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

 // Copyright 2020 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"
 	"os"
 	"path/filepath"
 	"sort"
 	"strings"
 	"sync"

 	"golang.org/x/mod/modfile"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
 	"golang.org/x/tools/internal/xcontext"
 	errors "golang.org/x/xerrors"
 )

 type workspaceSource int

 const (
 	legacyWorkspace = iota
 	goplsModWorkspace
 	fileSystemWorkspace
 )

 func (s workspaceSource) String() string {
 	switch s {
 	case legacyWorkspace:
 		return "legacy"
 	case goplsModWorkspace:
 		return "gopls.mod"
 	case fileSystemWorkspace:
 		return "file system"
 	default:
 		return "!(unknown module source)"
 	}
 }

 // workspace tracks go.mod files in the workspace, along with the
 // gopls.mod file, to provide support for multi-module workspaces.
 //
 // Specifically, it provides:
 //  - the set of modules contained within in the workspace root considered to
 //    be 'active'
 //  - the workspace modfile, to be used for the go command `-modfile` flag
 //  - the set of workspace directories
 //
 // This type is immutable (or rather, idempotent), so that it may be shared
 // across multiple snapshots.
 type workspace struct {
 	root         span.URI
 	moduleSource workspaceSource

 	// modFiles holds the active go.mod files.
 	modFiles map[span.URI]struct{}

 	// The workspace module is lazily re-built once after being invalidated.
 	// buildMu+built guards this reconstruction.
 	//
 	// file and wsDirs may be non-nil even if built == false, if they were copied
 	// from the previous workspace module version. In this case, they will be
 	// preserved if building fails.
 	buildMu  sync.Mutex
 	built    bool
 	buildErr error
 	file     *modfile.File
 	wsDirs   map[span.URI]struct{}
 }

 func newWorkspace(ctx context.Context, root span.URI, fs source.FileSource, experimental bool) (*workspace, error) {
 	if !experimental {
 		modFiles, err := getLegacyModules(ctx, root, fs)
 		if err != nil {
 			return nil, err
 		}
 		return &workspace{
 			root:         root,
 			modFiles:     modFiles,
 			moduleSource: legacyWorkspace,
 		}, nil
 	}
 	goplsModFH, err := fs.GetFile(ctx, goplsModURI(root))
 	if err != nil {
 		return nil, err
 	}
 	contents, err := goplsModFH.Read()
 	if err == nil {
 		file, modFiles, err := parseGoplsMod(root, goplsModFH.URI(), contents)
 		if err != nil {
 			return nil, err
 		}
 		return &workspace{
 			root:         root,
 			modFiles:     modFiles,
 			file:         file,
 			moduleSource: goplsModWorkspace,
 		}, nil
 	}
 	modFiles, err := findModules(ctx, root, 0, 0)
 	if err != nil {
 		return nil, err
 	}
 	return &workspace{
 		root:         root,
 		modFiles:     modFiles,
 		moduleSource: fileSystemWorkspace,
 	}, nil
 }

 func (wm *workspace) activeModFiles() map[span.URI]struct{} {
 	return wm.modFiles
 }

 // modFile gets the workspace modfile associated with this workspace,
 // computing it if it doesn't exist.
 //
 // A fileSource must be passed in to solve a chicken-egg problem: it is not
 // correct to pass in the snapshot file source to newWorkspace when
 // invalidating, because at the time these are called the snapshot is locked.
 // So we must pass it in later on when actually using the modFile.
 func (wm *workspace) modFile(ctx context.Context, fs source.FileSource) (*modfile.File, error) {
 	wm.build(ctx, fs)
 	return wm.file, wm.buildErr
 }

 func (wm *workspace) build(ctx context.Context, fs source.FileSource) {
 	wm.buildMu.Lock()
 	defer wm.buildMu.Unlock()

 	if wm.built {
 		return
 	}
 	// Building should never be cancelled. Since the workspace module is shared
 	// across multiple snapshots, doing so would put us in a bad state, and it
 	// would not be obvious to the user how to recover.
 	ctx = xcontext.Detach(ctx)

 	// If our module source is not gopls.mod, try to build the workspace module
 	// from modules. Fall back on the pre-existing mod file if parsing fails.
 	if wm.moduleSource != goplsModWorkspace {
 		file, err := buildWorkspaceModFile(ctx, wm.modFiles, fs)
 		switch {
 		case err == nil:
 			wm.file = file
 		case wm.file != nil:
 			// Parsing failed, but we have a previous file version.
 			event.Error(ctx, "building workspace mod file", err)
 		default:
 			// No file to fall back on.
 			wm.buildErr = err
 		}
 	}
 	if wm.file != nil {
 		wm.wsDirs = map[span.URI]struct{}{
 			wm.root: {},
 		}
 		for _, r := range wm.file.Replace {
 			// We may be replacing a module with a different version, not a path
 			// on disk.
 			if r.New.Version != "" {
 				continue
 			}
 			wm.wsDirs[span.URIFromPath(r.New.Path)] = struct{}{}
 		}
 	}
 	// Ensure that there is always at least the root dir.
 	if len(wm.wsDirs) == 0 {
 		wm.wsDirs = map[span.URI]struct{}{
 			wm.root: {},
 		}
 	}
 	wm.built = true
 }

 // dirs returns the workspace directories for the loaded modules.
 func (wm *workspace) dirs(ctx context.Context, fs source.FileSource) []span.URI {
 	wm.build(ctx, fs)
 	var dirs []span.URI
 	for d := range wm.wsDirs {
 		dirs = append(dirs, d)
 	}
 	sort.Slice(dirs, func(i, j int) bool {
 		return span.CompareURI(dirs[i], dirs[j]) < 0
 	})
 	return dirs
 }

 // invalidate returns a (possibly) new workspaceModule after invalidating
 // changedURIs. If wm is still valid in the presence of changedURIs, it returns
 // itself unmodified.
 func (wm *workspace) invalidate(ctx context.Context, changes map[span.URI]*fileChange) (*workspace, bool) {
 	// Prevent races to wm.modFile or wm.wsDirs below, if wm has not yet been
 	// built.
 	wm.buildMu.Lock()
 	defer wm.buildMu.Unlock()
 	// Any gopls.mod change is processed first, followed by go.mod changes, as
 	// changes to gopls.mod may affect the set of active go.mod files.
 	var (
 		// New values. We return a new workspace module if and only if modFiles is
 		// non-nil.
 		modFiles     map[span.URI]struct{}
 		moduleSource = wm.moduleSource
 		modFile      = wm.file
 		err          error
 	)
 	if wm.moduleSource == goplsModWorkspace {
 		// If we are currently reading the modfile from gopls.mod, we default to
 		// preserving it even if module metadata changes (which may be the case if
 		// a go.sum file changes).
 		modFile = wm.file
 	}
 	// First handle changes to the gopls.mod file.
 	if wm.moduleSource != legacyWorkspace {
 		// If gopls.mod has changed we need to either re-read it if it exists or
 		// walk the filesystem if it doesn't exist.
 		gmURI := goplsModURI(wm.root)
 		if change, ok := changes[gmURI]; ok {
 			if change.exists {
 				// Only invalidate if the gopls.mod actually parses. Otherwise, stick with the current gopls.mod
 				parsedFile, parsedModules, err := parseGoplsMod(wm.root, gmURI, change.content)
 				if err == nil {
 					modFile = parsedFile
 					moduleSource = goplsModWorkspace
 					modFiles = parsedModules
 				} else {
 					// Note that modFile is not invalidated here.
 					event.Error(ctx, "parsing gopls.mod", err)
 				}
 			} else {
 				// gopls.mod is deleted. search for modules again.
 				moduleSource = fileSystemWorkspace
 				modFiles, err = findModules(ctx, wm.root, 0, 0)
 				// the modFile is no longer valid.
 				if err != nil {
 					event.Error(ctx, "finding file system modules", err)
 				}
 				modFile = nil
 			}
 		}
 	}

 	// Next, handle go.mod changes that could affect our set of tracked modules.
 	// If we're reading our tracked modules from the gopls.mod, there's nothing
 	// to do here.
 	if wm.moduleSource != goplsModWorkspace {
 		for uri, change := range changes {
 			// If a go.mod file has changed, we may need to update the set of active
 			// modules.
 			if !isGoMod(uri) {
 				continue
 			}
 			if wm.moduleSource == legacyWorkspace && !equalURI(modURI(wm.root), uri) {
 				// Legacy mode only considers a module a workspace root.
 				continue
 			}
 			if !source.InDir(wm.root.Filename(), uri.Filename()) {
 				// Otherwise, the module must be contained within the workspace root.
 				continue
 			}
 			if modFiles == nil {
 				modFiles = make(map[span.URI]struct{})
 				for k := range wm.modFiles {
 					modFiles[k] = struct{}{}
 				}
 			}
 			if change.exists {
 				modFiles[uri] = struct{}{}
 			} else {
 				delete(modFiles, uri)
 			}
 		}
 	}
 	if modFiles != nil {
 		// Any change to modules triggers a new version.
 		return &workspace{
 			root:         wm.root,
 			moduleSource: moduleSource,
 			modFiles:     modFiles,
 			file:         modFile,
 			wsDirs:       wm.wsDirs,
 		}, true
 	}
 	// No change. Just return wm, since it is immutable.
 	return wm, false
 }

 func equalURI(left, right span.URI) bool {
 	return span.CompareURI(left, right) == 0
 }

 // goplsModURI returns the URI for the gopls.mod file contained in root.
 func goplsModURI(root span.URI) span.URI {
 	return span.URIFromPath(filepath.Join(root.Filename(), "gopls.mod"))
 }

 // modURI returns the URI for the go.mod file contained in root.
 func modURI(root span.URI) span.URI {
 	return span.URIFromPath(filepath.Join(root.Filename(), "go.mod"))
 }

 // isGoMod reports if uri is a go.mod file.
 func isGoMod(uri span.URI) bool {
 	return filepath.Base(uri.Filename()) == "go.mod"
 }

 // fileExists reports if the file uri exists within source.
 func fileExists(ctx context.Context, uri span.URI, source source.FileSource) (bool, error) {
 	fh, err := source.GetFile(ctx, uri)
 	if err != nil {
 		return false, err
 	}
 	return fileHandleExists(fh)
 }

 // fileHandleExists reports if the file underlying fh actually exits.
 func fileHandleExists(fh source.FileHandle) (bool, error) {
 	_, err := fh.Read()
 	if err == nil {
 		return true, nil
 	}
 	if os.IsNotExist(err) {
 		return false, nil
 	}
 	return false, err
 }

 // TODO(rFindley): replace this (and similar) with a uripath package analogous
 // to filepath.
 func dirURI(uri span.URI) span.URI {
 	return span.URIFromPath(filepath.Dir(uri.Filename()))
 }

 // getLegacyModules returns a module set containing at most the root module.
 func getLegacyModules(ctx context.Context, root span.URI, fs source.FileSource) (map[span.URI]struct{}, error) {
 	uri := span.URIFromPath(filepath.Join(root.Filename(), "go.mod"))
 	modules := make(map[span.URI]struct{})
 	exists, err := fileExists(ctx, uri, fs)
 	if err != nil {
 		return nil, err
 	}
 	if exists {
 		modules[uri] = struct{}{}
 	}
 	return modules, nil
 }

 func parseGoplsMod(root, uri span.URI, contents []byte) (*modfile.File, map[span.URI]struct{}, error) {
 	modFile, err := modfile.Parse(uri.Filename(), contents, nil)
 	if err != nil {
 		return nil, nil, errors.Errorf("parsing gopls.mod: %w", err)
 	}
 	modFiles := make(map[span.URI]struct{})
 	for _, replace := range modFile.Replace {
 		if replace.New.Version != "" {
 			return nil, nil, errors.Errorf("gopls.mod: replaced module %q@%q must not have version", replace.New.Path, replace.New.Version)
 		}
 		dirFP := filepath.FromSlash(replace.New.Path)
 		if !filepath.IsAbs(dirFP) {
 			dirFP = filepath.Join(root.Filename(), dirFP)
 			// The resulting modfile must use absolute paths, so that it can be
 			// written to a temp directory.
 			replace.New.Path = dirFP
 		}
 		modURI := span.URIFromPath(filepath.Join(dirFP, "go.mod"))
 		modFiles[modURI] = struct{}{}
 	}
 	return modFile, modFiles, nil
 }

 // errExhausted is returned by findModules if the file scan limit is reached.
 var errExhausted = errors.New("exhausted")

 // findModules recursively walks the root directory looking for go.mod files,
 // returning the set of modules it discovers. If modLimit is non-zero,
 // searching stops once modLimit modules have been found. If fileLimit is
 // non-zero, searching stops once fileLimit files have been checked.
 // TODO(rfindley): consider overlays.
 func findModules(ctx context.Context, root span.URI, modLimit, fileLimit int) (map[span.URI]struct{}, error) {
 	// Walk the view's folder to find all modules in the view.
 	modFiles := make(map[span.URI]struct{})
 	searched := 0

 	errDone := errors.New("done")
 	err := filepath.Walk(root.Filename(), func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			// Probably a permission error. Keep looking.
 			return filepath.SkipDir
 		}
 		// For any path that is not the workspace folder, check if the path
 		// would be ignored by the go command. Vendor directories also do not
 		// contain workspace modules.
 		if info.IsDir() && path != root.Filename() {
 			suffix := strings.TrimPrefix(path, root.Filename())
 			switch {
 			case checkIgnored(suffix),
 				strings.Contains(filepath.ToSlash(suffix), "/vendor/"):
 				return filepath.SkipDir
 			}
 		}
 		// We're only interested in go.mod files.
 		uri := span.URIFromPath(path)
 		if isGoMod(uri) {
 			modFiles[uri] = struct{}{}
 		}
 		if modLimit > 0 && len(modFiles) >= modLimit {
 			return errDone
 		}
 		searched++
 		if fileLimit > 0 && searched >= fileLimit {
 			return errExhausted
 		}
 		return nil
 	})
 	if err == errDone {
 		return modFiles, nil
 	}
 	return modFiles, err
 }
	// Copyright 2020 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"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"

	"golang.org/x/mod/modfile"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/lsp/source"
	"golang.org/x/tools/internal/span"
	"golang.org/x/tools/internal/xcontext"
	errors "golang.org/x/xerrors"
	)

	type workspaceSource int

	const (
	legacyWorkspace = iota
	goplsModWorkspace
	fileSystemWorkspace
	)

	func (s workspaceSource) String() string {
	switch s {
	case legacyWorkspace:
	return "legacy"
	case goplsModWorkspace:
	return "gopls.mod"
	case fileSystemWorkspace:
	return "file system"
	default:
	return "!(unknown module source)"
	}
	}

	// workspace tracks go.mod files in the workspace, along with the
	// gopls.mod file, to provide support for multi-module workspaces.
	//
	// Specifically, it provides:
	// - the set of modules contained within in the workspace root considered to
	// be 'active'
	// - the workspace modfile, to be used for the go command `-modfile` flag
	// - the set of workspace directories
	//
	// This type is immutable (or rather, idempotent), so that it may be shared
	// across multiple snapshots.
	type workspace struct {
	root span.URI
	moduleSource workspaceSource

	// modFiles holds the active go.mod files.
	modFiles map[span.URI]struct{}

	// The workspace module is lazily re-built once after being invalidated.
	// buildMu+built guards this reconstruction.
	//
	// file and wsDirs may be non-nil even if built == false, if they were copied
	// from the previous workspace module version. In this case, they will be
	// preserved if building fails.
	buildMu sync.Mutex
	built bool
	buildErr error
	file *modfile.File
	wsDirs map[span.URI]struct{}
	}

	func newWorkspace(ctx context.Context, root span.URI, fs source.FileSource, experimental bool) (*workspace, error) {
	if !experimental {
	modFiles, err := getLegacyModules(ctx, root, fs)
	if err != nil {
	return nil, err
	}
	return &workspace{
	root: root,
	modFiles: modFiles,
	moduleSource: legacyWorkspace,
	}, nil
	}
	goplsModFH, err := fs.GetFile(ctx, goplsModURI(root))
	if err != nil {
	return nil, err
	}
	contents, err := goplsModFH.Read()
	if err == nil {
	file, modFiles, err := parseGoplsMod(root, goplsModFH.URI(), contents)
	if err != nil {
	return nil, err
	}
	return &workspace{
	root: root,
	modFiles: modFiles,
	file: file,
	moduleSource: goplsModWorkspace,
	}, nil
	}
	modFiles, err := findModules(ctx, root, 0, 0)
	if err != nil {
	return nil, err
	}
	return &workspace{
	root: root,
	modFiles: modFiles,
	moduleSource: fileSystemWorkspace,
	}, nil
	}

	func (wm *workspace) activeModFiles() map[span.URI]struct{} {
	return wm.modFiles
	}

	// modFile gets the workspace modfile associated with this workspace,
	// computing it if it doesn't exist.
	//
	// A fileSource must be passed in to solve a chicken-egg problem: it is not
	// correct to pass in the snapshot file source to newWorkspace when
	// invalidating, because at the time these are called the snapshot is locked.
	// So we must pass it in later on when actually using the modFile.
	func (wm workspace) modFile(ctx context.Context, fs source.FileSource) (modfile.File, error) {
	wm.build(ctx, fs)
	return wm.file, wm.buildErr
	}

	func (wm *workspace) build(ctx context.Context, fs source.FileSource) {
	wm.buildMu.Lock()
	defer wm.buildMu.Unlock()

	if wm.built {
	return
	}
	// Building should never be cancelled. Since the workspace module is shared
	// across multiple snapshots, doing so would put us in a bad state, and it
	// would not be obvious to the user how to recover.
	ctx = xcontext.Detach(ctx)

	// If our module source is not gopls.mod, try to build the workspace module
	// from modules. Fall back on the pre-existing mod file if parsing fails.
	if wm.moduleSource != goplsModWorkspace {
	file, err := buildWorkspaceModFile(ctx, wm.modFiles, fs)
	switch {
	case err == nil:
	wm.file = file
	case wm.file != nil:
	// Parsing failed, but we have a previous file version.
	event.Error(ctx, "building workspace mod file", err)
	default:
	// No file to fall back on.
	wm.buildErr = err
	}
	}
	if wm.file != nil {
	wm.wsDirs = map[span.URI]struct{}{
	wm.root: {},
	}
	for _, r := range wm.file.Replace {
	// We may be replacing a module with a different version, not a path
	// on disk.
	if r.New.Version != "" {
	continue
	}
	wm.wsDirs[span.URIFromPath(r.New.Path)] = struct{}{}
	}
	}
	// Ensure that there is always at least the root dir.
	if len(wm.wsDirs) == 0 {
	wm.wsDirs = map[span.URI]struct{}{
	wm.root: {},
	}
	}
	wm.built = true
	}

	// dirs returns the workspace directories for the loaded modules.
	func (wm *workspace) dirs(ctx context.Context, fs source.FileSource) []span.URI {
	wm.build(ctx, fs)
	var dirs []span.URI
	for d := range wm.wsDirs {
	dirs = append(dirs, d)
	}
	sort.Slice(dirs, func(i, j int) bool {
	return span.CompareURI(dirs[i], dirs[j]) < 0
	})
	return dirs
	}

	// invalidate returns a (possibly) new workspaceModule after invalidating
	// changedURIs. If wm is still valid in the presence of changedURIs, it returns
	// itself unmodified.
	func (wm workspace) invalidate(ctx context.Context, changes map[span.URI]fileChange) (*workspace, bool) {
	// Prevent races to wm.modFile or wm.wsDirs below, if wm has not yet been
	// built.
	wm.buildMu.Lock()
	defer wm.buildMu.Unlock()
	// Any gopls.mod change is processed first, followed by go.mod changes, as
	// changes to gopls.mod may affect the set of active go.mod files.
	var (
	// New values. We return a new workspace module if and only if modFiles is
	// non-nil.
	modFiles map[span.URI]struct{}
	moduleSource = wm.moduleSource
	modFile = wm.file
	err error
	)
	if wm.moduleSource == goplsModWorkspace {
	// If we are currently reading the modfile from gopls.mod, we default to
	// preserving it even if module metadata changes (which may be the case if
	// a go.sum file changes).
	modFile = wm.file
	}
	// First handle changes to the gopls.mod file.
	if wm.moduleSource != legacyWorkspace {
	// If gopls.mod has changed we need to either re-read it if it exists or
	// walk the filesystem if it doesn't exist.
	gmURI := goplsModURI(wm.root)
	if change, ok := changes[gmURI]; ok {
	if change.exists {
	// Only invalidate if the gopls.mod actually parses. Otherwise, stick with the current gopls.mod
	parsedFile, parsedModules, err := parseGoplsMod(wm.root, gmURI, change.content)
	if err == nil {
	modFile = parsedFile
	moduleSource = goplsModWorkspace
	modFiles = parsedModules
	} else {
	// Note that modFile is not invalidated here.
	event.Error(ctx, "parsing gopls.mod", err)
	}
	} else {
	// gopls.mod is deleted. search for modules again.
	moduleSource = fileSystemWorkspace
	modFiles, err = findModules(ctx, wm.root, 0, 0)
	// the modFile is no longer valid.
	if err != nil {
	event.Error(ctx, "finding file system modules", err)
	}
	modFile = nil
	}
	}
	}

	// Next, handle go.mod changes that could affect our set of tracked modules.
	// If we're reading our tracked modules from the gopls.mod, there's nothing
	// to do here.
	if wm.moduleSource != goplsModWorkspace {
	for uri, change := range changes {
	// If a go.mod file has changed, we may need to update the set of active
	// modules.
	if !isGoMod(uri) {
	continue
	}
	if wm.moduleSource == legacyWorkspace && !equalURI(modURI(wm.root), uri) {
	// Legacy mode only considers a module a workspace root.
	continue
	}
	if !source.InDir(wm.root.Filename(), uri.Filename()) {
	// Otherwise, the module must be contained within the workspace root.
	continue
	}
	if modFiles == nil {
	modFiles = make(map[span.URI]struct{})
	for k := range wm.modFiles {
	modFiles[k] = struct{}{}
	}
	}
	if change.exists {
	modFiles[uri] = struct{}{}
	} else {
	delete(modFiles, uri)
	}
	}
	}
	if modFiles != nil {
	// Any change to modules triggers a new version.
	return &workspace{
	root: wm.root,
	moduleSource: moduleSource,
	modFiles: modFiles,
	file: modFile,
	wsDirs: wm.wsDirs,
	}, true
	}
	// No change. Just return wm, since it is immutable.
	return wm, false
	}

	func equalURI(left, right span.URI) bool {
	return span.CompareURI(left, right) == 0
	}

	// goplsModURI returns the URI for the gopls.mod file contained in root.
	func goplsModURI(root span.URI) span.URI {
	return span.URIFromPath(filepath.Join(root.Filename(), "gopls.mod"))
	}

	// modURI returns the URI for the go.mod file contained in root.
	func modURI(root span.URI) span.URI {
	return span.URIFromPath(filepath.Join(root.Filename(), "go.mod"))
	}

	// isGoMod reports if uri is a go.mod file.
	func isGoMod(uri span.URI) bool {
	return filepath.Base(uri.Filename()) == "go.mod"
	}

	// fileExists reports if the file uri exists within source.
	func fileExists(ctx context.Context, uri span.URI, source source.FileSource) (bool, error) {
	fh, err := source.GetFile(ctx, uri)
	if err != nil {
	return false, err
	}
	return fileHandleExists(fh)
	}

	// fileHandleExists reports if the file underlying fh actually exits.
	func fileHandleExists(fh source.FileHandle) (bool, error) {
	_, err := fh.Read()
	if err == nil {
	return true, nil
	}
	if os.IsNotExist(err) {
	return false, nil
	}
	return false, err
	}

	// TODO(rFindley): replace this (and similar) with a uripath package analogous
	// to filepath.
	func dirURI(uri span.URI) span.URI {
	return span.URIFromPath(filepath.Dir(uri.Filename()))
	}

	// getLegacyModules returns a module set containing at most the root module.
	func getLegacyModules(ctx context.Context, root span.URI, fs source.FileSource) (map[span.URI]struct{}, error) {
	uri := span.URIFromPath(filepath.Join(root.Filename(), "go.mod"))
	modules := make(map[span.URI]struct{})
	exists, err := fileExists(ctx, uri, fs)
	if err != nil {
	return nil, err
	}
	if exists {
	modules[uri] = struct{}{}
	}
	return modules, nil
	}

	func parseGoplsMod(root, uri span.URI, contents []byte) (*modfile.File, map[span.URI]struct{}, error) {
	modFile, err := modfile.Parse(uri.Filename(), contents, nil)
	if err != nil {
	return nil, nil, errors.Errorf("parsing gopls.mod: %w", err)
	}
	modFiles := make(map[span.URI]struct{})
	for _, replace := range modFile.Replace {
	if replace.New.Version != "" {
	return nil, nil, errors.Errorf("gopls.mod: replaced module %q@%q must not have version", replace.New.Path, replace.New.Version)
	}
	dirFP := filepath.FromSlash(replace.New.Path)
	if !filepath.IsAbs(dirFP) {
	dirFP = filepath.Join(root.Filename(), dirFP)
	// The resulting modfile must use absolute paths, so that it can be
	// written to a temp directory.
	replace.New.Path = dirFP
	}
	modURI := span.URIFromPath(filepath.Join(dirFP, "go.mod"))
	modFiles[modURI] = struct{}{}
	}
	return modFile, modFiles, nil
	}

	// errExhausted is returned by findModules if the file scan limit is reached.
	var errExhausted = errors.New("exhausted")

	// findModules recursively walks the root directory looking for go.mod files,
	// returning the set of modules it discovers. If modLimit is non-zero,
	// searching stops once modLimit modules have been found. If fileLimit is
	// non-zero, searching stops once fileLimit files have been checked.
	// TODO(rfindley): consider overlays.
	func findModules(ctx context.Context, root span.URI, modLimit, fileLimit int) (map[span.URI]struct{}, error) {
	// Walk the view's folder to find all modules in the view.
	modFiles := make(map[span.URI]struct{})
	searched := 0

	errDone := errors.New("done")
	err := filepath.Walk(root.Filename(), func(path string, info os.FileInfo, err error) error {
	if err != nil {
	// Probably a permission error. Keep looking.
	return filepath.SkipDir
	}
	// For any path that is not the workspace folder, check if the path
	// would be ignored by the go command. Vendor directories also do not
	// contain workspace modules.
	if info.IsDir() && path != root.Filename() {
	suffix := strings.TrimPrefix(path, root.Filename())
	switch {
	case checkIgnored(suffix),
	strings.Contains(filepath.ToSlash(suffix), "/vendor/"):
	return filepath.SkipDir
	}
	}
	// We're only interested in go.mod files.
	uri := span.URIFromPath(path)
	if isGoMod(uri) {
	modFiles[uri] = struct{}{}
	}
	if modLimit > 0 && len(modFiles) >= modLimit {
	return errDone
	}
	searched++
	if fileLimit > 0 && searched >= fileLimit {
	return errExhausted
	}
	return nil
	})
	if err == errDone {
	return modFiles, nil
	}
	return modFiles, err
	}