Name.Name, path)
+		}
+	}
+
+	if d.Type.Params != nil {
+		for _, field := range d.Type.Params.List {
+			expr := field.Type
+			if path := lockPath(f.pkg.typesPkg, f.pkg.types[expr].Type); path != nil {
+				f.Badf(expr.Pos(), "%s passes Lock by value: %v", d.Name.Name, path)
+			}
+		}
+	}
+
+	if d.Type.Results != nil {
+		for _, field := range d.Type.Results.List {
+			expr := field.Type
+			if path := lockPath(f.pkg.typesPkg, f.pkg.types[expr].Type); path != nil {
+				f.Badf(expr.Pos(), "%s returns Lock by value: %v", d.Name.Name, path)
+			}
+		}
+	}
+}
+
+// checkCopyLocksRange checks whether a range statement
+// might inadvertently copy a lock by checking whether
+// any of the range variables are locks.
+func checkCopyLocksRange(f *File, r *ast.RangeStmt) {
+	checkCopyLocksRangeVar(f, r.Tok, r.Key)
+	checkCopyLocksRangeVar(f, r.Tok, r.Value)
+}
+
+func checkCopyLocksRangeVar(f *File, rtok token.Token, e ast.Expr) {
+	if e == nil {
+		return
+	}
+	id, isId := e.(*ast.Ident)
+	if isId && id.Name == "_" {
+		return
+	}
+
+	var typ types.Type
+	if rtok == token.DEFINE {
+		if !isId {
+			return
+		}
+		obj := f.pkg.defs[id]
+		if obj == nil {
+			return
+		}
+		typ = obj.Type()
+	} else {
+		typ = f.pkg.types[e].Type
+	}
+
+	if typ == nil {
+		return
+	}
+	if path := lockPath(f.pkg.typesPkg, typ); path != nil {
+		f.Badf(e.Pos(), "range var %s copies Lock: %v", f.gofmt(e), path)
+	}
+}
+
+type typePath []types.Type
+
+// String pretty-prints a typePath.
+func (path typePath) String() string {
+	n := len(path)
+	var buf bytes.Buffer
+	for i := range path {
+		if i > 0 {
+			fmt.Fprint(&buf, " contains ")
+		}
+		// The human-readable path is in reverse order, outermost to innermost.
+		fmt.Fprint(&buf, path[n-i-1].String())
+	}
+	return buf.String()
+}
+
+// lockPath returns a typePath describing the location of a lock value
+// contained in typ. If there is no contained lock, it returns nil.
+func lockPath(tpkg *types.Package, typ types.Type) typePath {
+	if typ == nil {
+		return nil
+	}
+
+	// We're only interested in the case in which the underlying
+	// type is a struct. (Interfaces and pointers are safe to copy.)
+	styp, ok := typ.Underlying().(*types.Struct)
+	if !ok {
+		return nil
+	}
+
+	// We're looking for cases in which a reference to this type
+	// can be locked, but a value cannot. This differentiates
+	// embedded interfaces from embedded values.
+	if plock := types.NewMethodSet(types.NewPointer(typ)).Lookup(tpkg, "Lock"); plock != nil {
+		if lock := types.NewMethodSet(typ).Lookup(tpkg, "Lock"); lock == nil {
+			return []types.Type{typ}
+		}
+	}
+
+	nfields := styp.NumFields()
+	for i := 0; i < nfields; i++ {
+		ftyp := styp.Field(i).Type()
+		subpath := lockPath(tpkg, ftyp)
+		if subpath != nil {
+			return append(subpath, typ)
+		}
+	}
+
+	return nil
+}

src/cmd/vet/deadcode.go

+// 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.
+
+// Check for syntactically unreachable code.
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+func init() {
+	register("unreachable",
+		"check for unreachable code",
+		checkUnreachable,
+		funcDecl, funcLit)
+}
+
+type deadState struct {
+	f           *File
+	hasBreak    map[ast.Stmt]bool
+	hasGoto     map[string]bool
+	labels      map[string]ast.Stmt
+	breakTarget ast.Stmt
+
+	reachable bool
+}
+
+// checkUnreachable checks a function body for dead code.
+func checkUnreachable(f *File, node ast.Node) {
+	var body *ast.BlockStmt
+	switch n := node.(type) {
+	case *ast.FuncDecl:
+		body = n.Body
+	case *ast.FuncLit:
+		body = n.Body
+	}
+	if body == nil {
+		return
+	}
+
+	d := &deadState{
+		f:        f,
+		hasBreak: make(map[ast.Stmt]bool),
+		hasGoto:  make(map[string]bool),
+		labels:   make(map[string]ast.Stmt),
+	}
+
+	d.findLabels(body)
+
+	d.reachable = true
+	d.findDead(body)
+}
+
+// findLabels gathers information about the labels defined and used by stmt
+// and about which statements break, whether a label is involved or not.
+func (d *deadState) findLabels(stmt ast.Stmt) {
+	switch x := stmt.(type) {
+	default:
+		d.f.Warnf(x.Pos(), "internal error in findLabels: unexpected statement %T", x)
+
+	case *ast.AssignStmt,
+		*ast.BadStmt,
+		*ast.DeclStmt,
+		*ast.DeferStmt,
+		*ast.EmptyStmt,
+		*ast.ExprStmt,
+		*ast.GoStmt,
+		*ast.IncDecStmt,
+		*ast.ReturnStmt,
+		*ast.SendStmt:
+		// no statements inside
+
+	case *ast.BlockStmt:
+		for _, stmt := range x.List {
+			d.findLabels(stmt)
+		}
+
+	case *ast.BranchStmt:
+		switch x.Tok {
+		case token.GOTO:
+			if x.Label != nil {
+				d.hasGoto[x.Label.Name] = true
+			}
+
+		case token.BREAK:
+			stmt := d.breakTarget
+			if x.Label != nil {
+				stmt = d.labels[x.Label.Name]
+			}
+			if stmt != nil {
+				d.hasBreak[stmt] = true
+			}
+		}
+
+	case *ast.IfStmt:
+		d.findLabels(x.Body)
+		if x.Else != nil {
+			d.findLabels(x.Else)
+		}
+
+	case *ast.LabeledStmt:
+		d.labels[x.Label.Name] = x.Stmt
+		d.findLabels(x.Stmt)
+
+	// These cases are all the same, but the x.Body only works
+	// when the specific type of x is known, so the cases cannot
+	// be merged.
+	case *ast.ForStmt:
+		outer := d.breakTarget
+		d.breakTarget = x
+		d.findLabels(x.Body)
+		d.breakTarget = outer
+
+	case *ast.RangeStmt:
+		outer := d.breakTarget
+		d.breakTarget = x
+		d.findLabels(x.Body)
+		d.breakTarget = outer
+
+	case *ast.SelectStmt:
+		outer := d.breakTarget
+		d.breakTarget = x
+		d.findLabels(x.Body)
+		d.breakTarget = outer
+
+	case *ast.SwitchStmt:
+		outer := d.breakTarget
+		d.breakTarget = x
+		d.findLabels(x.Body)
+		d.breakTarget = outer
+
+	case *ast.TypeSwitchStmt:
+		outer := d.breakTarget
+		d.breakTarget = x
+		d.findLabels(x.Body)
+		d.breakTarget = outer
+
+	case *ast.CommClause:
+		for _, stmt := range x.Body {
+			d.findLabels(stmt)
+		}
+
+	case *ast.CaseClause:
+		for _, stmt := range x.Body {
+			d.findLabels(stmt)
+		}
+	}
+}
+
+// findDead walks the statement looking for dead code.
+// If d.reachable is false on entry, stmt itself is dead.
+// When findDead returns, d.reachable tells whether the
+// statement following stmt is reachable.
+func (d *deadState) findDead(stmt ast.Stmt) {
+	// Is this a labeled goto target?
+	// If so, assume it is reachable due to the goto.
+	// This is slightly conservative, in that we don't
+	// check that the goto is reachable, so
+	//	L: goto L
+	// will not provoke a warning.
+	// But it's good enough.
+	if x, isLabel := stmt.(*ast.LabeledStmt); isLabel && d.hasGoto[x.Label.Name] {
+		d.reachable = true
+	}
+
+	if !d.reachable {
+		switch stmt.(type) {
+		case *ast.EmptyStmt:
+			// do not warn about unreachable empty statements
+		default:
+			d.f.Bad(stmt.Pos(), "unreachable code")
+			d.reachable = true // silence error about next statement
+		}
+	}
+
+	switch x := stmt.(type) {
+	default:
+		d.f.Warnf(x.Pos(), "internal error in findDead: unexpected statement %T", x)
+
+	case *ast.AssignStmt,
+		*ast.BadStmt,
+		*ast.DeclStmt,
+		*ast.DeferStmt,
+		*ast.EmptyStmt,
+		*ast.GoStmt,
+		*ast.IncDecStmt,
+		*ast.SendStmt:
+		// no control flow
+
+	case *ast.BlockStmt:
+		for _, stmt := range x.List {
+			d.findDead(stmt)
+		}
+
+	case *ast.BranchStmt:
+		switch x.Tok {
+		case token.BREAK, token.GOTO, token.FALLTHROUGH:
+			d.reachable = false
+		case token.CONTINUE:
+			// NOTE: We accept "continue" statements as terminating.
+			// They are not necessary in the spec definition of terminating,
+			// because a continue statement cannot be the final statement
+			// before a return. But for the more general problem of syntactically
+			// identifying dead code, continue redirects control flow just
+			// like the other terminating statements.
+			d.reachable = false
+		}
+
+	case *ast.ExprStmt:
+		// Call to panic?
+		call, ok := x.X.(*ast.CallExpr)
+		if ok {
+			name, ok := call.Fun.(*ast.Ident)
+			if ok && name.Name == "panic" && name.Obj == nil {
+				d.reachable = false
+			}
+		}
+
+	case *ast.ForStmt:
+		d.findDead(x.Body)
+		d.reachable = x.Cond != nil || d.hasBreak[x]
+
+	case *ast.IfStmt:
+		d.findDead(x.Body)
+		if x.Else != nil {
+			r := d.reachable
+			d.reachable = true
+			d.findDead(x.Else)
+			d.reachable = d.reachable || r
+		} else {
+			// might not have executed if statement
+			d.reachable = true
+		}
+
+	case *ast.LabeledStmt:
+		d.findDead(x.Stmt)
+
+	case *ast.RangeStmt:
+		d.findDead(x.Body)
+		d.reachable = true
+
+	case *ast.ReturnStmt:
+		d.reachable = false
+
+	case *ast.SelectStmt:
+		// NOTE: Unlike switch and type switch below, we don't care
+		// whether a select has a default, because a select without a
+		// default blocks until one of the cases can run. That's different
+		// from a switch without a default, which behaves like it has
+		// a default with an empty body.
+		anyReachable := false
+		for _, comm := range x.Body.List {
+			d.reachable = true
+			for _, stmt := range comm.(*ast.CommClause).Body {
+				d.findDead(stmt)
+			}
+			anyReachable = anyReachable || d.reachable
+		}
+		d.reachable = anyReachable || d.hasBreak[x]
+
+	case *ast.SwitchStmt:
+		anyReachable := false
+		hasDefault := false
+		for _, cas := range x.Body.List {
+			cc := cas.(*ast.CaseClause)
+			if cc.List == nil {
+				hasDefault = true
+			}
+			d.reachable = true
+			for _, stmt := range cc.Body {
+				d.findDead(stmt)
+			}
+			anyReachable = anyReachable || d.reachable
+		}
+		d.reachable = anyReachable || d.hasBreak[x] || !hasDefault
+
+	case *ast.TypeSwitchStmt:
+		anyReachable := false
+		hasDefault := false
+		for _, cas := range x.Body.List {
+			cc := cas.(*ast.CaseClause)
+			if cc.List == nil {
+				hasDefault = true
+			}
+			d.reachable = true
+			for _, stmt := range cc.Body {
+				d.findDead(stmt)
+			}
+			anyReachable = anyReachable || d.reachable
+		}
+		d.reachable = anyReachable || d.hasBreak[x] || !hasDefault
+	}
+}

src/cmd/vet/doc.go

+// Copyright 2010 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.
+
+/*
+
+Vet examines Go source code and reports suspicious constructs, such as Printf
+calls whose arguments do not align with the format string. Vet uses heuristics
+that do not guarantee all reports are genuine problems, but it can find errors
+not caught by the compilers.
+
+It can be invoked three ways:
+
+By package, from the go tool:
+	go vet package/path/name
+vets the package whose path is provided.
+
+By files:
+	go tool vet source/directory/*.go
+vets the files named, all of which must be in the same package.
+
+By directory:
+	go tool vet source/directory
+recursively descends the directory, vetting each package it finds.
+
+Vet's exit code is 2 for erroneous invocation of the tool, 1 if a
+problem was reported, and 0 otherwise. Note that the tool does not
+check every possible problem and depends on unreliable heuristics
+so it should be used as guidance only, not as a firm indicator of
+program correctness.
+
+By default all checks are performed. If any flags are explicitly set
+to true, only those tests are run. Conversely, if any flag is
+explicitly set to false, only those tests are disabled.
+Thus -printf=true runs the printf check, -printf=false runs all checks
+except the printf check.
+
+Available checks:
+
+Printf family
+
+Flag: -printf
+
+Suspicious calls to functions in the Printf family, including any functions
+with these names, disregarding case:
+	Print Printf Println
+	Fprint Fprintf Fprintln
+	Sprint Sprintf Sprintln
+	Error Errorf
+	Fatal Fatalf
+	Log Logf
+	Panic Panicf Panicln
+If the function name ends with an 'f', the function is assumed to take
+a format descriptor string in the manner of fmt.Printf. If not, vet
+complains about arguments that look like format descriptor strings.
+
+It also checks for errors such as using a Writer as the first argument of
+Printf.
+
+Methods
+
+Flag: -methods
+
+Non-standard signatures for methods with familiar names, including:
+	Format GobEncode GobDecode MarshalJSON MarshalXML
+	Peek ReadByte ReadFrom ReadRune Scan Seek
+	UnmarshalJSON UnreadByte UnreadRune WriteByte
+	WriteTo
+
+Struct tags
+
+Flag: -structtags
+
+Struct tags that do not follow the format understood by reflect.StructTag.Get.
+Well-known encoding struct tags (json, xml) used with unexported fields.
+
+Unkeyed composite literals
+
+Flag: -composites
+
+Composite struct literals that do not use the field-keyed syntax.
+
+Assembly declarations
+
+Flag: -asmdecl
+
+Mismatches between assembly files and Go function declarations.
+
+Useless assignments
+
+Flag: -assign
+
+Check for useless assignments.
+
+Atomic mistakes
+
+Flag: -atomic
+
+Common mistaken usages of the sync/atomic package.
+
+Boolean conditions
+
+Flag: -bool
+
+Mistakes involving boolean operators.
+
+Build tags
+
+Flag: -buildtags
+
+Badly formed or misplaced +build tags.
+
+Copying locks
+
+Flag: -copylocks
+
+Locks that are erroneously passed by value.
+
+Nil function comparison
+
+Flag: -nilfunc
+
+Comparisons between functions and nil.
+
+Range loop variables
+
+Flag: -rangeloops
+
+Incorrect uses of range loop variables in closures.
+
+Unreachable code
+
+Flag: -unreachable
+
+Unreachable code.
+
+Shadowed variables
+
+Flag: -shadow=false (experimental; must be set explicitly)
+
+Variables that may have been unintentionally shadowed.
+
+Misuse of unsafe Pointers
+
+Flag: -unsafeptr
+
+Likely incorrect uses of unsafe.Pointer to convert integers to pointers.
+A conversion from uintptr to unsafe.Pointer is invalid if it implies that
+there is a uintptr-typed word in memory that holds a pointer value,
+because that word will be invisible to stack copying and to the garbage
+collector.
+
+Unused result of certain function calls
+
+Flag: -unusedresult
+
+Calls to well-known functions and methods that return a value that is
+discarded.  By default, this includes functions like fmt.Errorf and
+fmt.Sprintf and methods like String and Error. The flags -unusedfuncs
+and -unusedstringmethods control the set.
+
+Shifts
+
+Flag: -shift
+
+Shifts equal to or longer than the variable's length.
+
+Other flags
+
+These flags configure the behavior of vet:
+
+	-all (default true)
+		Check everything; disabled if any explicit check is requested.
+	-v
+		Verbose mode
+	-printfuncs
+		A comma-separated list of print-like functions to supplement
+		the standard list.  Each entry is in the form Name:N where N
+		is the zero-based argument position of the first argument
+		involved in the print: either the format or the first print
+		argument for non-formatted prints.  For example,
+		if you have Warn and Warnf functions that take an
+		io.Writer as their first argument, like Fprintf,
+			-printfuncs=Warn:1,Warnf:1
+	-shadowstrict
+		Whether to be strict about shadowing; can be noisy.
+	-test
+		For testing only: sets -all and -shadow.
+*/
+package main // import "golang.org/x/tools/cmd/vet"

src/cmd/vet/method.go

+// Copyright 2010 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.
+
+// This file contains the code to check canonical methods.
+
+package main
+
+import (
+	"fmt"
+	"go/ast"
+	"go/printer"
+	"strings"
+)
+
+func init() {
+	register("methods",
+		"check that canonically named methods are canonically defined",
+		checkCanonicalMethod,
+		funcDecl, interfaceType)
+}
+
+type MethodSig struct {
+	args    []string
+	results []string
+}
+
+// canonicalMethods lists the input and output types for Go methods
+// that are checked using dynamic interface checks.  Because the
+// checks are dynamic, such methods would not cause a compile error
+// if they have the wrong signature: instead the dynamic check would
+// fail, sometimes mysteriously.  If a method is found with a name listed
+// here but not the input/output types listed here, vet complains.
+//
+// A few of the canonical methods have very common names.
+// For example, a type might implement a Scan method that
+// has nothing to do with fmt.Scanner, but we still want to check
+// the methods that are intended to implement fmt.Scanner.
+// To do that, the arguments that have a = prefix are treated as
+// signals that the canonical meaning is intended: if a Scan
+// method doesn't have a fmt.ScanState as its first argument,
+// we let it go.  But if it does have a fmt.ScanState, then the
+// rest has to match.
+var canonicalMethods = map[string]MethodSig{
+	// "Flush": {{}, {"error"}}, // http.Flusher and jpeg.writer conflict
+	"Format":        {[]string{"=fmt.State", "rune"}, []string{}},                      // fmt.Formatter
+	"GobDecode":     {[]string{"[]byte"}, []string{"error"}},                           // gob.GobDecoder
+	"GobEncode":     {[]string{}, []string{"[]byte", "error"}},                         // gob.GobEncoder
+	"MarshalJSON":   {[]string{}, []string{"[]byte", "error"}},                         // json.Marshaler
+	"MarshalXML":    {[]string{"*xml.Encoder", "xml.StartElement"}, []string{"error"}}, // xml.Marshaler
+	"Peek":          {[]string{"=int"}, []string{"[]byte", "error"}},                   // image.reader (matching bufio.Reader)
+	"ReadByte":      {[]string{}, []string{"byte", "error"}},                           // io.ByteReader
+	"ReadFrom":      {[]string{"=io.Reader"}, []string{"int64", "error"}},              // io.ReaderFrom
+	"ReadRune":      {[]string{}, []string{"rune", "int", "error"}},                    // io.RuneReader
+	"Scan":          {[]string{"=fmt.ScanState", "rune"}, []string{"error"}},           // fmt.Scanner
+	"Seek":          {[]string{"=int64", "int"}, []string{"int64", "error"}},           // io.Seeker
+	"UnmarshalJSON": {[]string{"[]byte"}, []string{"error"}},                           // json.Unmarshaler
+	"UnmarshalXML":  {[]string{"*xml.Decoder", "xml.StartElement"}, []string{"error"}}, // xml.Unmarshaler
+	"UnreadByte":    {[]string{}, []string{"error"}},
+	"UnreadRune":    {[]string{}, []string{"error"}},
+	"WriteByte":     {[]string{"byte"}, []string{"error"}},                // jpeg.writer (matching bufio.Writer)
+	"WriteTo":       {[]string{"=io.Writer"}, []string{"int64", "error"}}, // io.WriterTo
+}
+
+func checkCanonicalMethod(f *File, node ast.Node) {
+	switch n := node.(type) {
+	case *ast.FuncDecl:
+		if n.Recv != nil {
+			canonicalMethod(f, n.Name, n.Type)
+		}
+	case *ast.InterfaceType:
+		for _, field := range n.Methods.List {
+			for _, id := range field.Names {
+				canonicalMethod(f, id, field.Type.(*ast.FuncType))
+			}
+		}
+	}
+}
+
+func canonicalMethod(f *File, id *ast.Ident, t *ast.FuncType) {
+	// Expected input/output.
+	expect, ok := canonicalMethods[id.Name]
+	if !ok {
+		return
+	}
+
+	// Actual input/output
+	args := typeFlatten(t.Params.List)
+	var results []ast.Expr
+	if t.Results != nil {
+		results = typeFlatten(t.Results.List)
+	}
+
+	// Do the =s (if any) all match?
+	if !f.matchParams(expect.args, args, "=") || !f.matchParams(expect.results, results, "=") {
+		return
+	}
+
+	// Everything must match.
+	if !f.matchParams(expect.args, args, "") || !f.matchParams(expect.results, results, "") {
+		expectFmt := id.Name + "(" + argjoin(expect.args) + ")"
+		if len(expect.results) == 1 {
+			expectFmt += " " + argjoin(expect.results)
+		} else if len(expect.results) > 1 {
+			expectFmt += " (" + argjoin(expect.results) + ")"
+		}
+
+		f.b.Reset()
+		if err := printer.Fprint(&f.b, f.fset, t); err != nil {
+			fmt.Fprintf(&f.b, "<%s>", err)
+		}
+		actual := f.b.String()
+		actual = strings.TrimPrefix(actual, "func")
+		actual = id.Name + actual
+
+		f.Badf(id.Pos(), "method %s should have signature %s", actual, expectFmt)
+	}
+}
+
+func argjoin(x []string) string {
+	y := make([]string, len(x))
+	for i, s := range x {
+		if s[0] == '=' {
+			s = s[1:]
+		}
+		y[i] = s
+	}
+	return strings.Join(y, ", ")
+}
+
+// Turn parameter list into slice of types
+// (in the ast, types are Exprs).
+// Have to handle f(int, bool) and f(x, y, z int)
+// so not a simple 1-to-1 conversion.
+func typeFlatten(l []*ast.Field) []ast.Expr {
+	var t []ast.Expr
+	for _, f := range l {
+		if len(f.Names) == 0 {
+			t = append(t, f.Type)
+			continue
+		}
+		for _ = range f.Names {
+			t = append(t, f.Type)
+		}
+	}
+	return t
+}
+
+// Does each type in expect with the given prefix match the corresponding type in actual?
+func (f *File) matchParams(expect []string, actual []ast.Expr, prefix string) bool {
+	for i, x := range expect {
+		if !strings.HasPrefix(x, prefix) {
+			continue
+		}
+		if i >= len(actual) {
+			return false
+		}
+		if !f.matchParamType(x, actual[i]) {
+			return false
+		}
+	}
+	if prefix == "" && len(actual) > len(expect) {
+		return false
+	}
+	return true
+}
+
+// Does this one type match?
+func (f *File) matchParamType(expect string, actual ast.Expr) bool {
+	if strings.HasPrefix(expect, "=") {
+		expect = expect[1:]
+	}
+	// Strip package name if we're in that package.
+	if n := len(f.file.Name.Name); len(expect) > n && expect[:n] == f.file.Name.Name && expect[n] == '.' {
+		expect = expect[n+1:]
+	}
+
+	// Overkill but easy.
+	f.b.Reset()
+	printer.Fprint(&f.b, f.fset, actual)
+	return f.b.String() == expect
+}

src/cmd/vet/nilfunc.go

+// 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.
+
+/*
+This file contains the code to check for useless function comparisons.
+A useless comparison is one like f == nil as opposed to f() == nil.
+*/
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+
+	"golang.org/x/tools/go/types"
+)
+
+func init() {
+	register("nilfunc",
+		"check for comparisons between functions and nil",
+		checkNilFuncComparison,
+		binaryExpr)
+}
+
+func checkNilFuncComparison(f *File, node ast.Node) {
+	e := node.(*ast.BinaryExpr)
+
+	// Only want == or != comparisons.
+	if e.Op != token.EQL && e.Op != token.NEQ {
+		return
+	}
+
+	// Only want comparisons with a nil identifier on one side.
+	var e2 ast.Expr
+	switch {
+	case f.isNil(e.X):
+		e2 = e.Y
+	case f.isNil(e.Y):
+		e2 = e.X
+	default:
+		return
+	}
+
+	// Only want identifiers or selector expressions.
+	var obj types.Object
+	switch v := e2.(type) {
+	case *ast.Ident:
+		obj = f.pkg.uses[v]
+	case *ast.SelectorExpr:
+		obj = f.pkg.uses[v.Sel]
+	default:
+		return
+	}
+
+	// Only want functions.
+	if _, ok := obj.(*types.Func); !ok {
+		return
+	}
+
+	f.Badf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ)
+}
+
+// isNil reports whether the provided expression is the built-in nil
+// identifier.
+func (f *File) isNil(e ast.Expr) bool {
+	return f.pkg.types[e].Type == types.Typ[types.UntypedNil]
+}

src/cmd/vet/rangeloop.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+This file contains the code to check range loop variables bound inside function
+literals that are deferred or launched in new goroutines. We only check
+instances where the defer or go statement is the last statement in the loop
+body, as otherwise we would need whole program analysis.
+
+For example:
+
+	for i, v := range s {
+		go func() {
+			println(i, v) // not what you might expect
+		}()
+	}
+
+See: http://golang.org/doc/go_faq.html#closures_and_goroutines
+*/
+
+package main
+
+import "go/ast"
+
+func init() {
+	register("rangeloops",
+		"check that range loop variables are used correctly",
+		checkRangeLoop,
+		rangeStmt)
+}
+
+// checkRangeLoop walks the body of the provided range statement, checking if
+// its index or value variables are used unsafely inside goroutines or deferred
+// function literals.
+func checkRangeLoop(f *File, node ast.Node) {
+	n := node.(*ast.RangeStmt)
+	key, _ := n.Key.(*ast.Ident)
+	val, _ := n.Value.(*ast.Ident)
+	if key == nil && val == nil {
+		return
+	}
+	sl := n.Body.List
+	if len(sl) == 0 {
+		return
+	}
+	var last *ast.CallExpr
+	switch s := sl[len(sl)-1].(type) {
+	case *ast.GoStmt:
+		last = s.Call
+	case *ast.DeferStmt:
+		last = s.Call
+	default:
+		return
+	}
+	lit, ok := last.Fun.(*ast.FuncLit)
+	if !ok {
+		return
+	}
+	ast.Inspect(lit.Body, func(n ast.Node) bool {
+		id, ok := n.(*ast.Ident)
+		if !ok || id.Obj == nil {
+			return true
+		}
+		if key != nil && id.Obj == key.Obj || val != nil && id.Obj == val.Obj {
+			f.Bad(id.Pos(), "range variable", id.Name, "captured by func literal")
+		}
+		return true
+	})
+}

src/cmd/vet/shadow.go

+// 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.
+
+/*
+This file contains the code to check for shadowed variables.
+A shadowed variable is a variable declared in an inner scope
+with the same name and type as a variable in an outer scope,
+and where the outer variable is mentioned after the inner one
+is declared.
+
+(This definition can be refined; the module generates too many
+false positives and is not yet enabled by default.)
+
+For example:
+
+	func BadRead(f *os.File, buf []byte) error {
+		var err error
+		for {
+			n, err := f.Read(buf) // shadows the function variable 'err'
+			if err != nil {
+				break // causes return of wrong value
+			}
+			foo(buf)
+		}
+		return err
+	}
+
+*/
+
+package main
+
+import (
+	"flag"
+	"go/ast"
+	"go/token"
+
+	"golang.org/x/tools/go/types"
+)
+
+var strictShadowing = flag.Bool("shadowstrict", false, "whether to be strict about shadowing; can be noisy")
+
+func init() {
+	register("shadow",
+		"check for shadowed variables (experimental; must be set explicitly)",
+		checkShadow,
+		assignStmt, genDecl)
+	experimental["shadow"] = true
+}
+
+func checkShadow(f *File, node ast.Node) {
+	switch n := node.(type) {
+	case *ast.AssignStmt:
+		checkShadowAssignment(f, n)
+	case *ast.GenDecl:
+		checkShadowDecl(f, n)
+	}
+}
+
+// Span stores the minimum range of byte positions in the file in which a
+// given variable (types.Object) is mentioned. It is lexically defined: it spans
+// from the beginning of its first mention to the end of its last mention.
+// A variable is considered shadowed (if *strictShadowing is off) only if the
+// shadowing variable is declared within the span of the shadowed variable.
+// In other words, if a variable is shadowed but not used after the shadowed
+// variable is declared, it is inconsequential and not worth complaining about.
+// This simple check dramatically reduces the nuisance rate for the shadowing
+// check, at least until something cleverer comes along.
+//
+// One wrinkle: A "naked return" is a silent use of a variable that the Span
+// will not capture, but the compilers catch naked returns of shadowed
+// variables so we don't need to.
+//
+// Cases this gets wrong (TODO):
+// - If a for loop's continuation statement mentions a variable redeclared in
+// the block, we should complain about it but don't.
+// - A variable declared inside a function literal can falsely be identified
+// as shadowing a variable in the outer function.
+//
+type Span struct {
+	min token.Pos
+	max token.Pos
+}
+
+// contains reports whether the position is inside the span.
+func (s Span) contains(pos token.Pos) bool {
+	return s.min <= pos && pos < s.max
+}
+
+// growSpan expands the span for the object to contain the instance represented
+// by the identifier.
+func (pkg *Package) growSpan(ident *ast.Ident, obj types.Object) {
+	if *strictShadowing {
+		return // No need
+	}
+	pos := ident.Pos()
+	end := ident.End()
+	span, ok := pkg.spans[obj]
+	if ok {
+		if span.min > pos {
+			span.min = pos
+		}
+		if span.max < end {
+			span.max = end
+		}
+	} else {
+		span = Span{pos, end}
+	}
+	pkg.spans[obj] = span
+}
+
+// checkShadowAssignment checks for shadowing in a short variable declaration.
+func checkShadowAssignment(f *File, a *ast.AssignStmt) {
+	if a.Tok != token.DEFINE {
+		return
+	}
+	if f.idiomaticShortRedecl(a) {
+		return
+	}
+	for _, expr := range a.Lhs {
+		ident, ok := expr.(*ast.Ident)
+		if !ok {
+			f.Badf(expr.Pos(), "invalid AST: short variable declaration of non-identifier")
+			return
+		}
+		checkShadowing(f, ident)
+	}
+}
+
+// idiomaticShortRedecl reports whether this short declaration can be ignored for
+// the purposes of shadowing, that is, that any redeclarations it contains are deliberate.
+func (f *File) idiomaticShortRedecl(a *ast.AssignStmt) bool {
+	// Don't complain about deliberate redeclarations of the form
+	//	i := i
+	// Such constructs are idiomatic in range loops to create a new variable
+	// for each iteration. Another example is
+	//	switch n := n.(type)
+	if len(a.Rhs) != len(a.Lhs) {
+		return false
+	}
+	// We know it's an assignment, so the LHS must be all identifiers. (We check anyway.)
+	for i, expr := range a.Lhs {
+		lhs, ok := expr.(*ast.Ident)
+		if !ok {
+			f.Badf(expr.Pos(), "invalid AST: short variable declaration of non-identifier")
+			return true // Don't do any more processing.
+		}
+		switch rhs := a.Rhs[i].(type) {
+		case *ast.Ident:
+			if lhs.Name != rhs.Name {
+				return false
+			}
+		case *ast.TypeAssertExpr:
+			if id, ok := rhs.X.(*ast.Ident); ok {
+				if lhs.Name != id.Name {
+					return false
+				}
+			}
+		}
+	}
+	return true
+}
+
+// idiomaticRedecl reports whether this declaration spec can be ignored for
+// the purposes of shadowing, that is, that any redeclarations it contains are deliberate.
+func (f *File) idiomaticRedecl(d *ast.ValueSpec) bool {
+	// Don't complain about deliberate redeclarations of the form
+	//	var i, j = i, j
+	if len(d.Names) != len(d.Values) {
+		return false
+	}
+	for i, lhs := range d.Names {
+		if rhs, ok := d.Values[i].(*ast.Ident); ok {
+			if lhs.Name != rhs.Name {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// checkShadowDecl checks for shadowing in a general variable declaration.
+func checkShadowDecl(f *File, d *ast.GenDecl) {
+	if d.Tok != token.VAR {
+		return
+	}
+	for _, spec := range d.Specs {
+		valueSpec, ok := spec.(*ast.ValueSpec)
+		if !ok {
+			f.Badf(spec.Pos(), "invalid AST: var GenDecl not ValueSpec")
+			return
+		}
+		// Don't complain about deliberate redeclarations of the form
+		//	var i = i
+		if f.idiomaticRedecl(valueSpec) {
+			return
+		}
+		for _, ident := range valueSpec.Names {
+			checkShadowing(f, ident)
+		}
+	}
+}
+
+// checkShadowing checks whether the identifier shadows an identifier in an outer scope.
+func checkShadowing(f *File, ident *ast.Ident) {
+	if ident.Name == "_" {
+		// Can't shadow the blank identifier.
+		return
+	}
+	obj := f.pkg.defs[ident]
+	if obj == nil {
+		return
+	}
+	// obj.Parent.Parent is the surrounding scope. If we can find another declaration
+	// starting from there, we have a shadowed identifier.
+	_, shadowed := obj.Parent().Parent().LookupParent(obj.Name())
+	if shadowed == nil {
+		return
+	}
+	// Don't complain if it's shadowing a universe-declared identifier; that's fine.
+	if shadowed.Parent() == types.Universe {
+		return
+	}
+	if *strictShadowing {
+		// The shadowed identifier must appear before this one to be an instance of shadowing.
+		if shadowed.Pos() > ident.Pos() {
+			return
+		}
+	} else {
+		// Don't complain if the span of validity of the shadowed identifier doesn't include
+		// the shadowing identifier.
+		span, ok := f.pkg.spans[shadowed]
+		if !ok {
+			f.Badf(ident.Pos(), "internal error: no range for %s", ident.Name)
+			return
+		}
+		if !span.contains(ident.Pos()) {
+			return
+		}
+	}
+	// Don't complain if the types differ: that implies the programmer really wants two different things.
+	if types.Identical(obj.Type(), shadowed.Type()) {
+		f.Badf(ident.Pos(), "declaration of %s shadows declaration at %s", obj.Name(), f.loc(shadowed.Pos()))
+	}
+}

src/cmd/vet/shift.go

+// Copyright 2014 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.
+
+/*
+This file contains the code to check for suspicious shifts.
+*/
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+
+	"golang.org/x/tools/go/exact"
+	"golang.org/x/tools/go/types"
+)
+
+func init() {
+	register("shift",
+		"check for useless shifts",
+		checkShift,
+		binaryExpr, assignStmt)
+}
+
+func checkShift(f *File, node ast.Node) {
+	switch node := node.(type) {
+	case *ast.BinaryExpr:
+		if node.Op == token.SHL || node.Op == token.SHR {
+			checkLongShift(f, node, node.X, node.Y)
+		}
+	case *ast.AssignStmt:
+		if len(node.Lhs) != 1 || len(node.Rhs) != 1 {
+			return
+		}
+		if node.Tok == token.SHL_ASSIGN || node.Tok == token.SHR_ASSIGN {
+			checkLongShift(f, node, node.Lhs[0], node.Rhs[0])
+		}
+	}
+}
+
+// checkLongShift checks if shift or shift-assign operations shift by more than
+// the length of the underlying variable.
+func checkLongShift(f *File, node ast.Node, x, y ast.Expr) {
+	v := f.pkg.types[y].Value
+	if v == nil {
+		return
+	}
+	amt, ok := exact.Int64Val(v)
+	if !ok {
+		return
+	}
+	t := f.pkg.types[x].Type
+	if t == nil {
+		return
+	}
+	b, ok := t.Underlying().(*types.Basic)
+	if !ok {
+		return
+	}
+	var size int64
+	var msg string
+	switch b.Kind() {
+	case types.Uint8, types.Int8:
+		size = 8
+	case types.Uint16, types.Int16:
+		size = 16
+	case types.Uint32, types.Int32:
+		size = 32
+	case types.Uint64, types.Int64:
+		size = 64
+	case types.Int, types.Uint, types.Uintptr:
+		// These types may be as small as 32 bits, but no smaller.
+		size = 32
+		msg = "might be "
+	default:
+		return
+	}
+	if amt >= size {
+		ident := f.gofmt(x)
+		f.Badf(node.Pos(), "%s %stoo small for shift of %d", ident, msg, amt)
+	}
+}

src/cmd/vet/structtag.go

+// Copyright 2010 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.
+
+// This file contains the test for canonical struct tags.
+
+package main
+
+import (
+	"errors"
+	"go/ast"
+	"reflect"
+	"strconv"
+)
+
+func init() {
+	register("structtags",
+		"check that struct field tags have canonical format and apply to exported fields as needed",
+		checkCanonicalFieldTag,
+		field)
+}
+
+// checkCanonicalFieldTag checks a struct field tag.
+func checkCanonicalFieldTag(f *File, node ast.Node) {
+	field := node.(*ast.Field)
+	if field.Tag == nil {
+		return
+	}
+
+	tag, err := strconv.Unquote(field.Tag.Value)
+	if err != nil {
+		f.Badf(field.Pos(), "unable to read struct tag %s", field.Tag.Value)
+		return
+	}
+
+	if err := validateStructTag(tag); err != nil {
+		f.Badf(field.Pos(), "struct field tag %s not compatible with reflect.StructTag.Get: %s", field.Tag.Value, err)
+	}
+
+	// Check for use of json or xml tags with unexported fields.
+
+	// Embedded struct. Nothing to do for now, but that
+	// may change, depending on what happens with issue 7363.
+	if len(field.Names) == 0 {
+		return
+	}
+
+	if field.Names[0].IsExported() {
+		return
+	}
+
+	st := reflect.StructTag(tag)
+	for _, enc := range [...]string{"json", "xml"} {
+		if st.Get(enc) != "" {
+			f.Badf(field.Pos(), "struct field %s has %s tag but is not exported", field.Names[0].Name, enc)
+			return
+		}
+	}
+}
+
+var (
+	errTagSyntax      = errors.New("bad syntax for struct tag pair")
+	errTagKeySyntax   = errors.New("bad syntax for struct tag key")
+	errTagValueSyntax = errors.New("bad syntax for struct tag value")
+)
+
+// validateStructTag parses the struct tag and returns an error if it is not
+// in the canonical format, which is a space-separated list of key:"value"
+// settings. The value may contain spaces.
+func validateStructTag(tag string) error {
+	// This code is based on the StructTag.Get code in package reflect.
+
+	for tag != "" {
+		// Skip leading space.
+		i := 0
+		for i < len(tag) && tag[i] == ' ' {
+			i++
+		}
+		tag = tag[i:]
+		if tag == "" {
+			break
+		}
+
+		// Scan to colon. A space, a quote or a control character is a syntax error.
+		// Strictly speaking, control chars include the range [0x7f, 0x9f], not just
+		// [0x00, 0x1f], but in practice, we ignore the multi-byte control characters
+		// as it is simpler to inspect the tag's bytes than the tag's runes.
+		i = 0
+		for i < len(tag) && tag[i] > ' ' && tag[i] != ':' && tag[i] != '"' && tag[i] != 0x7f {
+			i++
+		}
+		if i == 0 {
+			return errTagKeySyntax
+		}
+		if i+1 >= len(tag) || tag[i] != ':' {
+			return errTagSyntax
+		}
+		if tag[i+1] != '"' {
+			return errTagValueSyntax
+		}
+		tag = tag[i+1:]
+
+		// Scan quoted string to find value.
+		i = 1
+		for i < len(tag) && tag[i] != '"' {
+			if tag[i] == '\\' {
+				i++
+			}
+			i++
+		}
+		if i >= len(tag) {
+			return errTagValueSyntax
+		}
+		qvalue := string(tag[:i+1])
+		tag = tag[i+1:]
+
+		if _, err := strconv.Unquote(qvalue); err != nil {
+			return errTagValueSyntax
+		}
+	}
+	return nil
+}

src/cmd/vet/testdata/asm.go

+// Copyright 2010 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.
+
+// +build ignore
+
+// This file contains declarations to test the assembly in test_asm.s.
+
+package testdata
+
+func arg1(x int8, y uint8)
+func arg2(x int16, y uint16)
+func arg4(x int32, y uint32)
+func arg8(x int64, y uint64)
+func argint(x int, y uint)
+func argptr(x *byte, y *byte, c chan int, m map[int]int, f func())
+func argstring(x, y string)
+func argslice(x, y []string)
+func argiface(x interface{}, y interface {
+	m()
+})
+func returnint() int
+func returnbyte(x int) byte
+func returnnamed(x byte) (r1 int, r2 int16, r3 string, r4 byte)
+func returnintmissing() int
+func leaf(x, y int) int
+
+func noprof(x int)
+func dupok(x int)
+func nosplit(x int)
+func rodata(x int)
+func noptr(x int)
+func wrapper(x int)

src/cmd/vet/testdata/asm3.s

+// 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.
+
+// +build arm
+// +build vet_test
+
+TEXT ·arg1(SB),0,$0-2
+	MOVB	x+0(FP), AX
+	MOVB	y+1(FP), BX
+	MOVH	x+0(FP), AX // ERROR "\[arm\] arg1: invalid MOVH of x\+0\(FP\); int8 is 1-byte value"
+	MOVH	y+1(FP), AX // ERROR "invalid MOVH of y\+1\(FP\); uint8 is 1-byte value"
+	MOVW	x+0(FP), AX // ERROR "invalid MOVW of x\+0\(FP\); int8 is 1-byte value"
+	MOVW	y+1(FP), AX // ERROR "invalid MOVW of y\+1\(FP\); uint8 is 1-byte value"
+	MOVB	x+1(FP), AX // ERROR "invalid offset x\+1\(FP\); expected x\+0\(FP\)"
+	MOVB	y+2(FP), AX // ERROR "invalid offset y\+2\(FP\); expected y\+1\(FP\)"
+	MOVB	8(R13), AX // ERROR "8\(R13\) should be x\+0\(FP\)"
+	MOVB	9(R13), AX // ERROR "9\(R13\) should be y\+1\(FP\)"
+	MOVB	10(R13), AX // ERROR "use of 10\(R13\) points beyond argument frame"
+	RET
+
+TEXT ·arg2(SB),0,$0-4
+	MOVB	x+0(FP), AX // ERROR "arg2: invalid MOVB of x\+0\(FP\); int16 is 2-byte value"
+	MOVB	y+2(FP), AX // ERROR "invalid MOVB of y\+2\(FP\); uint16 is 2-byte value"
+	MOVH	x+0(FP), AX
+	MOVH	y+2(FP), BX
+	MOVW	x+0(FP), AX // ERROR "invalid MOVW of x\+0\(FP\); int16 is 2-byte value"
+	MOVW	y+2(FP), AX // ERROR "invalid MOVW of y\+2\(FP\); uint16 is 2-byte value"
+	MOVH	x+2(FP), AX // ERROR "invalid offset x\+2\(FP\); expected x\+0\(FP\)"
+	MOVH	y+0(FP), AX // ERROR "invalid offset y\+0\(FP\); expected y\+2\(FP\)"
+	RET
+
+TEXT ·arg4(SB),0,$0-2 // ERROR "arg4: wrong argument size 2; expected \$\.\.\.-8"
+	MOVB	x+0(FP), AX // ERROR "invalid MOVB of x\+0\(FP\); int32 is 4-byte value"
+	MOVB	y+4(FP), BX // ERROR "invalid MOVB of y\+4\(FP\); uint32 is 4-byte value"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); int32 is 4-byte value"
+	MOVH	y+4(FP), AX // ERROR "invalid MOVH of y\+4\(FP\); uint32 is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVW	y+4(FP), AX
+	MOVW	x+4(FP), AX // ERROR "invalid offset x\+4\(FP\); expected x\+0\(FP\)"
+	MOVW	y+2(FP), AX // ERROR "invalid offset y\+2\(FP\); expected y\+4\(FP\)"
+	RET
+
+TEXT ·arg8(SB),7,$0-2 // ERROR "wrong argument size 2; expected \$\.\.\.-16"
+	MOVB	x+0(FP), AX // ERROR "invalid MOVB of x\+0\(FP\); int64 is 8-byte value"
+	MOVB	y+8(FP), BX // ERROR "invalid MOVB of y\+8\(FP\); uint64 is 8-byte value"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); int64 is 8-byte value"
+	MOVH	y+8(FP), AX // ERROR "invalid MOVH of y\+8\(FP\); uint64 is 8-byte value"
+	MOVW	x+0(FP), AX // ERROR "invalid MOVW of x\+0\(FP\); int64 is 8-byte value containing x_lo\+0\(FP\) and x_hi\+4\(FP\)"
+	MOVW	x_lo+0(FP), AX
+	MOVW	x_hi+4(FP), AX
+	MOVW	y+8(FP), AX // ERROR "invalid MOVW of y\+8\(FP\); uint64 is 8-byte value containing y_lo\+8\(FP\) and y_hi\+12\(FP\)"
+	MOVW	y_lo+8(FP), AX
+	MOVW	y_hi+12(FP), AX
+	MOVQ	x+0(FP), AX
+	MOVQ	y+8(FP), AX
+	MOVQ	x+8(FP), AX // ERROR "invalid offset x\+8\(FP\); expected x\+0\(FP\)"
+	MOVQ	y+2(FP), AX // ERROR "invalid offset y\+2\(FP\); expected y\+8\(FP\)"
+	RET
+
+TEXT ·argint(SB),0,$0-2 // ERROR "wrong argument size 2; expected \$\.\.\.-8"
+	MOVB	x+0(FP), AX // ERROR "invalid MOVB of x\+0\(FP\); int is 4-byte value"
+	MOVB	y+4(FP), BX // ERROR "invalid MOVB of y\+4\(FP\); uint is 4-byte value"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); int is 4-byte value"
+	MOVH	y+4(FP), AX // ERROR "invalid MOVH of y\+4\(FP\); uint is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVW	y+4(FP), AX
+	MOVQ	x+4(FP), AX // ERROR "invalid offset x\+4\(FP\); expected x\+0\(FP\)"
+	MOVQ	y+2(FP), AX // ERROR "invalid offset y\+2\(FP\); expected y\+4\(FP\)"
+	RET
+
+TEXT ·argptr(SB),7,$0-2 // ERROR "wrong argument size 2; expected \$\.\.\.-20"
+	MOVB	x+0(FP), AX // ERROR "invalid MOVB of x\+0\(FP\); \*byte is 4-byte value"
+	MOVB	y+4(FP), BX // ERROR "invalid MOVB of y\+4\(FP\); \*byte is 4-byte value"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); \*byte is 4-byte value"
+	MOVH	y+4(FP), AX // ERROR "invalid MOVH of y\+4\(FP\); \*byte is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVW	y+4(FP), AX
+	MOVQ	x+4(FP), AX // ERROR "invalid offset x\+4\(FP\); expected x\+0\(FP\)"
+	MOVQ	y+2(FP), AX // ERROR "invalid offset y\+2\(FP\); expected y\+4\(FP\)"
+	MOVH	c+8(FP), AX // ERROR "invalid MOVH of c\+8\(FP\); chan int is 4-byte value"
+	MOVH	m+12(FP), AX // ERROR "invalid MOVH of m\+12\(FP\); map\[int\]int is 4-byte value"
+	MOVH	f+16(FP), AX // ERROR "invalid MOVH of f\+16\(FP\); func\(\) is 4-byte value"
+	RET
+
+TEXT ·argstring(SB),0,$16 // ERROR "wrong argument size 0; expected \$\.\.\.-16"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); string base is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVH	x_base+0(FP), AX // ERROR "invalid MOVH of x_base\+0\(FP\); string base is 4-byte value"
+	MOVW	x_base+0(FP), AX
+	MOVH	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVW	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVQ	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVH	x_len+4(FP), AX // ERROR "invalid MOVH of x_len\+4\(FP\); string len is 4-byte value"
+	MOVW	x_len+4(FP), AX
+	MOVQ	y+0(FP), AX // ERROR "invalid offset y\+0\(FP\); expected y\+8\(FP\)"
+	MOVQ	y_len+4(FP), AX // ERROR "invalid offset y_len\+4\(FP\); expected y_len\+12\(FP\)"
+	RET
+
+TEXT ·argslice(SB),0,$24 // ERROR "wrong argument size 0; expected \$\.\.\.-24"
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); slice base is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVH	x_base+0(FP), AX // ERROR "invalid MOVH of x_base\+0\(FP\); slice base is 4-byte value"
+	MOVW	x_base+0(FP), AX
+	MOVH	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVW	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVQ	x_len+0(FP), AX // ERROR "invalid offset x_len\+0\(FP\); expected x_len\+4\(FP\)"
+	MOVH	x_len+4(FP), AX // ERROR "invalid MOVH of x_len\+4\(FP\); slice len is 4-byte value"
+	MOVW	x_len+4(FP), AX
+	MOVH	x_cap+0(FP), AX // ERROR "invalid offset x_cap\+0\(FP\); expected x_cap\+8\(FP\)"
+	MOVW	x_cap+0(FP), AX // ERROR "invalid offset x_cap\+0\(FP\); expected x_cap\+8\(FP\)"
+	MOVQ	x_cap+0(FP), AX // ERROR "invalid offset x_cap\+0\(FP\); expected x_cap\+8\(FP\)"
+	MOVH	x_cap+8(FP), AX // ERROR "invalid MOVH of x_cap\+8\(FP\); slice cap is 4-byte value"
+	MOVW	x_cap+8(FP), AX
+	MOVQ	y+0(FP), AX // ERROR "invalid offset y\+0\(FP\); expected y\+12\(FP\)"
+	MOVQ	y_len+4(FP), AX // ERROR "invalid offset y_len\+4\(FP\); expected y_len\+16\(FP\)"
+	MOVQ	y_cap+8(FP), AX // ERROR "invalid offset y_cap\+8\(FP\); expected y_cap\+20\(FP\)"
+	RET
+
+TEXT ·argiface(SB),0,$0-16
+	MOVH	x+0(FP), AX // ERROR "invalid MOVH of x\+0\(FP\); interface type is 4-byte value"
+	MOVW	x+0(FP), AX
+	MOVH	x_type+0(FP), AX // ERROR "invalid MOVH of x_type\+0\(FP\); interface type is 4-byte value"
+	MOVW	x_type+0(FP), AX
+	MOVQ	x_itable+0(FP), AX // ERROR "unknown variable x_itable; offset 0 is x_type\+0\(FP\)"
+	MOVQ	x_itable+1(FP), AX // ERROR "unknown variable x_itable; offset 1 is x_type\+0\(FP\)"
+	MOVH	x_data+0(FP), AX // ERROR "invalid offset x_data\+0\(FP\); expected x_data\+4\(FP\)"
+	MOVW	x_data+0(FP), AX // ERROR "invalid offset x_data\+0\(FP\); expected x_data\+4\(FP\)"
+	MOVQ	x_data+0(FP), AX // ERROR "invalid offset x_data\+0\(FP\); expected x_data\+4\(FP\)"
+	MOVH	x_data+4(FP), AX // ERROR "invalid MOVH of x_data\+4\(FP\); interface data is 4-byte value"
+	MOVW	x_data+4(FP), AX
+	MOVH	y+8(FP), AX // ERROR "invalid MOVH of y\+8\(FP\); interface itable is 4-byte value"
+	MOVW	y+8(FP), AX
+	MOVH	y_itable+8(FP), AX // ERROR "invalid MOVH of y_itable\+8\(FP\); interface itable is 4-byte value"
+	MOVW	y_itable+8(FP), AX
+	MOVQ	y_type+8(FP), AX // ERROR "unknown variable y_type; offset 8 is y_itable\+8\(FP\)"
+	MOVH	y_data+8(FP), AX // ERROR "invalid offset y_data\+8\(FP\); expected y_data\+12\(FP\)"
+	MOVW	y_data+8(FP), AX // ERROR "invalid offset y_data\+8\(FP\); expected y_data\+12\(FP\)"
+	MOVQ	y_data+8(FP), AX // ERROR "invalid offset y_data\+8\(FP\); expected y_data\+12\(FP\)"
+	MOVH	y_data+12(FP), AX // ERROR "invalid MOVH of y_data\+12\(FP\); interface data is 4-byte value"
+	MOVW	y_data+12(FP), AX
+	RET
+
+TEXT ·returnint(SB),0,$0-4
+	MOVB	AX, ret+0(FP) // ERROR "invalid MOVB of ret\+0\(FP\); int is 4-byte value"
+	MOVH	AX, ret+0(FP) // ERROR "invalid MOVH of ret\+0\(FP\); int is 4-byte value"
+	MOVW	AX, ret+0(FP)
+	MOVQ	AX, ret+1(FP) // ERROR "invalid offset ret\+1\(FP\); expected ret\+0\(FP\)"
+	MOVQ	AX, r+0(FP) // ERROR "unknown variable r; offset 0 is ret\+0\(FP\)"
+	RET
+
+TEXT ·returnbyte(SB),0,$0-5
+	MOVW	x+0(FP), AX
+	MOVB	AX, ret+4(FP)
+	MOVH	AX, ret+4(FP) // ERROR "invalid MOVH of ret\+4\(FP\); byte is 1-byte value"
+	MOVW	AX, ret+4(FP) // ERROR "invalid MOVW of ret\+4\(FP\); byte is 1-byte value"
+	MOVB	AX, ret+3(FP) // ERROR "invalid offset ret\+3\(FP\); expected ret\+4\(FP\)"
+	RET
+
+TEXT ·returnnamed(SB),0,$0-21
+	MOVB	x+0(FP), AX
+	MOVW	AX, r1+4(FP)
+	MOVH	AX, r2+8(FP)
+	MOVW	AX, r3+12(FP)
+	MOVW	AX, r3_base+12(FP)
+	MOVW	AX, r3_len+16(FP)
+	MOVB	AX, r4+20(FP)
+	MOVB	AX, r1+4(FP) // ERROR "invalid MOVB of r1\+4\(FP\); int is 4-byte value"
+	RET
+
+TEXT ·returnintmissing(SB),0,$0-4
+	RET // ERROR "RET without writing to 4-byte ret\+0\(FP\)"
+
+TEXT ·leaf(SB),0,$-4-12
+	MOVW	x+0(FP), AX
+	MOVW	y+4(FP), AX
+	MOVW	AX, ret+8(FP)
+	RET

src/cmd/vet/testdata/asm4.s

+// 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.
+
+// +build amd64
+// +build vet_test
+
+// Test cases for symbolic NOSPLIT etc. on TEXT symbols.
+
+TEXT ·noprof(SB),NOPROF,$0-8
+	RET
+
+TEXT ·dupok(SB),DUPOK,$0-8
+	RET
+
+TEXT ·nosplit(SB),NOSPLIT,$0
+	RET
+
+TEXT ·rodata(SB),RODATA,$0-8
+	RET
+
+TEXT ·noptr(SB),NOPTR|NOSPLIT,$0
+	RET
+
+TEXT ·wrapper(SB),WRAPPER,$0-8
+	RET

src/cmd/vet/testdata/assign.go

+// 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.
+
+// This file contains tests for the useless-assignment checker.
+
+package testdata
+
+type ST struct {
+	x int
+}
+
+func (s *ST) SetX(x int) {
+	// Accidental self-assignment; it should be "s.x = x"
+	x = x // ERROR "self-assignment of x to x"
+	// Another mistake
+	s.x = s.x // ERROR "self-assignment of s.x to s.x"
+}

src/cmd/vet/testdata/atomic.go

+// 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.
+
+// This file contains tests for the atomic checker.
+
+package testdata
+
+import (
+	"sync/atomic"
+)
+
+type Counter uint64
+
+func AtomicTests() {
+	x := uint64(1)
+	x = atomic.AddUint64(&x, 1)        // ERROR "direct assignment to atomic value"
+	_, x = 10, atomic.AddUint64(&x, 1) // ERROR "direct assignment to atomic value"
+	x, _ = atomic.AddUint64(&x, 1), 10 // ERROR "direct assignment to atomic value"
+
+	y := &x
+	*y = atomic.AddUint64(y, 1) // ERROR "direct assignment to atomic value"
+
+	var su struct{ Counter uint64 }
+	su.Counter = atomic.AddUint64(&su.Counter, 1) // ERROR "direct assignment to atomic value"
+	z1 := atomic.AddUint64(&su.Counter, 1)
+	_ = z1 // Avoid err "z declared and not used"
+
+	var sp struct{ Counter *uint64 }
+	*sp.Counter = atomic.AddUint64(sp.Counter, 1) // ERROR "direct assignment to atomic value"
+	z2 := atomic.AddUint64(sp.Counter, 1)
+	_ = z2 // Avoid err "z declared and not used"
+
+	au := []uint64{10, 20}
+	au[0] = atomic.AddUint64(&au[0], 1) // ERROR "direct assignment to atomic value"
+	au[1] = atomic.AddUint64(&au[0], 1)
+
+	ap := []*uint64{&au[0], &au[1]}
+	*ap[0] = atomic.AddUint64(ap[0], 1) // ERROR "direct assignment to atomic value"
+	*ap[1] = atomic.AddUint64(ap[0], 1)
+
+	x = atomic.AddUint64() // Used to make vet crash; now silently ignored.
+}

src/cmd/vet/testdata/bool.go

+// Copyright 2014 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.
+
+// This file contains tests for the bool checker.
+
+package testdata
+
+import "io"
+
+func RatherStupidConditions() {
+	var f, g func() int
+	if f() == 0 || f() == 0 { // OK f might have side effects
+	}
+	if v, w := f(), g(); v == w || v == w { // ERROR "redundant or: v == w || v == w"
+	}
+	_ = f == nil || f == nil // ERROR "redundant or: f == nil || f == nil"
+
+	_ = i == byte(1) || i == byte(1) // TODO conversions are treated as if they may have side effects
+
+	var c chan int
+	_ = 0 == <-c || 0 == <-c                                  // OK subsequent receives may yield different values
+	for i, j := <-c, <-c; i == j || i == j; i, j = <-c, <-c { // ERROR "redundant or: i == j || i == j"
+	}
+
+	var i, j, k int
+	_ = i+1 == 1 || i+1 == 1         // ERROR "redundant or: i\+1 == 1 || i\+1 == 1"
+	_ = i == 1 || j+1 == i || i == 1 // ERROR "redundant or: i == 1 || i == 1"
+
+	_ = i == 1 || i == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || f() == 1 || i == 1 // OK f may alter i as a side effect
+	_ = f() == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
+
+	// Test partition edge cases
+	_ = f() == 1 || i == 1 || i == 1 || j == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = f() == 1 || j == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || f() == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || i == 1 || f() == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || i == 1 || j == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = j == 1 || i == 1 || i == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || f() == 1 || f() == 1 || i == 1
+
+	_ = i == 1 || (i == 1 || i == 2)             // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || (f() == 1 || i == 1)           // OK f may alter i as a side effect
+	_ = i == 1 || (i == 1 || f() == 1)           // ERROR "redundant or: i == 1 || i == 1"
+	_ = i == 1 || (i == 2 || (i == 1 || i == 3)) // ERROR "redundant or: i == 1 || i == 1"
+
+	var a, b bool
+	_ = i == 1 || (a || (i == 1 || b)) // ERROR "redundant or: i == 1 || i == 1"
+
+	// Check that all redundant ors are flagged
+	_ = j == 0 ||
+		i == 1 ||
+		f() == 1 ||
+		j == 0 || // ERROR "redundant or: j == 0 || j == 0"
+		i == 1 || // ERROR "redundant or: i == 1 || i == 1"
+		i == 1 || // ERROR "redundant or: i == 1 || i == 1"
+		i == 1 ||
+		j == 0 ||
+		k == 0
+
+	_ = i == 1*2*3 || i == 1*2*3 // ERROR "redundant or: i == 1\*2\*3 || i == 1\*2\*3"
+
+	// These test that redundant, suspect expressions do not trigger multiple errors.
+	_ = i != 0 || i != 0 // ERROR "redundant or: i != 0 || i != 0"
+	_ = i == 0 && i == 0 // ERROR "redundant and: i == 0 && i == 0"
+
+	// and is dual to or; check the basics and
+	// let the or tests pull the rest of the weight.
+	_ = 0 != <-c && 0 != <-c         // OK subsequent receives may yield different values
+	_ = f() != 0 && f() != 0         // OK f might have side effects
+	_ = f != nil && f != nil         // ERROR "redundant and: f != nil && f != nil"
+	_ = i != 1 && i != 1 && f() != 1 // ERROR "redundant and: i != 1 && i != 1"
+	_ = i != 1 && f() != 1 && i != 1 // OK f may alter i as a side effect
+	_ = f() != 1 && i != 1 && i != 1 // ERROR "redundant and: i != 1 && i != 1"
+}
+
+func RoyallySuspectConditions() {
+	var i, j int
+
+	_ = i == 0 || i == 1 // OK
+	_ = i != 0 || i != 1 // ERROR "suspect or: i != 0 || i != 1"
+	_ = i != 0 || 1 != i // ERROR "suspect or: i != 0 || 1 != i"
+	_ = 0 != i || 1 != i // ERROR "suspect or: 0 != i || 1 != i"
+	_ = 0 != i || i != 1 // ERROR "suspect or: 0 != i || i != 1"
+
+	_ = (0 != i) || i != 1 // ERROR "suspect or: 0 != i || i != 1"
+
+	_ = i+3 != 7 || j+5 == 0 || i+3 != 9 // ERROR "suspect or: i\+3 != 7 || i\+3 != 9"
+
+	_ = i != 0 || j == 0 || i != 1 // ERROR "suspect or: i != 0 || i != 1"
+
+	_ = i != 0 || i != 1<<4 // ERROR "suspect or: i != 0 || i != 1<<4"
+
+	_ = i != 0 || j != 0
+	_ = 0 != i || 0 != j
+
+	var s string
+	_ = s != "one" || s != "the other" // ERROR "suspect or: s != .one. || s != .the other."
+
+	_ = "et" != "alii" || "et" != "cetera"         // ERROR "suspect or: .et. != .alii. || .et. != .cetera."
+	_ = "me gustas" != "tu" || "le gustas" != "tu" // OK we could catch this case, but it's not worth the code
+
+	var err error
+	_ = err != nil || err != io.EOF // TODO catch this case?
+
+	// Sanity check and.
+	_ = i != 0 && i != 1 // OK
+	_ = i == 0 && i == 1 // ERROR "suspect and: i == 0 && i == 1"
+	_ = i == 0 && 1 == i // ERROR "suspect and: i == 0 && 1 == i"
+	_ = 0 == i && 1 == i // ERROR "suspect and: 0 == i && 1 == i"
+	_ = 0 == i && i == 1 // ERROR "suspect and: 0 == i && i == 1"
+}

src/cmd/vet/testdata/buildtag.go

+// 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.
+
+// This file contains tests for the buildtag checker.
+
+// +builder // ERROR "possible malformed \+build comment"
+// +build !ignore
+
+package testdata
+
+// +build toolate // ERROR "build comment must appear before package clause and be followed by a blank line"
+
+var _ = 3

src/cmd/vet/testdata/buildtag_bad.go

+// This file contains misplaced or malformed build constraints.
+// The Go tool will skip it, because the constraints are invalid.
+// It serves only to test the tag checker during make test.
+
+// Mention +build // ERROR "possible malformed \+build comment"
+
+// +build !!bang // ERROR "invalid double negative in build constraint"
+// +build @#$ // ERROR "invalid non-alphanumeric build constraint"
+
+// +build toolate // ERROR "build comment must appear before package clause and be followed by a blank line"
+package bad
+
+// This is package 'bad' rather than 'main' so the erroneous build
+// tag doesn't end up looking like a package doc for the vet command
+// when examined by godoc.

src/cmd/vet/testdata/composite.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains tests for the untagged struct literal checker.
+
+// This file contains the test for untagged struct literals.
+
+package testdata
+
+import (
+	"flag"
+	"go/scanner"
+)
+
+var Okay1 = []string{
+	"Name",
+	"Usage",
+	"DefValue",
+}
+
+var Okay2 = map[string]bool{
+	"Name":     true,
+	"Usage":    true,
+	"DefValue": true,
+}
+
+var Okay3 = struct {
+	X string
+	Y string
+	Z string
+}{
+	"Name",
+	"Usage",
+	"DefValue",
+}
+
+type MyStruct struct {
+	X string
+	Y string
+	Z string
+}
+
+var Okay4 = MyStruct{
+	"Name",
+	"Usage",
+	"DefValue",
+}
+
+// Testing is awkward because we need to reference things from a separate package
+// to trigger the warnings.
+
+var BadStructLiteralUsedInTests = flag.Flag{ // ERROR "unkeyed fields"
+	"Name",
+	"Usage",
+	nil, // Value
+	"DefValue",
+}
+
+// Used to test the check for slices and arrays: If that test is disabled and
+// vet is run with --compositewhitelist=false, this line triggers an error.
+// Clumsy but sufficient.
+var scannerErrorListTest = scanner.ErrorList{nil, nil}

src/cmd/vet/testdata/copylock_func.go

+// 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.
+
+// This file contains tests for the copylock checker's
+// function declaration analysis.
+
+package testdata
+
+import "sync"
+
+func OkFunc(*sync.Mutex) {}
+func BadFunc(sync.Mutex) {} // ERROR "BadFunc passes Lock by value: sync.Mutex"
+func OkRet() *sync.Mutex {}
+func BadRet() sync.Mutex {} // ERROR "BadRet returns Lock by value: sync.Mutex"
+
+type EmbeddedRWMutex struct {
+	sync.RWMutex
+}
+
+func (*EmbeddedRWMutex) OkMeth() {}
+func (EmbeddedRWMutex) BadMeth() {} // ERROR "BadMeth passes Lock by value: testdata.EmbeddedRWMutex"
+func OkFunc(e *EmbeddedRWMutex)  {}
+func BadFunc(EmbeddedRWMutex)    {} // ERROR "BadFunc passes Lock by value: testdata.EmbeddedRWMutex"
+func OkRet() *EmbeddedRWMutex    {}
+func BadRet() EmbeddedRWMutex    {} // ERROR "BadRet returns Lock by value: testdata.EmbeddedRWMutex"
+
+type FieldMutex struct {
+	s sync.Mutex
+}
+
+func (*FieldMutex) OkMeth()   {}
+func (FieldMutex) BadMeth()   {} // ERROR "BadMeth passes Lock by value: testdata.FieldMutex contains sync.Mutex"
+func OkFunc(*FieldMutex)      {}
+func BadFunc(FieldMutex, int) {} // ERROR "BadFunc passes Lock by value: testdata.FieldMutex contains sync.Mutex"
+
+type L0 struct {
+	L1
+}
+
+type L1 struct {
+	l L2
+}
+
+type L2 struct {
+	sync.Mutex
+}
+
+func (*L0) Ok() {}
+func (L0) Bad() {} // ERROR "Bad passes Lock by value: testdata.L0 contains testdata.L1 contains testdata.L2"
+
+type EmbeddedMutexPointer struct {
+	s *sync.Mutex // safe to copy this pointer
+}
+
+func (*EmbeddedMutexPointer) Ok()      {}
+func (EmbeddedMutexPointer) AlsoOk()   {}
+func StillOk(EmbeddedMutexPointer)     {}
+func LookinGood() EmbeddedMutexPointer {}
+
+type EmbeddedLocker struct {
+	sync.Locker // safe to copy interface values
+}
+
+func (*EmbeddedLocker) Ok()    {}
+func (EmbeddedLocker) AlsoOk() {}
+
+type CustomLock struct{}
+
+func (*CustomLock) Lock()   {}
+func (*CustomLock) Unlock() {}
+
+func Ok(*CustomLock) {}
+func Bad(CustomLock) {} // ERROR "Bad passes Lock by value: testdata.CustomLock"
+
+// TODO: Unfortunate cases
+
+// Non-ideal error message:
+// Since we're looking for Lock methods, sync.Once's underlying
+// sync.Mutex gets called out, but without any reference to the sync.Once.
+type LocalOnce sync.Once
+
+func (LocalOnce) Bad() {} // ERROR "Bad passes Lock by value: testdata.LocalOnce contains sync.Mutex"
+
+// False negative:
+// LocalMutex doesn't have a Lock method.
+// Nevertheless, it is probably a bad idea to pass it by value.
+type LocalMutex sync.Mutex
+
+func (LocalMutex) Bad() {} // WANTED: An error here :(

src/cmd/vet/testdata/copylock_range.go

+// Copyright 2014 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.
+
+// This file contains tests for the copylock checker's
+// range statement analysis.
+
+package testdata
+
+import "sync"
+
+func rangeMutex() {
+	var mu sync.Mutex
+	var i int
+
+	var s []sync.Mutex
+	for range s {
+	}
+	for i = range s {
+	}
+	for i := range s {
+	}
+	for i, _ = range s {
+	}
+	for i, _ := range s {
+	}
+	for _, mu = range s { // ERROR "range var mu copies Lock: sync.Mutex"
+	}
+	for _, m := range s { // ERROR "range var m copies Lock: sync.Mutex"
+	}
+	for i, mu = range s { // ERROR "range var mu copies Lock: sync.Mutex"
+	}
+	for i, m := range s { // ERROR "range var m copies Lock: sync.Mutex"
+	}
+
+	var a [3]sync.Mutex
+	for _, m := range a { // ERROR "range var m copies Lock: sync.Mutex"
+	}
+
+	var m map[sync.Mutex]sync.Mutex
+	for k := range m { // ERROR "range var k copies Lock: sync.Mutex"
+	}
+	for mu, _ = range m { // ERROR "range var mu copies Lock: sync.Mutex"
+	}
+	for k, _ := range m { // ERROR "range var k copies Lock: sync.Mutex"
+	}
+	for _, mu = range m { // ERROR "range var mu copies Lock: sync.Mutex"
+	}
+	for _, v := range m { // ERROR "range var v copies Lock: sync.Mutex"
+	}
+
+	var c chan sync.Mutex
+	for range c {
+	}
+	for mu = range c { // ERROR "range var mu copies Lock: sync.Mutex"
+	}
+	for v := range c { // ERROR "range var v copies Lock: sync.Mutex"
+	}
+
+	// Test non-idents in range variables
+	var t struct {
+		i  int
+		mu sync.Mutex
+	}
+	for t.i, t.mu = range s { // ERROR "range var t.mu copies Lock: sync.Mutex"
+	}
+}

src/cmd/vet/testdata/method.go

+// Copyright 2010 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.
+
+// This file contains tests for the canonical method checker.
+
+// This file contains the code to check canonical methods.
+
+package testdata
+
+import (
+	"fmt"
+)
+
+type MethodTest int
+
+func (t *MethodTest) Scan(x fmt.ScanState, c byte) { // ERROR "should have signature Scan"
+}
+
+type MethodTestInterface interface {
+	ReadByte() byte // ERROR "should have signature ReadByte"
+}

src/cmd/vet/testdata/nilfunc.go

+// 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 testdata
+
+func F() {}
+
+type T struct {
+	F func()
+}
+
+func (T) M() {}
+
+var Fv = F
+
+func Comparison() {
+	var t T
+	var fn func()
+	if fn == nil || Fv == nil || t.F == nil {
+		// no error; these func vars or fields may be nil
+	}
+	if F == nil { // ERROR "comparison of function F == nil is always false"
+		panic("can't happen")
+	}
+	if t.M == nil { // ERROR "comparison of function M == nil is always false"
+		panic("can't happen")
+	}
+	if F != nil { // ERROR "comparison of function F != nil is always true"
+		if t.M != nil { // ERROR "comparison of function M != nil is always true"
+			return
+		}
+	}
+	panic("can't happen")
+}

src/cmd/vet/testdata/rangeloop.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains tests for the rangeloop checker.
+
+package testdata
+
+func RangeLoopTests() {
+	var s []int
+	for i, v := range s {
+		go func() {
+			println(i) // ERROR "range variable i captured by func literal"
+			println(v) // ERROR "range variable v captured by func literal"
+		}()
+	}
+	for i, v := range s {
+		defer func() {
+			println(i) // ERROR "range variable i captured by func literal"
+			println(v) // ERROR "range variable v captured by func literal"
+		}()
+	}
+	for i := range s {
+		go func() {
+			println(i) // ERROR "range variable i captured by func literal"
+		}()
+	}
+	for _, v := range s {
+		go func() {
+			println(v) // ERROR "range variable v captured by func literal"
+		}()
+	}
+	for i, v := range s {
+		go func() {
+			println(i, v)
+		}()
+		println("unfortunately, we don't catch the error above because of this statement")
+	}
+	for i, v := range s {
+		go func(i, v int) {
+			println(i, v)
+		}(i, v)
+	}
+	for i, v := range s {
+		i, v := i, v
+		go func() {
+			println(i, v)
+		}()
+	}
+	// If the key of the range statement is not an identifier
+	// the code should not panic (it used to).
+	var x [2]int
+	var f int
+	for x[0], f = range s {
+		go func() {
+			_ = f // ERROR "range variable f captured by func literal"
+		}()
+	}
+}

src/cmd/vet/testdata/structtag.go

+// Copyright 2010 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.
+
+// This file contains the test for canonical struct tags.
+
+package testdata
+
+type StructTagTest struct {
+	A   int "hello"            // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag pair"
+	B   int "\tx:\"y\""        // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag key"
+	C   int "x:\"y\"\tx:\"y\"" // ERROR "not compatible with reflect.StructTag.Get"
+	D   int "x:`y`"            // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag value"
+	E   int "ct\brl:\"char\""  // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag pair"
+	F   int `:"emptykey"`      // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag key"
+	G   int `x:"noEndQuote`    // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag value"
+	H   int `x:"trunc\x0"`     // ERROR "not compatible with reflect.StructTag.Get: bad syntax for struct tag value"
+	OK0 int `x:"y" u:"v" w:""`
+	OK1 int `x:"y:z" u:"v" w:""` // note multiple colons.
+	OK2 int "k0:\"values contain spaces\" k1:\"literal\ttabs\" k2:\"and\\tescaped\\tabs\""
+	OK3 int `under_scores:"and" CAPS:"ARE_OK"`
+}
+
+type UnexportedEncodingTagTest struct {
+	x int `json:"xx"` // ERROR "struct field x has json tag but is not exported"
+	y int `xml:"yy"`  // ERROR "struct field y has xml tag but is not exported"
+	z int
+	A int `json:"aa" xml:"bb"`
+}
+
+type unexp struct{}
+
+type JSONEmbeddedField struct {
+	UnexportedEncodingTagTest `is:"embedded"`
+	unexp                     `is:"embedded,notexported" json:"unexp"` // OK for now, see issue 7363
+}

src/cmd/vet/testdata/tagtest/file1.go

+// Copyright 2015 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.
+
+// +build testtag
+
+package main
+
+func main() {
+}