From: Jason Merrill <jason@redhat.com>
Date: Tue, 23 Sep 2025 10:19:49 +0000 (+0100)
Subject: c++: concepts and conversions [PR112632]
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a0536f80ffa6cde5900644dcd129d2086c237a8a;p=thirdparty%2Fgcc.git

c++: concepts and conversions [PR112632]

One case missed in my fix for this PR: Here we were omitting the
IMPLICIT_CONV_EXPR that expresses the conversion from int to char because
the target type was non-dependent and the argument was not type-dependent.
But we still need it if the argument is value-dependent.

	PR c++/112632

gcc/cp/ChangeLog:

	* pt.cc (convert_template_argument): Also force IMPLICIT_CONV_EXPR
	if the argument is value-dependent.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-conv4.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 96ead4f1b55..bd60d515653 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8927,8 +8927,9 @@ convert_template_argument (tree parm,
 	  && same_type_p (TREE_TYPE (orig_arg), t))
 	orig_arg = TREE_OPERAND (orig_arg, 0);
 
-      if (!type_dependent_expression_p (orig_arg)
-	  && !uses_template_parms (t))
+      if (!uses_template_parms (t)
+	  && !(force_conv ? uses_template_parms (orig_arg)
+	       : type_dependent_expression_p (orig_arg)))
 	/* We used to call digest_init here.  However, digest_init
 	   will report errors, which we don't want when complain
 	   is zero.  More importantly, digest_init will try too
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-conv4.C b/gcc/testsuite/g++.dg/cpp2a/concepts-conv4.C
new file mode 100644
index 00000000000..107a1bbe4d9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-conv4.C
@@ -0,0 +1,9 @@
+// PR c++/112632
+// { dg-do compile { target c++20 } }
+
+template<int N> concept A = N != 0;
+template<char C> concept B = A<C>;
+template<int N> concept C = B<N>;
+
+static_assert(A<256>);
+static_assert(!C<256>);