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diff: ensure correct lifetime of external_diff_cmd

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According to getenv(3)'s notes:

    The implementation of getenv() is not required to be reentrant.  The
    string pointed to by the return value of getenv() may be statically
    allocated, and can be modified by a subsequent call to getenv(),
    putenv(3), setenv(3), or unsetenv(3).

Since strings returned by getenv() are allowed to change on subsequent
calls to getenv(), make sure to duplicate when caching external_diff_cmd
from environment.

This problem becomes apparent on Git for Windows since fe21c6b285
(mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)),
when the getenv() implementation provided in compat/mingw.c was changed
to keep a certain amount of alloc'ed strings and freeing them on
subsequent calls.

This fixes https://github.com/git-for-windows/git/issues/2007:

    $ yes n | git -c difftool.prompt=yes difftool fe21c6b285 fe21c6b285df~100

    Viewing (1/404): '.gitignore'
    Launch 'bc3' [Y/n]?
    Viewing (2/404): 'Documentation/.gitignore'
    Launch 'bc3' [Y/n]?
    Viewing (3/404): 'Documentation/Makefile'
    Launch 'bc3' [Y/n]?
    Viewing (4/404): 'Documentation/RelNotes/2.14.5.txt'
    Launch 'bc3' [Y/n]?
    Viewing (5/404): 'Documentation/RelNotes/2.15.3.txt'
    Launch 'bc3' [Y/n]?
    Viewing (6/404): 'Documentation/RelNotes/2.16.5.txt'
    Launch 'bc3' [Y/n]?
    Viewing (7/404): 'Documentation/RelNotes/2.17.2.txt'
    Launch 'bc3' [Y/n]?
    Viewing (8/404): 'Documentation/RelNotes/2.18.1.txt'
    Launch 'bc3' [Y/n]?
    Viewing (9/404): 'Documentation/RelNotes/2.19.0.txt'
    Launch 'bc3' [Y/n]? error: cannot spawn ¦?: No such file or directory
    fatal: external diff died, stopping at Documentation/RelNotes/2.19.1.txt

Signed-off-by: Kim Gybels <kgybels@infogroep.be>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Kim Gybels
2019-01-11 21:26:08 +01:00
committed by Junio C Hamano
parent 0d0ac3826a
commit 6776a84dae
1 changed files with 1 additions and 1 deletions
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2
diff.c
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@ -489,7 +489,7 @@ static const char *external_diff(void)
if (done_preparing)
return external_diff_cmd;
external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
external_diff_cmd = xstrdup_or_null(getenv("GIT_EXTERNAL_DIFF"));
if (!external_diff_cmd)
external_diff_cmd = external_diff_cmd_cfg;
done_preparing = 1;