fix(cwd): E812 when a message opens a window during a file read #41458

Problem:
When ui2 is enabled, opening an already-open file in another Neovim
instance results in the error `E812: Autocommands changed buffer…`.

Analysis:
On E812 the file is not loaded.  The default SwapExists handler notifies
`W325: Ignoring swapfile…`, and ui2 shows that message by opening
a window, which is a temp context switch.  `ctx_dirs_restore()`
re-shortens every buffer name on the way out, and `shorten_buf_fname()`
always frees and reallocates `b_sfname`.  `readfile()` aliases `b_fname`
across `check_need_swap()` and compares the pointer to detect a rename.

Regression by b296666e419c, which replaced the `cs_save_sfname` restore
(that kept curbuf's pointer) with `shorten_fnames(true)`.

Solution:
Keep the allocation in `shorten_buf_fname()` when the short name is
unchanged.  Pointer stability is what the E200/E201/E812 guards actually
assert.

0 files changed, 0 insertions, 0 deletions