internal/lsp: add support for implements to the LSP

This adds support for the LSP implemention call, based
on the guru code for getting implementations. The guru code
did much more than we need, so some of the code has been
dropped, and other parts of it are ignored (for now).

Fixes golang/go#32973

Change-Id: I1a24450e17d5364f25c4b4120be5320b13ac822b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/203918
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cmd/test/cmdtest.go

@@ -90,6 +90,10 @@ func (r *runner) Link(t *testing.T, uri span.URI, wantLinks []tests.Link) {
 	//TODO: add command line link tests when it works
 }
 
+func (r *runner) Implementation(t *testing.T, spn span.Span, imp tests.Implementations) {
+	//TODO: add implements tests when it works
+}
+
 func CaptureStdOut(t testing.TB, f func()) string {
 	r, out, err := os.Pipe()
 	if err != nil {

internal/lsp/implementation.go

@@ -0,0 +1,24 @@
+// 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 lsp
+
+import (
+	"context"
+
+	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/lsp/source"
+	"golang.org/x/tools/internal/span"
+)
+
+func (s *Server) implementation(ctx context.Context, params *protocol.ImplementationParams) ([]protocol.Location, error) {
+	uri := span.NewURI(params.TextDocument.URI)
+	view := s.session.ViewOf(uri)
+	f, err := view.GetFile(ctx, uri)
+	if err != nil {
+		return nil, err
+	}
+
+	return source.Implementation(ctx, view, f, params.Position)
+}

internal/lsp/lsp_test.go

@@ -426,6 +426,44 @@ func (r *runner) Definition(t *testing.T, spn span.Span, d tests.Definition) {
 	}
 }
 
+func (r *runner) Implementation(t *testing.T, spn span.Span, m tests.Implementations) {
+	sm, err := r.data.Mapper(m.Src.URI())
+	if err != nil {
+		t.Fatal(err)
+	}
+	loc, err := sm.Location(m.Src)
+	if err != nil {
+		t.Fatalf("failed for %v: %v", m.Src, err)
+	}
+	tdpp := protocol.TextDocumentPositionParams{
+		TextDocument: protocol.TextDocumentIdentifier{URI: loc.URI},
+		Position:     loc.Range.Start,
+	}
+	var locs []protocol.Location
+	params := &protocol.ImplementationParams{
+		TextDocumentPositionParams: tdpp,
+	}
+	locs, err = r.server.Implementation(r.ctx, params)
+	if err != nil {
+		t.Fatalf("failed for %v: %v", m.Src, err)
+	}
+	if len(locs) != len(m.Implementations) {
+		t.Fatalf("got %d locations for implementation, expected %d", len(locs), len(m.Implementations))
+	}
+	for i := range locs {
+		locURI := span.NewURI(locs[i].URI)
+		lm, err := r.data.Mapper(locURI)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if imp, err := lm.Span(locs[i]); err != nil {
+			t.Fatalf("failed for %v: %v", locs[i], err)
+		} else if imp != m.Implementations[i] {
+			t.Errorf("for %dth implementation of %v got %v want %v", i, m.Src, imp, m.Implementations[i])
+		}
+	}
+}
+
 func (r *runner) Highlight(t *testing.T, name string, locations []span.Span) {
 	m, err := r.data.Mapper(locations[0].URI())
 	if err != nil {

internal/lsp/server.go

@@ -181,8 +181,8 @@ func (s *Server) TypeDefinition(ctx context.Context, params *protocol.TypeDefini
 	return s.typeDefinition(ctx, params)
 }
 
-func (s *Server) Implementation(context.Context, *protocol.ImplementationParams) ([]protocol.Location, error) {
-	return nil, notImplemented("Implementation")
+func (s *Server) Implementation(ctx context.Context, params *protocol.ImplementationParams) ([]protocol.Location, error) {
+	return s.implementation(ctx, params)
 }
 
 func (s *Server) References(ctx context.Context, params *protocol.ReferenceParams) ([]protocol.Location, error) {

internal/lsp/source/implementation.go

@@ -0,0 +1,154 @@
+// 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.
+
+// The code in this file is based largely on the code in
+// cmd/guru/implements.go. The guru implementation supports
+// looking up "implementers" of methods also, but that
+// code has been cut out here for now for simplicity.
+
+package source
+
+import (
+	"context"
+	"go/types"
+	"sort"
+
+	"golang.org/x/tools/go/types/typeutil"
+	"golang.org/x/tools/internal/lsp/protocol"
+)
+
+func Implementation(ctx context.Context, view View, f File, position protocol.Position) ([]protocol.Location, error) {
+	// Find all references to the identifier at the position.
+	ident, err := Identifier(ctx, view, f, position)
+	if err != nil {
+		return nil, err
+	}
+
+	res, err := ident.implementations(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	var locations []protocol.Location
+	for _, t := range res.to {
+		// We'll provide implementations that are named types and pointers to named types.
+		if p, ok := t.(*types.Pointer); ok {
+			t = p.Elem()
+		}
+		if n, ok := t.(*types.Named); ok {
+			ph, pkg, err := view.FindFileInPackage(ctx, f.URI(), ident.pkg)
+			if err != nil {
+				return nil, err
+			}
+			f, _, _, err := ph.Cached()
+			if err != nil {
+				return nil, err
+			}
+			ident, err := findIdentifier(ctx, view.Snapshot(), pkg, f, n.Obj().Pos())
+			if err != nil {
+				return nil, err
+			}
+			decRange, err := ident.Declaration.Range()
+			if err != nil {
+				return nil, err
+			}
+			locations = append(locations, protocol.Location{
+				URI:   protocol.NewURI(ident.Declaration.URI()),
+				Range: decRange,
+			})
+		}
+	}
+
+	return locations, nil
+}
+
+func (i *IdentifierInfo) implementations(ctx context.Context) (implementsResult, error) {
+	T := i.Type.Object.Type()
+
+	// Find all named types, even local types (which can have
+	// methods due to promotion) and the built-in "error".
+	// We ignore aliases 'type M = N' to avoid duplicate
+	// reporting of the Named type N.
+	var allNamed []*types.Named
+	info := i.pkg.GetTypesInfo()
+	for _, obj := range info.Defs {
+		if obj, ok := obj.(*types.TypeName); ok && !obj.IsAlias() {
+			if named, ok := obj.Type().(*types.Named); ok {
+				allNamed = append(allNamed, named)
+			}
+		}
+	}
+
+	allNamed = append(allNamed, types.Universe.Lookup("error").Type().(*types.Named))
+
+	var msets typeutil.MethodSetCache
+
+	// TODO(matloob): We only use the to result for now. Figure out if we want to
+	// surface the from and fromPtr results to users.
+	// Test each named type.
+	var to, from, fromPtr []types.Type
+	for _, U := range allNamed {
+		if isInterface(T) {
+			if msets.MethodSet(T).Len() == 0 {
+				continue // empty interface
+			}
+			if isInterface(U) {
+				if msets.MethodSet(U).Len() == 0 {
+					continue // empty interface
+				}
+
+				// T interface, U interface
+				if !types.Identical(T, U) {
+					if types.AssignableTo(U, T) {
+						to = append(to, U)
+					}
+					if types.AssignableTo(T, U) {
+						from = append(from, U)
+					}
+				}
+			} else {
+				// T interface, U concrete
+				if types.AssignableTo(U, T) {
+					to = append(to, U)
+				} else if pU := types.NewPointer(U); types.AssignableTo(pU, T) {
+					to = append(to, pU)
+				}
+			}
+		} else if isInterface(U) {
+			if msets.MethodSet(U).Len() == 0 {
+				continue // empty interface
+			}
+
+			// T concrete, U interface
+			if types.AssignableTo(T, U) {
+				from = append(from, U)
+			} else if pT := types.NewPointer(T); types.AssignableTo(pT, U) {
+				fromPtr = append(fromPtr, U)
+			}
+		}
+	}
+
+	// Sort types (arbitrarily) to ensure test determinism.
+	sort.Sort(typesByString(to))
+	sort.Sort(typesByString(from))
+	sort.Sort(typesByString(fromPtr))
+
+	// TODO(matloob): Perhaps support calling implements on methods instead of just interface types,
+	// as guru does.
+
+	return implementsResult{to, from, fromPtr}, nil
+}
+
+// implementsResult contains the results of an implements query.
+type implementsResult struct {
+	to      []types.Type // named or ptr-to-named types assignable to interface T
+	from    []types.Type // named interfaces assignable from T
+	fromPtr []types.Type // named interfaces assignable only from *T
+}
+
+type typesByString []types.Type
+
+func (p typesByString) Len() int           { return len(p) }
+func (p typesByString) Less(i, j int) bool { return p[i].String() < p[j].String() }
+func (p typesByString) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }

internal/lsp/source/source_test.go

@@ -541,6 +541,42 @@ func (r *runner) Definition(t *testing.T, spn span.Span, d tests.Definition) {
 	}
 }
 
+func (r *runner) Implementation(t *testing.T, spn span.Span, m tests.Implementations) {
+	ctx := r.ctx
+	f, err := r.view.GetFile(ctx, m.Src.URI())
+	if err != nil {
+		t.Fatalf("failed for %v: %v", m.Src, err)
+	}
+	sm, err := r.data.Mapper(m.Src.URI())
+	if err != nil {
+		t.Fatal(err)
+	}
+	loc, err := sm.Location(m.Src)
+	if err != nil {
+		t.Fatalf("failed for %v: %v", m.Src, err)
+	}
+	var locs []protocol.Location
+	locs, err = source.Implementation(r.ctx, r.view, f, loc.Range.Start)
+	if err != nil {
+		t.Fatalf("failed for %v: %v", m.Src, err)
+	}
+	if len(locs) != len(m.Implementations) {
+		t.Fatalf("got %d locations for implementation, expected %d", len(locs), len(m.Implementations))
+	}
+	for i := range locs {
+		locURI := span.NewURI(locs[i].URI)
+		lm, err := r.data.Mapper(locURI)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if imp, err := lm.Span(locs[i]); err != nil {
+			t.Fatalf("failed for %v: %v", locs[i], err)
+		} else if imp != m.Implementations[i] {
+			t.Errorf("for %dth implementation of %v got %v want %v", i, m.Src, imp, m.Implementations[i])
+		}
+	}
+}
+
 func (r *runner) Highlight(t *testing.T, name string, locations []span.Span) {
 	ctx := r.ctx
 	src := locations[0]

internal/lsp/testdata/implementation/implementation.go

@@ -0,0 +1,21 @@
+package implementation
+
+type ImpP struct{} //@ImpP
+
+func (*ImpP) Laugh() {
+
+}
+
+type ImpS struct{} //@ImpS
+
+func (ImpS) Laugh() {
+
+}
+
+type ImpI interface { //@ImpI
+	Laugh()
+}
+
+type Laugher interface { //@implementations("augher", ImpP),implementations("augher", ImpI),implementations("augher", ImpS),
+	Laugh()
+}