This patch makes coerce_template_template_parm consider a coercion
successful if the result of calling tsubst on a template template parm
is a dependent type even when the desired argument type is non-dependent.
For the test case below, TREE_TYPE (parm) is B and TREE_TYPE (arg) is
int. After calling tsubst on the parm the resulting type is still B, a
dependent type. Without checking that the resulting type is dependent,
the function would return 0 because same_type_p would return false.
Bootstrap + regtest of this change was successful on
x86_64-unknown-linux-gnu. Does this patch look OK?
gcc/cp/ChangeLog:
* pt.c (coerce_template_template_parm) [PARM_DECL]: Don't
return 0 if tsubst returns a dependent type.
gcc/testsuite/ChangeLog:
* g++.dg/template/pr66686.C: New test.
---
gcc/cp/pt.c | 12 +++++++-----
gcc/testsuite/g++.dg/template/pr66686.C | 15 +++++++++++++++
2 files changed, 22 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/pr66686.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 2b37460..d7768a8 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -6357,11 +6357,13 @@ coerce_template_template_parm (tree parm,
D<int, C> d;
i.e. the parameter list of TT depends on earlier parameters. */
- if (!uses_template_parms (TREE_TYPE (arg))
- && !same_type_p
- (tsubst (TREE_TYPE (parm), outer_args, complain, in_decl),
- TREE_TYPE (arg)))
- return 0;
+ if (!uses_template_parms (TREE_TYPE (arg)))
+ {
+ tree t = tsubst (TREE_TYPE (parm), outer_args, complain, in_decl);
+ if (!uses_template_parms (t)
+ && !same_type_p (t, TREE_TYPE (arg)))
+ return 0;
+ }
if (TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (arg))
&& !TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm)))
diff --git a/gcc/testsuite/g++.dg/template/pr66686.C
b/gcc/testsuite/g++.dg/template/pr66686.C
new file mode 100644
index 0000000..d8aea62
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr66686.C
@@ -0,0 +1,15 @@
+// PR c++/66686
+
+template <int>
+struct Y { };
+
+template <class B, template <template <B> class Z> class C>
+struct X
+{
+ C<Y> a; // { dg-bogus "mismatch" }
+};
+
+template <template <int> class>
+struct A { };
+
+X<int, A> a;
--
2.5.0.rc0.5.g91e10c5.dirty
