[PATCHv2 06/14] completion: don't disambiguate tags and branches

["SZEDER Gábor" <szeder.dev@gmail.com>]

When the completion script has to list only tags or only branches, it
uses the 'git for-each-ref' format 'refname:short', which makes sure
that all listed tags and branches are unambiguous.  However,
disambiguating tags and branches in these cases is wrong, because:

  - __git_tags(), the helper function listing possible tagname
    arguments for 'git tag', lists an ambiguous tag
    'refs/tags/ambiguous' as 'tags/ambiguous'.  Its only consumer,
    'git tag' expects its tagname argument to be under 'refs/tags/',
    thus it interprets that abgiguous tag as
    'refs/tags/tags/ambiguous'.  Clearly wrong.

  - __git_heads() lists possible branchname arguments for 'git branch'
    and possible 'branch.<branchname>' configuration subsections.
    Both of these expect branchnames to be under 'refs/heads/' and
    misinterpret a disambiguated branchname like 'heads/ambiguous'.

Furthermore, disambiguation involves several stat() syscalls for each
tag or branch, thus comes at a steep cost especially on Windows and/or
when there are a lot of tags or branches to be listed.

Use the 'git for-each-ref' format 'refname:strip=2' instead of
'refname:short' to avoid harmful disambiguation of tags and branches
in __git_tags() and __git_heads().

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 contrib/completion/git-completion.bash | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 882635f97..e129f674e 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -340,12 +340,12 @@ __git_index_files ()
 
 __git_heads ()
 {
-	__git for-each-ref --format='%(refname:short)' refs/heads
+	__git for-each-ref --format='%(refname:strip=2)' refs/heads
 }
 
 __git_tags ()
 {
-	__git for-each-ref --format='%(refname:short)' refs/tags
+	__git for-each-ref --format='%(refname:strip=2)' refs/tags
 }
 
 # Lists refs from the local (by default) or from a remote repository.
-- 
2.12.1.485.g1616aa492