internal/lsp/cache/mod.go - tools - Git at Google

 // Copyright 2019 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package cache

 import (
 	"context"
 	"fmt"
 	"path/filepath"
 	"regexp"
 	"strings"

 	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/module"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/gocommand"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/memoize"
 	"golang.org/x/tools/internal/span"
 )

 const (
 	SyntaxError    = "syntax"
 	GoCommandError = "go command"
 )

 type parseModHandle struct {
 	handle *memoize.Handle
 }

 type parseModData struct {
 	parsed *source.ParsedModule

 	// err is any error encountered while parsing the file.
 	err error
 }

 func (mh *parseModHandle) parse(ctx context.Context, snapshot *snapshot) (*source.ParsedModule, error) {
 	v, err := mh.handle.Get(ctx, snapshot.generation, snapshot)
 	if err != nil {
 		return nil, err
 	}
 	data := v.(*parseModData)
 	return data.parsed, data.err
 }

 func (s *snapshot) ParseMod(ctx context.Context, modFH source.FileHandle) (*source.ParsedModule, error) {
 	if handle := s.getParseModHandle(modFH.URI()); handle != nil {
 		return handle.parse(ctx, s)
 	}
 	h := s.generation.Bind(modFH.FileIdentity(), func(ctx context.Context, _ memoize.Arg) interface{} {
 		_, done := event.Start(ctx, "cache.ParseModHandle", tag.URI.Of(modFH.URI()))
 		defer done()

 		contents, err := modFH.Read()
 		if err != nil {
 			return &parseModData{err: err}
 		}
 		m := &protocol.ColumnMapper{
 			URI:       modFH.URI(),
 			Converter: span.NewContentConverter(modFH.URI().Filename(), contents),
 			Content:   contents,
 		}
 		file, err := modfile.Parse(modFH.URI().Filename(), contents, nil)

 		// Attempt to convert the error to a standardized parse error.
 		var parseErrors []*source.Error
 		if err != nil {
 			if parseErr := extractErrorWithPosition(ctx, err.Error(), s); parseErr != nil {
 				parseErrors = []*source.Error{parseErr}
 			}
 		}
 		return &parseModData{
 			parsed: &source.ParsedModule{
 				URI:         modFH.URI(),
 				Mapper:      m,
 				File:        file,
 				ParseErrors: parseErrors,
 			},
 			err: err,
 		}
 	}, nil)

 	pmh := &parseModHandle{handle: h}
 	s.mu.Lock()
 	s.parseModHandles[modFH.URI()] = pmh
 	s.mu.Unlock()

 	return pmh.parse(ctx, s)
 }

 // goSum reads the go.sum file for the go.mod file at modURI, if it exists. If
 // it doesn't exist, it returns nil.
 func (s *snapshot) goSum(ctx context.Context, modURI span.URI) []byte {
 	// Get the go.sum file, either from the snapshot or directly from the
 	// cache. Avoid (*snapshot).GetFile here, as we don't want to add
 	// nonexistent file handles to the snapshot if the file does not exist.
 	sumURI := span.URIFromPath(sumFilename(modURI))
 	var sumFH source.FileHandle = s.FindFile(sumURI)
 	if sumFH == nil {
 		var err error
 		sumFH, err = s.view.session.cache.getFile(ctx, sumURI)
 		if err != nil {
 			return nil
 		}
 	}
 	content, err := sumFH.Read()
 	if err != nil {
 		return nil
 	}
 	return content
 }

 func sumFilename(modURI span.URI) string {
 	return strings.TrimSuffix(modURI.Filename(), ".mod") + ".sum"
 }

 // modKey is uniquely identifies cached data for `go mod why` or dependencies
 // to upgrade.
 type modKey struct {
 	sessionID, env, view string
 	mod                  source.FileIdentity
 	verb                 modAction
 }

 type modAction int

 const (
 	why modAction = iota
 	upgrade
 )

 type modWhyHandle struct {
 	handle *memoize.Handle
 }

 type modWhyData struct {
 	// why keeps track of the `go mod why` results for each require statement
 	// in the go.mod file.
 	why map[string]string

 	err error
 }

 func (mwh *modWhyHandle) why(ctx context.Context, snapshot *snapshot) (map[string]string, error) {
 	v, err := mwh.handle.Get(ctx, snapshot.generation, snapshot)
 	if err != nil {
 		return nil, err
 	}
 	data := v.(*modWhyData)
 	return data.why, data.err
 }

 func (s *snapshot) ModWhy(ctx context.Context, fh source.FileHandle) (map[string]string, error) {
 	if fh.Kind() != source.Mod {
 		return nil, fmt.Errorf("%s is not a go.mod file", fh.URI())
 	}
 	if handle := s.getModWhyHandle(fh.URI()); handle != nil {
 		return handle.why(ctx, s)
 	}
 	key := modKey{
 		sessionID: s.view.session.id,
 		env:       hashEnv(s),
 		mod:       fh.FileIdentity(),
 		view:      s.view.rootURI.Filename(),
 		verb:      why,
 	}
 	h := s.generation.Bind(key, func(ctx context.Context, arg memoize.Arg) interface{} {
 		ctx, done := event.Start(ctx, "cache.ModWhyHandle", tag.URI.Of(fh.URI()))
 		defer done()

 		snapshot := arg.(*snapshot)

 		pm, err := snapshot.ParseMod(ctx, fh)
 		if err != nil {
 			return &modWhyData{err: err}
 		}
 		// No requires to explain.
 		if len(pm.File.Require) == 0 {
 			return &modWhyData{}
 		}
 		// Run `go mod why` on all the dependencies.
 		inv := &gocommand.Invocation{
 			Verb:       "mod",
 			Args:       []string{"why", "-m"},
 			WorkingDir: filepath.Dir(fh.URI().Filename()),
 		}
 		for _, req := range pm.File.Require {
 			inv.Args = append(inv.Args, req.Mod.Path)
 		}
 		stdout, err := snapshot.RunGoCommandDirect(ctx, source.Normal, inv)
 		if err != nil {
 			return &modWhyData{err: err}
 		}
 		whyList := strings.Split(stdout.String(), "\n\n")
 		if len(whyList) != len(pm.File.Require) {
 			return &modWhyData{
 				err: fmt.Errorf("mismatched number of results: got %v, want %v", len(whyList), len(pm.File.Require)),
 			}
 		}
 		why := make(map[string]string, len(pm.File.Require))
 		for i, req := range pm.File.Require {
 			why[req.Mod.Path] = whyList[i]
 		}
 		return &modWhyData{why: why}
 	}, nil)

 	mwh := &modWhyHandle{handle: h}
 	s.mu.Lock()
 	s.modWhyHandles[fh.URI()] = mwh
 	s.mu.Unlock()

 	return mwh.why(ctx, s)
 }

 // extractGoCommandError tries to parse errors that come from the go command
 // and shape them into go.mod diagnostics.
 func (s *snapshot) extractGoCommandErrors(ctx context.Context, snapshot source.Snapshot, fh source.FileHandle, goCmdError string) []*source.Error {
 	var srcErrs []*source.Error
 	if srcErr := s.parseModError(ctx, fh, goCmdError); srcErr != nil {
 		srcErrs = append(srcErrs, srcErr)
 	}
 	// If the error message contains a position, use that. Don't pass a file
 	// handle in, as it might not be the file associated with the error.
 	if srcErr := extractErrorWithPosition(ctx, goCmdError, s); srcErr != nil {
 		srcErrs = append(srcErrs, srcErr)
 	} else if srcErr := s.matchErrorToModule(ctx, fh, goCmdError); srcErr != nil {
 		srcErrs = append(srcErrs, srcErr)
 	}
 	return srcErrs
 }

 var moduleVersionInErrorRe = regexp.MustCompile(`[:\s]([+-._~0-9A-Za-z]+)@([+-._~0-9A-Za-z]+)[:\s]`)

 // matchErrorToModule attempts to match module version in error messages.
 // Some examples:
 //
 //    example.com@v1.2.2: reading example.com/@v/v1.2.2.mod: no such file or directory
 //    go: github.com/cockroachdb/apd/v2@v2.0.72: reading github.com/cockroachdb/apd/go.mod at revision v2.0.72: unknown revision v2.0.72
 //    go: example.com@v1.2.3 requires\n\trandom.org@v1.2.3: parsing go.mod:\n\tmodule declares its path as: bob.org\n\tbut was required as: random.org
 //
 // We search for module@version, starting from the end to find the most
 // relevant module, e.g. random.org@v1.2.3 above. Then we associate the error
 // with a directive that references any of the modules mentioned.
 func (s *snapshot) matchErrorToModule(ctx context.Context, fh source.FileHandle, goCmdError string) *source.Error {
 	pm, err := s.ParseMod(ctx, fh)
 	if err != nil {
 		return nil
 	}

 	var innermost *module.Version
 	var reference *modfile.Line
 	matches := moduleVersionInErrorRe.FindAllStringSubmatch(goCmdError, -1)

 outer:
 	for i := len(matches) - 1; i >= 0; i-- {
 		ver := module.Version{Path: matches[i][1], Version: matches[i][2]}
 		// Any module versions that come from the workspace module should not
 		// be shown to the user.
 		if source.IsWorkspaceModuleVersion(ver.Version) {
 			continue
 		}
 		if err := module.Check(ver.Path, ver.Version); err != nil {
 			continue
 		}
 		if innermost == nil {
 			innermost = &ver
 		}

 		for _, req := range pm.File.Require {
 			if req.Mod == ver {
 				reference = req.Syntax
 				break outer
 			}
 		}
 		for _, ex := range pm.File.Exclude {
 			if ex.Mod == ver {
 				reference = ex.Syntax
 				break outer
 			}
 		}
 		for _, rep := range pm.File.Replace {
 			if rep.New == ver || rep.Old == ver {
 				reference = rep.Syntax
 				break outer
 			}
 		}
 	}

 	if reference == nil {
 		// No match for the module path was found in the go.mod file.
 		// Show the error on the module declaration, if one exists.
 		if pm.File.Module == nil {
 			return nil
 		}
 		reference = pm.File.Module.Syntax
 	}

 	rng, err := rangeFromPositions(pm.Mapper, reference.Start, reference.End)
 	if err != nil {
 		return nil
 	}
 	disabledByGOPROXY := strings.Contains(goCmdError, "disabled by GOPROXY=off")
 	shouldAddDep := strings.Contains(goCmdError, "to add it")
 	if innermost != nil && (disabledByGOPROXY || shouldAddDep) {
 		args, err := source.MarshalArgs(fh.URI(), false, []string{fmt.Sprintf("%v@%v", innermost.Path, innermost.Version)})
 		if err != nil {
 			return nil
 		}
 		msg := goCmdError
 		if disabledByGOPROXY {
 			msg = fmt.Sprintf("%v@%v has not been downloaded", innermost.Path, innermost.Version)
 		}
 		return &source.Error{
 			Message: msg,
 			Kind:    source.ListError,
 			Range:   rng,
 			URI:     fh.URI(),
 			SuggestedFixes: []source.SuggestedFix{{
 				Title: fmt.Sprintf("Download %v@%v", innermost.Path, innermost.Version),
 				Command: &protocol.Command{
 					Title:     source.CommandAddDependency.Title,
 					Command:   source.CommandAddDependency.ID(),
 					Arguments: args,
 				},
 			}},
 		}
 	}
 	return &source.Error{
 		Message: goCmdError,
 		Range:   rng,
 		URI:     fh.URI(),
 		Kind:    source.ListError,
 	}
 }

 // errorPositionRe matches errors messages of the form <filename>:<line>:<col>,
 // where the <col> is optional.
 var errorPositionRe = regexp.MustCompile(`(?P<pos>.*:([\d]+)(:([\d]+))?): (?P<msg>.+)`)

 // extractErrorWithPosition returns a structured error with position
 // information for the given unstructured error. If a file handle is provided,
 // the error position will be on that file. This is useful for parse errors,
 // where we already know the file with the error.
 func extractErrorWithPosition(ctx context.Context, goCmdError string, src source.FileSource) *source.Error {
 	matches := errorPositionRe.FindStringSubmatch(strings.TrimSpace(goCmdError))
 	if len(matches) == 0 {
 		return nil
 	}
 	var pos, msg string
 	for i, name := range errorPositionRe.SubexpNames() {
 		if name == "pos" {
 			pos = matches[i]
 		}
 		if name == "msg" {
 			msg = matches[i]
 		}
 	}
 	spn := span.Parse(pos)
 	fh, err := src.GetFile(ctx, spn.URI())
 	if err != nil {
 		return nil
 	}
 	content, err := fh.Read()
 	if err != nil {
 		return nil
 	}
 	m := &protocol.ColumnMapper{
 		URI:       spn.URI(),
 		Converter: span.NewContentConverter(spn.URI().Filename(), content),
 		Content:   content,
 	}
 	rng, err := m.Range(spn)
 	if err != nil {
 		return nil
 	}
 	category := GoCommandError
 	if fh != nil {
 		category = SyntaxError
 	}
 	return &source.Error{
 		Category: category,
 		Message:  msg,
 		Range:    rng,
 		URI:      spn.URI(),
 	}
 }
	// Copyright 2019 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package cache

	import (
	"context"
	"fmt"
	"path/filepath"
	"regexp"
	"strings"

	"golang.org/x/mod/modfile"
	"golang.org/x/mod/module"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/gocommand"
	"golang.org/x/tools/internal/lsp/debug/tag"
	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/lsp/source"
	"golang.org/x/tools/internal/memoize"
	"golang.org/x/tools/internal/span"
	)

	const (
	SyntaxError = "syntax"
	GoCommandError = "go command"
	)

	type parseModHandle struct {
	handle *memoize.Handle
	}

	type parseModData struct {
	parsed *source.ParsedModule

	// err is any error encountered while parsing the file.
	err error
	}

	func (mh parseModHandle) parse(ctx context.Context, snapshot snapshot) (*source.ParsedModule, error) {
	v, err := mh.handle.Get(ctx, snapshot.generation, snapshot)
	if err != nil {
	return nil, err
	}
	data := v.(*parseModData)
	return data.parsed, data.err
	}

	func (s snapshot) ParseMod(ctx context.Context, modFH source.FileHandle) (source.ParsedModule, error) {
	if handle := s.getParseModHandle(modFH.URI()); handle != nil {
	return handle.parse(ctx, s)
	}
	h := s.generation.Bind(modFH.FileIdentity(), func(ctx context.Context, _ memoize.Arg) interface{} {
	_, done := event.Start(ctx, "cache.ParseModHandle", tag.URI.Of(modFH.URI()))
	defer done()

	contents, err := modFH.Read()
	if err != nil {
	return &parseModData{err: err}
	}
	m := &protocol.ColumnMapper{
	URI: modFH.URI(),
	Converter: span.NewContentConverter(modFH.URI().Filename(), contents),
	Content: contents,
	}
	file, err := modfile.Parse(modFH.URI().Filename(), contents, nil)

	// Attempt to convert the error to a standardized parse error.
	var parseErrors []*source.Error
	if err != nil {
	if parseErr := extractErrorWithPosition(ctx, err.Error(), s); parseErr != nil {
	parseErrors = []*source.Error{parseErr}
	}
	}
	return &parseModData{
	parsed: &source.ParsedModule{
	URI: modFH.URI(),
	Mapper: m,
	File: file,
	ParseErrors: parseErrors,
	},
	err: err,
	}
	}, nil)

	pmh := &parseModHandle{handle: h}
	s.mu.Lock()
	s.parseModHandles[modFH.URI()] = pmh
	s.mu.Unlock()

	return pmh.parse(ctx, s)
	}

	// goSum reads the go.sum file for the go.mod file at modURI, if it exists. If
	// it doesn't exist, it returns nil.
	func (s *snapshot) goSum(ctx context.Context, modURI span.URI) []byte {
	// Get the go.sum file, either from the snapshot or directly from the
	// cache. Avoid (*snapshot).GetFile here, as we don't want to add
	// nonexistent file handles to the snapshot if the file does not exist.
	sumURI := span.URIFromPath(sumFilename(modURI))
	var sumFH source.FileHandle = s.FindFile(sumURI)
	if sumFH == nil {
	var err error
	sumFH, err = s.view.session.cache.getFile(ctx, sumURI)
	if err != nil {
	return nil
	}
	}
	content, err := sumFH.Read()
	if err != nil {
	return nil
	}
	return content
	}

	func sumFilename(modURI span.URI) string {
	return strings.TrimSuffix(modURI.Filename(), ".mod") + ".sum"
	}

	// modKey is uniquely identifies cached data for `go mod why` or dependencies
	// to upgrade.
	type modKey struct {
	sessionID, env, view string
	mod source.FileIdentity
	verb modAction
	}

	type modAction int

	const (
	why modAction = iota
	upgrade
	)

	type modWhyHandle struct {
	handle *memoize.Handle
	}

	type modWhyData struct {
	// why keeps track of the `go mod why` results for each require statement
	// in the go.mod file.
	why map[string]string

	err error
	}

	func (mwh modWhyHandle) why(ctx context.Context, snapshot snapshot) (map[string]string, error) {
	v, err := mwh.handle.Get(ctx, snapshot.generation, snapshot)
	if err != nil {
	return nil, err
	}
	data := v.(*modWhyData)
	return data.why, data.err
	}

	func (s *snapshot) ModWhy(ctx context.Context, fh source.FileHandle) (map[string]string, error) {
	if fh.Kind() != source.Mod {
	return nil, fmt.Errorf("%s is not a go.mod file", fh.URI())
	}
	if handle := s.getModWhyHandle(fh.URI()); handle != nil {
	return handle.why(ctx, s)
	}
	key := modKey{
	sessionID: s.view.session.id,
	env: hashEnv(s),
	mod: fh.FileIdentity(),
	view: s.view.rootURI.Filename(),
	verb: why,
	}
	h := s.generation.Bind(key, func(ctx context.Context, arg memoize.Arg) interface{} {
	ctx, done := event.Start(ctx, "cache.ModWhyHandle", tag.URI.Of(fh.URI()))
	defer done()

	snapshot := arg.(*snapshot)

	pm, err := snapshot.ParseMod(ctx, fh)
	if err != nil {
	return &modWhyData{err: err}
	}
	// No requires to explain.
	if len(pm.File.Require) == 0 {
	return &modWhyData{}
	}
	// Run `go mod why` on all the dependencies.
	inv := &gocommand.Invocation{
	Verb: "mod",
	Args: []string{"why", "-m"},
	WorkingDir: filepath.Dir(fh.URI().Filename()),
	}
	for _, req := range pm.File.Require {
	inv.Args = append(inv.Args, req.Mod.Path)
	}
	stdout, err := snapshot.RunGoCommandDirect(ctx, source.Normal, inv)
	if err != nil {
	return &modWhyData{err: err}
	}
	whyList := strings.Split(stdout.String(), "\n\n")
	if len(whyList) != len(pm.File.Require) {
	return &modWhyData{
	err: fmt.Errorf("mismatched number of results: got %v, want %v", len(whyList), len(pm.File.Require)),
	}
	}
	why := make(map[string]string, len(pm.File.Require))
	for i, req := range pm.File.Require {
	why[req.Mod.Path] = whyList[i]
	}
	return &modWhyData{why: why}
	}, nil)

	mwh := &modWhyHandle{handle: h}
	s.mu.Lock()
	s.modWhyHandles[fh.URI()] = mwh
	s.mu.Unlock()

	return mwh.why(ctx, s)
	}

	// extractGoCommandError tries to parse errors that come from the go command
	// and shape them into go.mod diagnostics.
	func (s snapshot) extractGoCommandErrors(ctx context.Context, snapshot source.Snapshot, fh source.FileHandle, goCmdError string) []source.Error {
	var srcErrs []*source.Error
	if srcErr := s.parseModError(ctx, fh, goCmdError); srcErr != nil {
	srcErrs = append(srcErrs, srcErr)
	}
	// If the error message contains a position, use that. Don't pass a file
	// handle in, as it might not be the file associated with the error.
	if srcErr := extractErrorWithPosition(ctx, goCmdError, s); srcErr != nil {
	srcErrs = append(srcErrs, srcErr)
	} else if srcErr := s.matchErrorToModule(ctx, fh, goCmdError); srcErr != nil {
	srcErrs = append(srcErrs, srcErr)
	}
	return srcErrs
	}

	var moduleVersionInErrorRe = regexp.MustCompile(`[:\s]([+-._~0-9A-Za-z]+)@([+-._~0-9A-Za-z]+)[:\s]`)

	// matchErrorToModule attempts to match module version in error messages.
	// Some examples:
	//
	// example.com@v1.2.2: reading example.com/@v/v1.2.2.mod: no such file or directory
	// go: github.com/cockroachdb/apd/v2@v2.0.72: reading github.com/cockroachdb/apd/go.mod at revision v2.0.72: unknown revision v2.0.72
	// go: example.com@v1.2.3 requires\n\trandom.org@v1.2.3: parsing go.mod:\n\tmodule declares its path as: bob.org\n\tbut was required as: random.org
	//
	// We search for module@version, starting from the end to find the most
	// relevant module, e.g. random.org@v1.2.3 above. Then we associate the error
	// with a directive that references any of the modules mentioned.
	func (s snapshot) matchErrorToModule(ctx context.Context, fh source.FileHandle, goCmdError string) source.Error {
	pm, err := s.ParseMod(ctx, fh)
	if err != nil {
	return nil
	}

	var innermost *module.Version
	var reference *modfile.Line
	matches := moduleVersionInErrorRe.FindAllStringSubmatch(goCmdError, -1)

	outer:
	for i := len(matches) - 1; i >= 0; i-- {
	ver := module.Version{Path: matches[i][1], Version: matches[i][2]}
	// Any module versions that come from the workspace module should not
	// be shown to the user.
	if source.IsWorkspaceModuleVersion(ver.Version) {
	continue
	}
	if err := module.Check(ver.Path, ver.Version); err != nil {
	continue
	}
	if innermost == nil {
	innermost = &ver
	}

	for _, req := range pm.File.Require {
	if req.Mod == ver {
	reference = req.Syntax
	break outer
	}
	}
	for _, ex := range pm.File.Exclude {
	if ex.Mod == ver {
	reference = ex.Syntax
	break outer
	}
	}
	for _, rep := range pm.File.Replace {
	if rep.New == ver \|\| rep.Old == ver {
	reference = rep.Syntax
	break outer
	}
	}
	}

	if reference == nil {
	// No match for the module path was found in the go.mod file.
	// Show the error on the module declaration, if one exists.
	if pm.File.Module == nil {
	return nil
	}
	reference = pm.File.Module.Syntax
	}

	rng, err := rangeFromPositions(pm.Mapper, reference.Start, reference.End)
	if err != nil {
	return nil
	}
	disabledByGOPROXY := strings.Contains(goCmdError, "disabled by GOPROXY=off")
	shouldAddDep := strings.Contains(goCmdError, "to add it")
	if innermost != nil && (disabledByGOPROXY \|\| shouldAddDep) {
	args, err := source.MarshalArgs(fh.URI(), false, []string{fmt.Sprintf("%v@%v", innermost.Path, innermost.Version)})
	if err != nil {
	return nil
	}
	msg := goCmdError
	if disabledByGOPROXY {
	msg = fmt.Sprintf("%v@%v has not been downloaded", innermost.Path, innermost.Version)
	}
	return &source.Error{
	Message: msg,
	Kind: source.ListError,
	Range: rng,
	URI: fh.URI(),
	SuggestedFixes: []source.SuggestedFix{{
	Title: fmt.Sprintf("Download %v@%v", innermost.Path, innermost.Version),
	Command: &protocol.Command{
	Title: source.CommandAddDependency.Title,
	Command: source.CommandAddDependency.ID(),
	Arguments: args,
	},
	}},
	}
	}
	return &source.Error{
	Message: goCmdError,
	Range: rng,
	URI: fh.URI(),
	Kind: source.ListError,
	}
	}

	// errorPositionRe matches errors messages of the form <filename>:<line>:<col>,
	// where the <col> is optional.
	var errorPositionRe = regexp.MustCompile(`(?P<pos>.*:([\d]+)(:([\d]+))?): (?P<msg>.+)`)

	// extractErrorWithPosition returns a structured error with position
	// information for the given unstructured error. If a file handle is provided,
	// the error position will be on that file. This is useful for parse errors,
	// where we already know the file with the error.
	func extractErrorWithPosition(ctx context.Context, goCmdError string, src source.FileSource) *source.Error {
	matches := errorPositionRe.FindStringSubmatch(strings.TrimSpace(goCmdError))
	if len(matches) == 0 {
	return nil
	}
	var pos, msg string
	for i, name := range errorPositionRe.SubexpNames() {
	if name == "pos" {
	pos = matches[i]
	}
	if name == "msg" {
	msg = matches[i]
	}
	}
	spn := span.Parse(pos)
	fh, err := src.GetFile(ctx, spn.URI())
	if err != nil {
	return nil
	}
	content, err := fh.Read()
	if err != nil {
	return nil
	}
	m := &protocol.ColumnMapper{
	URI: spn.URI(),
	Converter: span.NewContentConverter(spn.URI().Filename(), content),
	Content: content,
	}
	rng, err := m.Range(spn)
	if err != nil {
	return nil
	}
	category := GoCommandError
	if fh != nil {
	category = SyntaxError
	}
	return &source.Error{
	Category: category,
	Message: msg,
	Range: rng,
	URI: spn.URI(),
	}
	}