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cmd/compile/internal/types2: disallow aliases for generic types
The existing approach (alias name stands for generic type name) is an exception: it's the only place where a generic type could be used without explicit instantiation. The correct solution is currently under discussion (see proposal issue #46477). This CL requires that the RHS of an alias type declaration be an instantiated non-generic type. If #46477 is accepted, the implementation will require proper representation of alias types. Change-Id: Ie85b923213a64f39837e56e38e14757458272b93 Reviewed-on: https://go-review.googlesource.com/c/go/+/346294 Trust: Robert Griesemer <gri@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>
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@ -555,7 +555,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named
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}
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obj.typ = Typ[Invalid]
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rhs = check.anyType(tdecl.Type)
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rhs = check.varType(tdecl.Type)
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obj.typ = rhs
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return
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}
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@ -17,13 +17,15 @@ type T2[P any] struct {
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type List[P any] []P
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// Alias type declarations cannot have type parameters. Syntax error.
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// Alias type declarations cannot have type parameters.
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// Issue #46477 proposses to change that.
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type A1[P any] = /* ERROR cannot be alias */ P
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// But an alias may refer to a generic, uninstantiated type.
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type A2 = List
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// Pending clarification of #46477 we disallow aliases
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// of generic types.
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type A2 = List // ERROR cannot use generic type
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var _ A2[int]
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var _ A2 /* ERROR without instantiation */
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var _ A2
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type A3 = List[int]
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var _ A3
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@ -5,9 +5,9 @@
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package p
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type T[P any] P
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type A = T
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type A = T // ERROR cannot use generic type
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var x A[int]
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var _ A /* ERROR cannot use generic type */
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var _ A
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type B = T[int]
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var y B = x
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@ -16,5 +16,5 @@ var _ B /* ERROR not a generic type */ [int]
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// test case from issue
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type Vector[T any] []T
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type VectorAlias = Vector
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type VectorAlias = Vector // ERROR cannot use generic type
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var v Vector[int]
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@ -8,7 +8,7 @@ type T[P any] struct{}
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func (T[P]) m1()
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type A1 = T
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type A1 = T // ERROR cannot use generic type
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func (A1[P]) m2() {}
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@ -38,12 +38,15 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *Named, wantType boo
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}
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return
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case universeAny, universeComparable:
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// complain if necessary but keep going
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// complain if necessary
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if !check.allowVersion(check.pkg, 1, 18) {
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check.softErrorf(e, "undeclared name: %s (requires version go1.18 or later)", e.Value)
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} else if obj == universeAny {
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check.errorf(e, "undeclared name: %s (requires version go1.18 or later)", e.Value)
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return // avoid follow-on errors
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}
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if obj == universeAny {
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// If we allow "any" for general use, this if-statement can be removed (issue #33232).
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check.softErrorf(e, "cannot use any outside constraint position")
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// ok to continue
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}
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}
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check.recordUse(e, obj)
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@ -159,15 +162,6 @@ func (check *Checker) varType(e syntax.Expr) Type {
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return typ
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}
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// anyType type-checks the type expression e and returns its type, or Typ[Invalid].
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// The type may be generic or instantiated.
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func (check *Checker) anyType(e syntax.Expr) Type {
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typ := check.typInternal(e, nil)
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assert(isTyped(typ))
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check.recordTypeAndValue(e, typexpr, typ, nil)
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return typ
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}
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// definedType is like typ but also accepts a type name def.
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// If def != nil, e is the type specification for the defined type def, declared
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// in a type declaration, and def.underlying will be set to the type of e before
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@ -10,16 +10,18 @@ type R[T any] struct {
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F T
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}
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type S = R
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// type S = R // disallowed for now
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type Sint = R[int]
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type Simp = a.Rimp
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// type Simp = a.Rimp // disallowed for now
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type SimpString Simp[string]
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// type SimpString Simp[string] // disallowed for now
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type SimpString a.Rimp[string]
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func main() {
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var s S[int]
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// var s S[int] // disallowed for now
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var s R[int]
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if s.F != 0 {
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panic(s.F)
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}
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@ -27,7 +29,8 @@ func main() {
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if s2.F != 0 {
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panic(s2.F)
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}
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var s3 Simp[string]
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// var s3 Simp[string] // disallowed for now
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var s3 a.Rimp[string]
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if s3.F != "" {
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panic(s3.F)
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}
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