@@ -5454,7 +5454,7 @@ unify_overload_resolution_failure (bool explain_p, tree arg)
static tree
convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
{
- tree expr_type;
+ tree expr_type, initial_expr = expr;
/* Detect immediately string literals as invalid non-type argument.
This special-case is not needed for correctness (we would easily
@@ -5658,10 +5658,10 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
}
else
{
- tree decl;
+ tree decl = STRIP_NOPS (initial_expr);
- decl = ((TREE_CODE (expr) == ADDR_EXPR)
- ? TREE_OPERAND (expr, 0) : expr);
+ decl = ((TREE_CODE (initial_expr) == ADDR_EXPR)
+ ? TREE_OPERAND (initial_expr, 0) : initial_expr);
if (TREE_CODE (decl) != VAR_DECL)
{
error ("%qE is not a valid template argument of type %qT "
new file mode 100644
@@ -0,0 +1,15 @@
+// Origin PR c++/55311
+// { dg-do compile { target c++11 } }
+
+template <const char *const C, typename T>
+struct A
+{};
+
+struct B {};
+
+extern constexpr char HELLO_WORLD[] = "hello world";
+
+A<HELLO_WORLD, B> g; // <-- This works fine
+
+template <typename T>
+using PartiallySpecialized = A<HELLO_WORLD, T>; // <-- This fails
Hello, Consider this test case: 1 template <const char *const C, typename T> 2 struct A 3 {}; 4 5 struct B {}; 6 7 extern constexpr char HELLO_WORLD[] = "hello world"; 8 9 A<HELLO_WORLD, B> g; // <-- This works fine 10 11 template <typename T> 12 using PartiallySpecialized = A<HELLO_WORLD, T>; // <-- This fails 13 At line 12 G++ fails to instantiate the alias template that has a string variable initialized with a string literal, with the error message: test.cc:12:46: error: ‘"hello world"’ is not a valid template argument of type ‘const char*’ because ‘"hello world"’ is not a variable using PartiallySpecialized = A<HELLO_WORLD, T>; // <-- This fails ^ Note that instantiating the template A at line 9 with the same arguments as in the problematic case above works. This happens in the context of lookup_template_class_1, when it handles the alias template instantiation A<HELLO_WORLD, T> and thus passes the VAR_DECL for HELLO_WORLD to convert_nontype_argument. Note that from there decay_conversion replaces the the VAR_DECL with its STRING_CST initializer[1]. Latter on, convert_nontype_argument checks that the HELLO_WORLD constant it received as argument was indeed a VAR_DECL: else { tree decl; decl = ((TREE_CODE (expr) == ADDR_EXPR) ? TREE_OPERAND (expr, 0) : expr); if (TREE_CODE (decl) != VAR_DECL) { error ("%qE is not a valid template argument of type %qT " "because %qE is not a variable", expr, type, decl); return NULL_TREE; } But the issue is, that VAR_DECL has been replaced by STRING_CST, so the last 'if' above fails. The idea of the patch I am proposing is to do the test above on the argument received by convert_nontype_argument rather than on its modified (decayed?) form. [1]: The relacement of the VAR_DECL by its initializer is done by decay_conversion by callig decl_constant_value_safe. That replacement doesn't happen if processing_template_decl is not set. That's why it doesn't happen for the class template instantiation at line 9, leading to no error message there. Bootstrapped and tested on x86_64-unknown-linux-gnu against trunk. gcc/cp/ PR c++/55311 * pt.c (convert_nontype_argument<array arguments>): Perform the sanity tests on the initial expression otherwise decay_conversion might have made us loose some information. gcc/testsuite/ PR c++/55311 * g++.dg/cpp0x/alias-decl-30.C: New test. --- gcc/cp/pt.c | 8 ++++---- gcc/testsuite/g++.dg/cpp0x/alias-decl-30.C | 15 +++++++++++++++ 2 files changed, 19 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-30.C