[Valgrind-developers] Proposed VALGRIND_TRY_OPTS patch

[D. J. B. <dj...@cr...>]

This patch adds support for VALGRIND_TRY_OPTS that's like VALGRIND_OPTS
but skips unsupported options.

VALGRIND_TRY_OPTS is always after VALGRIND_OPTS. For more fine-grained
control over order, there's also a new --try that skips the next option
if the next option is unsupported. If support for --try is added to the
forthcoming 3.26 via this patch, and then support for some specific --X
is added in (say) valgrind 3.30 or valgrind 2027.10, then scripts can
use --try --X to opportunistically enable --X without breaking 3.26,
3.27, 3.28, and 3.29. Of course, setting --X in VALGRIND_TRY_OPTS has
the big advantage of also not breaking 3.25, 3.24, etc. Anyway,
VALGRIND_TRY_OPTS is implemented internally on top of --try.

The patch adds user-facing documentation of VALGRIND_TRY_OPTS and --try
in docs/xml/manual-core.xml and in valgrind --help. This patch is on top
of HEAD, and adds 18 tests for VALGRIND_TRY_OPTS and --try, while also
tweaking a few existing tests to reflect the changes to --help. A full
"make regtest" under Debian 12 on a Zen 2 shows no new failures compared
to HEAD.

The existing documentation of default options was missing a statement
that default options don't work for pre-early options, and a statement
that default options are disabled by --command-line-only=yes. This patch
includes the missing documentation. This is conceptually separate from
the rest of the patch, but I think anyone reviewing the code+tests for
the rest of the patch will naturally end up bumping into these issues.

---D. J. Bernstein