internal/lsp: support implements for methods on an interface

This change copies the code in guru's implements implementation
that finds implementations of methods over to gopls, and uses
the information determined to resolve implements requests on
methods. Implements still only works only within packages.

Updates golang/go#32973

Change-Id: I0bd7849a9224fbef7ab8385070b18fbb30703e2b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/206150
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/implementation.go

@@ -11,7 +11,7 @@ package source
 
 import (
 	"context"
-	"errors"
+	"fmt"
 	"go/types"
 	"sort"
 
@@ -31,44 +31,71 @@ func Implementation(ctx context.Context, view View, f File, position protocol.Po
 		return nil, err
 	}
 
+	var objs []types.Object
+
+	if res.toMethod != nil {
+		// If we looked up a method, results are in toMethod.
+		for _, s := range res.toMethod {
+			objs = append(objs, s.Obj())
+		}
+	} else {
+		// Otherwise, the results are in to.
+		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 {
+				objs = append(objs, n.Obj())
+			}
+		}
+	}
+
 	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()
+	ph, pkg, err := view.FindFileInPackage(ctx, f.URI(), ident.pkg)
+	if err != nil {
+		return nil, err
+	}
+	af, _, _, err := ph.Cached()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, obj := range objs {
+		ident, err := findIdentifier(ctx, view.Snapshot(), pkg, af, obj.Pos())
+		if err != nil {
+			return nil, err
 		}
-		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,
-			})
+		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) {
+	var T types.Type
+	var method *types.Func
 	if i.Type.Object == nil {
-		return implementsResult{}, errors.New("no type info object for identifier")
+		// This isn't a type. Is it a method?
+		obj, ok := i.Declaration.obj.(*types.Func)
+		if !ok {
+			return implementsResult{}, fmt.Errorf("no type info object for identifier %q", i.Name)
+		}
+		recv := obj.Type().(*types.Signature).Recv()
+		if recv == nil {
+			return implementsResult{}, fmt.Errorf("this function is not a method")
+		}
+		method = obj
+		T = recv.Type()
+	} else {
+		T = i.Type.Object.Type()
 	}
-	T := i.Type.Object.Type()
 
 	// Find all named types, even local types (which can have
 	// methods due to promotion) and the built-in "error".
@@ -88,7 +115,7 @@ func (i *IdentifierInfo) implementations(ctx context.Context) (implementsResult,
 
 	var msets typeutil.MethodSetCache
 
-	// TODO(matloob): We only use the to result for now. Figure out if we want to
+	// TODO(matloob): We only use the to and toMethod 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
@@ -138,17 +165,23 @@ func (i *IdentifierInfo) implementations(ctx context.Context) (implementsResult,
 	sort.Sort(typesByString(from))
 	sort.Sort(typesByString(fromPtr))
 
-	// TODO(matloob): Perhaps support calling implements on methods instead of just interface types,
-	// as guru does.
+	var toMethod []*types.Selection // contain nils
+	if method != nil {
+		for _, t := range to {
+			toMethod = append(toMethod,
+				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
+		}
+	}
 
-	return implementsResult{to, from, fromPtr}, nil
+	return implementsResult{to, from, fromPtr, toMethod}, 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
+	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
+	toMethod []*types.Selection
 }
 
 type typesByString []types.Type

internal/lsp/testdata/implementation/implementation.go

@@ -2,20 +2,18 @@ package implementation
 
 type ImpP struct{} //@ImpP
 
-func (*ImpP) Laugh() {
-
+func (*ImpP) Laugh() { //@mark(LaughP, "Laugh")
 }
 
 type ImpS struct{} //@ImpS
 
-func (ImpS) Laugh() {
-
+func (ImpS) Laugh() { //@mark(LaughS, "Laugh")
 }
 
 type ImpI interface { //@ImpI
-	Laugh()
+	Laugh() //@mark(LaughI, "Laugh"),implementations("augh", LaughP),implementations("augh", LaughS),implementations("augh", LaughL)
 }
 
-type Laugher interface { //@implementations("augher", ImpP),implementations("augher", ImpI),implementations("augher", ImpS),
-	Laugh()
+type Laugher interface { //@Laugher,implementations("augher", ImpP),implementations("augher", ImpI),implementations("augher", ImpS),
+	Laugh() //@mark(LaughL, "Laugh"),implementations("augh", LaughP),implementations("augh", LaughI),implementations("augh", LaughS)
 }