mirror of
git://gcc.gnu.org/git/gcc.git
synced 2025-04-06 11:40:50 +08:00
9bdae0133d
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But the issue is, that VAR_DECL has been replaced by STRING_CST, so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 fix is to teach decay_conversion to return the address of array,
rather than returning its initializer.
Bootstrapped and tested on x86_64-unknown-linux-gnu against trunk.
gcc/cp/
PR c++/55311
* pt.c (decay_conversion): Do not return the initializer of an array.
gcc/testsuite/
PR c++/55311
* g++.dg/cpp0x/alias-decl-30.C: New test.
* g++.dg/init/array21.C: New test.
From-SVN: r194961
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.