internal/lsp/source/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 source

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

 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/lsp/fuzzy"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
 )

 // Symbol holds a precomputed symbol value. Note: we avoid using the
 // protocol.SymbolInformation struct here in order to reduce the size of each
 // symbol.
 type Symbol struct {
 	Name  string
 	Kind  protocol.SymbolKind
 	Range protocol.Range
 }

 // 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, matcherType SymbolMatcher, style SymbolStyle, views []View, query string) ([]protocol.SymbolInformation, error) {
 	ctx, done := event.Start(ctx, "source.WorkspaceSymbols")
 	defer done()
 	if query == "" {
 		return nil, nil
 	}
 	sc := newSymbolCollector(matcherType, style, query)
 	return sc.walk(ctx, views)
 }

 // 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.
 type symbolizer func(name string, pkg Metadata, m matcherFunc) ([]string, float64)

 func fullyQualifiedSymbolMatch(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
 	_, score := dynamicSymbolMatch(name, pkg, matcher)
 	if score > 0 {
 		return []string{pkg.PackagePath(), ".", name}, score
 	}
 	return nil, 0
 }

 func dynamicSymbolMatch(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
 	var score float64

 	endsInPkgName := strings.HasSuffix(pkg.PackagePath(), pkg.PackageName())

 	// 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 := []string{pkg.PackageName(), ".", name}
 		idx, score := matcher(pkgQualified)
 		nameStart := len(pkg.PackageName()) + 1
 		if score > 0 {
 			// If our match is contained entirely within the unqualified portion,
 			// just return that.
 			if idx >= nameStart {
 				return []string{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 := []string{pkg.PackagePath(), ".", name}
 	idx, score := matcher(fullyQualified)

 	// As above, check if we matched just the unqualified symbol name.
 	nameStart := len(pkg.PackagePath()) + 1
 	if idx >= nameStart {
 		return []string{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.PackagePath()) - len(pkg.PackageName())
 		if idx >= pkgStart {
 			return []string{pkg.PackageName(), ".", 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(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
 	qualified := []string{pkg.PackageName(), ".", name}
 	if _, s := matcher(qualified); s > 0 {
 		return qualified, s
 	}
 	return nil, 0
 }

 // symbolCollector holds context as we walk Packages, gathering symbols that
 // match a given query.
 //
 // How we match 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.
 type symbolCollector struct {
 	// These types parameterize the symbol-matching pass.
 	matchers   []matcherFunc
 	symbolizer symbolizer

 	seen map[span.URI]bool
 	symbolStore
 }

 func newSymbolCollector(matcher SymbolMatcher, style SymbolStyle, query string) *symbolCollector {
 	var s symbolizer
 	switch style {
 	case DynamicSymbols:
 		s = dynamicSymbolMatch
 	case FullyQualifiedSymbols:
 		s = fullyQualifiedSymbolMatch
 	case PackageQualifiedSymbols:
 		s = packageSymbolMatch
 	default:
 		panic(fmt.Errorf("unknown symbol style: %v", style))
 	}
 	sc := &symbolCollector{symbolizer: s}
 	sc.matchers = make([]matcherFunc, runtime.GOMAXPROCS(-1))
 	for i := range sc.matchers {
 		sc.matchers[i] = buildMatcher(matcher, query)
 	}
 	return sc
 }

 func buildMatcher(matcher SymbolMatcher, query string) matcherFunc {
 	switch matcher {
 	case SymbolFuzzy:
 		return parseQuery(query)
 	case SymbolFastFuzzy:
 		return fuzzy.NewSymbolMatcher(query).Match
 	case SymbolCaseSensitive:
 		return matchExact(query)
 	case 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))
 }

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

 func (sc *symbolCollector) walk(ctx context.Context, views []View) ([]protocol.SymbolInformation, error) {
 	// Use the root view URIs for determining (lexically) whether a uri is in any
 	// open workspace.
 	var roots []string
 	for _, v := range views {
 		roots = append(roots, strings.TrimRight(string(v.Folder()), "/"))
 	}

 	results := make(chan *symbolStore)
 	matcherlen := len(sc.matchers)
 	files := make(map[span.URI]symbolFile)

 	for _, v := range views {
 		snapshot, release := v.Snapshot(ctx)
 		defer release()
 		psyms, err := snapshot.Symbols(ctx)
 		if err != nil {
 			return nil, err
 		}

 		filters := v.Options().DirectoryFilters
 		folder := filepath.ToSlash(v.Folder().Filename())
 		for uri, syms := range psyms {
 			norm := filepath.ToSlash(uri.Filename())
 			nm := strings.TrimPrefix(norm, folder)
 			if FiltersDisallow(nm, filters) {
 				continue
 			}
 			// Only scan each file once.
 			if _, ok := files[uri]; ok {
 				continue
 			}
 			mds, err := snapshot.MetadataForFile(ctx, uri)
 			if err != nil {
 				event.Error(ctx, fmt.Sprintf("missing metadata for %q", uri), err)
 				continue
 			}
 			if len(mds) == 0 {
 				// TODO: should use the bug reporting API
 				continue
 			}
 			files[uri] = symbolFile{uri, mds[0], syms}
 		}
 	}

 	var work []symbolFile
 	for _, f := range files {
 		work = append(work, f)
 	}

 	// Compute matches concurrently. Each symbolWorker has its own symbolStore,
 	// which we merge at the end.
 	for i, matcher := range sc.matchers {
 		go func(i int, matcher matcherFunc) {
 			w := &symbolWorker{
 				symbolizer: sc.symbolizer,
 				matcher:    matcher,
 				ss:         &symbolStore{},
 				roots:      roots,
 			}
 			for j := i; j < len(work); j += matcherlen {
 				w.matchFile(work[j])
 			}
 			results <- w.ss
 		}(i, matcher)
 	}

 	for i := 0; i < matcherlen; i++ {
 		ss := <-results
 		for _, si := range ss.res {
 			sc.store(si)
 		}
 	}
 	return sc.results(), nil
 }

 // FilterDisallow is code from the body of cache.pathExcludedByFilter in cache/view.go
 // Exporting and using that function would cause an import cycle.
 // Moving it here and exporting it would leave behind view_test.go.
 // (This code is exported and used in the body of cache.pathExcludedByFilter)
 func FiltersDisallow(path string, filters []string) bool {
 	path = strings.TrimPrefix(path, "/")
 	var excluded bool
 	for _, filter := range filters {
 		op, prefix := filter[0], filter[1:]
 		// Non-empty prefixes have to be precise directory matches.
 		if prefix != "" {
 			prefix = prefix + "/"
 			path = path + "/"
 		}
 		if !strings.HasPrefix(path, prefix) {
 			continue
 		}
 		excluded = op == '-'
 	}
 	return excluded
 }

 // symbolFile holds symbol information for a single file.
 type symbolFile struct {
 	uri  span.URI
 	md   Metadata
 	syms []Symbol
 }

 // symbolWorker matches symbols and captures the highest scoring results.
 type symbolWorker struct {
 	symbolizer symbolizer
 	matcher    matcherFunc
 	ss         *symbolStore
 	roots      []string
 }

 func (w *symbolWorker) matchFile(i symbolFile) {
 	for _, sym := range i.syms {
 		symbolParts, score := w.symbolizer(sym.Name, i.md, w.matcher)

 		// Check if the score is too low before applying any downranking.
 		if w.ss.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 of any active
 			// 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 of
 			// any active 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.
 			depthFactor = 0.2
 		)

 		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
 			}
 		}

 		inWorkspace := false
 		for _, root := range w.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 w.ss.tooLow(score) {
 			continue
 		}

 		si := symbolInformation{
 			score:     score,
 			symbol:    strings.Join(symbolParts, ""),
 			kind:      sym.Kind,
 			uri:       i.uri,
 			rng:       sym.Range,
 			container: i.md.PackagePath(),
 		}
 		w.ss.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
 }

 func typeToKind(typ types.Type) protocol.SymbolKind {
 	switch typ := typ.Underlying().(type) {
 	case *types.Interface:
 		return protocol.Interface
 	case *types.Struct:
 		return protocol.Struct
 	case *types.Signature:
 		if typ.Recv() != nil {
 			return protocol.Method
 		}
 		return protocol.Function
 	case *types.Named:
 		return typeToKind(typ.Underlying())
 	case *types.Basic:
 		i := typ.Info()
 		switch {
 		case i&types.IsNumeric != 0:
 			return protocol.Number
 		case i&types.IsBoolean != 0:
 			return protocol.Boolean
 		case i&types.IsString != 0:
 			return protocol.String
 		}
 	}
 	return protocol.Variable
 }

 // 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       span.URI
 	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:   protocol.URIFromSpanURI(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 source

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

	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/lsp/fuzzy"
	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/span"
	)

	// Symbol holds a precomputed symbol value. Note: we avoid using the
	// protocol.SymbolInformation struct here in order to reduce the size of each
	// symbol.
	type Symbol struct {
	Name string
	Kind protocol.SymbolKind
	Range protocol.Range
	}

	// 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, matcherType SymbolMatcher, style SymbolStyle, views []View, query string) ([]protocol.SymbolInformation, error) {
	ctx, done := event.Start(ctx, "source.WorkspaceSymbols")
	defer done()
	if query == "" {
	return nil, nil
	}
	sc := newSymbolCollector(matcherType, style, query)
	return sc.walk(ctx, views)
	}

	// 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.
	type symbolizer func(name string, pkg Metadata, m matcherFunc) ([]string, float64)

	func fullyQualifiedSymbolMatch(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
	_, score := dynamicSymbolMatch(name, pkg, matcher)
	if score > 0 {
	return []string{pkg.PackagePath(), ".", name}, score
	}
	return nil, 0
	}

	func dynamicSymbolMatch(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
	var score float64

	endsInPkgName := strings.HasSuffix(pkg.PackagePath(), pkg.PackageName())

	// 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 := []string{pkg.PackageName(), ".", name}
	idx, score := matcher(pkgQualified)
	nameStart := len(pkg.PackageName()) + 1
	if score > 0 {
	// If our match is contained entirely within the unqualified portion,
	// just return that.
	if idx >= nameStart {
	return []string{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 := []string{pkg.PackagePath(), ".", name}
	idx, score := matcher(fullyQualified)

	// As above, check if we matched just the unqualified symbol name.
	nameStart := len(pkg.PackagePath()) + 1
	if idx >= nameStart {
	return []string{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.PackagePath()) - len(pkg.PackageName())
	if idx >= pkgStart {
	return []string{pkg.PackageName(), ".", 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(name string, pkg Metadata, matcher matcherFunc) ([]string, float64) {
	qualified := []string{pkg.PackageName(), ".", name}
	if _, s := matcher(qualified); s > 0 {
	return qualified, s
	}
	return nil, 0
	}

	// symbolCollector holds context as we walk Packages, gathering symbols that
	// match a given query.
	//
	// How we match 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.
	type symbolCollector struct {
	// These types parameterize the symbol-matching pass.
	matchers []matcherFunc
	symbolizer symbolizer

	seen map[span.URI]bool
	symbolStore
	}

	func newSymbolCollector(matcher SymbolMatcher, style SymbolStyle, query string) *symbolCollector {
	var s symbolizer
	switch style {
	case DynamicSymbols:
	s = dynamicSymbolMatch
	case FullyQualifiedSymbols:
	s = fullyQualifiedSymbolMatch
	case PackageQualifiedSymbols:
	s = packageSymbolMatch
	default:
	panic(fmt.Errorf("unknown symbol style: %v", style))
	}
	sc := &symbolCollector{symbolizer: s}
	sc.matchers = make([]matcherFunc, runtime.GOMAXPROCS(-1))
	for i := range sc.matchers {
	sc.matchers[i] = buildMatcher(matcher, query)
	}
	return sc
	}

	func buildMatcher(matcher SymbolMatcher, query string) matcherFunc {
	switch matcher {
	case SymbolFuzzy:
	return parseQuery(query)
	case SymbolFastFuzzy:
	return fuzzy.NewSymbolMatcher(query).Match
	case SymbolCaseSensitive:
	return matchExact(query)
	case 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))
	}

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

	func (sc *symbolCollector) walk(ctx context.Context, views []View) ([]protocol.SymbolInformation, error) {
	// Use the root view URIs for determining (lexically) whether a uri is in any
	// open workspace.
	var roots []string
	for _, v := range views {
	roots = append(roots, strings.TrimRight(string(v.Folder()), "/"))
	}

	results := make(chan *symbolStore)
	matcherlen := len(sc.matchers)
	files := make(map[span.URI]symbolFile)

	for _, v := range views {
	snapshot, release := v.Snapshot(ctx)
	defer release()
	psyms, err := snapshot.Symbols(ctx)
	if err != nil {
	return nil, err
	}

	filters := v.Options().DirectoryFilters
	folder := filepath.ToSlash(v.Folder().Filename())
	for uri, syms := range psyms {
	norm := filepath.ToSlash(uri.Filename())
	nm := strings.TrimPrefix(norm, folder)
	if FiltersDisallow(nm, filters) {
	continue
	}
	// Only scan each file once.
	if _, ok := files[uri]; ok {
	continue
	}
	mds, err := snapshot.MetadataForFile(ctx, uri)
	if err != nil {
	event.Error(ctx, fmt.Sprintf("missing metadata for %q", uri), err)
	continue
	}
	if len(mds) == 0 {
	// TODO: should use the bug reporting API
	continue
	}
	files[uri] = symbolFile{uri, mds[0], syms}
	}
	}

	var work []symbolFile
	for _, f := range files {
	work = append(work, f)
	}

	// Compute matches concurrently. Each symbolWorker has its own symbolStore,
	// which we merge at the end.
	for i, matcher := range sc.matchers {
	go func(i int, matcher matcherFunc) {
	w := &symbolWorker{
	symbolizer: sc.symbolizer,
	matcher: matcher,
	ss: &symbolStore{},
	roots: roots,
	}
	for j := i; j < len(work); j += matcherlen {
	w.matchFile(work[j])
	}
	results <- w.ss
	}(i, matcher)
	}

	for i := 0; i < matcherlen; i++ {
	ss := <-results
	for _, si := range ss.res {
	sc.store(si)
	}
	}
	return sc.results(), nil
	}

	// FilterDisallow is code from the body of cache.pathExcludedByFilter in cache/view.go
	// Exporting and using that function would cause an import cycle.
	// Moving it here and exporting it would leave behind view_test.go.
	// (This code is exported and used in the body of cache.pathExcludedByFilter)
	func FiltersDisallow(path string, filters []string) bool {
	path = strings.TrimPrefix(path, "/")
	var excluded bool
	for _, filter := range filters {
	op, prefix := filter[0], filter[1:]
	// Non-empty prefixes have to be precise directory matches.
	if prefix != "" {
	prefix = prefix + "/"
	path = path + "/"
	}
	if !strings.HasPrefix(path, prefix) {
	continue
	}
	excluded = op == '-'
	}
	return excluded
	}

	// symbolFile holds symbol information for a single file.
	type symbolFile struct {
	uri span.URI
	md Metadata
	syms []Symbol
	}

	// symbolWorker matches symbols and captures the highest scoring results.
	type symbolWorker struct {
	symbolizer symbolizer
	matcher matcherFunc
	ss *symbolStore
	roots []string
	}

	func (w *symbolWorker) matchFile(i symbolFile) {
	for _, sym := range i.syms {
	symbolParts, score := w.symbolizer(sym.Name, i.md, w.matcher)

	// Check if the score is too low before applying any downranking.
	if w.ss.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 of any active
	// 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 of
	// any active 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.
	depthFactor = 0.2
	)

	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
	}
	}

	inWorkspace := false
	for _, root := range w.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 w.ss.tooLow(score) {
	continue
	}

	si := symbolInformation{
	score: score,
	symbol: strings.Join(symbolParts, ""),
	kind: sym.Kind,
	uri: i.uri,
	rng: sym.Range,
	container: i.md.PackagePath(),
	}
	w.ss.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
	}

	func typeToKind(typ types.Type) protocol.SymbolKind {
	switch typ := typ.Underlying().(type) {
	case *types.Interface:
	return protocol.Interface
	case *types.Struct:
	return protocol.Struct
	case *types.Signature:
	if typ.Recv() != nil {
	return protocol.Method
	}
	return protocol.Function
	case *types.Named:
	return typeToKind(typ.Underlying())
	case *types.Basic:
	i := typ.Info()
	switch {
	case i&types.IsNumeric != 0:
	return protocol.Number
	case i&types.IsBoolean != 0:
	return protocol.Boolean
	case i&types.IsString != 0:
	return protocol.String
	}
	}
	return protocol.Variable
	}

	// 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 span.URI
	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: protocol.URIFromSpanURI(s.uri),
	Range: s.rng,
	},
	ContainerName: s.container,
	}
	}