diagnostics: Add new option -fdiagnostics-plain-output

Adds the new option -fdiagnostics-plain-output, which is an alias for
several others:

    -fno-diagnostics-show-caret
    -fno-diagnostics-show-line-numbers
    -fdiagnostics-color=never
    -fdiagnostics-urls=never

The idea is that in the future, if the default behavior of diagnostics is
changed to add some fancy feature or other, then the
-fdiagnostics-plain-output option will also be changed accordingly so that
the old behavior is preserved in the presence of this option. This allows
us to use -fdiagnostics-plain-output in in the testsuite, such that the
testsuite (specifically the setting of TEST_ALWAYS_FLAGS in prune.exp)
does not need to be touched whenever diagnostics get a new look. This also
removes the need to add workarounds to compat.exp for every new option
that may be needed in a newer version of the compiler, but is not
supported in older versions.

gcc/ChangeLog:

	* common.opt: Add new option -fdiagnostics-plain-output.
	* doc/invoke.texi: Document it.
	* opts-common.c (decode_cmdline_options_to_array): Implement it.
	(decode_cmdline_option): Add missing const qualifier to argv.

libstdc++-v3/ChangeLog:

	* testsuite/lib/libstdc++.exp: Use the new option
	-fdiagnostics-plain-output.

gcc/testsuite/ChangeLog:

	* lib/prune.exp: Change TEST_ALWAYS_FLAGS to use -fdiagnostics-plain-output.
	* lib/c-compat.exp: Adapt to the prune.exp change.

1 files changed, 14 insertions, 0 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index dea1e18..70dc1ab 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -280,6 +280,7 @@ Objective-C and Objective-C++ Dialects}.
 @item Diagnostic Message Formatting Options
 @xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}.
 @gccoptlist{-fmessage-length=@var{n}  @gol
+-fdiagnostics-plain-output @gol
 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}  @gol
 -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]}  @gol
 -fdiagnostics-urls=@r{[}auto@r{|}never@r{|}always@r{]}  @gol
@@ -4291,6 +4292,19 @@ Note - this option also affects the display of the @samp{#error} and
 function/type/variable attribute.  It does not however affect the
 @samp{pragma GCC warning} and @samp{pragma GCC error} pragmas.
 
+@item -fdiagnostics-plain-output
+This option requests that diagnostic output look as plain as possible, which
+may be useful when running @command{dejagnu} or other utilities that need to
+parse diagnostics output and prefer that it remain more stable over time.
+@option{-fdiagnostics-plain-output} is currently equivalent to the following
+options:
+@gccoptlist{-fno-diagnostics-show-caret @gol
+-fno-diagnostics-show-line-numbers @gol
+-fdiagnostics-color=never @gol
+-fdiagnostics-urls=never}
+In the future, if GCC changes the default appearance of its diagnostics, the
+corresponding option to disable the new behavior will be added to this list.
+
 @item -fdiagnostics-show-location=once
 @opindex fdiagnostics-show-location
 Only meaningful in line-wrapping mode.  Instructs the diagnostic messages