Fix generation failure when multiple type parameters are in the receiver

Also fixes duplicate method generation for already implemented methods
of structs with type parameters.

impl_test.go

@@ -318,11 +318,19 @@ func TestValidReceiver(t *testing.T) {
 		want bool
 	}{
 		{recv: "f", want: true},
+		{recv: "f[T]", want: true},
+		{recv: "f[T, U]", want: true},
 		{recv: "F", want: true},
+		{recv: "*F[T]", want: true},
+		{recv: "*F[T, U]", want: true},
 		{recv: "f F", want: true},
 		{recv: "f *F", want: true},
+		{recv: "f *F[T]", want: true},
+		{recv: "f *F[T, U]", want: true},
 		{recv: "", want: false},
 		{recv: "a+b", want: false},
+		{recv: "[T]", want: false},
+		{recv: "[T, U]", want: false},
 	}
 
 	for _, tt := range cases {
@@ -676,6 +684,20 @@ func TestStubGenerationForImplemented(t *testing.T) {
 			recvPkg: "testdata",
 			want:    testdata.Interface4Output,
 		},
+		{
+			desc:    "without implemeted methods, with generic receiver",
+			iface:   "github.com/josharian/impl/testdata.Interface3",
+			recv:    "r *ImplementedGeneric[Type1]",
+			recvPkg: "testdata",
+			want:    testdata.Interface4GenericOutput,
+		},
+		{
+			desc:    "without implemeted methods, with generic receiver with multiple params",
+			iface:   "github.com/josharian/impl/testdata.Interface3",
+			recv:    "r *ImplementedGenericMultipleParams[Type1, Type2]",
+			recvPkg: "testdata",
+			want:    testdata.Interface4GenericMultipleParamsOutput,
+		},
 		{
 			desc:    "without implemeted methods and receiver variable",
 			iface:   "github.com/josharian/impl/testdata.Interface3",
@@ -690,13 +712,41 @@ func TestStubGenerationForImplemented(t *testing.T) {
 			recvPkg: "testdata",
 			want:    testdata.Interface5Output,
 		},
+		{
+			desc:    "generic receiver and interface in the same package",
+			iface:   "github.com/josharian/impl/testdata.Interface5",
+			recv:    "r *ImplementedGeneric[Type1]",
+			recvPkg: "testdata",
+			want:    testdata.Interface5GenericOutput,
+		},
+		{
+			desc:    "generic receiver with multiple params and interface in the same package",
+			iface:   "github.com/josharian/impl/testdata.Interface5",
+			recv:    "r *ImplementedGenericMultipleParams[Type1, Type2]",
+			recvPkg: "testdata",
+			want:    testdata.Interface5GenericMultipleParamsOutput,
+		},
 		{
 			desc:    "receiver and interface in a different package",
 			iface:   "github.com/josharian/impl/testdata.Interface5",
 			recv:    "r *Implemented",
 			recvPkg: "test",
 			want:    testdata.Interface6Output,
 		},
+		{
+			desc:    "generic receiver and interface in a different package",
+			iface:   "github.com/josharian/impl/testdata.Interface5",
+			recv:    "r *ImplementedGeneric[Type1]",
+			recvPkg: "test",
+			want:    testdata.Interface6GenericOutput,
+		},
+		{
+			desc:    "generic receiver with multiple params and interface in a different package",
+			iface:   "github.com/josharian/impl/testdata.Interface5",
+			recv:    "r *ImplementedGenericMultipleParams[Type1, Type2]",
+			recvPkg: "test",
+			want:    testdata.Interface6GenericMultipleParamsOutput,
+		},
 	}
 	for _, tt := range cases {
 		t.Run(tt.desc, func(t *testing.T) {

implemented.go

@@ -31,8 +31,17 @@ func implementedFuncs(fns []Func, recv string, srcDir string) (map[string]bool,
 		for _, v := range mf.Recv.List {
 			switch xv := v.Type.(type) {
 			case *ast.StarExpr:
-				if si, ok := xv.X.(*ast.Ident); ok {
-					return si.Name
+				switch xxv := xv.X.(type) {
+				case *ast.Ident:
+					return xxv.Name
+				case *ast.IndexExpr: // type with one type parameter.
+					if si, ok := xxv.X.(*ast.Ident); ok {
+						return si.Name
+					}
+				case *ast.IndexListExpr: // type with mutiple type parameters.
+					if si, ok := xxv.X.(*ast.Ident); ok {
+						return si.Name
+					}
 				}
 			case *ast.Ident:
 				return xv.Name
@@ -82,6 +91,10 @@ func getReceiverType(recv string) string {
 	// VSCode adds a trailing space to receiver (it runs impl like: impl 'r *Receiver ' io.Writer)
 	// so we have to remove spaces.
 	recv = strings.TrimSpace(recv)
+
+	// Remove type parameters. They can contain spaces too, for example 'r *Receiver[T, U]'.
+	recv, _, _ = strings.Cut(recv, "[")
+
 	parts := strings.Split(recv, " ")
 	switch len(parts) {
 	case 1: // (SomeType)

testdata/interfaces.go

@@ -268,3 +268,69 @@ func (r *Receiver) Method3(_ string) bool {
 }
 
 `
+
+type ImplementedGeneric[Type1 any] struct{}
+
+func (r *ImplementedGeneric[Type1]) Method1(arg1 string, arg2 string) (result string, err error) {
+	return "", nil
+}
+
+var Interface4GenericOutput = `// Method2 is the second method of Interface3.
+func (r *ImplementedGeneric[Type1]) Method2(_ int, arg2 int) (_ int, err error) {
+	panic("not implemented") // TODO: Implement
+}
+
+// Method3 is the third method of Interface3.
+func (r *ImplementedGeneric[Type1]) Method3(arg1 bool, arg2 bool) (result1 bool, result2 bool) {
+	panic("not implemented") // TODO: Implement
+}
+
+`
+
+var Interface5GenericOutput = `// Method is the first method of Interface5.
+func (r *ImplementedGeneric[Type1]) Method2(arg1 string, arg2 Interface2, arg3 Struct5) (Interface3, error) {
+	panic("not implemented") // TODO: Implement
+}
+
+`
+
+// Interface6GenericOutput receiver not in current package
+var Interface6GenericOutput = `// Method is the first method of Interface5.
+func (r *ImplementedGeneric[Type1]) Method2(arg1 string, arg2 testdata.Interface2, arg3 testdata.Struct5) (testdata.Interface3, error) {
+	panic("not implemented") // TODO: Implement
+}
+
+`
+
+type ImplementedGenericMultipleParams[Type1 any, Type2 comparable] struct{}
+
+func (r *ImplementedGenericMultipleParams[Type1, Type2]) Method1(arg1 string, arg2 string) (result string, err error) {
+	return "", nil
+}
+
+var Interface4GenericMultipleParamsOutput = `// Method2 is the second method of Interface3.
+func (r *ImplementedGenericMultipleParams[Type1, Type2]) Method2(_ int, arg2 int) (_ int, err error) {
+	panic("not implemented") // TODO: Implement
+}
+
+// Method3 is the third method of Interface3.
+func (r *ImplementedGenericMultipleParams[Type1, Type2]) Method3(arg1 bool, arg2 bool) (result1 bool, result2 bool) {
+	panic("not implemented") // TODO: Implement
+}
+
+`
+
+var Interface5GenericMultipleParamsOutput = `// Method is the first method of Interface5.
+func (r *ImplementedGenericMultipleParams[Type1, Type2]) Method2(arg1 string, arg2 Interface2, arg3 Struct5) (Interface3, error) {
+	panic("not implemented") // TODO: Implement
+}
+
+`
+
+// Interface6GenericMultipleParamsOutput receiver not in current package
+var Interface6GenericMultipleParamsOutput = `// Method is the first method of Interface5.
+func (r *ImplementedGenericMultipleParams[Type1, Type2]) Method2(arg1 string, arg2 testdata.Interface2, arg3 testdata.Struct5) (testdata.Interface3, error) {
+	panic("not implemented") // TODO: Implement
+}
+
+`