b28b621ac6
This patch makes tsubst_requires_expr avoid substituting into a requires-expression when partially instantiating a generic lambda. This is necessary in general to ensure that we always check requirements in lexical order (as in the first testcase below). A mechanism similar to PACK_EXPANSION_EXTRA_ARGS is added to remember template arguments and defer substitution of requires-expressions. Incidentally, this change also fixes the two mentioned PRs -- the problem there is that tsubst_requires_expr was performing semantic checks on template trees, and some of the checks are not prepared to handle such trees. With this patch, tsubst_requires_expr no longer does any semantic checking at all when processing_template_decl. gcc/cp/ChangeLog: PR c++/96409 PR c++/96410 * constraint.cc (tsubst_requires_expr): Use REQUIRES_EXPR_PARMS and REQUIRES_EXPR_REQS. Use REQUIRES_EXPR_EXTRA_ARGS, add_extra_args and build_extra_args to defer substitution until we have all the template arguments. (finish_requires_expr): Adjust the call to build_min so that REQUIRES_EXPR_EXTRA_ARGS gets set to NULL_TREE. * cp-tree.def (REQUIRES_EXPR): Give it a third operand. * cp-tree.h (REQUIRES_EXPR_PARMS, REQUIRES_EXPR_REQS, REQUIRES_EXPR_EXTRA_ARGS): Define. (add_extra_args, build_extra_args): Declare. gcc/testsuite/ChangeLog: PR c++/96409 PR c++/96410 * g++.dg/cpp2a/concepts-lambda13.C: New test. * g++.dg/cpp2a/concepts-lambda14.C: New test.
19 lines
430 B
C
19 lines
430 B
C
// { dg-do compile { target c++20 } }
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template<typename T>
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struct S {
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using type = T::type; // { dg-bogus "" }
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};
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template<typename T>
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auto f() {
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return [] <typename U> (U) {
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// Verify that partial instantiation of this generic lambda doesn't cause
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// these requirements to get checked out of order.
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static_assert(!requires { typename U::type; typename S<T>::type; });
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return 0;
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};
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}
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int a = f<int>()(0);
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