From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 15 May 2025 15:07:53 +0000 (-0400)
Subject: c++: unifying specializations of non-primary tmpls [PR120161]
X-Git-Tag: releases/gcc-15.2.0~511
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=488c997aeb6669c333287a1f0063ce5fb706a8b5;p=thirdparty%2Fgcc.git

c++: unifying specializations of non-primary tmpls [PR120161]

Here unification of P=Wrap<int>::type, A=Wrap<long>::type wrongly
succeeds ever since r14-4112 which made the RECORD_TYPE case of unify
no longer recurse into template arguments for non-primary templates
(since they're a non-deduced context) and so the int/long mismatch that
makes the two types distinct goes unnoticed.

In the case of (comparing specializations of) a non-primary template,
unify should still go on to compare the types directly before returning
success.

	PR c++/120161

gcc/cp/ChangeLog:

	* pt.cc (unify) <case RECORD_TYPE>: When comparing specializations
	of a non-primary template, still perform a type comparison.

gcc/testsuite/ChangeLog:

	* g++.dg/template/unify13.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 0c430503f2849ebb20105695b8ad40d43d797c7b)
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 96230b444c0..be9af50f44f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -25797,10 +25797,10 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 			  INNERMOST_TEMPLATE_ARGS (CLASSTYPE_TI_ARGS (parm)),
 			  INNERMOST_TEMPLATE_ARGS (CLASSTYPE_TI_ARGS (t)),
 			  UNIFY_ALLOW_NONE, explain_p);
-	  else
-	    return unify_success (explain_p);
+	  gcc_checking_assert (t == arg);
 	}
-      else if (!same_type_ignoring_top_level_qualifiers_p (parm, arg))
+
+      if (!same_type_ignoring_top_level_qualifiers_p (parm, arg))
 	return unify_type_mismatch (explain_p, parm, arg);
       return unify_success (explain_p);
 
diff --git a/gcc/testsuite/g++.dg/template/unify13.C b/gcc/testsuite/g++.dg/template/unify13.C
new file mode 100644
index 00000000000..ec7ca9d17a4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/unify13.C
@@ -0,0 +1,18 @@
+// PR c++/120161
+
+template<class T, class U>
+struct mp_list { };
+
+template<class T>
+struct Wrap { struct type { }; };
+
+struct A : mp_list<Wrap<int>::type, void>
+         , mp_list<Wrap<long>::type, void> { };
+
+template<class U>
+void f(mp_list<Wrap<int>::type, U>*);
+
+int main() {
+  A a;
+  f(&a);
+}