EditorCore::save() wrote unconditionally via save_atomic and only THEN
recorded the new FileMeta. It never compared the on-disk identity against
the one the buffer read. So another editor's writes, or a `git checkout`,
were destroyed without a word --- the single worst data-loss path in the
editor, on its most-used command.
The comparison seam already existed and no caller used it: FileMeta is
PartialEq (mtime + size, sized so same-second edits still differ) and
file_io::current_meta reads it. The file_io module docstring even said
callers "should" compare before saving. Nobody did.
save() now refuses when writing would destroy content the buffer has
never seen:
* the buffer recorded a meta and the on-disk meta differs --- someone
else wrote the file;
* the buffer recorded NO meta (a `[new file]`, or a path set without
reading) yet a file now exists --- it was created underneath us.
A *missing* file is not a clobber: there is nothing to destroy, so
recreating a deleted file saves normally. An unstattable path falls
through and save_atomic reports the real error.
On refusal the status line says what happened and how to override, the
buffer keeps its unsaved edits, and `buffer.after-save` does not fire.
`M-x buffer.save-anyway` (ed.save_ignoring_disk_changes) overwrites
deliberately and re-syncs the meta, so an ordinary save works again.
Named `buffer.save-anyway`, not `save-buffer-anyway`, for two reasons: it
belongs in the `buffer.` namespace next to `buffer.save`, and the latter
outranked `buffer.save` as an M-x completion for "save" (which a lib test
caught).
This is the bug the autosave arc kept circling: Q#AS5's Fresh/Stale guard
refuses to auto-offer a recovery for an externally-changed file, but
nothing stopped save() from overwriting that same file.
Tests: tests/save_clobber_guard_acceptance.rs (6) --- refuses and leaves
their content intact, after-save does not fire on refusal, save-anyway
overwrites and re-syncs meta, unchanged files save repeatedly (the guard
must not trip on our own writes), a deleted file is recreated not
refused, and a `[new file]` buffer refuses once someone else creates the
file. Verified the tests bite: 4 of 6 fail with the guard disabled.
Gates: fmt + workspace clippy clean; lib 1499; crdt 1670; clobber 6; m1/m3
/m4 90/m5.8/m7.8/m8 10+15; autosave 29; desktop 11; persistence 5;
query-replace/completion/listview/overlay/cua green; GPU 58;
git diff --check clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
