[PATCH 1/4] bash: improve aliased command recognition

To support completion for aliases, the completion script tries to figure out which git command is invoked by an alias. Its implementation in __git_aliased_command() is rather straightforward: it returns the first word from the alias. For simple aliases starting with the git command (e.g. alias.last = cat-file commit HEAD) this gives the right results. Unfortunately, it does not work with shell command aliases, which can get rather complex, as illustrated by one of Junio's aliases:

[alias]
    lgm = "!sh -c 'GIT_NOTES_REF=refs/notes/amlog git log \"$@\" || :' -"

In this case the current implementation returns "!sh" as the aliased git command, which is obviosly wrong.

The full parsing of a shell command alias like that in the completion code is clearly unfeasible. However, we can easily improve on aliased command recognition by eleminating stuff that is definitely not a git command: shell commands (anything starting with '!'), command line options (anything starting with '-'), environment variables (anything with a '=' in it), and git itself. This way the above alias would be handled correctly, and the completion script would correctly recognize "log" as the aliased git command.

Of course, this solution is not perfect either, and could be fooled easily. It's not hard to construct an alias, in which a word does not match any of these filter patterns, but is still not a git command (e.g. by setting an environment variable to a value which contains spaces). It may even return false positives, when the output of a git command is piped into an other git command, and the second gets the command line options via $@, but options for the first one are offered. However, the following patches will enable the user to supply custom completion scripts for aliases, which can be used to remedy these problematic cases.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
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 contrib/completion/git-completion.bash |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)