go/analysis/analysistest/analysistest.go - tools - Git at Google

 // Package analysistest provides utilities for testing analyzers.
 package analysistest

 import (
 	"fmt"
 	"go/token"
 	"go/types"
 	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
 	"regexp"
 	"sort"
 	"strconv"
 	"strings"
 	"text/scanner"

 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/internal/checker"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/testenv"
 )

 // WriteFiles is a helper function that creates a temporary directory
 // and populates it with a GOPATH-style project using filemap (which
 // maps file names to contents). On success it returns the name of the
 // directory and a cleanup function to delete it.
 func WriteFiles(filemap map[string]string) (dir string, cleanup func(), err error) {
 	gopath, err := ioutil.TempDir("", "analysistest")
 	if err != nil {
 		return "", nil, err
 	}
 	cleanup = func() { os.RemoveAll(gopath) }

 	for name, content := range filemap {
 		filename := filepath.Join(gopath, "src", name)
 		os.MkdirAll(filepath.Dir(filename), 0777) // ignore error
 		if err := ioutil.WriteFile(filename, []byte(content), 0666); err != nil {
 			cleanup()
 			return "", nil, err
 		}
 	}
 	return gopath, cleanup, nil
 }

 // TestData returns the effective filename of
 // the program's "testdata" directory.
 // This function may be overridden by projects using
 // an alternative build system (such as Blaze) that
 // does not run a test in its package directory.
 var TestData = func() string {
 	testdata, err := filepath.Abs("testdata")
 	if err != nil {
 		log.Fatal(err)
 	}
 	return testdata
 }

 // Testing is an abstraction of a *testing.T.
 type Testing interface {
 	Errorf(format string, args ...interface{})
 }

 // Run applies an analysis to the packages denoted by the "go list" patterns.
 //
 // It loads the packages from the specified GOPATH-style project
 // directory using golang.org/x/tools/go/packages, runs the analysis on
 // them, and checks that each analysis emits the expected diagnostics
 // and facts specified by the contents of '// want ...' comments in the
 // package's source files.
 //
 // An expectation of a Diagnostic is specified by a string literal
 // containing a regular expression that must match the diagnostic
 // message. For example:
 //
 //	fmt.Printf("%s", 1) // want `cannot provide int 1 to %s`
 //
 // An expectation of a Fact associated with an object is specified by
 // 'name:"pattern"', where name is the name of the object, which must be
 // declared on the same line as the comment, and pattern is a regular
 // expression that must match the string representation of the fact,
 // fmt.Sprint(fact). For example:
 //
 //	func panicf(format string, args interface{}) { // want panicf:"printfWrapper"
 //
 // Package facts are specified by the name "package" and appear on
 // line 1 of the first source file of the package.
 //
 // A single 'want' comment may contain a mixture of diagnostic and fact
 // expectations, including multiple facts about the same object:
 //
 //	// want "diag" "diag2" x:"fact1" x:"fact2" y:"fact3"
 //
 // Unexpected diagnostics and facts, and unmatched expectations, are
 // reported as errors to the Testing.
 //
 // Run reports an error to the Testing if loading or analysis failed.
 // Run also returns a Result for each package for which analysis was
 // attempted, even if unsuccessful. It is safe for a test to ignore all
 // the results, but a test may use it to perform additional checks.
 func Run(t Testing, dir string, a *analysis.Analyzer, patterns ...string) []*Result {
 	if t, ok := t.(testenv.Testing); ok {
 		testenv.NeedsGoPackages(t)
 	}

 	pkgs, err := loadPackages(dir, patterns...)
 	if err != nil {
 		t.Errorf("loading %s: %v", patterns, err)
 		return nil
 	}

 	results := checker.TestAnalyzer(a, pkgs)
 	for _, result := range results {
 		if result.Err != nil {
 			t.Errorf("error analyzing %s: %v", result.Pass, result.Err)
 		} else {
 			check(t, dir, result.Pass, result.Diagnostics, result.Facts)
 		}
 	}
 	return results
 }

 // A Result holds the result of applying an analyzer to a package.
 type Result = checker.TestAnalyzerResult

 // loadPackages uses go/packages to load a specified packages (from source, with
 // dependencies) from dir, which is the root of a GOPATH-style project
 // tree. It returns an error if any package had an error, or the pattern
 // matched no packages.
 func loadPackages(dir string, patterns ...string) ([]*packages.Package, error) {
 	// packages.Load loads the real standard library, not a minimal
 	// fake version, which would be more efficient, especially if we
 	// have many small tests that import, say, net/http.
 	// However there is no easy way to make go/packages to consume
 	// a list of packages we generate and then do the parsing and
 	// typechecking, though this feature seems to be a recurring need.

 	cfg := &packages.Config{
 		Mode:  packages.LoadAllSyntax,
 		Dir:   dir,
 		Tests: true,
 		Env:   append(os.Environ(), "GOPATH="+dir, "GO111MODULE=off", "GOPROXY=off"),
 	}
 	pkgs, err := packages.Load(cfg, patterns...)
 	if err != nil {
 		return nil, err
 	}

 	// Print errors but do not stop:
 	// some Analyzers may be disposed to RunDespiteErrors.
 	packages.PrintErrors(pkgs)

 	if len(pkgs) == 0 {
 		return nil, fmt.Errorf("no packages matched %s", patterns)
 	}
 	return pkgs, nil
 }

 // check inspects an analysis pass on which the analysis has already
 // been run, and verifies that all reported diagnostics and facts match
 // specified by the contents of "// want ..." comments in the package's
 // source files, which must have been parsed with comments enabled.
 func check(t Testing, gopath string, pass *analysis.Pass, diagnostics []analysis.Diagnostic, facts map[types.Object][]analysis.Fact) {

 	type key struct {
 		file string
 		line int
 	}

 	want := make(map[key][]expectation)

 	// processComment parses expectations out of comments.
 	processComment := func(filename string, linenum int, text string) {
 		text = strings.TrimSpace(text)

 		// Any comment starting with "want" is treated
 		// as an expectation, even without following whitespace.
 		if rest := strings.TrimPrefix(text, "want"); rest != text {
 			expects, err := parseExpectations(rest)
 			if err != nil {
 				t.Errorf("%s:%d: in 'want' comment: %s", filename, linenum, err)
 				return
 			}
 			if expects != nil {
 				want[key{filename, linenum}] = expects
 			}
 		}
 	}

 	// Extract 'want' comments from Go files.
 	for _, f := range pass.Files {
 		for _, cgroup := range f.Comments {
 			for _, c := range cgroup.List {

 				text := strings.TrimPrefix(c.Text, "//")
 				if text == c.Text {
 					continue // not a //-comment
 				}

 				// Hack: treat a comment of the form "//...// want..."
 				// as if it starts at 'want'.
 				// This allows us to add comments on comments,
 				// as required when testing the buildtag analyzer.
 				if i := strings.Index(text, "// want"); i >= 0 {
 					text = text[i+len("// "):]
 				}

 				// It's tempting to compute the filename
 				// once outside the loop, but it's
 				// incorrect because it can change due
 				// to //line directives.
 				posn := pass.Fset.Position(c.Pos())
 				filename := sanitize(gopath, posn.Filename)
 				processComment(filename, posn.Line, text)
 			}
 		}
 	}

 	// Extract 'want' comments from non-Go files.
 	// TODO(adonovan): we may need to handle //line directives.
 	for _, filename := range pass.OtherFiles {
 		data, err := ioutil.ReadFile(filename)
 		if err != nil {
 			t.Errorf("can't read '// want' comments from %s: %v", filename, err)
 			continue
 		}
 		filename := sanitize(gopath, filename)
 		linenum := 0
 		for _, line := range strings.Split(string(data), "\n") {
 			linenum++
 			if i := strings.Index(line, "//"); i >= 0 {
 				line = line[i+len("//"):]
 				processComment(filename, linenum, line)
 			}
 		}
 	}

 	checkMessage := func(posn token.Position, kind, name, message string) {
 		posn.Filename = sanitize(gopath, posn.Filename)
 		k := key{posn.Filename, posn.Line}
 		expects := want[k]
 		var unmatched []string
 		for i, exp := range expects {
 			if exp.kind == kind && exp.name == name {
 				if exp.rx.MatchString(message) {
 					// matched: remove the expectation.
 					expects[i] = expects[len(expects)-1]
 					expects = expects[:len(expects)-1]
 					want[k] = expects
 					return
 				}
 				unmatched = append(unmatched, fmt.Sprintf("%q", exp.rx))
 			}
 		}
 		if unmatched == nil {
 			t.Errorf("%v: unexpected %s: %v", posn, kind, message)
 		} else {
 			t.Errorf("%v: %s %q does not match pattern %s",
 				posn, kind, message, strings.Join(unmatched, " or "))
 		}
 	}

 	// Check the diagnostics match expectations.
 	for _, f := range diagnostics {
 		// TODO(matloob): Support ranges in analysistest.
 		posn := pass.Fset.Position(f.Pos)
 		checkMessage(posn, "diagnostic", "", f.Message)
 	}

 	// Check the facts match expectations.
 	// Report errors in lexical order for determinism.
 	// (It's only deterministic within each file, not across files,
 	// because go/packages does not guarantee file.Pos is ascending
 	// across the files of a single compilation unit.)
 	var objects []types.Object
 	for obj := range facts {
 		objects = append(objects, obj)
 	}
 	sort.Slice(objects, func(i, j int) bool {
 		// Package facts compare less than object facts.
 		ip, jp := objects[i] == nil, objects[j] == nil // whether i, j is a package fact
 		if ip != jp {
 			return ip && !jp
 		}
 		return objects[i].Pos() < objects[j].Pos()
 	})
 	for _, obj := range objects {
 		var posn token.Position
 		var name string
 		if obj != nil {
 			// Object facts are reported on the declaring line.
 			name = obj.Name()
 			posn = pass.Fset.Position(obj.Pos())
 		} else {
 			// Package facts are reported at the start of the file.
 			name = "package"
 			posn = pass.Fset.Position(pass.Files[0].Pos())
 			posn.Line = 1
 		}

 		for _, fact := range facts[obj] {
 			checkMessage(posn, "fact", name, fmt.Sprint(fact))
 		}
 	}

 	// Reject surplus expectations.
 	//
 	// Sometimes an Analyzer reports two similar diagnostics on a
 	// line with only one expectation. The reader may be confused by
 	// the error message.
 	// TODO(adonovan): print a better error:
 	// "got 2 diagnostics here; each one needs its own expectation".
 	var surplus []string
 	for key, expects := range want {
 		for _, exp := range expects {
 			err := fmt.Sprintf("%s:%d: no %s was reported matching %q", key.file, key.line, exp.kind, exp.rx)
 			surplus = append(surplus, err)
 		}
 	}
 	sort.Strings(surplus)
 	for _, err := range surplus {
 		t.Errorf("%s", err)
 	}
 }

 type expectation struct {
 	kind string // either "fact" or "diagnostic"
 	name string // name of object to which fact belongs, or "package" ("fact" only)
 	rx   *regexp.Regexp
 }

 func (ex expectation) String() string {
 	return fmt.Sprintf("%s %s:%q", ex.kind, ex.name, ex.rx) // for debugging
 }

 // parseExpectations parses the content of a "// want ..." comment
 // and returns the expectations, a mixture of diagnostics ("rx") and
 // facts (name:"rx").
 func parseExpectations(text string) ([]expectation, error) {
 	var scanErr string
 	sc := new(scanner.Scanner).Init(strings.NewReader(text))
 	sc.Error = func(s *scanner.Scanner, msg string) {
 		scanErr = msg // e.g. bad string escape
 	}
 	sc.Mode = scanner.ScanIdents | scanner.ScanStrings | scanner.ScanRawStrings

 	scanRegexp := func(tok rune) (*regexp.Regexp, error) {
 		if tok != scanner.String && tok != scanner.RawString {
 			return nil, fmt.Errorf("got %s, want regular expression",
 				scanner.TokenString(tok))
 		}
 		pattern, _ := strconv.Unquote(sc.TokenText()) // can't fail
 		return regexp.Compile(pattern)
 	}

 	var expects []expectation
 	for {
 		tok := sc.Scan()
 		switch tok {
 		case scanner.String, scanner.RawString:
 			rx, err := scanRegexp(tok)
 			if err != nil {
 				return nil, err
 			}
 			expects = append(expects, expectation{"diagnostic", "", rx})

 		case scanner.Ident:
 			name := sc.TokenText()
 			tok = sc.Scan()
 			if tok != ':' {
 				return nil, fmt.Errorf("got %s after %s, want ':'",
 					scanner.TokenString(tok), name)
 			}
 			tok = sc.Scan()
 			rx, err := scanRegexp(tok)
 			if err != nil {
 				return nil, err
 			}
 			expects = append(expects, expectation{"fact", name, rx})

 		case scanner.EOF:
 			if scanErr != "" {
 				return nil, fmt.Errorf("%s", scanErr)
 			}
 			return expects, nil

 		default:
 			return nil, fmt.Errorf("unexpected %s", scanner.TokenString(tok))
 		}
 	}
 }

 // sanitize removes the GOPATH portion of the filename,
 // typically a gnarly /tmp directory, and returns the rest.
 func sanitize(gopath, filename string) string {
 	prefix := gopath + string(os.PathSeparator) + "src" + string(os.PathSeparator)
 	return filepath.ToSlash(strings.TrimPrefix(filename, prefix))
 }
	// Package analysistest provides utilities for testing analyzers.
	package analysistest

	import (
	"fmt"
	"go/token"
	"go/types"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"text/scanner"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/analysis/internal/checker"
	"golang.org/x/tools/go/packages"
	"golang.org/x/tools/internal/testenv"
	)

	// WriteFiles is a helper function that creates a temporary directory
	// and populates it with a GOPATH-style project using filemap (which
	// maps file names to contents). On success it returns the name of the
	// directory and a cleanup function to delete it.
	func WriteFiles(filemap map[string]string) (dir string, cleanup func(), err error) {
	gopath, err := ioutil.TempDir("", "analysistest")
	if err != nil {
	return "", nil, err
	}
	cleanup = func() { os.RemoveAll(gopath) }

	for name, content := range filemap {
	filename := filepath.Join(gopath, "src", name)
	os.MkdirAll(filepath.Dir(filename), 0777) // ignore error
	if err := ioutil.WriteFile(filename, []byte(content), 0666); err != nil {
	cleanup()
	return "", nil, err
	}
	}
	return gopath, cleanup, nil
	}

	// TestData returns the effective filename of
	// the program's "testdata" directory.
	// This function may be overridden by projects using
	// an alternative build system (such as Blaze) that
	// does not run a test in its package directory.
	var TestData = func() string {
	testdata, err := filepath.Abs("testdata")
	if err != nil {
	log.Fatal(err)
	}
	return testdata
	}

	// Testing is an abstraction of a *testing.T.
	type Testing interface {
	Errorf(format string, args ...interface{})
	}

	// Run applies an analysis to the packages denoted by the "go list" patterns.
	//
	// It loads the packages from the specified GOPATH-style project
	// directory using golang.org/x/tools/go/packages, runs the analysis on
	// them, and checks that each analysis emits the expected diagnostics
	// and facts specified by the contents of '// want ...' comments in the
	// package's source files.
	//
	// An expectation of a Diagnostic is specified by a string literal
	// containing a regular expression that must match the diagnostic
	// message. For example:
	//
	// fmt.Printf("%s", 1) // want `cannot provide int 1 to %s`
	//
	// An expectation of a Fact associated with an object is specified by
	// 'name:"pattern"', where name is the name of the object, which must be
	// declared on the same line as the comment, and pattern is a regular
	// expression that must match the string representation of the fact,
	// fmt.Sprint(fact). For example:
	//
	// func panicf(format string, args interface{}) { // want panicf:"printfWrapper"
	//
	// Package facts are specified by the name "package" and appear on
	// line 1 of the first source file of the package.
	//
	// A single 'want' comment may contain a mixture of diagnostic and fact
	// expectations, including multiple facts about the same object:
	//
	// // want "diag" "diag2" x:"fact1" x:"fact2" y:"fact3"
	//
	// Unexpected diagnostics and facts, and unmatched expectations, are
	// reported as errors to the Testing.
	//
	// Run reports an error to the Testing if loading or analysis failed.
	// Run also returns a Result for each package for which analysis was
	// attempted, even if unsuccessful. It is safe for a test to ignore all
	// the results, but a test may use it to perform additional checks.
	func Run(t Testing, dir string, a analysis.Analyzer, patterns ...string) []Result {
	if t, ok := t.(testenv.Testing); ok {
	testenv.NeedsGoPackages(t)
	}

	pkgs, err := loadPackages(dir, patterns...)
	if err != nil {
	t.Errorf("loading %s: %v", patterns, err)
	return nil
	}

	results := checker.TestAnalyzer(a, pkgs)
	for _, result := range results {
	if result.Err != nil {
	t.Errorf("error analyzing %s: %v", result.Pass, result.Err)
	} else {
	check(t, dir, result.Pass, result.Diagnostics, result.Facts)
	}
	}
	return results
	}

	// A Result holds the result of applying an analyzer to a package.
	type Result = checker.TestAnalyzerResult

	// loadPackages uses go/packages to load a specified packages (from source, with
	// dependencies) from dir, which is the root of a GOPATH-style project
	// tree. It returns an error if any package had an error, or the pattern
	// matched no packages.
	func loadPackages(dir string, patterns ...string) ([]*packages.Package, error) {
	// packages.Load loads the real standard library, not a minimal
	// fake version, which would be more efficient, especially if we
	// have many small tests that import, say, net/http.
	// However there is no easy way to make go/packages to consume
	// a list of packages we generate and then do the parsing and
	// typechecking, though this feature seems to be a recurring need.

	cfg := &packages.Config{
	Mode: packages.LoadAllSyntax,
	Dir: dir,
	Tests: true,
	Env: append(os.Environ(), "GOPATH="+dir, "GO111MODULE=off", "GOPROXY=off"),
	}
	pkgs, err := packages.Load(cfg, patterns...)
	if err != nil {
	return nil, err
	}

	// Print errors but do not stop:
	// some Analyzers may be disposed to RunDespiteErrors.
	packages.PrintErrors(pkgs)

	if len(pkgs) == 0 {
	return nil, fmt.Errorf("no packages matched %s", patterns)
	}
	return pkgs, nil
	}

	// check inspects an analysis pass on which the analysis has already
	// been run, and verifies that all reported diagnostics and facts match
	// specified by the contents of "// want ..." comments in the package's
	// source files, which must have been parsed with comments enabled.
	func check(t Testing, gopath string, pass *analysis.Pass, diagnostics []analysis.Diagnostic, facts map[types.Object][]analysis.Fact) {

	type key struct {
	file string
	line int
	}

	want := make(map[key][]expectation)

	// processComment parses expectations out of comments.
	processComment := func(filename string, linenum int, text string) {
	text = strings.TrimSpace(text)

	// Any comment starting with "want" is treated
	// as an expectation, even without following whitespace.
	if rest := strings.TrimPrefix(text, "want"); rest != text {
	expects, err := parseExpectations(rest)
	if err != nil {
	t.Errorf("%s:%d: in 'want' comment: %s", filename, linenum, err)
	return
	}
	if expects != nil {
	want[key{filename, linenum}] = expects
	}
	}
	}

	// Extract 'want' comments from Go files.
	for _, f := range pass.Files {
	for _, cgroup := range f.Comments {
	for _, c := range cgroup.List {

	text := strings.TrimPrefix(c.Text, "//")
	if text == c.Text {
	continue // not a //-comment
	}

	// Hack: treat a comment of the form "//...// want..."
	// as if it starts at 'want'.
	// This allows us to add comments on comments,
	// as required when testing the buildtag analyzer.
	if i := strings.Index(text, "// want"); i >= 0 {
	text = text[i+len("// "):]
	}

	// It's tempting to compute the filename
	// once outside the loop, but it's
	// incorrect because it can change due
	// to //line directives.
	posn := pass.Fset.Position(c.Pos())
	filename := sanitize(gopath, posn.Filename)
	processComment(filename, posn.Line, text)
	}
	}
	}

	// Extract 'want' comments from non-Go files.
	// TODO(adonovan): we may need to handle //line directives.
	for _, filename := range pass.OtherFiles {
	data, err := ioutil.ReadFile(filename)
	if err != nil {
	t.Errorf("can't read '// want' comments from %s: %v", filename, err)
	continue
	}
	filename := sanitize(gopath, filename)
	linenum := 0
	for _, line := range strings.Split(string(data), "\n") {
	linenum++
	if i := strings.Index(line, "//"); i >= 0 {
	line = line[i+len("//"):]
	processComment(filename, linenum, line)
	}
	}
	}

	checkMessage := func(posn token.Position, kind, name, message string) {
	posn.Filename = sanitize(gopath, posn.Filename)
	k := key{posn.Filename, posn.Line}
	expects := want[k]
	var unmatched []string
	for i, exp := range expects {
	if exp.kind == kind && exp.name == name {
	if exp.rx.MatchString(message) {
	// matched: remove the expectation.
	expects[i] = expects[len(expects)-1]
	expects = expects[:len(expects)-1]
	want[k] = expects
	return
	}
	unmatched = append(unmatched, fmt.Sprintf("%q", exp.rx))
	}
	}
	if unmatched == nil {
	t.Errorf("%v: unexpected %s: %v", posn, kind, message)
	} else {
	t.Errorf("%v: %s %q does not match pattern %s",
	posn, kind, message, strings.Join(unmatched, " or "))
	}
	}

	// Check the diagnostics match expectations.
	for _, f := range diagnostics {
	// TODO(matloob): Support ranges in analysistest.
	posn := pass.Fset.Position(f.Pos)
	checkMessage(posn, "diagnostic", "", f.Message)
	}

	// Check the facts match expectations.
	// Report errors in lexical order for determinism.
	// (It's only deterministic within each file, not across files,
	// because go/packages does not guarantee file.Pos is ascending
	// across the files of a single compilation unit.)
	var objects []types.Object
	for obj := range facts {
	objects = append(objects, obj)
	}
	sort.Slice(objects, func(i, j int) bool {
	// Package facts compare less than object facts.
	ip, jp := objects[i] == nil, objects[j] == nil // whether i, j is a package fact
	if ip != jp {
	return ip && !jp
	}
	return objects[i].Pos() < objects[j].Pos()
	})
	for _, obj := range objects {
	var posn token.Position
	var name string
	if obj != nil {
	// Object facts are reported on the declaring line.
	name = obj.Name()
	posn = pass.Fset.Position(obj.Pos())
	} else {
	// Package facts are reported at the start of the file.
	name = "package"
	posn = pass.Fset.Position(pass.Files[0].Pos())
	posn.Line = 1
	}

	for _, fact := range facts[obj] {
	checkMessage(posn, "fact", name, fmt.Sprint(fact))
	}
	}

	// Reject surplus expectations.
	//
	// Sometimes an Analyzer reports two similar diagnostics on a
	// line with only one expectation. The reader may be confused by
	// the error message.
	// TODO(adonovan): print a better error:
	// "got 2 diagnostics here; each one needs its own expectation".
	var surplus []string
	for key, expects := range want {
	for _, exp := range expects {
	err := fmt.Sprintf("%s:%d: no %s was reported matching %q", key.file, key.line, exp.kind, exp.rx)
	surplus = append(surplus, err)
	}
	}
	sort.Strings(surplus)
	for _, err := range surplus {
	t.Errorf("%s", err)
	}
	}

	type expectation struct {
	kind string // either "fact" or "diagnostic"
	name string // name of object to which fact belongs, or "package" ("fact" only)
	rx *regexp.Regexp
	}

	func (ex expectation) String() string {
	return fmt.Sprintf("%s %s:%q", ex.kind, ex.name, ex.rx) // for debugging
	}

	// parseExpectations parses the content of a "// want ..." comment
	// and returns the expectations, a mixture of diagnostics ("rx") and
	// facts (name:"rx").
	func parseExpectations(text string) ([]expectation, error) {
	var scanErr string
	sc := new(scanner.Scanner).Init(strings.NewReader(text))
	sc.Error = func(s *scanner.Scanner, msg string) {
	scanErr = msg // e.g. bad string escape
	}
	sc.Mode = scanner.ScanIdents \| scanner.ScanStrings \| scanner.ScanRawStrings

	scanRegexp := func(tok rune) (*regexp.Regexp, error) {
	if tok != scanner.String && tok != scanner.RawString {
	return nil, fmt.Errorf("got %s, want regular expression",
	scanner.TokenString(tok))
	}
	pattern, _ := strconv.Unquote(sc.TokenText()) // can't fail
	return regexp.Compile(pattern)
	}

	var expects []expectation
	for {
	tok := sc.Scan()
	switch tok {
	case scanner.String, scanner.RawString:
	rx, err := scanRegexp(tok)
	if err != nil {
	return nil, err
	}
	expects = append(expects, expectation{"diagnostic", "", rx})

	case scanner.Ident:
	name := sc.TokenText()
	tok = sc.Scan()
	if tok != ':' {
	return nil, fmt.Errorf("got %s after %s, want ':'",
	scanner.TokenString(tok), name)
	}
	tok = sc.Scan()
	rx, err := scanRegexp(tok)
	if err != nil {
	return nil, err
	}
	expects = append(expects, expectation{"fact", name, rx})

	case scanner.EOF:
	if scanErr != "" {
	return nil, fmt.Errorf("%s", scanErr)
	}
	return expects, nil

	default:
	return nil, fmt.Errorf("unexpected %s", scanner.TokenString(tok))
	}
	}
	}

	// sanitize removes the GOPATH portion of the filename,
	// typically a gnarly /tmp directory, and returns the rest.
	func sanitize(gopath, filename string) string {
	prefix := gopath + string(os.PathSeparator) + "src" + string(os.PathSeparator)
	return filepath.ToSlash(strings.TrimPrefix(filename, prefix))
	}