internal/lsp: refactor find-implementation handling

This is the start of a significant refactoring to implementations,
references, and rename (i.e. everything that searches across
packages). The main goal of the refactoring is to push the package
variant logic from internal/lsp into internal/source so that all users
of source benefit, not just internal/lsp. It also makes it easier to
write tests for various cases because the source tests invoke the
source package directly (so previously did not include all the package
variants).

Currently source.Identifer() handles lots of disparate use cases.
Things like definition and hover don't care about package variants but
do care about other random bits of info that may not apply to
implementations or references. So, I'm splitting implementations out
from source.Identifier. As I work through references and rename
hopefully things will end up separated into smaller chunks.

I also improved implementation deduping to happen earlier. I thought I
could dedupe using obj.Pos(), but mirror objects in package variants
have different positions (suggesting they aren't reusing the
same *ast.File). Instead I used token.Position to dedupe.

Change-Id: I81c2b3ec33bf12640accb852be9ecdea4aa24d69
Reviewed-on: https://go-review.googlesource.com/c/tools/+/211718
Run-TryBot: Muir Manders <muir@mnd.rs>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/implementation.go

@@ -9,9 +9,7 @@ import (
 
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
-	"golang.org/x/tools/internal/lsp/telemetry"
 	"golang.org/x/tools/internal/span"
-	"golang.org/x/tools/internal/telemetry/log"
 )
 
 func (s *Server) implementation(ctx context.Context, params *protocol.ImplementationParams) ([]protocol.Location, error) {
@@ -28,43 +26,5 @@ func (s *Server) implementation(ctx context.Context, params *protocol.Implementa
 	if fh.Identity().Kind != source.Go {
 		return nil, nil
 	}
-	phs, err := snapshot.PackageHandles(ctx, fh)
-	if err != nil {
-		return nil, err
-	}
-	var (
-		allLocs []protocol.Location
-		seen    = make(map[protocol.Location]bool)
-	)
-	for _, ph := range phs {
-		ctx := telemetry.Package.With(ctx, ph.ID())
-
-		ident, err := source.Identifier(ctx, snapshot, fh, params.Position, source.SpecificPackageHandle(ph.ID()))
-		if err != nil {
-			if err == source.ErrNoIdentFound {
-				return nil, err
-			}
-			log.Error(ctx, "failed to find Identifer", err)
-			continue
-		}
-
-		locs, err := ident.Implementation(ctx)
-		if err != nil {
-			if err == source.ErrNotAnInterface {
-				return nil, err
-			}
-			log.Error(ctx, "failed to find Implemenation", err)
-			continue
-		}
-
-		for _, loc := range locs {
-			if seen[loc] {
-				continue
-			}
-			seen[loc] = true
-			allLocs = append(allLocs, loc)
-		}
-	}
-
-	return allLocs, nil
+	return source.Implementation(ctx, snapshot, fh, params.Position)
 }

internal/lsp/source/implementation.go

@@ -6,18 +6,22 @@ package source
 
 import (
 	"context"
+	"fmt"
+	"go/ast"
+	"go/token"
 	"go/types"
 
 	"golang.org/x/tools/internal/lsp/protocol"
-	"golang.org/x/tools/internal/lsp/telemetry"
 	"golang.org/x/tools/internal/telemetry/log"
+	"golang.org/x/tools/internal/telemetry/trace"
 	errors "golang.org/x/xerrors"
 )
 
-func (i *IdentifierInfo) Implementation(ctx context.Context) ([]protocol.Location, error) {
-	ctx = telemetry.Package.With(ctx, i.pkg.ID())
+func Implementation(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Position) ([]protocol.Location, error) {
+	ctx, done := trace.StartSpan(ctx, "source.Implementation")
+	defer done()
 
-	impls, err := i.implementations(ctx)
+	impls, err := implementations(ctx, s, f, pp)
 	if err != nil {
 		return nil, err
 	}
@@ -28,27 +32,21 @@ func (i *IdentifierInfo) Implementation(ctx context.Context) ([]protocol.Locatio
 			continue
 		}
 
-		file, _, err := i.Snapshot.View().FindPosInPackage(impl.pkg, impl.obj.Pos())
-		if err != nil {
-			log.Error(ctx, "Error getting file for object", err)
-			continue
-		}
-
-		ident, err := findIdentifier(i.Snapshot, impl.pkg, file, impl.obj.Pos())
-		if err != nil {
-			log.Error(ctx, "Error getting ident for object", err)
-			continue
-		}
-
-		decRange, err := ident.Declaration.Range()
+		rng, err := objToMappedRange(s.View(), impl.pkg, impl.obj)
 		if err != nil {
 			log.Error(ctx, "Error getting range for object", err)
 			continue
 		}
 
+		pr, err := rng.Range()
+		if err != nil {
+			log.Error(ctx, "Error getting protocol range for object", err)
+			continue
+		}
+
 		locations = append(locations, protocol.Location{
-			URI:   protocol.NewURI(ident.Declaration.URI()),
-			Range: decRange,
+			URI:   protocol.NewURI(rng.URI()),
+			Range: pr,
 		})
 	}
 	return locations, nil
@@ -56,13 +54,26 @@ func (i *IdentifierInfo) Implementation(ctx context.Context) ([]protocol.Locatio
 
 var ErrNotAnInterface = errors.New("not an interface or interface method")
 
-func (i *IdentifierInfo) implementations(ctx context.Context) ([]implementation, error) {
+func implementations(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Position) ([]implementation, error) {
+
+	var (
+		impls []implementation
+		seen  = make(map[token.Position]bool)
+		fset  = s.View().Session().Cache().FileSet()
+	)
+
+	objs, err := objectsAtProtocolPos(ctx, s, f, pp)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, obj := range objs {
 		var (
 			T      *types.Interface
 			method *types.Func
 		)
 
-	switch obj := i.Declaration.obj.(type) {
+		switch obj := obj.(type) {
 		case *types.Func:
 			method = obj
 			if recv := obj.Type().(*types.Signature).Recv(); recv != nil {
@@ -86,7 +97,7 @@ func (i *IdentifierInfo) implementations(ctx context.Context) ([]implementation,
 			allNamed []*types.Named
 			pkgs     = make(map[*types.Package]Package)
 		)
-	for _, pkg := range i.Snapshot.KnownPackages(ctx) {
+		for _, pkg := range s.KnownPackages(ctx) {
 			pkgs[pkg.GetTypes()] = pkg
 
 			info := pkg.GetTypesInfo()
@@ -103,11 +114,6 @@ func (i *IdentifierInfo) implementations(ctx context.Context) ([]implementation,
 			}
 		}
 
-	var (
-		impls []implementation
-		seen  = make(map[types.Object]bool)
-	)
-
 		// Find all the named types that implement our interface.
 		for _, U := range allNamed {
 			var concrete types.Type = U
@@ -124,17 +130,19 @@ func (i *IdentifierInfo) implementations(ctx context.Context) ([]implementation,
 				obj = types.NewMethodSet(concrete).Lookup(method.Pkg(), method.Name()).Obj()
 			}
 
-		if obj == method || seen[obj] {
+			pos := fset.Position(obj.Pos())
+			if obj == method || seen[pos] {
 				continue
 			}
 
-		seen[obj] = true
+			seen[pos] = true
 
 			impls = append(impls, implementation{
 				obj: obj,
 				pkg: pkgs[obj.Pkg()],
 			})
 		}
+	}
 
 	return impls, nil
 }
@@ -146,3 +154,99 @@ type implementation struct {
 	// pkg is the Package that contains obj's definition.
 	pkg Package
 }
+
+// objectsAtProtocolPos returns all the type.Objects referenced at the given position.
+// An object will be returned for every package that the file belongs to.
+func objectsAtProtocolPos(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Position) ([]types.Object, error) {
+	phs, err := s.PackageHandles(ctx, f)
+	if err != nil {
+		return nil, err
+	}
+
+	var objs []types.Object
+
+	// Check all the packages that the file belongs to.
+	for _, ph := range phs {
+		pkg, err := ph.Check(ctx)
+		if err != nil {
+			return nil, err
+		}
+
+		astFile, pos, err := getASTFile(pkg, f, pp)
+		if err != nil {
+			return nil, err
+		}
+
+		path := pathEnclosingIdent(astFile, pos)
+		if len(path) == 0 {
+			return nil, ErrNoIdentFound
+		}
+
+		ident := path[len(path)-1].(*ast.Ident)
+
+		obj := pkg.GetTypesInfo().ObjectOf(ident)
+		if obj == nil {
+			return nil, fmt.Errorf("no object for %q", ident.Name)
+		}
+
+		objs = append(objs, obj)
+	}
+
+	return objs, nil
+}
+
+func getASTFile(pkg Package, f FileHandle, pos protocol.Position) (*ast.File, token.Pos, error) {
+	pgh, err := pkg.File(f.Identity().URI)
+	if err != nil {
+		return nil, 0, err
+	}
+
+	file, m, _, err := pgh.Cached()
+	if err != nil {
+		return nil, 0, err
+	}
+
+	spn, err := m.PointSpan(pos)
+	if err != nil {
+		return nil, 0, err
+	}
+
+	rng, err := spn.Range(m.Converter)
+	if err != nil {
+		return nil, 0, err
+	}
+
+	return file, rng.Start, nil
+}
+
+// pathEnclosingIdent returns the ast path to the node that contains pos.
+// It is similar to astutil.PathEnclosingInterval, but simpler, and it
+// matches *ast.Ident nodes if pos is equal to node.End().
+func pathEnclosingIdent(f *ast.File, pos token.Pos) []ast.Node {
+	var (
+		path  []ast.Node
+		found bool
+	)
+
+	ast.Inspect(f, func(n ast.Node) bool {
+		if found {
+			return false
+		}
+
+		if n == nil {
+			path = path[:len(path)-1]
+			return false
+		}
+
+		switch n := n.(type) {
+		case *ast.Ident:
+			found = n.Pos() <= pos && pos <= n.End()
+		}
+
+		path = append(path, n)
+
+		return !found
+	})
+
+	return path
+}

internal/lsp/source/source_test.go

@@ -563,12 +563,7 @@ func (r *runner) Implementation(t *testing.T, spn span.Span, impls []span.Span)
 	if err != nil {
 		t.Fatal(err)
 	}
-	ident, err := source.Identifier(r.ctx, r.view.Snapshot(), fh, loc.Range.Start, source.WidestCheckPackageHandle)
-	if err != nil {
-		t.Fatalf("failed for %v: %v", spn, err)
-	}
-	var locs []protocol.Location
-	locs, err = ident.Implementation(r.ctx)
+	locs, err := source.Implementation(r.ctx, r.view.Snapshot(), fh, loc.Range.Start)
 	if err != nil {
 		t.Fatalf("failed for %v: %v", spn, err)
 	}

internal/lsp/testdata/implementation/other/other_test.go

@@ -0,0 +1,10 @@
+package other
+
+import (
+	"testing"
+)
+
+// This exists so the other.test package comes into existence.
+
+func TestOther(t *testing.T) {
+}