completion: add optional ignore-case when matching refs

If GIT_COMPLETION_IGNORE_CASE is set, --ignore-case will be added to
git for-each-ref calls so that refs can be matched case insensitively,
even when running on case sensitive filesystems.

Signed-off-by: Alison Winters <alisonatwork@outlook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -58,6 +58,12 @@
 #
 #     When set to "1" suggest all options, including options which are
 #     typically hidden (e.g. '--allow-empty' for 'git commit').
+#
+#   GIT_COMPLETION_IGNORE_CASE
+#
+#     When set, uses for-each-ref '--ignore-case' to find refs that match
+#     case insensitively, even on systems with case sensitive file systems
+#     (e.g., completing tag name "FOO" on "git checkout f<TAB>").
 
 case "$COMP_WORDBREAKS" in
 *:*) : great ;;
@@ -646,6 +652,7 @@ __git_heads ()
 	local pfx="${1-}" cur_="${2-}" sfx="${3-}"
 
 	__git for-each-ref --format="${pfx//\%/%%}%(refname:strip=2)$sfx" \
+			${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 			"refs/heads/$cur_*" "refs/heads/$cur_*/**"
 }
 
@@ -659,6 +666,7 @@ __git_remote_heads ()
 	local pfx="${1-}" cur_="${2-}" sfx="${3-}"
 
 	__git for-each-ref --format="${pfx//\%/%%}%(refname:strip=2)$sfx" \
+			${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 			"refs/remotes/$cur_*" "refs/remotes/$cur_*/**"
 }
 
@@ -669,6 +677,7 @@ __git_tags ()
 	local pfx="${1-}" cur_="${2-}" sfx="${3-}"
 
 	__git for-each-ref --format="${pfx//\%/%%}%(refname:strip=2)$sfx" \
+			${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 			"refs/tags/$cur_*" "refs/tags/$cur_*/**"
 }
 
@@ -688,6 +697,7 @@ __git_dwim_remote_heads ()
 	# but only output if the branch name is unique
 	__git for-each-ref --format="$fer_pfx%(refname:strip=3)$sfx" \
 		--sort="refname:strip=3" \
+		${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 		"refs/remotes/*/$cur_*" "refs/remotes/*/$cur_*/**" | \
 	uniq -u
 }
@@ -765,6 +775,7 @@ __git_refs ()
 			;;
 		esac
 		__git_dir="$dir" __git for-each-ref --format="$fer_pfx%($format)$sfx" \
+			${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 			"${refs[@]}"
 		if [ -n "$track" ]; then
 			__git_dwim_remote_heads "$pfx" "$match" "$sfx"
@@ -787,6 +798,7 @@ __git_refs ()
 			$match*)	echo "${pfx}HEAD$sfx" ;;
 			esac
 			__git for-each-ref --format="$fer_pfx%(refname:strip=3)$sfx" \
+				${GIT_COMPLETION_IGNORE_CASE+--ignore-case} \
 				"refs/remotes/$remote/$match*" \
 				"refs/remotes/$remote/$match*/**"
 		else

t/t9902-completion.sh

@@ -2255,6 +2255,21 @@ test_expect_success 'checkout completes ref names' '
 	EOF
 '
 
+test_expect_success 'checkout does not match ref names of a different case' '
+	test_completion "git checkout M" ""
+'
+
+test_expect_success 'checkout matches case insensitively with GIT_COMPLETION_IGNORE_CASE' '
+	(
+		GIT_COMPLETION_IGNORE_CASE=1 &&
+		test_completion "git checkout M" <<-\EOF
+		main Z
+		mybranch Z
+		mytag Z
+		EOF
+	)
+'
+
 test_expect_success 'git -C <path> checkout uses the right repo' '
 	test_completion "git -C subdir -C subsubdir -C .. -C ../otherrepo checkout b" <<-\EOF
 	branch-in-other Z