From edec2660ff4890ecf8cc191f7c92cf527de51fe2 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 10 Jun 2021 18:31:21 -0400
Subject: [PATCH] c++: matching deduced template template parameters [PR67829]
During deduction, when the template of the argument for a bound ttp
is a template template parameter, we need to consider the
TEMPLATE_TEMPLATE_PARAMETER for matching rather than the TEMPLATE_DECL
thereof, because the canonical form of a template template parameter as
a template argument is the former tree, not the latter.
PR c++/67829
gcc/cp/ChangeLog:
* pt.c (unify) <case BOUND_TEMPLATE_TEMPLATE_PARM>: When
the TEMPLATE_DECL of a BOUND_TEMPLATE_TEMPLATE_PARM argument is
a template template parameter, adjust to the
TEMPLATE_TEMPLATE_PARAMETER before falling through.
gcc/testsuite/ChangeLog:
* g++.dg/template/ttp34.C: New test.
* g++.dg/template/ttp34a.C: New test.
* g++.dg/template/ttp34b.C: New test.
---
gcc/cp/pt.c | 4 ++++
gcc/testsuite/g++.dg/template/ttp34.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/template/ttp34a.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/template/ttp34b.C | 14 ++++++++++++++
4 files changed, 46 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/template/ttp34.C
create mode 100644 gcc/testsuite/g++.dg/template/ttp34a.C
create mode 100644 gcc/testsuite/g++.dg/template/ttp34b.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index b0155a9c370a..d87382dba75e 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -23555,6 +23555,10 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
return 1;
arg = TYPE_TI_TEMPLATE (arg);
+ if (DECL_TEMPLATE_TEMPLATE_PARM_P (arg))
+ /* If the template is a template template parameter, use the
+ TEMPLATE_TEMPLATE_PARM for matching. */
+ arg = TREE_TYPE (arg);
/* Fall through to deduce template name. */
}
diff --git a/gcc/testsuite/g++.dg/template/ttp34.C b/gcc/testsuite/g++.dg/template/ttp34.C
new file mode 100644
index 000000000000..67094063ba51
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp34.C
@@ -0,0 +1,14 @@
+// PR c++/67829
+
+template<class> class Purr;
+
+template<template<class> class, class, class>
+class Meow;
+
+template<template<class> class P>
+class Meow<P, P<int>, int> { }; // 1
+
+template<template<class> class P, class T>
+class Meow<P, P<int>, T>; // 2
+
+Meow<Purr, Purr<int>, int> kitty;
diff --git a/gcc/testsuite/g++.dg/template/ttp34a.C b/gcc/testsuite/g++.dg/template/ttp34a.C
new file mode 100644
index 000000000000..e3303dcf2125
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp34a.C
@@ -0,0 +1,14 @@
+// PR c++/67829
+
+template<class> class Purr;
+
+template<template<class> class, class>
+class Meow;
+
+template<template<class> class P>
+class Meow<P, P<int> > { }; // 1
+
+template<template<class> class P, class T>
+class Meow<P, P<T> >; // 2
+
+Meow<Purr, Purr<int> > kitty;
diff --git a/gcc/testsuite/g++.dg/template/ttp34b.C b/gcc/testsuite/g++.dg/template/ttp34b.C
new file mode 100644
index 000000000000..ed3b3e8ab059
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp34b.C
@@ -0,0 +1,14 @@
+// PR c++/67829
+
+template<class> class Purr;
+
+template<class, template<class> class>
+class Meow;
+
+template<template<class> class P>
+class Meow<P<int>, P> { }; // 1
+
+template<template<class> class P, class T>
+class Meow<P<T>, P>; // 2
+
+Meow<Purr<int>, Purr> kitty;
--
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