check-ignore: Add option to ignore index contents

check-ignore currently shows how .gitignore rules would treat untracked
paths. Tracked paths do not generate useful output.  This prevents
debugging of why a path became tracked unexpectedly unless that path is
first removed from the index with `git rm --cached <path>`.

The option --no-index tells the command to bypass the check for the
path being in the index and hence allows tracked paths to be checked
too.

Whilst this behaviour deviates from the characteristics of `git add` and
`git status` its use case is unlikely to cause any user confusion.

Test scripts are augmented to check this option against the standard
ignores to ensure correct behaviour.

Signed-off-by: Dave Williams <dave@opensourcesolutions.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/git-check-ignore.txt b/Documentation/git-check-ignore.txt
index d2df487..ee2e091 100644
--- a/Documentation/git-check-ignore.txt
+++ b/Documentation/git-check-ignore.txt
@@ -45,6 +45,13 @@ OPTIONS
 	not be possible to distinguish between paths which match a
 	pattern and those which don't.
 
+--no-index::
+	Don't look in the index when undertaking the checks. This can
+	be used to debug why a path became tracked by e.g. `git add .`
+	and was not ignored by the rules as expected by the user or when
+	developing patterns including negation to match a path previously
+	added with `git add -f`.
+
 OUTPUT
 ------