On 7/27/22 7:09 PM, Joseph Myers wrote:
On Sun, 24 Jul 2022, Tom Honermann via Gcc-patches wrote:
Gcc's '#pragma GCC diagnostic' directives are processed in "early mode"
(see handle_pragma_diagnostic_early) for the C++ frontend and, as such,
require that the target diagnostic option be enabled for the preprocessor
(see c_option_is_from_cpp_diagnostics). This change modifies the
-Wc++20-compat option definition to register it as a preprocessor option
so that its associated diagnostics can be suppressed. The changes also
There are lots of C++ warning options, all of which should support pragma
suppression regardless of whether they are relevant to the preprocessor or
not. Do they all need this kind of handling, or is it only -Wc++20-compat
that has some kind of problem?
I had only checked -Wc++20-compat when working on the patch.
I did some spot checking now and confirmed that suppression works as
expected for C++ for at least the following warnings:
-Wuninitialized
-Warray-compare
-Wbool-compare
-Wtautological-compare
-Wterminate
I don't know the diagnostic framework well. As best I can tell, this
issue is specific to the -Wc++20-compat option and when the particular
diagnostic is issued (e.g., during lexing as opposed to during parsing).
The following call chains appear to be relevant.
cp_lexer_new_main -> cp_lexer_handle_early_pragma ->
c_invoke_early_pragma_handler
cp_parser_* -> cp_parser_pragma -> c_invoke_pragma_handler
(where * might be "declaration", "toplevel_declaration",
"class_head", "objc_interstitial_code", ...)
The -Wc++20-compat enabled warning regarding new keywords in C++20 is
issued from cp_lexer_get_preprocessor_token.
Tom.
