internal/lsp/source: support stubbing concrete type params

This CL adds support for generating method stubs for named types
that have type parameters and want to implement an interface.
See internal/lsp/testdata/stub/stub_generic_receiver.go for an example.
Note, this CL does not yet support type params on interface declarations.

Updates golang/go#37537

Change-Id: I2a2a18d364b2b489e2fbd8a74dfed88ae32d83b5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/389654
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Suzy Mueller <suzmue@golang.org>

Author: marwan-at-work

Diff for: internal/lsp/analysis/stubmethods/stubmethods.go

@@ -60,7 +60,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			endPos = analysisinternal.TypeErrorEndPos(pass.Fset, buf.Bytes(), err.Pos)
 		}
 		path, _ := astutil.PathEnclosingInterval(file, err.Pos, endPos)
-		si := GetStubInfo(pass.TypesInfo, path, pass.Pkg, err.Pos)
+		si := GetStubInfo(pass.TypesInfo, path, err.Pos)
 		if si == nil {
 			continue
 		}
@@ -91,20 +91,20 @@ type StubInfo struct {
 
 // GetStubInfo determines whether the "missing method error"
 // can be used to deduced what the concrete and interface types are.
-func GetStubInfo(ti *types.Info, path []ast.Node, pkg *types.Package, pos token.Pos) *StubInfo {
+func GetStubInfo(ti *types.Info, path []ast.Node, pos token.Pos) *StubInfo {
 	for _, n := range path {
 		switch n := n.(type) {
 		case *ast.ValueSpec:
-			return fromValueSpec(ti, n, pkg, pos)
+			return fromValueSpec(ti, n, pos)
 		case *ast.ReturnStmt:
 			// An error here may not indicate a real error the user should know about, but it may.
 			// Therefore, it would be best to log it out for debugging/reporting purposes instead of ignoring
 			// it. However, event.Log takes a context which is not passed via the analysis package.
 			// TODO(marwan-at-work): properly log this error.
-			si, _ := fromReturnStmt(ti, pos, path, n, pkg)
+			si, _ := fromReturnStmt(ti, pos, path, n)
 			return si
 		case *ast.AssignStmt:
-			return fromAssignStmt(ti, n, pkg, pos)
+			return fromAssignStmt(ti, n, pos)
 		}
 	}
 	return nil
@@ -115,7 +115,7 @@ func GetStubInfo(ti *types.Info, path []ast.Node, pkg *types.Package, pos token.
 //
 // For example, func() io.Writer { return myType{} }
 // would return StubInfo with the interface being io.Writer and the concrete type being myType{}.
-func fromReturnStmt(ti *types.Info, pos token.Pos, path []ast.Node, rs *ast.ReturnStmt, pkg *types.Package) (*StubInfo, error) {
+func fromReturnStmt(ti *types.Info, pos token.Pos, path []ast.Node, rs *ast.ReturnStmt) (*StubInfo, error) {
 	returnIdx := -1
 	for i, r := range rs.Results {
 		if pos >= r.Pos() && pos <= r.End() {
@@ -146,7 +146,7 @@ func fromReturnStmt(ti *types.Info, pos token.Pos, path []ast.Node, rs *ast.Retu
 
 // fromValueSpec returns *StubInfo from a variable declaration such as
 // var x io.Writer = &T{}
-func fromValueSpec(ti *types.Info, vs *ast.ValueSpec, pkg *types.Package, pos token.Pos) *StubInfo {
+func fromValueSpec(ti *types.Info, vs *ast.ValueSpec, pos token.Pos) *StubInfo {
 	var idx int
 	for i, vs := range vs.Values {
 		if pos >= vs.Pos() && pos <= vs.End() {
@@ -182,7 +182,7 @@ func fromValueSpec(ti *types.Info, vs *ast.ValueSpec, pkg *types.Package, pos to
 // fromAssignStmt returns *StubInfo from a variable re-assignment such as
 // var x io.Writer
 // x = &T{}
-func fromAssignStmt(ti *types.Info, as *ast.AssignStmt, pkg *types.Package, pos token.Pos) *StubInfo {
+func fromAssignStmt(ti *types.Info, as *ast.AssignStmt, pos token.Pos) *StubInfo {
 	idx := -1
 	var lhs, rhs ast.Expr
 	// Given a re-assignment interface conversion error,

Diff for: internal/lsp/source/completion/format.go

@@ -5,7 +5,6 @@
 package completion
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"go/ast"
@@ -65,7 +64,7 @@ func (c *completer) item(ctx context.Context, cand candidate) (CompletionItem, e
 		x := cand.obj.(*types.TypeName)
 		if named, ok := x.Type().(*types.Named); ok {
 			tp := typeparams.ForNamed(named)
-			label += string(formatTypeParams(tp))
+			label += source.FormatTypeParams(tp)
 			insert = label // maintain invariant above (label == insert)
 		}
 	}
@@ -339,19 +338,3 @@ func (c *completer) wantTypeParams() bool {
 	}
 	return false
 }
-
-func formatTypeParams(tp *typeparams.TypeParamList) []byte {
-	var buf bytes.Buffer
-	if tp == nil || tp.Len() == 0 {
-		return nil
-	}
-	buf.WriteByte('[')
-	for i := 0; i < tp.Len(); i++ {
-		if i > 0 {
-			buf.WriteString(", ")
-		}
-		buf.WriteString(tp.At(i).Obj().Name())
-	}
-	buf.WriteByte(']')
-	return buf.Bytes()
-}

Diff for: internal/lsp/source/stub.go

@@ -20,6 +20,7 @@ import (
 	"golang.org/x/tools/internal/lsp/analysis/stubmethods"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func stubSuggestedFixFunc(ctx context.Context, snapshot Snapshot, fh VersionedFileHandle, rng protocol.Range) (*analysis.SuggestedFix, error) {
@@ -31,7 +32,7 @@ func stubSuggestedFixFunc(ctx context.Context, snapshot Snapshot, fh VersionedFi
 	if err != nil {
 		return nil, fmt.Errorf("getNodes: %w", err)
 	}
-	si := stubmethods.GetStubInfo(pkg.GetTypesInfo(), nodes, pkg.GetTypes(), pos)
+	si := stubmethods.GetStubInfo(pkg.GetTypesInfo(), nodes, pos)
 	if si == nil {
 		return nil, fmt.Errorf("nil interface request")
 	}
@@ -134,7 +135,7 @@ func stubMethods(ctx context.Context, concreteFile *ast.File, si *stubmethods.St
 			_, err = methodsBuffer.Write(printStubMethod(methodData{
 				Method:    m.Name(),
 				Concrete:  getStubReceiver(si),
-				Interface: deduceIfaceName(si.Concrete.Obj().Pkg(), si.Interface.Pkg(), si.Concrete.Obj(), si.Interface),
+				Interface: deduceIfaceName(si.Concrete.Obj().Pkg(), si.Interface.Pkg(), si.Interface),
 				Signature: strings.TrimPrefix(sig, "func"),
 			}))
 			if err != nil {
@@ -159,13 +160,14 @@ func stubErr(ctx context.Context, concreteFile *ast.File, si *stubmethods.StubIn
 }
 
 // getStubReceiver returns the concrete type's name as a method receiver.
-// TODO(marwan-at-work): add type parameters to the receiver when the concrete type
-// is a generic one.
+// It accounts for type parameters if they exist.
 func getStubReceiver(si *stubmethods.StubInfo) string {
-	concrete := si.Concrete.Obj().Name()
+	var concrete string
 	if si.Pointer {
-		concrete = "*" + concrete
+		concrete += "*"
 	}
+	concrete += si.Concrete.Obj().Name()
+	concrete += FormatTypeParams(typeparams.ForNamed(si.Concrete))
 	return concrete
 }
 
@@ -203,7 +205,7 @@ func deducePkgFromTypes(ctx context.Context, snapshot Snapshot, ifaceObj types.O
 	return nil, fmt.Errorf("pkg %q not found", ifaceObj.Pkg().Path())
 }
 
-func deduceIfaceName(concretePkg, ifacePkg *types.Package, concreteObj, ifaceObj types.Object) string {
+func deduceIfaceName(concretePkg, ifacePkg *types.Package, ifaceObj types.Object) string {
 	if concretePkg.Path() == ifacePkg.Path() {
 		return ifaceObj.Name()
 	}

Diff for: internal/lsp/source/types_format.go

@@ -168,6 +168,25 @@ func formatFieldList(ctx context.Context, snapshot Snapshot, list *ast.FieldList
 	return result, writeResultParens
 }
 
+// FormatTypeParams turns TypeParamList into its Go representation, such as:
+// [T, Y]. Note that it does not print constraints as this is mainly used for
+// formatting type params in method receivers.
+func FormatTypeParams(tp *typeparams.TypeParamList) string {
+	if tp == nil || tp.Len() == 0 {
+		return ""
+	}
+	var buf bytes.Buffer
+	buf.WriteByte('[')
+	for i := 0; i < tp.Len(); i++ {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(tp.At(i).Obj().Name())
+	}
+	buf.WriteByte(']')
+	return buf.String()
+}
+
 // NewSignature returns formatted signature for a types.Signature struct.
 func NewSignature(ctx context.Context, s Snapshot, pkg Package, sig *types.Signature, comment *ast.CommentGroup, qf types.Qualifier) *signature {
 	params := make([]string, 0, sig.Params().Len())

Diff for: internal/lsp/testdata/stub/stub_generic_receiver.go

@@ -0,0 +1,15 @@
+//go:build go1.18
+// +build go1.18
+
+package stub
+
+import "io"
+
+// This file tests that that the stub method generator accounts for concrete
+// types that have type parameters defined.
+var _ io.ReaderFrom = &genReader[string, int]{} //@suggestedfix("&genReader", "refactor.rewrite")
+
+type genReader[T, Y any] struct {
+	T T
+	Y Y
+}

Diff for: internal/lsp/testdata/stub/stub_generic_receiver.go.golden

@@ -0,0 +1,22 @@
+-- suggestedfix_stub_generic_receiver_10_23 --
+//go:build go1.18
+// +build go1.18
+
+package stub
+
+import "io"
+
+// This file tests that that the stub method generator accounts for concrete
+// types that have type parameters defined.
+var _ io.ReaderFrom = &genReader[string, int]{} //@suggestedfix("&genReader", "refactor.rewrite")
+
+type genReader[T, Y any] struct {
+	T T
+	Y Y
+}
+
+// ReadFrom implements io.ReaderFrom
+func (*genReader[T, Y]) ReadFrom(r io.Reader) (n int64, err error) {
+	panic("unimplemented")
+}
+

Diff for: internal/lsp/testdata/summary_go1.18.txt.golden

@@ -13,7 +13,7 @@ FoldingRangesCount = 2
 FormatCount = 6
 ImportCount = 8
 SemanticTokenCount = 3
-SuggestedFixCount = 61
+SuggestedFixCount = 62
 FunctionExtractionCount = 25
 MethodExtractionCount = 6
 DefinitionsCount = 108