c++: constrained partial spec forward decl [PR96363]
Here during cp_parser_single_declaration for #2, we were calling associate_classtype_constraints for TPL<T> (the primary template type) before maybe_process_partial_specialization could get a chance to notice that we're in fact declaring a distinct constrained partial spec and not redeclaring the primary template. This caused us to emit a bogus error about differing constraints b/t the primary template and #2's constraints. This patch fixes this by moving the call to associate_classtype_constraints after the call to shadow_tag (which calls maybe_process_partial_specialization) and adjusting shadow_tag to use the return value of m_p_p_s. Moreover, if we later try to define a constrained partial specialization that's been declared earlier (as in the third testcase), then maybe_new_partial_specialization correctly notices it's a redeclaration and returns NULL_TREE. But in this case we also need to update TYPE to point to the redeclared partial spec (it'll otherwise continue pointing to the primary template type, eventually leading to a bogus error). PR c++/96363 gcc/cp/ChangeLog: * decl.cc (shadow_tag): Use the return value of maybe_process_partial_specialization. * parser.cc (cp_parser_single_declaration): Call shadow_tag before associate_classtype_constraints. * pt.cc (maybe_new_partial_specialization): Change return type to bool. Take 'type' argument by mutable reference. Set 'type' to point to the correct constrained specialization when appropriate. (maybe_process_partial_specialization): Adjust accordingly. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-partial-spec12.C: New test. * g++.dg/cpp2a/concepts-partial-spec12a.C: New test. * g++.dg/cpp2a/concepts-partial-spec13.C: New test.
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@ -5464,7 +5464,8 @@ shadow_tag (cp_decl_specifier_seq *declspecs)
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if (!t)
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return NULL_TREE;
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if (maybe_process_partial_specialization (t) == error_mark_node)
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t = maybe_process_partial_specialization (t);
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if (t == error_mark_node)
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return NULL_TREE;
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/* This is where the variables in an anonymous union are
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@ -31811,12 +31811,6 @@ cp_parser_single_declaration (cp_parser* parser,
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if (cp_parser_declares_only_class_p (parser)
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|| (declares_class_or_enum & 2))
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{
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/* If this is a declaration, but not a definition, associate
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any constraints with the type declaration. Constraints
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are associated with definitions in cp_parser_class_specifier. */
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if (declares_class_or_enum == 1)
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associate_classtype_constraints (decl_specifiers.type);
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decl = shadow_tag (&decl_specifiers);
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/* In this case:
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@ -31838,6 +31832,12 @@ cp_parser_single_declaration (cp_parser* parser,
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else
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decl = error_mark_node;
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/* If this is a declaration, but not a definition, associate
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any constraints with the type declaration. Constraints
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are associated with definitions in cp_parser_class_specifier. */
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if (declares_class_or_enum == 1)
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associate_classtype_constraints (TREE_TYPE (decl));
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/* Perform access checks for template parameters. */
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cp_parser_perform_template_parameter_access_checks (checks);
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38
gcc/cp/pt.cc
38
gcc/cp/pt.cc
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@ -874,12 +874,12 @@ check_explicit_instantiation_namespace (tree spec)
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spec, current_namespace, ns);
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}
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/* Returns the type of a template specialization only if that
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specialization needs to be defined. Otherwise (e.g., if the type has
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already been defined), the function returns NULL_TREE. */
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/* Returns true if TYPE is a new partial specialization that needs to be
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set up. This may also modify TYPE to point to the correct (new or
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existing) constrained partial specialization. */
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static tree
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maybe_new_partial_specialization (tree type)
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static bool
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maybe_new_partial_specialization (tree& type)
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{
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/* An implicit instantiation of an incomplete type implies
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the definition of a new class template.
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@ -893,7 +893,7 @@ maybe_new_partial_specialization (tree type)
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Here, S<T*> is an implicit instantiation of S whose type
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is incomplete. */
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if (CLASSTYPE_IMPLICIT_INSTANTIATION (type) && !COMPLETE_TYPE_P (type))
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return type;
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return true;
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/* It can also be the case that TYPE is a completed specialization.
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Continuing the previous example, suppose we also declare:
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@ -919,11 +919,11 @@ maybe_new_partial_specialization (tree type)
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/* If there are no template parameters, this cannot be a new
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partial template specialization? */
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if (!current_template_parms)
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return NULL_TREE;
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return false;
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/* The injected-class-name is not a new partial specialization. */
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if (DECL_SELF_REFERENCE_P (TYPE_NAME (type)))
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return NULL_TREE;
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return false;
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/* If the constraints are not the same as those of the primary
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then, we can probably create a new specialization. */
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@ -933,7 +933,7 @@ maybe_new_partial_specialization (tree type)
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{
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tree main_constr = get_constraints (tmpl);
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if (equivalent_constraints (type_constr, main_constr))
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return NULL_TREE;
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return false;
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}
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/* Also, if there's a pre-existing specialization with matching
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@ -946,7 +946,10 @@ maybe_new_partial_specialization (tree type)
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tree spec_constr = get_constraints (spec_tmpl);
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if (comp_template_args (args, spec_args)
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&& equivalent_constraints (type_constr, spec_constr))
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return NULL_TREE;
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{
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type = TREE_TYPE (spec_tmpl);
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return false;
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}
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specs = TREE_CHAIN (specs);
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}
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@ -971,10 +974,11 @@ maybe_new_partial_specialization (tree type)
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set_instantiating_module (d);
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DECL_MODULE_EXPORT_P (d) = DECL_MODULE_EXPORT_P (tmpl);
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return t;
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type = t;
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return true;
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}
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return NULL_TREE;
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return false;
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}
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/* The TYPE is being declared. If it is a template type, that means it
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@ -1030,16 +1034,16 @@ maybe_process_partial_specialization (tree type)
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Make sure that `C<int>' and `C<T*>' are implicit instantiations. */
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if (tree t = maybe_new_partial_specialization (type))
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if (maybe_new_partial_specialization (type))
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{
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if (!check_specialization_namespace (CLASSTYPE_TI_TEMPLATE (t))
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if (!check_specialization_namespace (CLASSTYPE_TI_TEMPLATE (type))
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&& !at_namespace_scope_p ())
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return error_mark_node;
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SET_CLASSTYPE_TEMPLATE_SPECIALIZATION (t);
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DECL_SOURCE_LOCATION (TYPE_MAIN_DECL (t)) = input_location;
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SET_CLASSTYPE_TEMPLATE_SPECIALIZATION (type);
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DECL_SOURCE_LOCATION (TYPE_MAIN_DECL (type)) = input_location;
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if (processing_template_decl)
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{
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tree decl = push_template_decl (TYPE_MAIN_DECL (t));
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tree decl = push_template_decl (TYPE_MAIN_DECL (type));
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if (decl == error_mark_node)
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return error_mark_node;
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return TREE_TYPE (decl);
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@ -0,0 +1,10 @@
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// PR c++/96363
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// { dg-do compile { target c++20 } }
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template<class T> class TPL;
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template<class T> requires true class TPL<T>; // #1
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template<class T> requires false class TPL<T>; // #2 error here
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template<class T> requires true class TPL<T*>; // #1
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template<class T> requires false class TPL<T*>; // #2 error here
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@ -0,0 +1,14 @@
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// PR c++/96363
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// { dg-do compile { target c++20 } }
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// A version of concepts-partial-spec12.C where the primary template is
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// constrained.
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template<class T> concept C = true;
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template<C T> class TPL;
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template<C T> requires true class TPL<T>; // #1
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template<C T> requires false class TPL<T>; // #2 error here
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template<C T> requires true class TPL<T*>; // #1
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template<C T> requires false class TPL<T*>; // #2 error here
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@ -0,0 +1,16 @@
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// PR c++/99501
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// { dg-do compile { target c++20 } }
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template<auto> struct X;
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template<auto V> requires requires{V.a;} struct X<V>;
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template<auto V> requires requires{V.b;} struct X<V>;
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template<auto V> requires requires{V.a;} struct X<V> { static const bool v = false; };
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template<auto V> requires requires{V.b;} struct X<V> { static const bool v = true; };
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struct A { int a; };
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static_assert(!X<A{}>::v);
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struct B { int b; };
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static_assert(X<B{}>::v);
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