Re: [PATCH v2] pager: do not unnecessarily set COLUMNS on Windows
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Jun 17, 2021, 02:20 UTC
- Message-ID
- <xmqqv96dmduh.fsf@gitster.g>
- In-Reply-To
- <pull.982.v2.git.1623847092299.gitgitgadget@gmail.com>
"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com> writes:
Show 43 quoted lines
> From: Johannes Schindelin <johannes.schindelin@gmx.de> > > Since https://github.com/gwsw/less/commit/bb0ee4e76c2, `less` prefers > the `COLUMNS` variable over asking ncurses itself. > > This is typically not a problem because we ask `TIOCGWINSZ` in Git, to > determine the correct value for `COLUMNS`, and then set that environment > variable. > > However, on Windows it _is_ a problem. The reason is that Git for > Windows uses a version of `less` that relies on the MSYS2 runtime to > interact with the pseudo terminal (typically inside a MinTTY window, > which is also aware of the MSYS2 runtime). Both MinTTY and `less.exe` > interact with that pseudo terminal via `ioctl()` calls (which the MSYS2 > runtime emulates even if there is no such thing on Windows). > > But `git.exe` itself is _not_ aware of the MSYS2 runtime, or for that > matter of that pseudo terminal, and has no way to call `ioctl()` or > `TIOCGWINSZ`. > > Therefore, `git.exe` will fall back to hard-coding 80 columns, no matter > what the actual terminal size is. > > But `less.exe` is totally able to interact with the MSYS2 runtime and > would not actually require Git's help (which actually makes things > worse here). So let's not override `COLUMNS` on Windows. > > Note: we do this _only_ on Windows, and _only_ if `TIOCGWINSZ` is not > defined, to reduce any potential undesired fall-out from this patch. > > This fixes https://github.com/git-for-windows/git/issues/3235 > > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> > --- > pager: do not unnecessarily set COLUMNS on Windows > > A recent upgrade of the "less" package in Git for Windows causes > problems. Here is a work-around. > > Changes since v1: > > * The commit message was reworded to clarify the underlying issue > better.
Thanks for an updated log message to clarify the problem description.
I think treating this as "less" specific band-aid is OK, but I do not think tying this to Windows is a good design choice.
The guiding principle for this change is more like "if we do not know and cannot learn the true value, internally assuming 80-columns as a last resort fallback may be OK, but do not export it for consumption for other people---they cannot tell if COLUMNS=80 they see us export is because we actually measured the terminal width and know it to be 80, or we just punted and used a fallback default", I think, and there is nothing Windows-specific in there, no?
In other words, if we use something like the attached as a "less specific band-aid" for now (i.e. direct replacement of your patch to fix the specific 'less' problem), and then later clean it up by actually returning -1 (or -80) from term_columns() as "we do not know" (or "we do not know---use the negation of this value as default"), we can help not just this paticular caller you touched, but all other callers of term_columns(), to make a more intelligent decision in the future if they wanted to. The root of the issue I think is because term_columns() does not give callers to tell if its returned value is merely a guess.
pager.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git c/pager.c w/pager.c index 3d37dd7ada..52f27a6765 100644 --- c/pager.c +++ w/pager.c @@ -11,6 +11,10 @@ static struct child_process pager_process = CHILD_PROCESS_INIT; static const char *pager_program; +/* Is the value coming back from term_columns() just a guess? */ +static int term_columns_guessed; + + static void close_pager_fds(void) { /* signal EOF to pager */ @@ -114,7 +118,8 @@ void setup_pager(void) { char buf[64]; xsnprintf(buf, sizeof(buf), "%d", term_columns()); - setenv("COLUMNS", buf, 0); + if (!term_columns_guessed) + setenv("COLUMNS", buf, 0); } setenv("GIT_PAGER_IN_USE", "true", 1); @@ -158,15 +163,20 @@ int term_columns(void) return term_columns_at_startup; term_columns_at_startup = 80; + term_columns_guessed = 1; col_string = getenv("COLUMNS"); - if (col_string && (n_cols = atoi(col_string)) > 0) + if (col_string && (n_cols = atoi(col_string)) > 0) { term_columns_at_startup = n_cols; + term_columns_guessed = 0; + } #ifdef TIOCGWINSZ else { struct winsize ws; - if (!ioctl(1, TIOCGWINSZ, &ws) && ws.ws_col) + if (!ioctl(1, TIOCGWINSZ, &ws) && ws.ws_col) { term_columns_at_startup = ws.ws_col; + term_columns_guessed = 0; + } } #endif