go/types, types2: avoid field/method lookup error on invalid types

Fixes #49541.

Change-Id: I27a52d0722a7408758682e7ddcd608c0a6c4881b
Reviewed-on: https://go-review.googlesource.com/c/go/+/378175
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/call.go

@@ -531,6 +531,11 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 
 	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
+		// Don't report another error if the underlying type was invalid (issue #49541).
+		if under(x.typ) == Typ[Invalid] {
+			goto Error
+		}
+
 		if index != nil {
 			// TODO(gri) should provide actual type where the conflict happens
 			check.errorf(e.Sel, "ambiguous selector %s.%s", x.expr, sel)

src/cmd/compile/internal/types2/instantiate.go

@@ -161,7 +161,10 @@ func (check *Checker) implements(V, T Type, qf Qualifier) error {
 	Vu := under(V)
 	Tu := under(T)
 	if Vu == Typ[Invalid] || Tu == Typ[Invalid] {
-		return nil
+		return nil // avoid follow-on errors
+	}
+	if p, _ := Vu.(*Pointer); p != nil && under(p.base) == Typ[Invalid] {
+		return nil // avoid follow-on errors (see issue #49541 for an example)
 	}
 
 	errorf := func(format string, args ...interface{}) error {

src/cmd/compile/internal/types2/testdata/fixedbugs/issue49541.go2

@@ -0,0 +1,44 @@
+// Copyright 2022 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 p
+
+type S[A, B any] struct {
+	f int
+}
+
+func (S[A, B]) m() {}
+
+// TODO(gri) We should only report one error below. See issue #50588.
+
+func _[A any](s S /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [A]) {
+	// we should see no follow-on errors below
+	s.f = 1
+	s.m()
+}
+
+// another test case from the issue
+
+func _() {
+	X(Interface[*F /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [string]](Impl{}))
+}
+
+func X[Q Qer](fs Interface[Q]) {
+}
+
+type Impl struct{}
+
+func (Impl) M() {}
+
+type Interface[Q Qer] interface {
+	M()
+}
+
+type Qer interface {
+	Q()
+}
+
+type F[A, B any] struct{}
+
+func (f *F[A, B]) Q() {}

src/cmd/compile/internal/types2/typeset.go

@@ -135,7 +135,7 @@ func (s *_TypeSet) is(f func(*term) bool) bool {
 
 // underIs calls f with the underlying types of the specific type terms
 // of s and reports whether all calls to f returned true. If there are
-// no specific terms, is returns the result of f(nil).
+// no specific terms, underIs returns the result of f(nil).
 func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	if !s.hasTerms() {
 		return f(nil)

src/go/types/call.go

@@ -533,6 +533,11 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 
 	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
+		// Don't report another error if the underlying type was invalid (issue #49541).
+		if under(x.typ) == Typ[Invalid] {
+			goto Error
+		}
+
 		if index != nil {
 			// TODO(gri) should provide actual type where the conflict happens
 			check.errorf(e.Sel, _AmbiguousSelector, "ambiguous selector %s.%s", x.expr, sel)

src/go/types/instantiate.go

@@ -161,7 +161,10 @@ func (check *Checker) implements(V, T Type, qf Qualifier) error {
 	Vu := under(V)
 	Tu := under(T)
 	if Vu == Typ[Invalid] || Tu == Typ[Invalid] {
-		return nil
+		return nil // avoid follow-on errors
+	}
+	if p, _ := Vu.(*Pointer); p != nil && under(p.base) == Typ[Invalid] {
+		return nil // avoid follow-on errors (see issue #49541 for an example)
 	}
 
 	errorf := func(format string, args ...any) error {

src/go/types/testdata/fixedbugs/issue49541.go2

@@ -0,0 +1,44 @@
+// Copyright 2022 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 p
+
+type S[A, B any] struct {
+	f int
+}
+
+func (S[A, B]) m() {}
+
+// TODO(gri) We should only report one error below. See issue #50588.
+
+func _[A any](s S /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [A]) {
+	// we should see no follow-on errors below
+	s.f = 1
+	s.m()
+}
+
+// another test case from the issue
+
+func _() {
+	X(Interface[*F /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [string]](Impl{}))
+}
+
+func X[Q Qer](fs Interface[Q]) {
+}
+
+type Impl struct{}
+
+func (Impl) M() {}
+
+type Interface[Q Qer] interface {
+	M()
+}
+
+type Qer interface {
+	Q()
+}
+
+type F[A, B any] struct{}
+
+func (f *F[A, B]) Q() {}

src/go/types/typeset.go

@@ -133,7 +133,7 @@ func (s *_TypeSet) is(f func(*term) bool) bool {
 
 // underIs calls f with the underlying types of the specific type terms
 // of s and reports whether all calls to f returned true. If there are
-// no specific terms, is returns the result of f(nil).
+// no specific terms, underIs returns the result of f(nil).
 func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	if !s.hasTerms() {
 		return f(nil)