When expanding an alias in a subdirectory, we setup the git_dir
(gently), read the config, and then restore the "env" (e.g. the current
working directory) so that the command specified by the alias can run
correctly.

What we failed to reset was the git_dir, meaning that in the most common
case, it was now pointing to a .git/ directory *in the subdirectory*.

This problem was identified in the GVFS fork, where a pre-command hook
was introduced to allow pre-fetching missing blobs.

An early quick fix in the GVFS fork simply built on top of the
save_env_before_alias() hack, introducing another hack that saves the
git_dir and restores it after an alias is expanded:

	https://github.com/Microsoft/git/commit/2d859ba3b

That is very hacky, though, and it is much better (although much more
involved, too) to fix this "properly", i.e. by replacing the ugly
save/restore logic by simply using the early config code path.

However, aliases are strange beasts.

When an alias refers to a single Git command (originally the sole
intention of aliases), the current working directory is restored to what
it had been before expanding the alias.

But when an alias starts with an exclamation point, i.e. referring to a
command-line to be interpreted by the shell, the current working
directory is no longer in the subdirectory but instead in the worktree's
top-level directory.

This is even true for worktrees added by `git worktree add`.

But when we are inside the .git/ directory, the current working
directory is *restored* to the subdirectory inside the .git/ directory.

In short, the logic is a bit complicated what is the expected current
working directory after expanding an alias and before actually running
it.

That is why this patch series had to expand the signature of the early
config machinery to return the additional information for aliases'
benefit.

Changes since v1:

- 1/8's commit message clarifies why the other early return in
  discover_git_directory() does not need an equivalent resetting of
  git_dir.

- 3/8's commit message fixes awkward language (thanks, Brandon!).

- the `worktree_dir` variables/parameters have been renamed to
  `cdup_dir` to clarify that they only get populated if the search for
  the .git/ directory determined that the current working directory
  is a subdirectory of the directory containing .git/.

Johannes Schindelin (8):
  discover_git_directory(): avoid setting invalid git_dir
  config: report correct line number upon error
  help: use early config when autocorrecting aliases
  read_early_config(): optionally return the worktree's top-level
    directory
  t1308: relax the test verifying that empty alias values are disallowed
  t7006: demonstrate a problem with aliases in subdirectories
  alias_lookup(): optionally return top-level directory
  Use the early config machinery to expand aliases

 alias.c                | 33 +++++++++++++++++++++-------
 builtin/help.c         |  2 +-
 cache.h                |  7 +++---
 config.c               |  7 +++---
 git.c                  | 59 ++++++--------------------------------------------
 help.c                 |  2 +-
 pager.c                |  4 ++--
 setup.c                | 13 +++++++++--
 t/helper/test-config.c |  2 +-
 t/t1308-config-set.sh  |  4 +++-
 t/t7006-pager.sh       | 11 ++++++++++
 11 files changed, 70 insertions(+), 74 deletions(-)

base-commit: 8d1b10321b20bd2a73a5b561cfc3cf2e8051b70b

Submitted-As: https://public-inbox.org/git/null