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c-family: Prevent -Wformat warnings with u8 strings [PR105626]

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The <https://gcc.gnu.org/pipermail/gcc/2022-May/238679.html> thread
seems to have concluded that -Wformat shouldn't warn about

  printf((const char*) u8"test %d\n", 1);

saying "format string is not an array of type 'char'".  This code
is not an aliasing violation, and there are no I/O functions for u8
strings, so the const char * cast is OK and shouldn't be disregarded.

	PR c++/105626

gcc/c-family/ChangeLog:

	* c-format.cc (check_format_arg): Don't emit -Wformat warnings with
	u8 strings.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wformat-char8_t-1.C: New test.
This commit is contained in:
Marek Polacek 2022-07-05 14:22:26 -04:00
parent 1d2aa26248
commit 543828e79b
2 changed files with 12 additions and 1 deletions
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3
gcc/c-family/c-format.cc
View file

@ -1742,7 +1742,8 @@ check_format_arg (void *ctx, tree format_tree,
}
tree underlying_type
= TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (format_tree)));
if (underlying_type != char_type_node)
if (underlying_type != char_type_node
&& !(flag_char8_t && underlying_type == char8_type_node))
{
if (underlying_type == char16_type_node
|| underlying_type == char32_type_node

10
gcc/testsuite/g++.dg/warn/Wformat-char8_t-1.C Normal file
View file

@ -0,0 +1,10 @@
// PR c++/105626
// { dg-do compile { target c++11 } }
// { dg-options "-Wformat" }
// { dg-additional-options "-fchar8_t" { target c++17_down } }
int main()
{
__builtin_printf((const char*) u8"test %d\n", 1); // { dg-bogus "format string" }
return 0;
}