gopls/internal/golang/workspace_symbol.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 golang

 import (
 	"context"
 	"fmt"
 	"path/filepath"
 	"runtime"
 	"sort"
 	"strings"
 	"unicode"

 	"golang.org/x/tools/gopls/internal/cache"
 	"golang.org/x/tools/gopls/internal/cache/metadata"
 	"golang.org/x/tools/gopls/internal/fuzzy"
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/settings"
 	"golang.org/x/tools/internal/event"
 )

 // maxSymbols defines the maximum number of symbol results that should ever be
 // sent in response to a client.
 const maxSymbols = 100

 // WorkspaceSymbols matches symbols across all views using the given query,
 // according to the match semantics parameterized by matcherType and style.
 //
 // The workspace symbol method is defined in the spec as follows:
 //
 //	The workspace symbol request is sent from the client to the server to
 //	list project-wide symbols matching the query string.
 //
 // It is unclear what "project-wide" means here, but given the parameters of
 // workspace/symbol do not include any workspace identifier, then it has to be
 // assumed that "project-wide" means "across all workspaces".  Hence why
 // WorkspaceSymbols receives the views []View.
 //
 // However, it then becomes unclear what it would mean to call WorkspaceSymbols
 // with a different configured SymbolMatcher per View. Therefore we assume that
 // Session level configuration will define the SymbolMatcher to be used for the
 // WorkspaceSymbols method.
 func WorkspaceSymbols(ctx context.Context, matcher settings.SymbolMatcher, style settings.SymbolStyle, snapshots []*cache.Snapshot, query string) ([]protocol.SymbolInformation, error) {
 	ctx, done := event.Start(ctx, "golang.WorkspaceSymbols")
 	defer done()
 	if query == "" {
 		return nil, nil
 	}

 	var s symbolizer
 	switch style {
 	case settings.DynamicSymbols:
 		s = dynamicSymbolMatch
 	case settings.FullyQualifiedSymbols:
 		s = fullyQualifiedSymbolMatch
 	case settings.PackageQualifiedSymbols:
 		s = packageSymbolMatch
 	default:
 		panic(fmt.Errorf("unknown symbol style: %v", style))
 	}

 	return collectSymbols(ctx, snapshots, matcher, s, query)
 }

 // A matcherFunc returns the index and score of a symbol match.
 //
 // See the comment for symbolCollector for more information.
 type matcherFunc func(chunks []string) (int, float64)

 // A symbolizer returns the best symbol match for a name with pkg, according to
 // some heuristic. The symbol name is passed as the slice nameParts of logical
 // name pieces. For example, for myType.field the caller can pass either
 // []string{"myType.field"} or []string{"myType.", "field"}.
 //
 // See the comment for symbolCollector for more information.
 //
 // The space argument is an empty slice with spare capacity that may be used
 // to allocate the result.
 type symbolizer func(space []string, name string, pkg *metadata.Package, m matcherFunc) ([]string, float64)

 func fullyQualifiedSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
 	if _, score := dynamicSymbolMatch(space, name, pkg, matcher); score > 0 {
 		return append(space, string(pkg.PkgPath), ".", name), score
 	}
 	return nil, 0
 }

 func dynamicSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
 	if metadata.IsCommandLineArguments(pkg.ID) {
 		// command-line-arguments packages have a non-sensical package path, so
 		// just use their package name.
 		return packageSymbolMatch(space, name, pkg, matcher)
 	}

 	var score float64

 	endsInPkgName := strings.HasSuffix(string(pkg.PkgPath), string(pkg.Name))

 	// If the package path does not end in the package name, we need to check the
 	// package-qualified symbol as an extra pass first.
 	if !endsInPkgName {
 		pkgQualified := append(space, string(pkg.Name), ".", name)
 		idx, score := matcher(pkgQualified)
 		nameStart := len(pkg.Name) + 1
 		if score > 0 {
 			// If our match is contained entirely within the unqualified portion,
 			// just return that.
 			if idx >= nameStart {
 				return append(space, name), score
 			}
 			// Lower the score for matches that include the package name.
 			return pkgQualified, score * 0.8
 		}
 	}

 	// Now try matching the fully qualified symbol.
 	fullyQualified := append(space, string(pkg.PkgPath), ".", name)
 	idx, score := matcher(fullyQualified)

 	// As above, check if we matched just the unqualified symbol name.
 	nameStart := len(pkg.PkgPath) + 1
 	if idx >= nameStart {
 		return append(space, name), score
 	}

 	// If our package path ends in the package name, we'll have skipped the
 	// initial pass above, so check if we matched just the package-qualified
 	// name.
 	if endsInPkgName && idx >= 0 {
 		pkgStart := len(pkg.PkgPath) - len(pkg.Name)
 		if idx >= pkgStart {
 			return append(space, string(pkg.Name), ".", name), score
 		}
 	}

 	// Our match was not contained within the unqualified or package qualified
 	// symbol. Return the fully qualified symbol but discount the score.
 	return fullyQualified, score * 0.6
 }

 func packageSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
 	qualified := append(space, string(pkg.Name), ".", name)
 	if _, s := matcher(qualified); s > 0 {
 		return qualified, s
 	}
 	return nil, 0
 }

 func buildMatcher(matcher settings.SymbolMatcher, query string) matcherFunc {
 	switch matcher {
 	case settings.SymbolFuzzy:
 		return parseQuery(query, newFuzzyMatcher)
 	case settings.SymbolFastFuzzy:
 		return parseQuery(query, func(query string) matcherFunc {
 			return fuzzy.NewSymbolMatcher(query).Match
 		})
 	case settings.SymbolCaseSensitive:
 		return matchExact(query)
 	case settings.SymbolCaseInsensitive:
 		q := strings.ToLower(query)
 		exact := matchExact(q)
 		wrapper := []string{""}
 		return func(chunks []string) (int, float64) {
 			s := strings.Join(chunks, "")
 			wrapper[0] = strings.ToLower(s)
 			return exact(wrapper)
 		}
 	}
 	panic(fmt.Errorf("unknown symbol matcher: %v", matcher))
 }

 func newFuzzyMatcher(query string) matcherFunc {
 	fm := fuzzy.NewMatcher(query)
 	return func(chunks []string) (int, float64) {
 		score := float64(fm.ScoreChunks(chunks))
 		ranges := fm.MatchedRanges()
 		if len(ranges) > 0 {
 			return ranges[0], score
 		}
 		return -1, score
 	}
 }

 // parseQuery parses a field-separated symbol query, extracting the special
 // characters listed below, and returns a matcherFunc corresponding to the AND
 // of all field queries.
 //
 // Special characters:
 //
 //	^  match exact prefix
 //	$  match exact suffix
 //	'  match exact
 //
 // In all three of these special queries, matches are 'smart-cased', meaning
 // they are case sensitive if the symbol query contains any upper-case
 // characters, and case insensitive otherwise.
 func parseQuery(q string, newMatcher func(string) matcherFunc) matcherFunc {
 	fields := strings.Fields(q)
 	if len(fields) == 0 {
 		return func([]string) (int, float64) { return -1, 0 }
 	}
 	var funcs []matcherFunc
 	for _, field := range fields {
 		var f matcherFunc
 		switch {
 		case strings.HasPrefix(field, "^"):
 			prefix := field[1:]
 			f = smartCase(prefix, func(chunks []string) (int, float64) {
 				s := strings.Join(chunks, "")
 				if strings.HasPrefix(s, prefix) {
 					return 0, 1
 				}
 				return -1, 0
 			})
 		case strings.HasPrefix(field, "'"):
 			exact := field[1:]
 			f = smartCase(exact, matchExact(exact))
 		case strings.HasSuffix(field, "$"):
 			suffix := field[0 : len(field)-1]
 			f = smartCase(suffix, func(chunks []string) (int, float64) {
 				s := strings.Join(chunks, "")
 				if strings.HasSuffix(s, suffix) {
 					return len(s) - len(suffix), 1
 				}
 				return -1, 0
 			})
 		default:
 			f = newMatcher(field)
 		}
 		funcs = append(funcs, f)
 	}
 	if len(funcs) == 1 {
 		return funcs[0]
 	}
 	return comboMatcher(funcs).match
 }

 func matchExact(exact string) matcherFunc {
 	return func(chunks []string) (int, float64) {
 		s := strings.Join(chunks, "")
 		if idx := strings.LastIndex(s, exact); idx >= 0 {
 			return idx, 1
 		}
 		return -1, 0
 	}
 }

 // smartCase returns a matcherFunc that is case-sensitive if q contains any
 // upper-case characters, and case-insensitive otherwise.
 func smartCase(q string, m matcherFunc) matcherFunc {
 	insensitive := strings.ToLower(q) == q
 	wrapper := []string{""}
 	return func(chunks []string) (int, float64) {
 		s := strings.Join(chunks, "")
 		if insensitive {
 			s = strings.ToLower(s)
 		}
 		wrapper[0] = s
 		return m(wrapper)
 	}
 }

 type comboMatcher []matcherFunc

 func (c comboMatcher) match(chunks []string) (int, float64) {
 	score := 1.0
 	first := 0
 	for _, f := range c {
 		idx, s := f(chunks)
 		if idx < first {
 			first = idx
 		}
 		score *= s
 	}
 	return first, score
 }

 // collectSymbols calls snapshot.Symbols to walk the syntax trees of
 // all files in the views' current snapshots, and returns a sorted,
 // scored list of symbols that best match the parameters.
 //
 // How it matches symbols is parameterized by two interfaces:
 //   - A matcherFunc determines how well a string symbol matches a query. It
 //     returns a non-negative score indicating the quality of the match. A score
 //     of zero indicates no match.
 //   - A symbolizer determines how we extract the symbol for an object. This
 //     enables the 'symbolStyle' configuration option.
 func collectSymbols(ctx context.Context, snapshots []*cache.Snapshot, matcherType settings.SymbolMatcher, symbolizer symbolizer, query string) ([]protocol.SymbolInformation, error) {
 	// Extract symbols from all files.
 	var work []symbolFile
 	var roots []string
 	seen := make(map[protocol.DocumentURI]bool)
 	// TODO(adonovan): opt: parallelize this loop? How often is len > 1?
 	for _, snapshot := range snapshots {
 		// Use the root view URIs for determining (lexically)
 		// whether a URI is in any open workspace.
 		folderURI := snapshot.Folder()
 		roots = append(roots, strings.TrimRight(string(folderURI), "/"))

 		filters := snapshot.Options().DirectoryFilters
 		filterer := cache.NewFilterer(filters)
 		folder := filepath.ToSlash(folderURI.Path())

 		workspaceOnly := true
 		if snapshot.Options().SymbolScope == settings.AllSymbolScope {
 			workspaceOnly = false
 		}
 		symbols, err := snapshot.Symbols(ctx, workspaceOnly)
 		if err != nil {
 			return nil, err
 		}

 		for uri, syms := range symbols {
 			norm := filepath.ToSlash(uri.Path())
 			nm := strings.TrimPrefix(norm, folder)
 			if filterer.Disallow(nm) {
 				continue
 			}
 			// Only scan each file once.
 			if seen[uri] {
 				continue
 			}
 			meta, err := NarrowestMetadataForFile(ctx, snapshot, uri)
 			if err != nil {
 				event.Error(ctx, fmt.Sprintf("missing metadata for %q", uri), err)
 				continue
 			}
 			seen[uri] = true
 			work = append(work, symbolFile{uri, meta, syms})
 		}
 	}

 	// Match symbols in parallel.
 	// Each worker has its own symbolStore,
 	// which we merge at the end.
 	nmatchers := runtime.GOMAXPROCS(-1) // matching is CPU bound
 	results := make(chan *symbolStore)
 	for i := 0; i < nmatchers; i++ {
 		go func(i int) {
 			matcher := buildMatcher(matcherType, query)
 			store := new(symbolStore)
 			// Assign files to workers in round-robin fashion.
 			for j := i; j < len(work); j += nmatchers {
 				matchFile(store, symbolizer, matcher, roots, work[j])
 			}
 			results <- store
 		}(i)
 	}

 	// Gather and merge results as they arrive.
 	var unified symbolStore
 	for i := 0; i < nmatchers; i++ {
 		store := <-results
 		for _, syms := range store.res {
 			unified.store(syms)
 		}
 	}
 	return unified.results(), nil
 }

 // symbolFile holds symbol information for a single file.
 type symbolFile struct {
 	uri  protocol.DocumentURI
 	mp   *metadata.Package
 	syms []cache.Symbol
 }

 // matchFile scans a symbol file and adds matching symbols to the store.
 func matchFile(store *symbolStore, symbolizer symbolizer, matcher matcherFunc, roots []string, i symbolFile) {
 	space := make([]string, 0, 3)
 	for _, sym := range i.syms {
 		symbolParts, score := symbolizer(space, sym.Name, i.mp, matcher)

 		// Check if the score is too low before applying any downranking.
 		if store.tooLow(score) {
 			continue
 		}

 		// Factors to apply to the match score for the purpose of downranking
 		// results.
 		//
 		// These numbers were crudely calibrated based on trial-and-error using a
 		// small number of sample queries. Adjust as necessary.
 		//
 		// All factors are multiplicative, meaning if more than one applies they are
 		// multiplied together.
 		const (
 			// nonWorkspaceFactor is applied to symbols outside the workspace.
 			// Developers are less likely to want to jump to code that they
 			// are not actively working on.
 			nonWorkspaceFactor = 0.5
 			// nonWorkspaceUnexportedFactor is applied to unexported symbols outside
 			// the workspace. Since one wouldn't usually jump to unexported
 			// symbols to understand a package API, they are particularly irrelevant.
 			nonWorkspaceUnexportedFactor = 0.5
 			// every field or method nesting level to access the field decreases
 			// the score by a factor of 1.0 - depth*depthFactor, up to a depth of
 			// 3.
 			//
 			// Use a small constant here, as this exists mostly to break ties
 			// (e.g. given a type Foo and a field x.Foo, prefer Foo).
 			depthFactor = 0.01
 		)

 		startWord := true
 		exported := true
 		depth := 0.0
 		for _, r := range sym.Name {
 			if startWord && !unicode.IsUpper(r) {
 				exported = false
 			}
 			if r == '.' {
 				startWord = true
 				depth++
 			} else {
 				startWord = false
 			}
 		}

 		// TODO(rfindley): use metadata to determine if the file is in a workspace
 		// package, rather than this heuristic.
 		inWorkspace := false
 		for _, root := range roots {
 			if strings.HasPrefix(string(i.uri), root) {
 				inWorkspace = true
 				break
 			}
 		}

 		// Apply downranking based on workspace position.
 		if !inWorkspace {
 			score *= nonWorkspaceFactor
 			if !exported {
 				score *= nonWorkspaceUnexportedFactor
 			}
 		}

 		// Apply downranking based on symbol depth.
 		if depth > 3 {
 			depth = 3
 		}
 		score *= 1.0 - depth*depthFactor

 		if store.tooLow(score) {
 			continue
 		}

 		si := symbolInformation{
 			score:     score,
 			symbol:    strings.Join(symbolParts, ""),
 			kind:      sym.Kind,
 			uri:       i.uri,
 			rng:       sym.Range,
 			container: string(i.mp.PkgPath),
 		}
 		store.store(si)
 	}
 }

 type symbolStore struct {
 	res [maxSymbols]symbolInformation
 }

 // store inserts si into the sorted results, if si has a high enough score.
 func (sc *symbolStore) store(si symbolInformation) {
 	if sc.tooLow(si.score) {
 		return
 	}
 	insertAt := sort.Search(len(sc.res), func(i int) bool {
 		// Sort by score, then symbol length, and finally lexically.
 		if sc.res[i].score != si.score {
 			return sc.res[i].score < si.score
 		}
 		if len(sc.res[i].symbol) != len(si.symbol) {
 			return len(sc.res[i].symbol) > len(si.symbol)
 		}
 		return sc.res[i].symbol > si.symbol
 	})
 	if insertAt < len(sc.res)-1 {
 		copy(sc.res[insertAt+1:], sc.res[insertAt:len(sc.res)-1])
 	}
 	sc.res[insertAt] = si
 }

 func (sc *symbolStore) tooLow(score float64) bool {
 	return score <= sc.res[len(sc.res)-1].score
 }

 func (sc *symbolStore) results() []protocol.SymbolInformation {
 	var res []protocol.SymbolInformation
 	for _, si := range sc.res {
 		if si.score <= 0 {
 			return res
 		}
 		res = append(res, si.asProtocolSymbolInformation())
 	}
 	return res
 }

 // symbolInformation is a cut-down version of protocol.SymbolInformation that
 // allows struct values of this type to be used as map keys.
 type symbolInformation struct {
 	score     float64
 	symbol    string
 	container string
 	kind      protocol.SymbolKind
 	uri       protocol.DocumentURI
 	rng       protocol.Range
 }

 // asProtocolSymbolInformation converts s to a protocol.SymbolInformation value.
 //
 // TODO: work out how to handle tags if/when they are needed.
 func (s symbolInformation) asProtocolSymbolInformation() protocol.SymbolInformation {
 	return protocol.SymbolInformation{
 		Name: s.symbol,
 		Kind: s.kind,
 		Location: protocol.Location{
 			URI:   s.uri,
 			Range: s.rng,
 		},
 		ContainerName: s.container,
 	}
 }
	// 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 golang

	import (
	"context"
	"fmt"
	"path/filepath"
	"runtime"
	"sort"
	"strings"
	"unicode"

	"golang.org/x/tools/gopls/internal/cache"
	"golang.org/x/tools/gopls/internal/cache/metadata"
	"golang.org/x/tools/gopls/internal/fuzzy"
	"golang.org/x/tools/gopls/internal/protocol"
	"golang.org/x/tools/gopls/internal/settings"
	"golang.org/x/tools/internal/event"
	)

	// maxSymbols defines the maximum number of symbol results that should ever be
	// sent in response to a client.
	const maxSymbols = 100

	// WorkspaceSymbols matches symbols across all views using the given query,
	// according to the match semantics parameterized by matcherType and style.
	//
	// The workspace symbol method is defined in the spec as follows:
	//
	// The workspace symbol request is sent from the client to the server to
	// list project-wide symbols matching the query string.
	//
	// It is unclear what "project-wide" means here, but given the parameters of
	// workspace/symbol do not include any workspace identifier, then it has to be
	// assumed that "project-wide" means "across all workspaces". Hence why
	// WorkspaceSymbols receives the views []View.
	//
	// However, it then becomes unclear what it would mean to call WorkspaceSymbols
	// with a different configured SymbolMatcher per View. Therefore we assume that
	// Session level configuration will define the SymbolMatcher to be used for the
	// WorkspaceSymbols method.
	func WorkspaceSymbols(ctx context.Context, matcher settings.SymbolMatcher, style settings.SymbolStyle, snapshots []*cache.Snapshot, query string) ([]protocol.SymbolInformation, error) {
	ctx, done := event.Start(ctx, "golang.WorkspaceSymbols")
	defer done()
	if query == "" {
	return nil, nil
	}

	var s symbolizer
	switch style {
	case settings.DynamicSymbols:
	s = dynamicSymbolMatch
	case settings.FullyQualifiedSymbols:
	s = fullyQualifiedSymbolMatch
	case settings.PackageQualifiedSymbols:
	s = packageSymbolMatch
	default:
	panic(fmt.Errorf("unknown symbol style: %v", style))
	}

	return collectSymbols(ctx, snapshots, matcher, s, query)
	}

	// A matcherFunc returns the index and score of a symbol match.
	//
	// See the comment for symbolCollector for more information.
	type matcherFunc func(chunks []string) (int, float64)

	// A symbolizer returns the best symbol match for a name with pkg, according to
	// some heuristic. The symbol name is passed as the slice nameParts of logical
	// name pieces. For example, for myType.field the caller can pass either
	// []string{"myType.field"} or []string{"myType.", "field"}.
	//
	// See the comment for symbolCollector for more information.
	//
	// The space argument is an empty slice with spare capacity that may be used
	// to allocate the result.
	type symbolizer func(space []string, name string, pkg *metadata.Package, m matcherFunc) ([]string, float64)

	func fullyQualifiedSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
	if _, score := dynamicSymbolMatch(space, name, pkg, matcher); score > 0 {
	return append(space, string(pkg.PkgPath), ".", name), score
	}
	return nil, 0
	}

	func dynamicSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
	if metadata.IsCommandLineArguments(pkg.ID) {
	// command-line-arguments packages have a non-sensical package path, so
	// just use their package name.
	return packageSymbolMatch(space, name, pkg, matcher)
	}

	var score float64

	endsInPkgName := strings.HasSuffix(string(pkg.PkgPath), string(pkg.Name))

	// If the package path does not end in the package name, we need to check the
	// package-qualified symbol as an extra pass first.
	if !endsInPkgName {
	pkgQualified := append(space, string(pkg.Name), ".", name)
	idx, score := matcher(pkgQualified)
	nameStart := len(pkg.Name) + 1
	if score > 0 {
	// If our match is contained entirely within the unqualified portion,
	// just return that.
	if idx >= nameStart {
	return append(space, name), score
	}
	// Lower the score for matches that include the package name.
	return pkgQualified, score * 0.8
	}
	}

	// Now try matching the fully qualified symbol.
	fullyQualified := append(space, string(pkg.PkgPath), ".", name)
	idx, score := matcher(fullyQualified)

	// As above, check if we matched just the unqualified symbol name.
	nameStart := len(pkg.PkgPath) + 1
	if idx >= nameStart {
	return append(space, name), score
	}

	// If our package path ends in the package name, we'll have skipped the
	// initial pass above, so check if we matched just the package-qualified
	// name.
	if endsInPkgName && idx >= 0 {
	pkgStart := len(pkg.PkgPath) - len(pkg.Name)
	if idx >= pkgStart {
	return append(space, string(pkg.Name), ".", name), score
	}
	}

	// Our match was not contained within the unqualified or package qualified
	// symbol. Return the fully qualified symbol but discount the score.
	return fullyQualified, score * 0.6
	}

	func packageSymbolMatch(space []string, name string, pkg *metadata.Package, matcher matcherFunc) ([]string, float64) {
	qualified := append(space, string(pkg.Name), ".", name)
	if _, s := matcher(qualified); s > 0 {
	return qualified, s
	}
	return nil, 0
	}

	func buildMatcher(matcher settings.SymbolMatcher, query string) matcherFunc {
	switch matcher {
	case settings.SymbolFuzzy:
	return parseQuery(query, newFuzzyMatcher)
	case settings.SymbolFastFuzzy:
	return parseQuery(query, func(query string) matcherFunc {
	return fuzzy.NewSymbolMatcher(query).Match
	})
	case settings.SymbolCaseSensitive:
	return matchExact(query)
	case settings.SymbolCaseInsensitive:
	q := strings.ToLower(query)
	exact := matchExact(q)
	wrapper := []string{""}
	return func(chunks []string) (int, float64) {
	s := strings.Join(chunks, "")
	wrapper[0] = strings.ToLower(s)
	return exact(wrapper)
	}
	}
	panic(fmt.Errorf("unknown symbol matcher: %v", matcher))
	}

	func newFuzzyMatcher(query string) matcherFunc {
	fm := fuzzy.NewMatcher(query)
	return func(chunks []string) (int, float64) {
	score := float64(fm.ScoreChunks(chunks))
	ranges := fm.MatchedRanges()
	if len(ranges) > 0 {
	return ranges[0], score
	}
	return -1, score
	}
	}

	// parseQuery parses a field-separated symbol query, extracting the special
	// characters listed below, and returns a matcherFunc corresponding to the AND
	// of all field queries.
	//
	// Special characters:
	//
	// ^ match exact prefix
	// $ match exact suffix
	// ' match exact
	//
	// In all three of these special queries, matches are 'smart-cased', meaning
	// they are case sensitive if the symbol query contains any upper-case
	// characters, and case insensitive otherwise.
	func parseQuery(q string, newMatcher func(string) matcherFunc) matcherFunc {
	fields := strings.Fields(q)
	if len(fields) == 0 {
	return func([]string) (int, float64) { return -1, 0 }
	}
	var funcs []matcherFunc
	for _, field := range fields {
	var f matcherFunc
	switch {
	case strings.HasPrefix(field, "^"):
	prefix := field[1:]
	f = smartCase(prefix, func(chunks []string) (int, float64) {
	s := strings.Join(chunks, "")
	if strings.HasPrefix(s, prefix) {
	return 0, 1
	}
	return -1, 0
	})
	case strings.HasPrefix(field, "'"):
	exact := field[1:]
	f = smartCase(exact, matchExact(exact))
	case strings.HasSuffix(field, "$"):
	suffix := field[0 : len(field)-1]
	f = smartCase(suffix, func(chunks []string) (int, float64) {
	s := strings.Join(chunks, "")
	if strings.HasSuffix(s, suffix) {
	return len(s) - len(suffix), 1
	}
	return -1, 0
	})
	default:
	f = newMatcher(field)
	}
	funcs = append(funcs, f)
	}
	if len(funcs) == 1 {
	return funcs[0]
	}
	return comboMatcher(funcs).match
	}

	func matchExact(exact string) matcherFunc {
	return func(chunks []string) (int, float64) {
	s := strings.Join(chunks, "")
	if idx := strings.LastIndex(s, exact); idx >= 0 {
	return idx, 1
	}
	return -1, 0
	}
	}

	// smartCase returns a matcherFunc that is case-sensitive if q contains any
	// upper-case characters, and case-insensitive otherwise.
	func smartCase(q string, m matcherFunc) matcherFunc {
	insensitive := strings.ToLower(q) == q
	wrapper := []string{""}
	return func(chunks []string) (int, float64) {
	s := strings.Join(chunks, "")
	if insensitive {
	s = strings.ToLower(s)
	}
	wrapper[0] = s
	return m(wrapper)
	}
	}

	type comboMatcher []matcherFunc

	func (c comboMatcher) match(chunks []string) (int, float64) {
	score := 1.0
	first := 0
	for _, f := range c {
	idx, s := f(chunks)
	if idx < first {
	first = idx
	}
	score *= s
	}
	return first, score
	}

	// collectSymbols calls snapshot.Symbols to walk the syntax trees of
	// all files in the views' current snapshots, and returns a sorted,
	// scored list of symbols that best match the parameters.
	//
	// How it matches symbols is parameterized by two interfaces:
	// - A matcherFunc determines how well a string symbol matches a query. It
	// returns a non-negative score indicating the quality of the match. A score
	// of zero indicates no match.
	// - A symbolizer determines how we extract the symbol for an object. This
	// enables the 'symbolStyle' configuration option.
	func collectSymbols(ctx context.Context, snapshots []*cache.Snapshot, matcherType settings.SymbolMatcher, symbolizer symbolizer, query string) ([]protocol.SymbolInformation, error) {
	// Extract symbols from all files.
	var work []symbolFile
	var roots []string
	seen := make(map[protocol.DocumentURI]bool)
	// TODO(adonovan): opt: parallelize this loop? How often is len > 1?
	for _, snapshot := range snapshots {
	// Use the root view URIs for determining (lexically)
	// whether a URI is in any open workspace.
	folderURI := snapshot.Folder()
	roots = append(roots, strings.TrimRight(string(folderURI), "/"))

	filters := snapshot.Options().DirectoryFilters
	filterer := cache.NewFilterer(filters)
	folder := filepath.ToSlash(folderURI.Path())

	workspaceOnly := true
	if snapshot.Options().SymbolScope == settings.AllSymbolScope {
	workspaceOnly = false
	}
	symbols, err := snapshot.Symbols(ctx, workspaceOnly)
	if err != nil {
	return nil, err
	}

	for uri, syms := range symbols {
	norm := filepath.ToSlash(uri.Path())
	nm := strings.TrimPrefix(norm, folder)
	if filterer.Disallow(nm) {
	continue
	}
	// Only scan each file once.
	if seen[uri] {
	continue
	}
	meta, err := NarrowestMetadataForFile(ctx, snapshot, uri)
	if err != nil {
	event.Error(ctx, fmt.Sprintf("missing metadata for %q", uri), err)
	continue
	}
	seen[uri] = true
	work = append(work, symbolFile{uri, meta, syms})
	}
	}

	// Match symbols in parallel.
	// Each worker has its own symbolStore,
	// which we merge at the end.
	nmatchers := runtime.GOMAXPROCS(-1) // matching is CPU bound
	results := make(chan *symbolStore)
	for i := 0; i < nmatchers; i++ {
	go func(i int) {
	matcher := buildMatcher(matcherType, query)
	store := new(symbolStore)
	// Assign files to workers in round-robin fashion.
	for j := i; j < len(work); j += nmatchers {
	matchFile(store, symbolizer, matcher, roots, work[j])
	}
	results <- store
	}(i)
	}

	// Gather and merge results as they arrive.
	var unified symbolStore
	for i := 0; i < nmatchers; i++ {
	store := <-results
	for _, syms := range store.res {
	unified.store(syms)
	}
	}
	return unified.results(), nil
	}

	// symbolFile holds symbol information for a single file.
	type symbolFile struct {
	uri protocol.DocumentURI
	mp *metadata.Package
	syms []cache.Symbol
	}

	// matchFile scans a symbol file and adds matching symbols to the store.
	func matchFile(store *symbolStore, symbolizer symbolizer, matcher matcherFunc, roots []string, i symbolFile) {
	space := make([]string, 0, 3)
	for _, sym := range i.syms {
	symbolParts, score := symbolizer(space, sym.Name, i.mp, matcher)

	// Check if the score is too low before applying any downranking.
	if store.tooLow(score) {
	continue
	}

	// Factors to apply to the match score for the purpose of downranking
	// results.
	//
	// These numbers were crudely calibrated based on trial-and-error using a
	// small number of sample queries. Adjust as necessary.
	//
	// All factors are multiplicative, meaning if more than one applies they are
	// multiplied together.
	const (
	// nonWorkspaceFactor is applied to symbols outside the workspace.
	// Developers are less likely to want to jump to code that they
	// are not actively working on.
	nonWorkspaceFactor = 0.5
	// nonWorkspaceUnexportedFactor is applied to unexported symbols outside
	// the workspace. Since one wouldn't usually jump to unexported
	// symbols to understand a package API, they are particularly irrelevant.
	nonWorkspaceUnexportedFactor = 0.5
	// every field or method nesting level to access the field decreases
	// the score by a factor of 1.0 - depth*depthFactor, up to a depth of
	// 3.
	//
	// Use a small constant here, as this exists mostly to break ties
	// (e.g. given a type Foo and a field x.Foo, prefer Foo).
	depthFactor = 0.01
	)

	startWord := true
	exported := true
	depth := 0.0
	for _, r := range sym.Name {
	if startWord && !unicode.IsUpper(r) {
	exported = false
	}
	if r == '.' {
	startWord = true
	depth++
	} else {
	startWord = false
	}
	}

	// TODO(rfindley): use metadata to determine if the file is in a workspace
	// package, rather than this heuristic.
	inWorkspace := false
	for _, root := range roots {
	if strings.HasPrefix(string(i.uri), root) {
	inWorkspace = true
	break
	}
	}

	// Apply downranking based on workspace position.
	if !inWorkspace {
	score *= nonWorkspaceFactor
	if !exported {
	score *= nonWorkspaceUnexportedFactor
	}
	}

	// Apply downranking based on symbol depth.
	if depth > 3 {
	depth = 3
	}
	score = 1.0 - depthdepthFactor

	if store.tooLow(score) {
	continue
	}

	si := symbolInformation{
	score: score,
	symbol: strings.Join(symbolParts, ""),
	kind: sym.Kind,
	uri: i.uri,
	rng: sym.Range,
	container: string(i.mp.PkgPath),
	}
	store.store(si)
	}
	}

	type symbolStore struct {
	res [maxSymbols]symbolInformation
	}

	// store inserts si into the sorted results, if si has a high enough score.
	func (sc *symbolStore) store(si symbolInformation) {
	if sc.tooLow(si.score) {
	return
	}
	insertAt := sort.Search(len(sc.res), func(i int) bool {
	// Sort by score, then symbol length, and finally lexically.
	if sc.res[i].score != si.score {
	return sc.res[i].score < si.score
	}
	if len(sc.res[i].symbol) != len(si.symbol) {
	return len(sc.res[i].symbol) > len(si.symbol)
	}
	return sc.res[i].symbol > si.symbol
	})
	if insertAt < len(sc.res)-1 {
	copy(sc.res[insertAt+1:], sc.res[insertAt:len(sc.res)-1])
	}
	sc.res[insertAt] = si
	}

	func (sc *symbolStore) tooLow(score float64) bool {
	return score <= sc.res[len(sc.res)-1].score
	}

	func (sc *symbolStore) results() []protocol.SymbolInformation {
	var res []protocol.SymbolInformation
	for _, si := range sc.res {
	if si.score <= 0 {
	return res
	}
	res = append(res, si.asProtocolSymbolInformation())
	}
	return res
	}

	// symbolInformation is a cut-down version of protocol.SymbolInformation that
	// allows struct values of this type to be used as map keys.
	type symbolInformation struct {
	score float64
	symbol string
	container string
	kind protocol.SymbolKind
	uri protocol.DocumentURI
	rng protocol.Range
	}

	// asProtocolSymbolInformation converts s to a protocol.SymbolInformation value.
	//
	// TODO: work out how to handle tags if/when they are needed.
	func (s symbolInformation) asProtocolSymbolInformation() protocol.SymbolInformation {
	return protocol.SymbolInformation{
	Name: s.symbol,
	Kind: s.kind,
	Location: protocol.Location{
	URI: s.uri,
	Range: s.rng,
	},
	ContainerName: s.container,
	}
	}