go/types: disallow aliases for generic types

This is a port of CL 346294 to go/types.

Change-Id: Ib70541a92e352c8df8123c8b82bb4eeedce3b89f
Reviewed-on: https://go-review.googlesource.com/c/go/+/346560
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 758ebf5d7fe84821fcb6a6d11c23545a6d552d3b..275d17c8266e261dac0775a091ad3f0b2ae864ae 100644 (file)
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -603,7 +603,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
                }
 
                obj.typ = Typ[Invalid]
-               rhs = check.anyType(tdecl.Type)
+               rhs = check.varType(tdecl.Type)
                obj.typ = rhs
                return
        }

diff --git a/src/go/types/testdata/check/typeinst.go2 b/src/go/types/testdata/check/typeinst.go2
index 069bd3bc1695fe8539f2ea9454ff28f2132b893d..4a8918ab86c263d872424cedeb4e3388523faf9a 100644 (file)
--- a/src/go/types/testdata/check/typeinst.go2
+++ b/src/go/types/testdata/check/typeinst.go2
@@ -17,13 +17,15 @@ type T2[P any] struct {
 
 type List[P any] []P
 
-// Alias type declarations cannot have type parameters. Syntax error.
+// Alias type declarations cannot have type parameters.
+// Issue #46477 proposses to change that.
 type A1[P any] = /* ERROR cannot be alias */ P
 
-// But an alias may refer to a generic, uninstantiated type.
-type A2 = List
+// Pending clarification of #46477 we disallow aliases
+// of generic types.
+type A2 = List // ERROR cannot use generic type
 var _ A2[int]
-var _ A2 /* ERROR without instantiation */
+var _ A2
 
 type A3 = List[int]
 var _ A3

diff --git a/src/go/types/testdata/fixedbugs/issue39768.go2 b/src/go/types/testdata/fixedbugs/issue39768.go2
index abac141d7f08dd359a26ba18c36b696d7970d40a..fb522733e0b83f0e86b388a561f458514ee15f3c 100644 (file)
--- a/src/go/types/testdata/fixedbugs/issue39768.go2
+++ b/src/go/types/testdata/fixedbugs/issue39768.go2
@@ -5,9 +5,9 @@
 package p
 
 type T[P any] P
-type A = T
+type A = T  // ERROR cannot use generic type
 var x A[int]
-var _ A /* ERROR cannot use generic type */
+var _ A
 
 type B = T[int]
 var y B = x
@@ -16,5 +16,5 @@ var _ B /* ERROR not a generic type */ [int]
 // test case from issue
 
 type Vector[T any] []T
-type VectorAlias = Vector
+type VectorAlias = Vector // ERROR cannot use generic type
 var v Vector[int]

diff --git a/src/go/types/testdata/fixedbugs/issue47968.go2 b/src/go/types/testdata/fixedbugs/issue47968.go2
index bbbe6805f2dd330c469d21072301906d5e73599c..711e50a55a1d5eeb9661ff259a03ea78618dd82e 100644 (file)
--- a/src/go/types/testdata/fixedbugs/issue47968.go2
+++ b/src/go/types/testdata/fixedbugs/issue47968.go2
@@ -8,7 +8,7 @@ type T[P any] struct{}
 
 func (T[P]) m1()
 
-type A1 = T
+type A1 = T // ERROR cannot use generic type
 
 func (A1[P]) m2() {}
 

diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 533f976f1d8bdf6d53f7f1230df712dc89bd8e6a..af5629714429d4bebd72cf1944bddaede2b2fdc1 100644 (file)
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -36,12 +36,15 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *Named, wantType bool)
                }
                return
        case universeAny, universeComparable:
-               // complain if necessary but keep going
+               // complain if necessary
                if !check.allowVersion(check.pkg, 1, 18) {
-                       check.softErrorf(e, _UndeclaredName, "undeclared name: %s (requires version go1.18 or later)", e.Name)
-               } else if obj == universeAny {
+                       check.errorf(e, _UndeclaredName, "undeclared name: %s (requires version go1.18 or later)", e.Name)
+                       return // avoid follow-on errors
+               }
+               if obj == universeAny {
                        // If we allow "any" for general use, this if-statement can be removed (issue #33232).
                        check.softErrorf(e, _Todo, "cannot use any outside constraint position")
+                       // ok to continue
                }
        }
        check.recordUse(e, obj)
@@ -155,15 +158,6 @@ func (check *Checker) varType(e ast.Expr) Type {
        return typ
 }
 
-// anyType type-checks the type expression e and returns its type, or Typ[Invalid].
-// The type may be generic or instantiated.
-func (check *Checker) anyType(e ast.Expr) Type {
-       typ := check.typInternal(e, nil)
-       assert(isTyped(typ))
-       check.recordTypeAndValue(e, typexpr, typ, nil)
-       return typ
-}
-
 // definedType is like typ but also accepts a type name def.
 // If def != nil, e is the type specification for the defined type def, declared
 // in a type declaration, and def.underlying will be set to the type of e before