diagnostics: Add %{...%} pretty-format support for URLs and use it in -Wpsabi diagnostics

The following patch attempts to use the diagnostics URL support if available
to provide more information about the C++17 empty base and C++20
[[no_unique_address]] empty class ABI changes in -Wpsabi diagnostics.

in GCC 10.1 at the end of the diagnostics is then in some terminals
underlined with a dotted line and points to a (to be written) anchor in
gcc-10/changes.html which we need to write anyway.

2020-04-29  Jakub Jelinek  <jakub@redhat.com>

	* configure.ac (-with-changes-root-url): New configure option,
	defaulting to https://gcc.gnu.org/.
	* Makefile.in (CFLAGS-opts.o): Define CHANGES_ROOT_URL for
	opts.c.
	* pretty-print.c (get_end_url_string): New function.
	(pp_format): Handle %{ and %} for URLs.
	(pp_begin_url): Use pp_string instead of pp_printf.
	(pp_end_url): Use get_end_url_string.
	* opts.h (get_changes_url): Declare.
	* opts.c (get_changes_url): New function.
	* config/rs6000/rs6000-call.c: Include opts.h.
	(rs6000_discover_homogeneous_aggregate): Use %{in GCC 10.1%} instead
	of just in GCC 10.1 in diagnostics and add URL.
	* config/arm/arm.c (aapcs_vfp_is_call_or_return_candidate): Likewise.
	* config/aarch64/aarch64.c (aarch64_vfp_is_call_or_return_candidate):
	Likewise.
	* config/s390/s390.c (s390_function_arg_vector,
	s390_function_arg_float): Likewise.
	* configure: Regenerated.

	* c-format.c (PP_FORMAT_CHAR_TABLE): Add %{ and %}.

1 files changed, 10 insertions, 0 deletions

diff --git a/gcc/opts.c b/gcc/opts.c
index c212a1a..12c0098 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -3190,6 +3190,16 @@ get_option_url (diagnostic_context *, int option_index)
     return NULL;
 }
 
+/* Given "gcc-10/changes.html#foobar", return that URL under
+   CHANGES_ROOT_URL (see --with-changes-root-url).
+   The caller is responsible for freeing the returned string.  */
+
+char *
+get_changes_url (const char *str)
+{
+  return concat (CHANGES_ROOT_URL, str, NULL);
+}
+
 #if CHECKING_P
 
 namespace selftest {