From: Jason Merrill <jason@redhat.com>
Date: Fri, 3 Oct 2025 17:10:36 +0000 (+0100)
Subject: c++: concepts and conversions, take 2 [PR122127]
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5ee5a05da06078975a933be849431eee1d4c6989;p=thirdparty%2Fgcc.git

c++: concepts and conversions, take 2 [PR122127]

My r16-4115 changed convert_template_argument (when called from
instantiate_alias_template) to take the maybe_convert_nontype_argument path
rather than convert_nontype_argument for this testcase.  This meant not
folding the use of the by-ref capture in the template argument to constant
1.  When we come back to convert_template_argument again when substituting
into resize<_Np> we strip the IMPLICIT_CONV_EXPR (since the types are the
same) and take the convert_nontype_argument path, but at this point we've
pushed into the alias template context and trying to fold away the capture
fails because current_lambda_expr() is now null.

Taking the convert_nontype_argument path in the same-type case where we
would later strip an IMPLICIT_CONV_EXPR fixes the problem.  Note that
maybe_convert_nontype_argument already shares the same-type check with the
stripping, but that isn't enough; it still doesn't fold away the capture
proxy.

	PR c++/122127
	PR c++/112632

gcc/cp/ChangeLog:

	* pt.cc (convert_template_argument): Don't add redundant
	IMPLICIT_CONV_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-template18.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index bd60d515653..9b32049e71b 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8928,8 +8928,11 @@ convert_template_argument (tree parm,
 	orig_arg = TREE_OPERAND (orig_arg, 0);
 
       if (!uses_template_parms (t)
-	  && !(force_conv ? uses_template_parms (orig_arg)
-	       : type_dependent_expression_p (orig_arg)))
+	  && !type_dependent_expression_p (orig_arg)
+	  && !(force_conv
+	       && !(same_type_ignoring_top_level_qualifiers_p
+		    (TREE_TYPE (orig_arg), t))
+	       && value_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/cpp0x/lambda/lambda-template18.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C
new file mode 100644
index 00000000000..e5e6e6a875b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C
@@ -0,0 +1,11 @@
+// PR c++/122127
+// { dg-do compile { target c++11 } }
+
+template <int> struct resize;
+template <int _Np> using resize_t = resize<_Np>;
+template <class _Ap> struct basic_mask {
+  void _M_chunk() {
+    constexpr int __rem = 1;
+    [&] { resize_t<__rem>(); }();
+  }
+};