Add cross-compilation Makefile targets and tar-based releases.

Revamp the build system to be more inline with other Prometheus exporters.
Notably add Darwin and Windows build targets, and add support for releases
using tar files.

tools/vendor/github.com/alexkohler/nakedret/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 Alex Kohler
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

tools/vendor/github.com/alexkohler/nakedret/README.md

@@ -0,0 +1,103 @@
+# nakedret
+
+nakedret is a Go static analysis tool to find naked returns in functions greater than a specified function length.
+
+## Installation
+
+    go get -u github.com/alexkohler/nakedret
+
+## Usage
+
+Similar to other Go static anaylsis tools (such as golint, go vet) , nakedret can be invoked with one or more filenames, directories, or packages named by its import path. Nakedret also supports the `...` wildcard. 
+
+    nakedret [flags] files/directories/packages
+
+Currently, the only flag supported is -l, which is an optional numeric flag to specify the maximum length a function can be (in terms of line length). If not specified, it defaults to 5.
+
+## Purpose
+
+As noted in Go's [Code Review comments](https://github.com/golang/go/wiki/CodeReviewComments#named-result-parameters):
+
+> Naked returns are okay if the function is a handful of lines. Once it's a medium sized function, be explicit with your return 
+> values. Corollary: it's not worth it to name result parameters just because it enables you to use naked returns. Clarity of docs is always more important than saving a line or two in your function.
+
+This tool aims to catch naked returns on non-trivial functions.
+
+## Example
+
+Let's take the `types` package in the Go source as an example:
+
+```Bash
+$ nakedret -l 25 types/
+types/check.go:245 checkFiles naked returns on 26 line function 
+types/typexpr.go:443 collectParams naked returns on 53 line function 
+types/stmt.go:275 caseTypes naked returns on 27 line function 
+types/lookup.go:275 MissingMethod naked returns on 39 line function
+```
+
+Below is one of the not so intuitive uses of naked returns in `types/lookup.go` found by nakedret (nakedret will return the line number of the last naked return in the function):
+
+
+```Go
+func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
+	// fast path for common case
+	if T.Empty() {
+		return
+	}
+
+	// TODO(gri) Consider using method sets here. Might be more efficient.
+
+	if ityp, _ := V.Underlying().(*Interface); ityp != nil {
+		// TODO(gri) allMethods is sorted - can do this more efficiently
+		for _, m := range T.allMethods {
+			_, obj := lookupMethod(ityp.allMethods, m.pkg, m.name)
+			switch {
+			case obj == nil:
+				if static {
+					return m, false
+				}
+			case !Identical(obj.Type(), m.typ):
+				return m, true
+			}
+		}
+		return
+	}
+
+	// A concrete type implements T if it implements all methods of T.
+	for _, m := range T.allMethods {
+		obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
+
+		f, _ := obj.(*Func)
+		if f == nil {
+			return m, false
+		}
+
+		if !Identical(f.typ, m.typ) {
+			return m, true
+		}
+	}
+
+	return
+}
+```
+
+## TODO
+
+- Unit tests (may require some refactoring to do correctly)
+- supporting toggling of `build.Context.UseAllFiles` may be useful for some. 
+- Configuration on whether or not to run on test files
+- Vim quickfix format?
+- Globbing support (e.g. nakedret *.go)
+
+
+## Contributing
+
+Pull requests welcome!
+
+
+## Other static analysis tools
+
+If you've enjoyed nakedret, take a look at my other static anaylsis tools!
+
+- [unimport](https://github.com/alexkohler/unimport) - Finds unnecessary import aliases
+- [prealloc](https://github.com/alexkohler/prealloc) - Finds slice declarations that could potentially be preallocated.

tools/vendor/github.com/alexkohler/nakedret/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, testdata and vendor directory trees.
+			_, elem := filepath.Split(path)
+			if strings.HasPrefix(elem, ".") || strings.HasPrefix(elem, "_") || elem == "testdata" || elem == "vendor" {
+				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, testdata and vendor directory trees, but do not avoid "." or "..".
+		_, elem := filepath.Split(path)
+		dot := strings.HasPrefix(elem, ".") && elem != "." && elem != ".."
+		if dot || strings.HasPrefix(elem, "_") || elem == "testdata" || elem == "vendor" {
+			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
+}

tools/vendor/github.com/alexkohler/nakedret/nakedret.go

@@ -0,0 +1,213 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/build"
+	"go/parser"
+	"go/token"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+const (
+	pwd = "./"
+)
+
+func init() {
+	//TODO allow build tags
+	build.Default.UseAllFiles = true
+}
+
+func usage() {
+	log.Printf("Usage of %s:\n", os.Args[0])
+	log.Printf("\nnakedret [flags] # runs on package in current directory\n")
+	log.Printf("\nnakedret [flags] [packages]\n")
+	log.Printf("Flags:\n")
+	flag.PrintDefaults()
+}
+
+type returnsVisitor struct {
+	f         *token.FileSet
+	maxLength uint
+}
+
+func main() {
+
+	// Remove log timestamp
+	log.SetFlags(0)
+
+	maxLength := flag.Uint("l", 5, "maximum number of lines for a naked return function")
+	flag.Usage = usage
+	flag.Parse()
+
+	if err := checkNakedReturns(flag.Args(), maxLength); err != nil {
+		log.Println(err)
+	}
+}
+
+func checkNakedReturns(args []string, maxLength *uint) error {
+
+	fset := token.NewFileSet()
+
+	files, err := parseInput(args, fset)
+	if err != nil {
+		return fmt.Errorf("could not parse input %v", err)
+	}
+
+	if maxLength == nil {
+		return errors.New("max length nil")
+	}
+
+	retVis := &returnsVisitor{
+		f:         fset,
+		maxLength: *maxLength,
+	}
+
+	for _, f := range files {
+		ast.Walk(retVis, f)
+	}
+
+	return nil
+}
+
+func parseInput(args []string, fset *token.FileSet) ([]*ast.File, error) {
+	var directoryList []string
+	var fileMode bool
+	files := make([]*ast.File, 0)
+
+	if len(args) == 0 {
+		directoryList = append(directoryList, pwd)
+	} else {
+		for _, arg := range args {
+			if strings.HasSuffix(arg, "/...") && isDir(arg[:len(arg)-len("/...")]) {
+
+				for _, dirname := range allPackagesInFS(arg) {
+					directoryList = append(directoryList, dirname)
+				}
+
+			} else if isDir(arg) {
+				directoryList = append(directoryList, arg)
+
+			} else if exists(arg) {
+				if strings.HasSuffix(arg, ".go") {
+					fileMode = true
+					f, err := parser.ParseFile(fset, arg, nil, 0)
+					if err != nil {
+						return nil, err
+					}
+					files = append(files, f)
+				} else {
+					return nil, fmt.Errorf("invalid file %v specified", arg)
+				}
+			} else {
+
+				//TODO clean this up a bit
+				imPaths := importPaths([]string{arg})
+				for _, importPath := range imPaths {
+					pkg, err := build.Import(importPath, ".", 0)
+					if err != nil {
+						return nil, err
+					}
+					var stringFiles []string
+					stringFiles = append(stringFiles, pkg.GoFiles...)
+					// files = append(files, pkg.CgoFiles...)
+					stringFiles = append(stringFiles, pkg.TestGoFiles...)
+					if pkg.Dir != "." {
+						for i, f := range stringFiles {
+							stringFiles[i] = filepath.Join(pkg.Dir, f)
+						}
+					}
+
+					fileMode = true
+					for _, stringFile := range stringFiles {
+						f, err := parser.ParseFile(fset, stringFile, nil, 0)
+						if err != nil {
+							return nil, err
+						}
+						files = append(files, f)
+					}
+
+				}
+			}
+		}
+	}
+
+	// if we're not in file mode, then we need to grab each and every package in each directory
+	// we can to grab all the files
+	if !fileMode {
+		for _, fpath := range directoryList {
+			pkgs, err := parser.ParseDir(fset, fpath, nil, 0)
+			if err != nil {
+				return nil, err
+			}
+
+			for _, pkg := range pkgs {
+				for _, f := range pkg.Files {
+					files = append(files, f)
+				}
+			}
+		}
+	}
+
+	return files, nil
+}
+
+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 (v *returnsVisitor) Visit(node ast.Node) ast.Visitor {
+	var namedReturns []*ast.Ident
+
+	funcDecl, ok := node.(*ast.FuncDecl)
+	if !ok {
+		return v
+	}
+	var functionLineLength int
+	// We've found a function
+	if funcDecl.Type != nil && funcDecl.Type.Results != nil {
+		for _, field := range funcDecl.Type.Results.List {
+			for _, ident := range field.Names {
+				if ident != nil {
+					namedReturns = append(namedReturns, ident)
+				}
+			}
+		}
+		file := v.f.File(funcDecl.Pos())
+		functionLineLength = file.Position(funcDecl.End()).Line - file.Position(funcDecl.Pos()).Line
+	}
+
+	if len(namedReturns) > 0 && funcDecl.Body != nil {
+		// Scan the body for usage of the named returns
+		for _, stmt := range funcDecl.Body.List {
+
+			switch s := stmt.(type) {
+			case *ast.ReturnStmt:
+				if len(s.Results) == 0 {
+					file := v.f.File(s.Pos())
+					if file != nil && uint(functionLineLength) > v.maxLength {
+						if funcDecl.Name != nil {
+							log.Printf("%v:%v %v naked returns on %v line function \n", file.Name(), file.Position(s.Pos()).Line, funcDecl.Name.Name, functionLineLength)
+						}
+					}
+					continue
+				}
+
+			default:
+			}
+		}
+	}
+
+	return v
+}