[PATCH v2 2/2] completion: checkout: complete paths when ref given

[cornelius.weig@tngtech.com]

From: Cornelius Weig <cornelius.weig@tngtech.com>

Git-checkout completes words starting with '--' as options and other
words as refs. Even after specifying a ref, further words not starting
with '--' are completed as refs, which is invalid for git-checkout.

This commit ensures that after specifying a ref, further non-option
words are completed as paths. Four cases are considered:

 - If the word contains a ':', do not treat it as reference and use
   regular revlist completion.
 - If no ref is found on the command line, complete non-options as refs
   as before.
 - If the ref is HEAD or @, complete only with modified files because
   checking out unmodified files is a noop.
   This case also applies if no ref is given, but '--' is present.
 - If a ref other than HEAD or @ is found, offer only valid paths from
   that revision.

Note that one corner-case is not covered by the current implementation:
if a refname contains a ':' and is followed by '--' the completion would
not recognize the valid refname.

Signed-off-by: Cornelius Weig <cornelius.weig@tngtech.com>
---
 contrib/completion/git-completion.bash | 39 +++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 4ab119d..df46f62 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1068,7 +1068,7 @@ _git_bundle ()
 
 _git_checkout ()
 {
-	__git_has_doubledash && return
+	local i c=2 ref="" seen_double_dash=""
 
 	case "$cur" in
 	--conflict=*)
@@ -1081,13 +1081,36 @@ _git_checkout ()
 			"
 		;;
 	*)
-		# check if --track, --no-track, or --no-guess was specified
-		# if so, disable DWIM mode
-		local flags="--track --no-track --no-guess" track=1
-		if [ -n "$(__git_find_on_cmdline "$flags")" ]; then
-			track=''
-		fi
-		__gitcomp_nl "$(__git_refs '' $track)"
+		while [ $c -lt $cword ]; do
+			i="${words[c]}"
+			case "$i" in
+			--) seen_double_dash=1 ;;
+			-*|?*:*) ;;
+			*) ref="$i"; break ;;
+			esac
+			((c++))
+		done
+
+		case "$ref,$seen_double_dash,$cur" in
+		,,*:*)
+		    __git_complete_revlist_file
+		    ;;
+		,,*)
+			# check for --track, --no-track, or --no-guess
+			# if so, disable DWIM mode
+			local flags="--track --no-track --no-guess" track=1
+			if [ -n "$(__git_find_on_cmdline "$flags")" ]; then
+				track=''
+			fi
+			__gitcomp_nl "$(__git_refs '' $track)"
+			;;
+		,1,*|@,*|HEAD,*)
+			__git_complete_index_file "--modified"
+			;;
+		*)
+			__git_complete_tree_file "$ref" "$cur"
+			;;
+		esac
 		;;
 	esac
 }
-- 
2.10.2