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sequencer: do not export GIT_DIR and GIT_WORK_TREE for 'exec'

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Commands executed from `git rebase --exec` can give different behavior
from within that environment than they would outside of it, due to the
fact that sequencer.c exports both GIT_DIR and GIT_WORK_TREE.  For
example, if the relevant script calls something like

  git -C ../otherdir log --format=%H --no-walk

the user may be surprised to find that the command above does not show a
commit hash from ../otherdir, because $GIT_DIR prevents automatic gitdir
detection and makes the -C option useless.

This is a regression in behavior from the original legacy
implemented-in-shell rebase.  It is perhaps rare for it to cause
problems in practice, especially since most small problems that were
caused by this area of bugs has been fixed-up in the past in a way that
masked the particular bug observed without fixing the real underlying
problem.

An explanation of how we arrived at the current situation is perhaps
merited.  The setting of GIT_DIR and GIT_WORK_TREE done by sequencer.c
arose from a sequence of historical accidents:

* When rebase was implemented as a shell command, it would call
  git-sh-setup, which among other things would set GIT_DIR -- but not
  export it.  This meant that when rebase --exec commands were run via
      /bin/sh -c "$COMMAND"
  they would not inherit the GIT_DIR setting.  The fact that GIT_DIR
  was not set in the run $COMMAND is the behavior we'd like to restore.

* When the rebase--helper builtin was introduced to allow incrementally
  replacing shell with C code, we had an implementation that was half
  shell, half C.  In particular, commit 18633e1a22 ("rebase -i: use the
  rebase--helper builtin", 2017-02-09) added calls to
      exec git rebase--helper ...
  which caused rebase--helper to inherit the GIT_DIR environment
  variable from the shell.  git's setup would change the environment
  variable from an absolute path to a relative one (".git"), but would
  leave it set.  This meant that when rebase --exec commands were run
  via
      run_command_v_opt(...)
  they would inherit the GIT_DIR setting.

* In commit 09d7b6c6fa ("sequencer: pass absolute GIT_DIR to exec
  commands", 2017-10-31), it was noted that the GIT_DIR caused problems
  with some commands; e.g.
      git rebase --exec 'cd subdir && git describe' ...
  would have GIT_DIR=.git which was invalid due to the change to the
  subdirectory.  Instead of questioning why GIT_DIR was set, that commit
  instead made sequencer change GIT_DIR to be an absolute path and
  explicitly export it via
      argv_array_pushf(&child_env, "GIT_DIR=%s", absolute_path(get_git_dir()));
      run_command_v_opt_cd_env(..., child_env.argv)

* In commit ab5e67d751 ("sequencer: pass absolute GIT_WORK_TREE to exec
  commands", 2018-07-14), it was noted that when GIT_DIR is set but
  GIT_WORK_TREE is not, that we do not discover GIT_WORK_TREE but just
  assume it is '.'.  That is incorrect if trying to run commands from a
  subdirectory.  However, rather than question why GIT_DIR was set, that
  commit instead also added GIT_WORK_TREE to the list of things to
  export.

Each of the above problems would have been fixed automatically when
git-rebase became a full builtin, had it not been for the fact that
sequencer.c started exporting GIT_DIR and GIT_WORK_TREE in the interim.
Stop exporting them now.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Acked-by: Johannes Altmanninger <aclopte@gmail.com>
Acked-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2021-12-04 05:36:59 +00:00 committed by Junio C Hamano
parent e9d7761bb9
commit 434e0636db
2 changed files with 24 additions and 8 deletions
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9
sequencer.c
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@ -3495,17 +3495,12 @@ static int error_failed_squash(struct repository *r,
static int do_exec(struct repository *r, const char *command_line)
{
struct strvec child_env = STRVEC_INIT;
const char *child_argv[] = { NULL, NULL };
int dirty, status;
fprintf(stderr, _("Executing: %s\n"), command_line);
child_argv[0] = command_line;
strvec_pushf(&child_env, "GIT_DIR=%s", absolute_path(get_git_dir()));
strvec_pushf(&child_env, "GIT_WORK_TREE=%s",
absolute_path(get_git_work_tree()));
status = run_command_v_opt_cd_env(child_argv, RUN_USING_SHELL, NULL,
child_env.v);
status = run_command_v_opt(child_argv, RUN_USING_SHELL);
/* force re-reading of the cache */
if (discard_index(r->index) < 0 || repo_read_index(r) < 0)
@ -3535,8 +3530,6 @@ static int do_exec(struct repository *r, const char *command_line)
status = 1;
}
strvec_clear(&child_env);
return status;
}

23
t/t3409-rebase-environ.sh Executable file
View File

@ -0,0 +1,23 @@
#!/bin/sh
test_description='git rebase interactive environment'
. ./test-lib.sh
test_expect_success 'setup' '
test_commit one &&
test_commit two &&
test_commit three
'
test_expect_success 'rebase --exec does not muck with GIT_DIR' '
git rebase --exec "printf %s \$GIT_DIR >environ" HEAD~1 &&
test_must_be_empty environ
'
test_expect_success 'rebase --exec does not muck with GIT_WORK_TREE' '
git rebase --exec "printf %s \$GIT_WORK_TREE >environ" HEAD~1 &&
test_must_be_empty environ
'
test_done