Re: possible bug in autocompletion

[Jeff King <peff@peff.net>]

On Tue, Jul 17, 2012 at 11:10:39AM +0200, Jeroen Meijer wrote:

> We have a tag name with some special characters. The tag name is
> 'Build%20V%20${bamboo.custom.jiraversion.name}%20Build%20721'. In
> somecases where autocompletion is used an error is given, such as
> 'bash: Build%20V%20${bamboo.custom.jiraversion.name}%20Build%20721:
> bad substitution'. This can be invoked by typing 'git checkout B' and
> then pressing tab.

Hrm. Weird. It is the "${}" in your tag name that causes the problem,
and it all boils down to bash trying to do parameter expansion on the
contents of "compgen -W". You can see it in a much simpler example:

  $ echo '${foo.bar}' ;# no expansion, works
  ${foo.bar}

  $ echo "${foo.bar}" ;# expansion, bash rightfully complains
  bash: ${foo.bar}: bad substitution

  $ compgen -W '${foo.bar}' f
  bash: ${foo.bar}: bad substitution

In the final command, we use single-quotes so there is no expansion
before the command execution. So it happens internally to compgen.
documentation for compgen says:

  -W wordlist
          The  wordlist is split using the characters in the IFS special vari‐
          able as delimiters, and each resultant word is expanded.  The possi‐
          ble  completions  are  the members of the resultant list which match
          the word being completed.

Which seems kind of crazy to me. It means that we need to be quoting
everything we feed to compgen to avoid accidental expansion. But I guess
bash is not likely to change anytime soon, so we probably need to work
around it.

> Of course; the tag is useless but still I guess this is a bug in the
> autocompletion of git.

Yeah, that tag is crazy. But this can happen anywhere that we feed
arbitrary data to compgen. Try this:

  echo content >'${foo.bar}' &&
  git add . &&
  git commit

  git show HEAD:<tab>

which generates the same error. Or even a file named "foo$bar", which is
much more likely; that will not generate an error, but it will expand
$bar and produce erroneous results. I think we also have issues with
files with single and double quotes in them.

Something like this seems to fix it for me:

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index ffedce7..2d20824 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -261,7 +261,12 @@ __gitcomp ()
 __gitcomp_nl ()
 {
 	local IFS=$'\n'
-	COMPREPLY=($(compgen -P "${2-}" -S "${4- }" -W "$1" -- "${3-$cur}"))
+	local words=$1
+	words=${words//\\/\\\\}
+	words=${words//\$/\\\$}
+	words=${words//\'/\\\'}
+	words=${words//\"/\\\"}
+	COMPREPLY=($(compgen -P "${2-}" -S "${4- }" -W "$words" -- "${3-$cur}"))
 }
 
 __git_heads ()

but it is awfully ugly. Maybe completion experts can offer a better
solution.

-Peff