From c847a2c9f024f47eee25c132f2d80e7037adea36 Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Thu, 30 Jun 2022 16:41:31 -0700
Subject: [PATCH] go/types, types2: document that exported predicates are
 unspecified for invalid type arguments

Per discussion on the issue.

For #53595.

Change-Id: Iefd161e5c7e792d454652cbe831a0c2d769f748e
Reviewed-on: https://go-review.googlesource.com/c/go/+/415574
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
---
 src/cmd/compile/internal/types2/api.go | 15 ++++++++-------
 src/go/types/api.go                    | 15 ++++++++-------
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index a22ea5d12fc..94c290b9ee7 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -418,7 +418,8 @@ func (conf *Config) Check(path string, files []*syntax.File, info *Info) (*Packa
 
 // AssertableTo reports whether a value of type V can be asserted to have type T.
 //
-// The behavior of AssertableTo is undefined in two cases:
+// The behavior of AssertableTo is unspecified in three cases:
+//   - if T is Typ[Invalid]
 //   - if V is a generalized interface; i.e., an interface that may only be used
 //     as a type constraint in Go code
 //   - if T is an uninstantiated generic type
@@ -434,8 +435,8 @@ func AssertableTo(V *Interface, T Type) bool {
 // AssignableTo reports whether a value of type V is assignable to a variable
 // of type T.
 //
-// The behavior of AssignableTo is undefined if V or T is an uninstantiated
-// generic type.
+// The behavior of AssignableTo is unspecified if V or T is Typ[Invalid] or an
+// uninstantiated generic type.
 func AssignableTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	ok, _ := x.assignableTo(nil, T, nil) // check not needed for non-constant x
@@ -445,8 +446,8 @@ func AssignableTo(V, T Type) bool {
 // ConvertibleTo reports whether a value of type V is convertible to a value of
 // type T.
 //
-// The behavior of ConvertibleTo is undefined if V or T is an uninstantiated
-// generic type.
+// The behavior of ConvertibleTo is unspecified if V or T is Typ[Invalid] or an
+// uninstantiated generic type.
 func ConvertibleTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	return x.convertibleTo(nil, T, nil) // check not needed for non-constant x
@@ -454,8 +455,8 @@ func ConvertibleTo(V, T Type) bool {
 
 // Implements reports whether type V implements interface T.
 //
-// The behavior of Implements is undefined if V is an uninstantiated generic
-// type.
+// The behavior of Implements is unspecified if V is Typ[Invalid] or an uninstantiated
+// generic type.
 func Implements(V Type, T *Interface) bool {
 	if T.Empty() {
 		// All types (even Typ[Invalid]) implement the empty interface.
diff --git a/src/go/types/api.go b/src/go/types/api.go
index 0915d6a6eee..5e7be29b3ca 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -413,7 +413,8 @@ func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, i
 
 // AssertableTo reports whether a value of type V can be asserted to have type T.
 //
-// The behavior of AssertableTo is undefined in two cases:
+// The behavior of AssertableTo is unspecified in three cases:
+//   - if T is Typ[Invalid]
 //   - if V is a generalized interface; i.e., an interface that may only be used
 //     as a type constraint in Go code
 //   - if T is an uninstantiated generic type
@@ -429,8 +430,8 @@ func AssertableTo(V *Interface, T Type) bool {
 // AssignableTo reports whether a value of type V is assignable to a variable
 // of type T.
 //
-// The behavior of AssignableTo is undefined if V or T is an uninstantiated
-// generic type.
+// The behavior of AssignableTo is unspecified if V or T is Typ[Invalid] or an
+// uninstantiated generic type.
 func AssignableTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	ok, _ := x.assignableTo(nil, T, nil) // check not needed for non-constant x
@@ -440,8 +441,8 @@ func AssignableTo(V, T Type) bool {
 // ConvertibleTo reports whether a value of type V is convertible to a value of
 // type T.
 //
-// The behavior of ConvertibleTo is undefined if V or T is an uninstantiated
-// generic type.
+// The behavior of ConvertibleTo is unspecified if V or T is Typ[Invalid] or an
+// uninstantiated generic type.
 func ConvertibleTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	return x.convertibleTo(nil, T, nil) // check not needed for non-constant x
@@ -449,8 +450,8 @@ func ConvertibleTo(V, T Type) bool {
 
 // Implements reports whether type V implements interface T.
 //
-// The behavior of Implements is undefined if V is an uninstantiated generic
-// type.
+// The behavior of Implements is unspecified if V is Typ[Invalid] or an uninstantiated
+// generic type.
 func Implements(V Type, T *Interface) bool {
 	if T.Empty() {
 		// All types (even Typ[Invalid]) implement the empty interface.