vendor: include source for tools

This change vendors the source for all our build, formatting, and
linting tools. Generated by running "dep ensure".

4 files changed, 2193 insertions, 0 deletions

diff --git a/vendor/github.com/golang/lint/LICENSE b/vendor/github.com/golang/lint/LICENSE
new file mode 100644
index 0000000..65d761b
--- /dev/null
+++ b/vendor/github.com/golang/lint/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2013 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/github.com/golang/lint/golint/golint.go b/vendor/github.com/golang/lint/golint/golint.go
new file mode 100644
index 0000000..d8360ad
--- /dev/null
+++ b/vendor/github.com/golang/lint/golint/golint.go
@@ -0,0 +1,159 @@
+// Copyright (c) 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 or at
+// https://developers.google.com/open-source/licenses/bsd.
+
+// golint lints the Go source files named on its command line.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"go/build"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/golang/lint"
+)
+
+var (
+	minConfidence = flag.Float64("min_confidence", 0.8, "minimum confidence of a problem to print it")
+	setExitStatus = flag.Bool("set_exit_status", false, "set exit status to 1 if any issues are found")
+	suggestions   int
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
+	fmt.Fprintf(os.Stderr, "\tgolint [flags] # runs on package in current directory\n")
+	fmt.Fprintf(os.Stderr, "\tgolint [flags] [packages]\n")
+	fmt.Fprintf(os.Stderr, "\tgolint [flags] [directories] # where a '/...' suffix includes all sub-directories\n")
+	fmt.Fprintf(os.Stderr, "\tgolint [flags] [files] # all must belong to a single package\n")
+	fmt.Fprintf(os.Stderr, "Flags:\n")
+	flag.PrintDefaults()
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+
+	if flag.NArg() == 0 {
+		lintDir(".")
+	} else {
+		// dirsRun, filesRun, and pkgsRun indicate whether golint is applied to
+		// directory, file or package targets. The distinction affects which
+		// checks are run. It is no valid to mix target types.
+		var dirsRun, filesRun, pkgsRun int
+		var args []string
+		for _, arg := range flag.Args() {
+			if strings.HasSuffix(arg, "/...") && isDir(arg[:len(arg)-len("/...")]) {
+				dirsRun = 1
+				for _, dirname := range allPackagesInFS(arg) {
+					args = append(args, dirname)
+				}
+			} else if isDir(arg) {
+				dirsRun = 1
+				args = append(args, arg)
+			} else if exists(arg) {
+				filesRun = 1
+				args = append(args, arg)
+			} else {
+				pkgsRun = 1
+				args = append(args, arg)
+			}
+		}
+
+		if dirsRun+filesRun+pkgsRun != 1 {
+			usage()
+			os.Exit(2)
+		}
+		switch {
+		case dirsRun == 1:
+			for _, dir := range args {
+				lintDir(dir)
+			}
+		case filesRun == 1:
+			lintFiles(args...)
+		case pkgsRun == 1:
+			for _, pkg := range importPaths(args) {
+				lintPackage(pkg)
+			}
+		}
+	}
+
+	if *setExitStatus && suggestions > 0 {
+		fmt.Fprintf(os.Stderr, "Found %d lint suggestions; failing.\n", suggestions)
+		os.Exit(1)
+	}
+}
+
+func isDir(filename string) bool {
+	fi, err := os.Stat(filename)
+	return err == nil && fi.IsDir()
+}
+
+func exists(filename string) bool {
+	_, err := os.Stat(filename)
+	return err == nil
+}
+
+func lintFiles(filenames ...string) {
+	files := make(map[string][]byte)
+	for _, filename := range filenames {
+		src, err := ioutil.ReadFile(filename)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+		files[filename] = src
+	}
+
+	l := new(lint.Linter)
+	ps, err := l.LintFiles(files)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		return
+	}
+	for _, p := range ps {
+		if p.Confidence >= *minConfidence {
+			fmt.Printf("%v: %s\n", p.Position, p.Text)
+			suggestions++
+		}
+	}
+}
+
+func lintDir(dirname string) {
+	pkg, err := build.ImportDir(dirname, 0)
+	lintImportedPackage(pkg, err)
+}
+
+func lintPackage(pkgname string) {
+	pkg, err := build.Import(pkgname, ".", 0)
+	lintImportedPackage(pkg, err)
+}
+
+func lintImportedPackage(pkg *build.Package, err error) {
+	if err != nil {
+		if _, nogo := err.(*build.NoGoError); nogo {
+			// Don't complain if the failure is due to no Go source files.
+			return
+		}
+		fmt.Fprintln(os.Stderr, err)
+		return
+	}
+
+	var files []string
+	files = append(files, pkg.GoFiles...)
+	files = append(files, pkg.CgoFiles...)
+	files = append(files, pkg.TestGoFiles...)
+	if pkg.Dir != "." {
+		for i, f := range files {
+			files[i] = filepath.Join(pkg.Dir, f)
+		}
+	}
+	// TODO(dsymonds): Do foo_test too (pkg.XTestGoFiles)
+
+	lintFiles(files...)
+}
diff --git a/vendor/github.com/golang/lint/golint/import.go b/vendor/github.com/golang/lint/golint/import.go
new file mode 100644
index 0000000..02a0daa
--- /dev/null
+++ b/vendor/github.com/golang/lint/golint/import.go
@@ -0,0 +1,310 @@
+package main
+
+/*
+
+This file holds a direct copy of the import path matching code of
+https://github.com/golang/go/blob/master/src/cmd/go/main.go. It can be
+replaced when https://golang.org/issue/8768 is resolved.
+
+It has been updated to follow upstream changes in a few ways.
+
+*/
+
+import (
+	"fmt"
+	"go/build"
+	"log"
+	"os"
+	"path"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strings"
+)
+
+var buildContext = build.Default
+
+var (
+	goroot    = filepath.Clean(runtime.GOROOT())
+	gorootSrc = filepath.Join(goroot, "src")
+)
+
+// importPathsNoDotExpansion returns the import paths to use for the given
+// command line, but it does no ... expansion.
+func importPathsNoDotExpansion(args []string) []string {
+	if len(args) == 0 {
+		return []string{"."}
+	}
+	var out []string
+	for _, a := range args {
+		// Arguments are supposed to be import paths, but
+		// as a courtesy to Windows developers, rewrite \ to /
+		// in command-line arguments.  Handles .\... and so on.
+		if filepath.Separator == '\\' {
+			a = strings.Replace(a, `\`, `/`, -1)
+		}
+
+		// Put argument in canonical form, but preserve leading ./.
+		if strings.HasPrefix(a, "./") {
+			a = "./" + path.Clean(a)
+			if a == "./." {
+				a = "."
+			}
+		} else {
+			a = path.Clean(a)
+		}
+		if a == "all" || a == "std" {
+			out = append(out, allPackages(a)...)
+			continue
+		}
+		out = append(out, a)
+	}
+	return out
+}
+
+// importPaths returns the import paths to use for the given command line.
+func importPaths(args []string) []string {
+	args = importPathsNoDotExpansion(args)
+	var out []string
+	for _, a := range args {
+		if strings.Contains(a, "...") {
+			if build.IsLocalImport(a) {
+				out = append(out, allPackagesInFS(a)...)
+			} else {
+				out = append(out, allPackages(a)...)
+			}
+			continue
+		}
+		out = append(out, a)
+	}
+	return out
+}
+
+// matchPattern(pattern)(name) reports whether
+// name matches pattern.  Pattern is a limited glob
+// pattern in which '...' means 'any string' and there
+// is no other special syntax.
+func matchPattern(pattern string) func(name string) bool {
+	re := regexp.QuoteMeta(pattern)
+	re = strings.Replace(re, `\.\.\.`, `.*`, -1)
+	// Special case: foo/... matches foo too.
+	if strings.HasSuffix(re, `/.*`) {
+		re = re[:len(re)-len(`/.*`)] + `(/.*)?`
+	}
+	reg := regexp.MustCompile(`^` + re + `$`)
+	return func(name string) bool {
+		return reg.MatchString(name)
+	}
+}
+
+// hasPathPrefix reports whether the path s begins with the
+// elements in prefix.
+func hasPathPrefix(s, prefix string) bool {
+	switch {
+	default:
+		return false
+	case len(s) == len(prefix):
+		return s == prefix
+	case len(s) > len(prefix):
+		if prefix != "" && prefix[len(prefix)-1] == '/' {
+			return strings.HasPrefix(s, prefix)
+		}
+		return s[len(prefix)] == '/' && s[:len(prefix)] == prefix
+	}
+}
+
+// treeCanMatchPattern(pattern)(name) reports whether
+// name or children of name can possibly match pattern.
+// Pattern is the same limited glob accepted by matchPattern.
+func treeCanMatchPattern(pattern string) func(name string) bool {
+	wildCard := false
+	if i := strings.Index(pattern, "..."); i >= 0 {
+		wildCard = true
+		pattern = pattern[:i]
+	}
+	return func(name string) bool {
+		return len(name) <= len(pattern) && hasPathPrefix(pattern, name) ||
+			wildCard && strings.HasPrefix(name, pattern)
+	}
+}
+
+// allPackages returns all the packages that can be found
+// under the $GOPATH directories and $GOROOT matching pattern.
+// The pattern is either "all" (all packages), "std" (standard packages)
+// or a path including "...".
+func allPackages(pattern string) []string {
+	pkgs := matchPackages(pattern)
+	if len(pkgs) == 0 {
+		fmt.Fprintf(os.Stderr, "warning: %q matched no packages\n", pattern)
+	}
+	return pkgs
+}
+
+func matchPackages(pattern string) []string {
+	match := func(string) bool { return true }
+	treeCanMatch := func(string) bool { return true }
+	if pattern != "all" && pattern != "std" {
+		match = matchPattern(pattern)
+		treeCanMatch = treeCanMatchPattern(pattern)
+	}
+
+	have := map[string]bool{
+		"builtin": true, // ignore pseudo-package that exists only for documentation
+	}
+	if !buildContext.CgoEnabled {
+		have["runtime/cgo"] = true // ignore during walk
+	}
+	var pkgs []string
+
+	// Commands
+	cmd := filepath.Join(goroot, "src/cmd") + string(filepath.Separator)
+	filepath.Walk(cmd, func(path string, fi os.FileInfo, err error) error {
+		if err != nil || !fi.IsDir() || path == cmd {
+			return nil
+		}
+		name := path[len(cmd):]
+		if !treeCanMatch(name) {
+			return filepath.SkipDir
+		}
+		// Commands are all in cmd/, not in subdirectories.
+		if strings.Contains(name, string(filepath.Separator)) {
+			return filepath.SkipDir
+		}
+
+		// We use, e.g., cmd/gofmt as the pseudo import path for gofmt.
+		name = "cmd/" + name
+		if have[name] {
+			return nil
+		}
+		have[name] = true
+		if !match(name) {
+			return nil
+		}
+		_, err = buildContext.ImportDir(path, 0)
+		if err != nil {
+			if _, noGo := err.(*build.NoGoError); !noGo {
+				log.Print(err)
+			}
+			return nil
+		}
+		pkgs = append(pkgs, name)
+		return nil
+	})
+
+	for _, src := range buildContext.SrcDirs() {
+		if (pattern == "std" || pattern == "cmd") && src != gorootSrc {
+			continue
+		}
+		src = filepath.Clean(src) + string(filepath.Separator)
+		root := src
+		if pattern == "cmd" {
+			root += "cmd" + string(filepath.Separator)
+		}
+		filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
+			if err != nil || !fi.IsDir() || path == src {
+				return nil
+			}
+
+			// Avoid .foo, _foo, and testdata directory trees.
+			_, elem := filepath.Split(path)
+			if strings.HasPrefix(elem, ".") || strings.HasPrefix(elem, "_") || elem == "testdata" {
+				return filepath.SkipDir
+			}
+
+			name := filepath.ToSlash(path[len(src):])
+			if pattern == "std" && (strings.Contains(name, ".") || name == "cmd") {
+				// The name "std" is only the standard library.
+				// If the name is cmd, it's the root of the command tree.
+				return filepath.SkipDir
+			}
+			if !treeCanMatch(name) {
+				return filepath.SkipDir
+			}
+			if have[name] {
+				return nil
+			}
+			have[name] = true
+			if !match(name) {
+				return nil
+			}
+			_, err = buildContext.ImportDir(path, 0)
+			if err != nil {
+				if _, noGo := err.(*build.NoGoError); noGo {
+					return nil
+				}
+			}
+			pkgs = append(pkgs, name)
+			return nil
+		})
+	}
+	return pkgs
+}
+
+// allPackagesInFS is like allPackages but is passed a pattern
+// beginning ./ or ../, meaning it should scan the tree rooted
+// at the given directory.  There are ... in the pattern too.
+func allPackagesInFS(pattern string) []string {
+	pkgs := matchPackagesInFS(pattern)
+	if len(pkgs) == 0 {
+		fmt.Fprintf(os.Stderr, "warning: %q matched no packages\n", pattern)
+	}
+	return pkgs
+}
+
+func matchPackagesInFS(pattern string) []string {
+	// Find directory to begin the scan.
+	// Could be smarter but this one optimization
+	// is enough for now, since ... is usually at the
+	// end of a path.
+	i := strings.Index(pattern, "...")
+	dir, _ := path.Split(pattern[:i])
+
+	// pattern begins with ./ or ../.
+	// path.Clean will discard the ./ but not the ../.
+	// We need to preserve the ./ for pattern matching
+	// and in the returned import paths.
+	prefix := ""
+	if strings.HasPrefix(pattern, "./") {
+		prefix = "./"
+	}
+	match := matchPattern(pattern)
+
+	var pkgs []string
+	filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
+		if err != nil || !fi.IsDir() {
+			return nil
+		}
+		if path == dir {
+			// filepath.Walk starts at dir and recurses. For the recursive case,
+			// the path is the result of filepath.Join, which calls filepath.Clean.
+			// The initial case is not Cleaned, though, so we do this explicitly.
+			//
+			// This converts a path like "./io/" to "io". Without this step, running
+			// "cd $GOROOT/src/pkg; go list ./io/..." would incorrectly skip the io
+			// package, because prepending the prefix "./" to the unclean path would
+			// result in "././io", and match("././io") returns false.
+			path = filepath.Clean(path)
+		}
+
+		// Avoid .foo, _foo, and testdata directory trees, but do not avoid "." or "..".
+		_, elem := filepath.Split(path)
+		dot := strings.HasPrefix(elem, ".") && elem != "." && elem != ".."
+		if dot || strings.HasPrefix(elem, "_") || elem == "testdata" {
+			return filepath.SkipDir
+		}
+
+		name := prefix + filepath.ToSlash(path)
+		if !match(name) {
+			return nil
+		}
+		if _, err = build.ImportDir(path, 0); err != nil {
+			if _, noGo := err.(*build.NoGoError); !noGo {
+				log.Print(err)
+			}
+			return nil
+		}
+		pkgs = append(pkgs, name)
+		return nil
+	})
+	return pkgs
+}
diff --git a/vendor/github.com/golang/lint/lint.go b/vendor/github.com/golang/lint/lint.go
new file mode 100644
index 0000000..8bb1faa
--- /dev/null
+++ b/vendor/github.com/golang/lint/lint.go
@@ -0,0 +1,1697 @@
+// Copyright (c) 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 or at
+// https://developers.google.com/open-source/licenses/bsd.
+
+// Package lint contains a linter for Go source code.
+package lint
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"go/types"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+
+	"golang.org/x/tools/go/gcexportdata"
+)
+
+const styleGuideBase = "https://golang.org/wiki/CodeReviewComments"
+
+// A Linter lints Go source code.
+type Linter struct {
+}
+
+// Problem represents a problem in some source code.
+type Problem struct {
+	Position   token.Position // position in source file
+	Text       string         // the prose that describes the problem
+	Link       string         // (optional) the link to the style guide for the problem
+	Confidence float64        // a value in (0,1] estimating the confidence in this problem's correctness
+	LineText   string         // the source line
+	Category   string         // a short name for the general category of the problem
+
+	// If the problem has a suggested fix (the minority case),
+	// ReplacementLine is a full replacement for the relevant line of the source file.
+	ReplacementLine string
+}
+
+func (p *Problem) String() string {
+	if p.Link != "" {
+		return p.Text + "\n\n" + p.Link
+	}
+	return p.Text
+}
+
+type byPosition []Problem
+
+func (p byPosition) Len() int      { return len(p) }
+func (p byPosition) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+func (p byPosition) Less(i, j int) bool {
+	pi, pj := p[i].Position, p[j].Position
+
+	if pi.Filename != pj.Filename {
+		return pi.Filename < pj.Filename
+	}
+	if pi.Line != pj.Line {
+		return pi.Line < pj.Line
+	}
+	if pi.Column != pj.Column {
+		return pi.Column < pj.Column
+	}
+
+	return p[i].Text < p[j].Text
+}
+
+// Lint lints src.
+func (l *Linter) Lint(filename string, src []byte) ([]Problem, error) {
+	return l.LintFiles(map[string][]byte{filename: src})
+}
+
+// LintFiles lints a set of files of a single package.
+// The argument is a map of filename to source.
+func (l *Linter) LintFiles(files map[string][]byte) ([]Problem, error) {
+	pkg := &pkg{
+		fset:  token.NewFileSet(),
+		files: make(map[string]*file),
+	}
+	var pkgName string
+	for filename, src := range files {
+		if isGenerated(src) {
+			continue // See issue #239
+		}
+		f, err := parser.ParseFile(pkg.fset, filename, src, parser.ParseComments)
+		if err != nil {
+			return nil, err
+		}
+		if pkgName == "" {
+			pkgName = f.Name.Name
+		} else if f.Name.Name != pkgName {
+			return nil, fmt.Errorf("%s is in package %s, not %s", filename, f.Name.Name, pkgName)
+		}
+		pkg.files[filename] = &file{
+			pkg:      pkg,
+			f:        f,
+			fset:     pkg.fset,
+			src:      src,
+			filename: filename,
+		}
+	}
+	if len(pkg.files) == 0 {
+		return nil, nil
+	}
+	return pkg.lint(), nil
+}
+
+var (
+	genHdr = []byte("// Code generated ")
+	genFtr = []byte(" DO NOT EDIT.")
+)
+
+// isGenerated reports whether the source file is generated code
+// according the rules from https://golang.org/s/generatedcode.
+func isGenerated(src []byte) bool {
+	sc := bufio.NewScanner(bytes.NewReader(src))
+	for sc.Scan() {
+		b := sc.Bytes()
+		if bytes.HasPrefix(b, genHdr) && bytes.HasSuffix(b, genFtr) && len(b) >= len(genHdr)+len(genFtr) {
+			return true
+		}
+	}
+	return false
+}
+
+// pkg represents a package being linted.
+type pkg struct {
+	fset  *token.FileSet
+	files map[string]*file
+
+	typesPkg  *types.Package
+	typesInfo *types.Info
+
+	// sortable is the set of types in the package that implement sort.Interface.
+	sortable map[string]bool
+	// main is whether this is a "main" package.
+	main bool
+
+	problems []Problem
+}
+
+func (p *pkg) lint() []Problem {
+	if err := p.typeCheck(); err != nil {
+		/* TODO(dsymonds): Consider reporting these errors when golint operates on entire packages.
+		if e, ok := err.(types.Error); ok {
+			pos := p.fset.Position(e.Pos)
+			conf := 1.0
+			if strings.Contains(e.Msg, "can't find import: ") {
+				// Golint is probably being run in a context that doesn't support
+				// typechecking (e.g. package files aren't found), so don't warn about it.
+				conf = 0
+			}
+			if conf > 0 {
+				p.errorfAt(pos, conf, category("typechecking"), e.Msg)
+			}
+
+			// TODO(dsymonds): Abort if !e.Soft?
+		}
+		*/
+	}
+
+	p.scanSortable()
+	p.main = p.isMain()
+
+	for _, f := range p.files {
+		f.lint()
+	}
+
+	sort.Sort(byPosition(p.problems))
+
+	return p.problems
+}
+
+// file represents a file being linted.
+type file struct {
+	pkg      *pkg
+	f        *ast.File
+	fset     *token.FileSet
+	src      []byte
+	filename string
+}
+
+func (f *file) isTest() bool { return strings.HasSuffix(f.filename, "_test.go") }
+
+func (f *file) lint() {
+	f.lintPackageComment()
+	f.lintImports()
+	f.lintBlankImports()
+	f.lintExported()
+	f.lintNames()
+	f.lintVarDecls()
+	f.lintElses()
+	f.lintIfError()
+	f.lintRanges()
+	f.lintErrorf()
+	f.lintErrors()
+	f.lintErrorStrings()
+	f.lintReceiverNames()
+	f.lintIncDec()
+	f.lintErrorReturn()
+	f.lintUnexportedReturn()
+	f.lintTimeNames()
+	f.lintContextKeyTypes()
+	f.lintContextArgs()
+}
+
+type link string
+type category string
+
+// The variadic arguments may start with link and category types,
+// and must end with a format string and any arguments.
+// It returns the new Problem.
+func (f *file) errorf(n ast.Node, confidence float64, args ...interface{}) *Problem {
+	pos := f.fset.Position(n.Pos())
+	if pos.Filename == "" {
+		pos.Filename = f.filename
+	}
+	return f.pkg.errorfAt(pos, confidence, args...)
+}
+
+func (p *pkg) errorfAt(pos token.Position, confidence float64, args ...interface{}) *Problem {
+	problem := Problem{
+		Position:   pos,
+		Confidence: confidence,
+	}
+	if pos.Filename != "" {
+		// The file might not exist in our mapping if a //line directive was encountered.
+		if f, ok := p.files[pos.Filename]; ok {
+			problem.LineText = srcLine(f.src, pos)
+		}
+	}
+
+argLoop:
+	for len(args) > 1 { // always leave at least the format string in args
+		switch v := args[0].(type) {
+		case link:
+			problem.Link = string(v)
+		case category:
+			problem.Category = string(v)
+		default:
+			break argLoop
+		}
+		args = args[1:]
+	}
+
+	problem.Text = fmt.Sprintf(args[0].(string), args[1:]...)
+
+	p.problems = append(p.problems, problem)
+	return &p.problems[len(p.problems)-1]
+}
+
+var newImporter = func(fset *token.FileSet) types.ImporterFrom {
+	return gcexportdata.NewImporter(fset, make(map[string]*types.Package))
+}
+
+func (p *pkg) typeCheck() error {
+	config := &types.Config{
+		// By setting a no-op error reporter, the type checker does as much work as possible.
+		Error:    func(error) {},
+		Importer: newImporter(p.fset),
+	}
+	info := &types.Info{
+		Types:  make(map[ast.Expr]types.TypeAndValue),
+		Defs:   make(map[*ast.Ident]types.Object),
+		Uses:   make(map[*ast.Ident]types.Object),
+		Scopes: make(map[ast.Node]*types.Scope),
+	}
+	var anyFile *file
+	var astFiles []*ast.File
+	for _, f := range p.files {
+		anyFile = f
+		astFiles = append(astFiles, f.f)
+	}
+	pkg, err := config.Check(anyFile.f.Name.Name, p.fset, astFiles, info)
+	// Remember the typechecking info, even if config.Check failed,
+	// since we will get partial information.
+	p.typesPkg = pkg
+	p.typesInfo = info
+	return err
+}
+
+func (p *pkg) typeOf(expr ast.Expr) types.Type {
+	if p.typesInfo == nil {
+		return nil
+	}
+	return p.typesInfo.TypeOf(expr)
+}
+
+func (p *pkg) isNamedType(typ types.Type, importPath, name string) bool {
+	n, ok := typ.(*types.Named)
+	if !ok {
+		return false
+	}
+	tn := n.Obj()
+	return tn != nil && tn.Pkg() != nil && tn.Pkg().Path() == importPath && tn.Name() == name
+}
+
+// scopeOf returns the tightest scope encompassing id.
+func (p *pkg) scopeOf(id *ast.Ident) *types.Scope {
+	var scope *types.Scope
+	if obj := p.typesInfo.ObjectOf(id); obj != nil {
+		scope = obj.Parent()
+	}
+	if scope == p.typesPkg.Scope() {
+		// We were given a top-level identifier.
+		// Use the file-level scope instead of the package-level scope.
+		pos := id.Pos()
+		for _, f := range p.files {
+			if f.f.Pos() <= pos && pos < f.f.End() {
+				scope = p.typesInfo.Scopes[f.f]
+				break
+			}
+		}
+	}
+	return scope
+}
+
+func (p *pkg) scanSortable() {
+	p.sortable = make(map[string]bool)
+
+	// bitfield for which methods exist on each type.
+	const (
+		Len = 1 << iota
+		Less
+		Swap
+	)
+	nmap := map[string]int{"Len": Len, "Less": Less, "Swap": Swap}
+	has := make(map[string]int)
+	for _, f := range p.files {
+		f.walk(func(n ast.Node) bool {
+			fn, ok := n.(*ast.FuncDecl)
+			if !ok || fn.Recv == nil || len(fn.Recv.List) == 0 {
+				return true
+			}
+			// TODO(dsymonds): We could check the signature to be more precise.
+			recv := receiverType(fn)
+			if i, ok := nmap[fn.Name.Name]; ok {
+				has[recv] |= i
+			}
+			return false
+		})
+	}
+	for typ, ms := range has {
+		if ms == Len|Less|Swap {
+			p.sortable[typ] = true
+		}
+	}
+}
+
+func (p *pkg) isMain() bool {
+	for _, f := range p.files {
+		if f.isMain() {
+			return true
+		}
+	}
+	return false
+}
+
+func (f *file) isMain() bool {
+	if f.f.Name.Name == "main" {
+		return true
+	}
+	return false
+}
+
+// lintPackageComment checks package comments. It complains if
+// there is no package comment, or if it is not of the right form.
+// This has a notable false positive in that a package comment
+// could rightfully appear in a different file of the same package,
+// but that's not easy to fix since this linter is file-oriented.
+func (f *file) lintPackageComment() {
+	if f.isTest() {
+		return
+	}
+
+	const ref = styleGuideBase + "#package-comments"
+	prefix := "Package " + f.f.Name.Name + " "
+
+	// Look for a detached package comment.
+	// First, scan for the last comment that occurs before the "package" keyword.
+	var lastCG *ast.CommentGroup
+	for _, cg := range f.f.Comments {
+		if cg.Pos() > f.f.Package {
+			// Gone past "package" keyword.
+			break
+		}
+		lastCG = cg
+	}
+	if lastCG != nil && strings.HasPrefix(lastCG.Text(), prefix) {
+		endPos := f.fset.Position(lastCG.End())
+		pkgPos := f.fset.Position(f.f.Package)
+		if endPos.Line+1 < pkgPos.Line {
+			// There isn't a great place to anchor this error;
+			// the start of the blank lines between the doc and the package statement
+			// is at least pointing at the location of the problem.
+			pos := token.Position{
+				Filename: endPos.Filename,
+				// Offset not set; it is non-trivial, and doesn't appear to be needed.
+				Line:   endPos.Line + 1,
+				Column: 1,
+			}
+			f.pkg.errorfAt(pos, 0.9, link(ref), category("comments"), "package comment is detached; there should be no blank lines between it and the package statement")
+			return
+		}
+	}
+
+	if f.f.Doc == nil {
+		f.errorf(f.f, 0.2, link(ref), category("comments"), "should have a package comment, unless it's in another file for this package")
+		return
+	}
+	s := f.f.Doc.Text()
+	if ts := strings.TrimLeft(s, " \t"); ts != s {
+		f.errorf(f.f.Doc, 1, link(ref), category("comments"), "package comment should not have leading space")
+		s = ts
+	}
+	// Only non-main packages need to keep to this form.
+	if !f.pkg.main && !strings.HasPrefix(s, prefix) {
+		f.errorf(f.f.Doc, 1, link(ref), category("comments"), `package comment should be of the form "%s..."`, prefix)
+	}
+}
+
+// lintBlankImports complains if a non-main package has blank imports that are
+// not documented.
+func (f *file) lintBlankImports() {
+	// In package main and in tests, we don't complain about blank imports.
+	if f.pkg.main || f.isTest() {
+		return
+	}
+
+	// The first element of each contiguous group of blank imports should have
+	// an explanatory comment of some kind.
+	for i, imp := range f.f.Imports {
+		pos := f.fset.Position(imp.Pos())
+
+		if !isBlank(imp.Name) {
+			continue // Ignore non-blank imports.
+		}
+		if i > 0 {
+			prev := f.f.Imports[i-1]
+			prevPos := f.fset.Position(prev.Pos())
+			if isBlank(prev.Name) && prevPos.Line+1 == pos.Line {
+				continue // A subsequent blank in a group.
+			}
+		}
+
+		// This is the first blank import of a group.
+		if imp.Doc == nil && imp.Comment == nil {
+			ref := ""
+			f.errorf(imp, 1, link(ref), category("imports"), "a blank import should be only in a main or test package, or have a comment justifying it")
+		}
+	}
+}
+
+// lintImports examines import blocks.
+func (f *file) lintImports() {
+	for i, is := range f.f.Imports {
+		_ = i
+		if is.Name != nil && is.Name.Name == "." && !f.isTest() {
+			f.errorf(is, 1, link(styleGuideBase+"#import-dot"), category("imports"), "should not use dot imports")
+		}
+
+	}
+}
+
+const docCommentsLink = styleGuideBase + "#doc-comments"
+
+// lintExported examines the exported names.
+// It complains if any required doc comments are missing,
+// or if they are not of the right form. The exact rules are in
+// lintFuncDoc, lintTypeDoc and lintValueSpecDoc; this function
+// also tracks the GenDecl structure being traversed to permit
+// doc comments for constants to be on top of the const block.
+// It also complains if the names stutter when combined with
+// the package name.
+func (f *file) lintExported() {
+	if f.isTest() {
+		return
+	}
+
+	var lastGen *ast.GenDecl // last GenDecl entered.
+
+	// Set of GenDecls that have already had missing comments flagged.
+	genDeclMissingComments := make(map[*ast.GenDecl]bool)
+
+	f.walk(func(node ast.Node) bool {
+		switch v := node.(type) {
+		case *ast.GenDecl:
+			if v.Tok == token.IMPORT {
+				return false
+			}
+			// token.CONST, token.TYPE or token.VAR
+			lastGen = v
+			return true
+		case *ast.FuncDecl:
+			f.lintFuncDoc(v)
+			if v.Recv == nil {
+				// Only check for stutter on functions, not methods.
+				// Method names are not used package-qualified.
+				f.checkStutter(v.Name, "func")
+			}
+			// Don't proceed inside funcs.
+			return false
+		case *ast.TypeSpec:
+			// inside a GenDecl, which usually has the doc
+			doc := v.Doc
+			if doc == nil {
+				doc = lastGen.Doc
+			}
+			f.lintTypeDoc(v, doc)
+			f.checkStutter(v.Name, "type")
+			// Don't proceed inside types.
+			return false
+		case *ast.ValueSpec:
+			f.lintValueSpecDoc(v, lastGen, genDeclMissingComments)
+			return false
+		}
+		return true
+	})
+}
+
+var allCapsRE = regexp.MustCompile(`^[A-Z0-9_]+$`)
+
+// knownNameExceptions is a set of names that are known to be exempt from naming checks.
+// This is usually because they are constrained by having to match names in the
+// standard library.
+var knownNameExceptions = map[string]bool{
+	"LastInsertId": true, // must match database/sql
+	"kWh":          true,
+}
+
+// lintNames examines all names in the file.
+// It complains if any use underscores or incorrect known initialisms.
+func (f *file) lintNames() {
+	// Package names need slightly different handling than other names.
+	if strings.Contains(f.f.Name.Name, "_") && !strings.HasSuffix(f.f.Name.Name, "_test") {
+		f.errorf(f.f, 1, link("http://golang.org/doc/effective_go.html#package-names"), category("naming"), "don't use an underscore in package name")
+	}
+
+	check := func(id *ast.Ident, thing string) {
+		if id.Name == "_" {
+			return
+		}
+		if knownNameExceptions[id.Name] {
+			return
+		}
+
+		// Handle two common styles from other languages that don't belong in Go.
+		if len(id.Name) >= 5 && allCapsRE.MatchString(id.Name) && strings.Contains(id.Name, "_") {
+			f.errorf(id, 0.8, link(styleGuideBase+"#mixed-caps"), category("naming"), "don't use ALL_CAPS in Go names; use CamelCase")
+			return
+		}
+		if len(id.Name) > 2 && id.Name[0] == 'k' && id.Name[1] >= 'A' && id.Name[1] <= 'Z' {
+			should := string(id.Name[1]+'a'-'A') + id.Name[2:]
+			f.errorf(id, 0.8, link(styleGuideBase+"#mixed-caps"), category("naming"), "don't use leading k in Go names; %s %s should be %s", thing, id.Name, should)
+		}
+
+		should := lintName(id.Name)
+		if id.Name == should {
+			return
+		}
+
+		if len(id.Name) > 2 && strings.Contains(id.Name[1:], "_") {
+			f.errorf(id, 0.9, link("http://golang.org/doc/effective_go.html#mixed-caps"), category("naming"), "don't use underscores in Go names; %s %s should be %s", thing, id.Name, should)
+			return
+		}
+		f.errorf(id, 0.8, link(styleGuideBase+"#initialisms"), category("naming"), "%s %s should be %s", thing, id.Name, should)
+	}
+	checkList := func(fl *ast.FieldList, thing string) {
+		if fl == nil {
+			return
+		}
+		for _, f := range fl.List {
+			for _, id := range f.Names {
+				check(id, thing)
+			}
+		}
+	}
+	f.walk(func(node ast.Node) bool {
+		switch v := node.(type) {
+		case *ast.AssignStmt:
+			if v.Tok == token.ASSIGN {
+				return true
+			}
+			for _, exp := range v.Lhs {
+				if id, ok := exp.(*ast.Ident); ok {
+					check(id, "var")
+				}
+			}
+		case *ast.FuncDecl:
+			if f.isTest() && (strings.HasPrefix(v.Name.Name, "Example") || strings.HasPrefix(v.Name.Name, "Test") || strings.HasPrefix(v.Name.Name, "Benchmark")) {
+				return true
+			}
+
+			thing := "func"
+			if v.Recv != nil {
+				thing = "method"
+			}
+
+			// Exclude naming warnings for functions that are exported to C but
+			// not exported in the Go API.
+			// See https://github.com/golang/lint/issues/144.
+			if ast.IsExported(v.Name.Name) || !isCgoExported(v) {
+				check(v.Name, thing)
+			}
+
+			checkList(v.Type.Params, thing+" parameter")
+			checkList(v.Type.Results, thing+" result")
+		case *ast.GenDecl:
+			if v.Tok == token.IMPORT {
+				return true
+			}
+			var thing string
+			switch v.Tok {
+			case token.CONST:
+				thing = "const"
+			case token.TYPE:
+				thing = "type"
+			case token.VAR:
+				thing = "var"
+			}
+			for _, spec := range v.Specs {
+				switch s := spec.(type) {
+				case *ast.TypeSpec:
+					check(s.Name, thing)
+				case *ast.ValueSpec:
+					for _, id := range s.Names {
+						check(id, thing)
+					}
+				}
+			}
+		case *ast.InterfaceType:
+			// Do not check interface method names.
+			// They are often constrainted by the method names of concrete types.
+			for _, x := range v.Methods.List {
+				ft, ok := x.Type.(*ast.FuncType)
+				if !ok { // might be an embedded interface name
+					continue
+				}
+				checkList(ft.Params, "interface method parameter")
+				checkList(ft.Results, "interface method result")
+			}
+		case *ast.RangeStmt:
+			if v.Tok == token.ASSIGN {
+				return true
+			}
+			if id, ok := v.Key.(*ast.Ident); ok {
+				check(id, "range var")
+			}
+			if id, ok := v.Value.(*ast.Ident); ok {
+				check(id, "range var")
+			}
+		case *ast.StructType:
+			for _, f := range v.Fields.List {
+				for _, id := range f.Names {
+					check(id, "struct field")
+				}
+			}
+		}
+		return true
+	})
+}
+
+// lintName returns a different name if it should be different.
+func lintName(name string) (should string) {
+	// Fast path for simple cases: "_" and all lowercase.
+	if name == "_" {
+		return name
+	}
+	allLower := true
+	for _, r := range name {
+		if !unicode.IsLower(r) {
+			allLower = false
+			break
+		}
+	}
+	if allLower {
+		return name
+	}
+
+	// Split camelCase at any lower->upper transition, and split on underscores.
+	// Check each word for common initialisms.
+	runes := []rune(name)
+	w, i := 0, 0 // index of start of word, scan
+	for i+1 <= len(runes) {
+		eow := false // whether we hit the end of a word
+		if i+1 == len(runes) {
+			eow = true
+		} else if runes[i+1] == '_' {
+			// underscore; shift the remainder forward over any run of underscores
+			eow = true
+			n := 1
+			for i+n+1 < len(runes) && runes[i+n+1] == '_' {
+				n++
+			}
+
+			// Leave at most one underscore if the underscore is between two digits
+			if i+n+1 < len(runes) && unicode.IsDigit(runes[i]) && unicode.IsDigit(runes[i+n+1]) {
+				n--
+			}
+
+			copy(runes[i+1:], runes[i+n+1:])
+			runes = runes[:len(runes)-n]
+		} else if unicode.IsLower(runes[i]) && !unicode.IsLower(runes[i+1]) {
+			// lower->non-lower
+			eow = true
+		}
+		i++
+		if !eow {
+			continue
+		}
+
+		// [w,i) is a word.
+		word := string(runes[w:i])
+		if u := strings.ToUpper(word); commonInitialisms[u] {
+			// Keep consistent case, which is lowercase only at the start.
+			if w == 0 && unicode.IsLower(runes[w]) {
+				u = strings.ToLower(u)
+			}
+			// All the common initialisms are ASCII,
+			// so we can replace the bytes exactly.
+			copy(runes[w:], []rune(u))
+		} else if w > 0 && strings.ToLower(word) == word {
+			// already all lowercase, and not the first word, so uppercase the first character.
+			runes[w] = unicode.ToUpper(runes[w])
+		}
+		w = i
+	}
+	return string(runes)
+}
+
+// commonInitialisms is a set of common initialisms.
+// Only add entries that are highly unlikely to be non-initialisms.
+// For instance, "ID" is fine (Freudian code is rare), but "AND" is not.
+var commonInitialisms = map[string]bool{
+	"ACL":   true,
+	"API":   true,
+	"ASCII": true,
+	"CPU":   true,
+	"CSS":   true,
+	"DNS":   true,
+	"EOF":   true,
+	"GUID":  true,
+	"HTML":  true,
+	"HTTP":  true,
+	"HTTPS": true,
+	"ID":    true,
+	"IP":    true,
+	"JSON":  true,
+	"LHS":   true,
+	"QPS":   true,
+	"RAM":   true,
+	"RHS":   true,
+	"RPC":   true,
+	"SLA":   true,
+	"SMTP":  true,
+	"SQL":   true,
+	"SSH":   true,
+	"TCP":   true,
+	"TLS":   true,
+	"TTL":   true,
+	"UDP":   true,
+	"UI":    true,
+	"UID":   true,
+	"UUID":  true,
+	"URI":   true,
+	"URL":   true,
+	"UTF8":  true,
+	"VM":    true,
+	"XML":   true,
+	"XMPP":  true,
+	"XSRF":  true,
+	"XSS":   true,
+}
+
+// lintTypeDoc examines the doc comment on a type.
+// It complains if they are missing from an exported type,
+// or if they are not of the standard form.
+func (f *file) lintTypeDoc(t *ast.TypeSpec, doc *ast.CommentGroup) {
+	if !ast.IsExported(t.Name.Name) {
+		return
+	}
+	if doc == nil {
+		f.errorf(t, 1, link(docCommentsLink), category("comments"), "exported type %v should have comment or be unexported", t.Name)
+		return
+	}
+
+	s := doc.Text()
+	articles := [...]string{"A", "An", "The"}
+	for _, a := range articles {
+		if strings.HasPrefix(s, a+" ") {
+			s = s[len(a)+1:]
+			break
+		}
+	}
+	if !strings.HasPrefix(s, t.Name.Name+" ") {
+		f.errorf(doc, 1, link(docCommentsLink), category("comments"), `comment on exported type %v should be of the form "%v ..." (with optional leading article)`, t.Name, t.Name)
+	}
+}
+
+var commonMethods = map[string]bool{
+	"Error":     true,
+	"Read":      true,
+	"ServeHTTP": true,
+	"String":    true,
+	"Write":     true,
+}
+
+// lintFuncDoc examines doc comments on functions and methods.
+// It complains if they are missing, or not of the right form.
+// It has specific exclusions for well-known methods (see commonMethods above).
+func (f *file) lintFuncDoc(fn *ast.FuncDecl) {
+	if !ast.IsExported(fn.Name.Name) {
+		// func is unexported
+		return
+	}
+	kind := "function"
+	name := fn.Name.Name
+	if fn.Recv != nil && len(fn.Recv.List) > 0 {
+		// method
+		kind = "method"
+		recv := receiverType(fn)
+		if !ast.IsExported(recv) {
+			// receiver is unexported
+			return
+		}
+		if commonMethods[name] {
+			return
+		}
+		switch name {
+		case "Len", "Less", "Swap":
+			if f.pkg.sortable[recv] {
+				return
+			}
+		}
+		name = recv + "." + name
+	}
+	if fn.Doc == nil {
+		f.errorf(fn, 1, link(docCommentsLink), category("comments"), "exported %s %s should have comment or be unexported", kind, name)
+		return
+	}
+	s := fn.Doc.Text()
+	prefix := fn.Name.Name + " "
+	if !strings.HasPrefix(s, prefix) {
+		f.errorf(fn.Doc, 1, link(docCommentsLink), category("comments"), `comment on exported %s %s should be of the form "%s..."`, kind, name, prefix)
+	}
+}
+
+// lintValueSpecDoc examines package-global variables and constants.
+// It complains if they are not individually declared,
+// or if they are not suitably documented in the right form (unless they are in a block that is commented).
+func (f *file) lintValueSpecDoc(vs *ast.ValueSpec, gd *ast.GenDecl, genDeclMissingComments map[*ast.GenDecl]bool) {
+	kind := "var"
+	if gd.Tok == token.CONST {
+		kind = "const"
+	}
+
+	if len(vs.Names) > 1 {
+		// Check that none are exported except for the first.
+		for _, n := range vs.Names[1:] {
+			if ast.IsExported(n.Name) {
+				f.errorf(vs, 1, category("comments"), "exported %s %s should have its own declaration", kind, n.Name)
+				return
+			}
+		}
+	}
+
+	// Only one name.
+	name := vs.Names[0].Name
+	if !ast.IsExported(name) {
+		return
+	}
+
+	if vs.Doc == nil && gd.Doc == nil {
+		if genDeclMissingComments[gd] {
+			return
+		}
+		block := ""
+		if kind == "const" && gd.Lparen.IsValid() {
+			block = " (or a comment on this block)"
+		}
+		f.errorf(vs, 1, link(docCommentsLink), category("comments"), "exported %s %s should have comment%s or be unexported", kind, name, block)
+		genDeclMissingComments[gd] = true
+		return
+	}
+	// If this GenDecl has parens and a comment, we don't check its comment form.
+	if gd.Lparen.IsValid() && gd.Doc != nil {
+		return
+	}
+	// The relevant text to check will be on either vs.Doc or gd.Doc.
+	// Use vs.Doc preferentially.
+	doc := vs.Doc
+	if doc == nil {
+		doc = gd.Doc
+	}
+	prefix := name + " "
+	if !strings.HasPrefix(doc.Text(), prefix) {
+		f.errorf(doc, 1, link(docCommentsLink), category("comments"), `comment on exported %s %s should be of the form "%s..."`, kind, name, prefix)
+	}
+}
+
+func (f *file) checkStutter(id *ast.Ident, thing string) {
+	pkg, name := f.f.Name.Name, id.Name
+	if !ast.IsExported(name) {
+		// unexported name
+		return
+	}
+	// A name stutters if the package name is a strict prefix
+	// and the next character of the name starts a new word.
+	if len(name) <= len(pkg) {
+		// name is too short to stutter.
+		// This permits the name to be the same as the package name.
+		return
+	}
+	if !strings.EqualFold(pkg, name[:len(pkg)]) {
+		return
+	}
+	// We can assume the name is well-formed UTF-8.
+	// If the next rune after the package name is uppercase or an underscore
+	// the it's starting a new word and thus this name stutters.
+	rem := name[len(pkg):]
+	if next, _ := utf8.DecodeRuneInString(rem); next == '_' || unicode.IsUpper(next) {
+		f.errorf(id, 0.8, link(styleGuideBase+"#package-names"), category("naming"), "%s name will be used as %s.%s by other packages, and that stutters; consider calling this %s", thing, pkg, name, rem)
+	}
+}
+
+// zeroLiteral is a set of ast.BasicLit values that are zero values.
+// It is not exhaustive.
+var zeroLiteral = map[string]bool{
+	"false": true, // bool
+	// runes
+	`'\x00'`: true,
+	`'\000'`: true,
+	// strings
+	`""`: true,
+	"``": true,
+	// numerics
+	"0":   true,
+	"0.":  true,
+	"0.0": true,
+	"0i":  true,
+}
+
+// lintVarDecls examines variable declarations. It complains about declarations with
+// redundant LHS types that can be inferred from the RHS.
+func (f *file) lintVarDecls() {
+	var lastGen *ast.GenDecl // last GenDecl entered.
+
+	f.walk(func(node ast.Node) bool {
+		switch v := node.(type) {
+		case *ast.GenDecl:
+			if v.Tok != token.CONST && v.Tok != token.VAR {
+				return false
+			}
+			lastGen = v
+			return true
+		case *ast.ValueSpec:
+			if lastGen.Tok == token.CONST {
+				return false
+			}
+			if len(v.Names) > 1 || v.Type == nil || len(v.Values) == 0 {
+				return false
+			}
+			rhs := v.Values[0]
+			// An underscore var appears in a common idiom for compile-time interface satisfaction,
+			// as in "var _ Interface = (*Concrete)(nil)".
+			if isIdent(v.Names[0], "_") {
+				return false
+			}
+			// If the RHS is a zero value, suggest dropping it.
+			zero := false
+			if lit, ok := rhs.(*ast.BasicLit); ok {
+				zero = zeroLiteral[lit.Value]
+			} else if isIdent(rhs, "nil") {
+				zero = true
+			}
+			if zero {
+				f.errorf(rhs, 0.9, category("zero-value"), "should drop = %s from declaration of var %s; it is the zero value", f.render(rhs), v.Names[0])
+				return false
+			}
+			lhsTyp := f.pkg.typeOf(v.Type)
+			rhsTyp := f.pkg.typeOf(rhs)
+
+			if !validType(lhsTyp) || !validType(rhsTyp) {
+				// Type checking failed (often due to missing imports).
+				return false
+			}
+
+			if !types.Identical(lhsTyp, rhsTyp) {
+				// Assignment to a different type is not redundant.
+				return false
+			}
+
+			// The next three conditions are for suppressing the warning in situations
+			// where we were unable to typecheck.
+
+			// If the LHS type is an interface, don't warn, since it is probably a
+			// concrete type on the RHS. Note that our feeble lexical check here
+			// will only pick up interface{} and other literal interface types;
+			// that covers most of the cases we care to exclude right now.
+			if _, ok := v.Type.(*ast.InterfaceType); ok {
+				return false
+			}
+			// If the RHS is an untyped const, only warn if the LHS type is its default type.
+			if defType, ok := f.isUntypedConst(rhs); ok && !isIdent(v.Type, defType) {
+				return false
+			}
+
+			f.errorf(v.Type, 0.8, category("type-inference"), "should omit type %s from declaration of var %s; it will be inferred from the right-hand side", f.render(v.Type), v.Names[0])
+			return false
+		}
+		return true
+	})
+}
+
+func validType(T types.Type) bool {
+	return T != nil &&
+		T != types.Typ[types.Invalid] &&
+		!strings.Contains(T.String(), "invalid type") // good but not foolproof
+}
+
+// lintElses examines else blocks. It complains about any else block whose if block ends in a return.
+func (f *file) lintElses() {
+	// We don't want to flag if { } else if { } else { } constructions.
+	// They will appear as an IfStmt whose Else field is also an IfStmt.
+	// Record such a node so we ignore it when we visit it.
+	ignore := make(map[*ast.IfStmt]bool)
+
+	f.walk(func(node ast.Node) bool {
+		ifStmt, ok := node.(*ast.IfStmt)
+		if !ok || ifStmt.Else == nil {
+			return true
+		}
+		if ignore[ifStmt] {
+			return true
+		}
+		if elseif, ok := ifStmt.Else.(*ast.IfStmt); ok {
+			ignore[elseif] = true
+			return true
+		}
+		if _, ok := ifStmt.Else.(*ast.BlockStmt); !ok {
+			// only care about elses without conditions
+			return true
+		}
+		if len(ifStmt.Body.List) == 0 {
+			return true
+		}
+		shortDecl := false // does the if statement have a ":=" initialization statement?
+		if ifStmt.Init != nil {
+			if as, ok := ifStmt.Init.(*ast.AssignStmt); ok && as.Tok == token.DEFINE {
+				shortDecl = true
+			}
+		}
+		lastStmt := ifStmt.Body.List[len(ifStmt.Body.List)-1]
+		if _, ok := lastStmt.(*ast.ReturnStmt); ok {
+			extra := ""
+			if shortDecl {
+				extra = " (move short variable declaration to its own line if necessary)"
+			}
+			f.errorf(ifStmt.Else, 1, link(styleGuideBase+"#indent-error-flow"), category("indent"), "if block ends with a return statement, so drop this else and outdent its block"+extra)
+		}
+		return true
+	})
+}
+
+// lintRanges examines range clauses. It complains about redundant constructions.
+func (f *file) lintRanges() {
+	f.walk(func(node ast.Node) bool {
+		rs, ok := node.(*ast.RangeStmt)
+		if !ok {
+			return true
+		}
+		if rs.Value == nil {
+			// for x = range m { ... }
+			return true // single var form
+		}
+		if !isIdent(rs.Value, "_") {
+			// for ?, y = range m { ... }
+			return true
+		}
+
+		p := f.errorf(rs.Value, 1, category("range-loop"), "should omit 2nd value from range; this loop is equivalent to `for %s %s range ...`", f.render(rs.Key), rs.Tok)
+
+		newRS := *rs // shallow copy
+		newRS.Value = nil
+		p.ReplacementLine = f.firstLineOf(&newRS, rs)
+
+		return true
+	})
+}
+
+// lintErrorf examines errors.New and testing.Error calls. It complains if its only argument is an fmt.Sprintf invocation.
+func (f *file) lintErrorf() {
+	f.walk(func(node ast.Node) bool {
+		ce, ok := node.(*ast.CallExpr)
+		if !ok || len(ce.Args) != 1 {
+			return true
+		}
+		isErrorsNew := isPkgDot(ce.Fun, "errors", "New")
+		var isTestingError bool
+		se, ok := ce.Fun.(*ast.SelectorExpr)
+		if ok && se.Sel.Name == "Error" {
+			if typ := f.pkg.typeOf(se.X); typ != nil {
+				isTestingError = typ.String() == "*testing.T"
+			}
+		}
+		if !isErrorsNew && !isTestingError {
+			return true
+		}
+		arg := ce.Args[0]
+		ce, ok = arg.(*ast.CallExpr)
+		if !ok || !isPkgDot(ce.Fun, "fmt", "Sprintf") {
+			return true
+		}
+		errorfPrefix := "fmt"
+		if isTestingError {
+			errorfPrefix = f.render(se.X)
+		}
+		p := f.errorf(node, 1, category("errors"), "should replace %s(fmt.Sprintf(...)) with %s.Errorf(...)", f.render(se), errorfPrefix)
+
+		m := f.srcLineWithMatch(ce, `^(.*)`+f.render(se)+`\(fmt\.Sprintf\((.*)\)\)(.*)$`)
+		if m != nil {
+			p.ReplacementLine = m[1] + errorfPrefix + ".Errorf(" + m[2] + ")" + m[3]
+		}
+
+		return true
+	})
+}
+
+// lintErrors examines global error vars. It complains if they aren't named in the standard way.
+func (f *file) lintErrors() {
+	for _, decl := range f.f.Decls {
+		gd, ok := decl.(*ast.GenDecl)
+		if !ok || gd.Tok != token.VAR {
+			continue
+		}
+		for _, spec := range gd.Specs {
+			spec := spec.(*ast.ValueSpec)
+			if len(spec.Names) != 1 || len(spec.Values) != 1 {
+				continue
+			}
+			ce, ok := spec.Values[0].(*ast.CallExpr)
+			if !ok {
+				continue
+			}
+			if !isPkgDot(ce.Fun, "errors", "New") && !isPkgDot(ce.Fun, "fmt", "Errorf") {
+				continue
+			}
+
+			id := spec.Names[0]
+			prefix := "err"
+			if id.IsExported() {
+				prefix = "Err"
+			}
+			if !strings.HasPrefix(id.Name, prefix) {
+				f.errorf(id, 0.9, category("naming"), "error var %s should have name of the form %sFoo", id.Name, prefix)
+			}
+		}
+	}
+}
+
+func lintErrorString(s string) (isClean bool, conf float64) {
+	const basicConfidence = 0.8
+	const capConfidence = basicConfidence - 0.2
+	first, firstN := utf8.DecodeRuneInString(s)
+	last, _ := utf8.DecodeLastRuneInString(s)
+	if last == '.' || last == ':' || last == '!' || last == '\n' {
+		return false, basicConfidence
+	}
+	if unicode.IsUpper(first) {
+		// People use proper nouns and exported Go identifiers in error strings,
+		// so decrease the confidence of warnings for capitalization.
+		if len(s) <= firstN {
+			return false, capConfidence
+		}
+		// Flag strings starting with something that doesn't look like an initialism.
+		if second, _ := utf8.DecodeRuneInString(s[firstN:]); !unicode.IsUpper(second) {
+			return false, capConfidence
+		}
+	}
+	return true, 0
+}
+
+// lintErrorStrings examines error strings.
+// It complains if they are capitalized or end in punctuation or a newline.
+func (f *file) lintErrorStrings() {
+	f.walk(func(node ast.Node) bool {
+		ce, ok := node.(*ast.CallExpr)
+		if !ok {
+			return true
+		}
+		if !isPkgDot(ce.Fun, "errors", "New") && !isPkgDot(ce.Fun, "fmt", "Errorf") {
+			return true
+		}
+		if len(ce.Args) < 1 {
+			return true
+		}
+		str, ok := ce.Args[0].(*ast.BasicLit)
+		if !ok || str.Kind != token.STRING {
+			return true
+		}
+		s, _ := strconv.Unquote(str.Value) // can assume well-formed Go
+		if s == "" {
+			return true
+		}
+		clean, conf := lintErrorString(s)
+		if clean {
+			return true
+		}
+
+		f.errorf(str, conf, link(styleGuideBase+"#error-strings"), category("errors"),
+			"error strings should not be capitalized or end with punctuation or a newline")
+		return true
+	})
+}
+
+// lintReceiverNames examines receiver names. It complains about inconsistent
+// names used for the same type and names such as "this".
+func (f *file) lintReceiverNames() {
+	typeReceiver := map[string]string{}
+	f.walk(func(n ast.Node) bool {
+		fn, ok := n.(*ast.FuncDecl)
+		if !ok || fn.Recv == nil || len(fn.Recv.List) == 0 {
+			return true
+		}
+		names := fn.Recv.List[0].Names
+		if len(names) < 1 {
+			return true
+		}
+		name := names[0].Name
+		const ref = styleGuideBase + "#receiver-names"
+		if name == "_" {
+			f.errorf(n, 1, link(ref), category("naming"), `receiver name should not be an underscore, omit the name if it is unused`)
+			return true
+		}
+		if name == "this" || name == "self" {
+			f.errorf(n, 1, link(ref), category("naming"), `receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"`)
+			return true
+		}
+		recv := receiverType(fn)
+		if prev, ok := typeReceiver[recv]; ok && prev != name {
+			f.errorf(n, 1, link(ref), category("naming"), "receiver name %s should be consistent with previous receiver name %s for %s", name, prev, recv)
+			return true
+		}
+		typeReceiver[recv] = name
+		return true
+	})
+}
+
+// lintIncDec examines statements that increment or decrement a variable.
+// It complains if they don't use x++ or x--.
+func (f *file) lintIncDec() {
+	f.walk(func(n ast.Node) bool {
+		as, ok := n.(*ast.AssignStmt)
+		if !ok {
+			return true
+		}
+		if len(as.Lhs) != 1 {
+			return true
+		}
+		if !isOne(as.Rhs[0]) {
+			return true
+		}
+		var suffix string
+		switch as.Tok {
+		case token.ADD_ASSIGN:
+			suffix = "++"
+		case token.SUB_ASSIGN:
+			suffix = "--"
+		default:
+			return true
+		}
+		f.errorf(as, 0.8, category("unary-op"), "should replace %s with %s%s", f.render(as), f.render(as.Lhs[0]), suffix)
+		return true
+	})
+}
+
+// lintErrorReturn examines function declarations that return an error.
+// It complains if the error isn't the last parameter.
+func (f *file) lintErrorReturn() {
+	f.walk(func(n ast.Node) bool {
+		fn, ok := n.(*ast.FuncDecl)
+		if !ok || fn.Type.Results == nil {
+			return true
+		}
+		ret := fn.Type.Results.List
+		if len(ret) <= 1 {
+			return true
+		}
+		// An error return parameter should be the last parameter.
+		// Flag any error parameters found before the last.
+		for _, r := range ret[:len(ret)-1] {
+			if isIdent(r.Type, "error") {
+				f.errorf(fn, 0.9, category("arg-order"), "error should be the last type when returning multiple items")
+				break // only flag one
+			}
+		}
+		return true
+	})
+}
+
+// lintUnexportedReturn examines exported function declarations.
+// It complains if any return an unexported type.
+func (f *file) lintUnexportedReturn() {
+	f.walk(func(n ast.Node) bool {
+		fn, ok := n.(*ast.FuncDecl)
+		if !ok {
+			return true
+		}
+		if fn.Type.Results == nil {
+			return false
+		}
+		if !fn.Name.IsExported() {
+			return false
+		}
+		thing := "func"
+		if fn.Recv != nil && len(fn.Recv.List) > 0 {
+			thing = "method"
+			if !ast.IsExported(receiverType(fn)) {
+				// Don't report exported methods of unexported types,
+				// such as private implementations of sort.Interface.
+				return false
+			}
+		}
+		for _, ret := range fn.Type.Results.List {
+			typ := f.pkg.typeOf(ret.Type)
+			if exportedType(typ) {
+				continue
+			}
+			f.errorf(ret.Type, 0.8, category("unexported-type-in-api"),
+				"exported %s %s returns unexported type %s, which can be annoying to use",
+				thing, fn.Name.Name, typ)
+			break // only flag one
+		}
+		return false
+	})
+}
+
+// exportedType reports whether typ is an exported type.
+// It is imprecise, and will err on the side of returning true,
+// such as for composite types.
+func exportedType(typ types.Type) bool {
+	switch T := typ.(type) {
+	case *types.Named:
+		// Builtin types have no package.
+		return T.Obj().Pkg() == nil || T.Obj().Exported()
+	case *types.Map:
+		return exportedType(T.Key()) && exportedType(T.Elem())
+	case interface {
+		Elem() types.Type
+	}: // array, slice, pointer, chan
+		return exportedType(T.Elem())
+	}
+	// Be conservative about other types, such as struct, interface, etc.
+	return true
+}
+
+// timeSuffixes is a list of name suffixes that imply a time unit.
+// This is not an exhaustive list.
+var timeSuffixes = []string{
+	"Sec", "Secs", "Seconds",
+	"Msec", "Msecs",
+	"Milli", "Millis", "Milliseconds",
+	"Usec", "Usecs", "Microseconds",
+	"MS", "Ms",
+}
+
+func (f *file) lintTimeNames() {
+	f.walk(func(node ast.Node) bool {
+		v, ok := node.(*ast.ValueSpec)
+		if !ok {
+			return true
+		}
+		for _, name := range v.Names {
+			origTyp := f.pkg.typeOf(name)
+			// Look for time.Duration or *time.Duration;
+			// the latter is common when using flag.Duration.
+			typ := origTyp
+			if pt, ok := typ.(*types.Pointer); ok {
+				typ = pt.Elem()
+			}
+			if !f.pkg.isNamedType(typ, "time", "Duration") {
+				continue
+			}
+			suffix := ""
+			for _, suf := range timeSuffixes {
+				if strings.HasSuffix(name.Name, suf) {
+					suffix = suf
+					break
+				}
+			}
+			if suffix == "" {
+				continue
+			}
+			f.errorf(v, 0.9, category("time"), "var %s is of type %v; don't use unit-specific suffix %q", name.Name, origTyp, suffix)
+		}
+		return true
+	})
+}
+
+// lintContextKeyTypes checks for call expressions to context.WithValue with
+// basic types used for the key argument.
+// See: https://golang.org/issue/17293
+func (f *file) lintContextKeyTypes() {
+	f.walk(func(node ast.Node) bool {
+		switch node := node.(type) {
+		case *ast.CallExpr:
+			f.checkContextKeyType(node)
+		}
+
+		return true
+	})
+}
+
+// checkContextKeyType reports an error if the call expression calls
+// context.WithValue with a key argument of basic type.
+func (f *file) checkContextKeyType(x *ast.CallExpr) {
+	sel, ok := x.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return
+	}
+	pkg, ok := sel.X.(*ast.Ident)
+	if !ok || pkg.Name != "context" {
+		return
+	}
+	if sel.Sel.Name != "WithValue" {
+		return
+	}
+
+	// key is second argument to context.WithValue
+	if len(x.Args) != 3 {
+		return
+	}
+	key := f.pkg.typesInfo.Types[x.Args[1]]
+
+	if ktyp, ok := key.Type.(*types.Basic); ok && ktyp.Kind() != types.Invalid {
+		f.errorf(x, 1.0, category("context"), fmt.Sprintf("should not use basic type %s as key in context.WithValue", key.Type))
+	}
+}
+
+// lintContextArgs examines function declarations that contain an
+// argument with a type of context.Context
+// It complains if that argument isn't the first parameter.
+func (f *file) lintContextArgs() {
+	f.walk(func(n ast.Node) bool {
+		fn, ok := n.(*ast.FuncDecl)
+		if !ok || len(fn.Type.Params.List) <= 1 {
+			return true
+		}
+		// A context.Context should be the first parameter of a function.
+		// Flag any that show up after the first.
+		for _, arg := range fn.Type.Params.List[1:] {
+			if isPkgDot(arg.Type, "context", "Context") {
+				f.errorf(fn, 0.9, link("https://golang.org/pkg/context/"), category("arg-order"), "context.Context should be the first parameter of a function")
+				break // only flag one
+			}
+		}
+		return true
+	})
+}
+
+// containsComments returns whether the interval [start, end) contains any
+// comments without "// MATCH " prefix.
+func (f *file) containsComments(start, end token.Pos) bool {
+	for _, cgroup := range f.f.Comments {
+		comments := cgroup.List
+		if comments[0].Slash >= end {
+			// All comments starting with this group are after end pos.
+			return false
+		}
+		if comments[len(comments)-1].Slash < start {
+			// Comments group ends before start pos.
+			continue
+		}
+		for _, c := range comments {
+			if start <= c.Slash && c.Slash < end && !strings.HasPrefix(c.Text, "// MATCH ") {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (f *file) lintIfError() {
+	f.walk(func(node ast.Node) bool {
+		switch v := node.(type) {
+		case *ast.BlockStmt:
+			for i := 0; i < len(v.List)-1; i++ {
+				// if var := whatever; var != nil { return var }
+				s, ok := v.List[i].(*ast.IfStmt)
+				if !ok || s.Body == nil || len(s.Body.List) != 1 || s.Else != nil {
+					continue
+				}
+				assign, ok := s.Init.(*ast.AssignStmt)
+				if !ok || len(assign.Lhs) != 1 || !(assign.Tok == token.DEFINE || assign.Tok == token.ASSIGN) {
+					continue
+				}
+				id, ok := assign.Lhs[0].(*ast.Ident)
+				if !ok {
+					continue
+				}
+				expr, ok := s.Cond.(*ast.BinaryExpr)
+				if !ok || expr.Op != token.NEQ {
+					continue
+				}
+				if lhs, ok := expr.X.(*ast.Ident); !ok || lhs.Name != id.Name {
+					continue
+				}
+				if rhs, ok := expr.Y.(*ast.Ident); !ok || rhs.Name != "nil" {
+					continue
+				}
+				r, ok := s.Body.List[0].(*ast.ReturnStmt)
+				if !ok || len(r.Results) != 1 {
+					continue
+				}
+				if r, ok := r.Results[0].(*ast.Ident); !ok || r.Name != id.Name {
+					continue
+				}
+
+				// return nil
+				r, ok = v.List[i+1].(*ast.ReturnStmt)
+				if !ok || len(r.Results) != 1 {
+					continue
+				}
+				if r, ok := r.Results[0].(*ast.Ident); !ok || r.Name != "nil" {
+					continue
+				}
+
+				// check if there are any comments explaining the construct, don't emit an error if there are some.
+				if f.containsComments(s.Pos(), r.Pos()) {
+					continue
+				}
+
+				f.errorf(v.List[i], 0.9, "redundant if ...; err != nil check, just return error instead.")
+			}
+		}
+		return true
+	})
+}
+
+// receiverType returns the named type of the method receiver, sans "*",
+// or "invalid-type" if fn.Recv is ill formed.
+func receiverType(fn *ast.FuncDecl) string {
+	switch e := fn.Recv.List[0].Type.(type) {
+	case *ast.Ident:
+		return e.Name
+	case *ast.StarExpr:
+		if id, ok := e.X.(*ast.Ident); ok {
+			return id.Name
+		}
+	}
+	// The parser accepts much more than just the legal forms.
+	return "invalid-type"
+}
+
+func (f *file) walk(fn func(ast.Node) bool) {
+	ast.Walk(walker(fn), f.f)
+}
+
+func (f *file) render(x interface{}) string {
+	var buf bytes.Buffer
+	if err := printer.Fprint(&buf, f.fset, x); err != nil {
+		panic(err)
+	}
+	return buf.String()
+}
+
+func (f *file) debugRender(x interface{}) string {
+	var buf bytes.Buffer
+	if err := ast.Fprint(&buf, f.fset, x, nil); err != nil {
+		panic(err)
+	}
+	return buf.String()
+}
+
+// walker adapts a function to satisfy the ast.Visitor interface.
+// The function return whether the walk should proceed into the node's children.
+type walker func(ast.Node) bool
+
+func (w walker) Visit(node ast.Node) ast.Visitor {
+	if w(node) {
+		return w
+	}
+	return nil
+}
+
+func isIdent(expr ast.Expr, ident string) bool {
+	id, ok := expr.(*ast.Ident)
+	return ok && id.Name == ident
+}
+
+// isBlank returns whether id is the blank identifier "_".
+// If id == nil, the answer is false.
+func isBlank(id *ast.Ident) bool { return id != nil && id.Name == "_" }
+
+func isPkgDot(expr ast.Expr, pkg, name string) bool {
+	sel, ok := expr.(*ast.SelectorExpr)
+	return ok && isIdent(sel.X, pkg) && isIdent(sel.Sel, name)
+}
+
+func isOne(expr ast.Expr) bool {
+	lit, ok := expr.(*ast.BasicLit)
+	return ok && lit.Kind == token.INT && lit.Value == "1"
+}
+
+func isCgoExported(f *ast.FuncDecl) bool {
+	if f.Recv != nil || f.Doc == nil {
+		return false
+	}
+
+	cgoExport := regexp.MustCompile(fmt.Sprintf("(?m)^//export %s$", regexp.QuoteMeta(f.Name.Name)))
+	for _, c := range f.Doc.List {
+		if cgoExport.MatchString(c.Text) {
+			return true
+		}
+	}
+	return false
+}
+
+var basicTypeKinds = map[types.BasicKind]string{
+	types.UntypedBool:    "bool",
+	types.UntypedInt:     "int",
+	types.UntypedRune:    "rune",
+	types.UntypedFloat:   "float64",
+	types.UntypedComplex: "complex128",
+	types.UntypedString:  "string",
+}
+
+// isUntypedConst reports whether expr is an untyped constant,
+// and indicates what its default type is.
+// scope may be nil.
+func (f *file) isUntypedConst(expr ast.Expr) (defType string, ok bool) {
+	// Re-evaluate expr outside of its context to see if it's untyped.
+	// (An expr evaluated within, for example, an assignment context will get the type of the LHS.)
+	exprStr := f.render(expr)
+	tv, err := types.Eval(f.fset, f.pkg.typesPkg, expr.Pos(), exprStr)
+	if err != nil {
+		return "", false
+	}
+	if b, ok := tv.Type.(*types.Basic); ok {
+		if dt, ok := basicTypeKinds[b.Kind()]; ok {
+			return dt, true
+		}
+	}
+
+	return "", false
+}
+
+// firstLineOf renders the given node and returns its first line.
+// It will also match the indentation of another node.
+func (f *file) firstLineOf(node, match ast.Node) string {
+	line := f.render(node)
+	if i := strings.Index(line, "\n"); i >= 0 {
+		line = line[:i]
+	}
+	return f.indentOf(match) + line
+}
+
+func (f *file) indentOf(node ast.Node) string {
+	line := srcLine(f.src, f.fset.Position(node.Pos()))
+	for i, r := range line {
+		switch r {
+		case ' ', '\t':
+		default:
+			return line[:i]
+		}
+	}
+	return line // unusual or empty line
+}
+
+func (f *file) srcLineWithMatch(node ast.Node, pattern string) (m []string) {
+	line := srcLine(f.src, f.fset.Position(node.Pos()))
+	line = strings.TrimSuffix(line, "\n")
+	rx := regexp.MustCompile(pattern)
+	return rx.FindStringSubmatch(line)
+}
+
+// srcLine returns the complete line at p, including the terminating newline.
+func srcLine(src []byte, p token.Position) string {
+	// Run to end of line in both directions if not at line start/end.
+	lo, hi := p.Offset, p.Offset+1
+	for lo > 0 && src[lo-1] != '\n' {
+		lo--
+	}
+	for hi < len(src) && src[hi-1] != '\n' {
+		hi++
+	}
+	return string(src[lo:hi])
+}