Merge branch 'fc/bash-completion-alias-of-alias'

The command line completion script (in contrib/) learned to expand
commands that are alias of alias.

* fc/bash-completion-alias-of-alias:
  completion: bash: improve alias loop detection
  completion: bash: check for alias loop
  completion: bash: support recursive aliases

contrib/completion/git-completion.bash

@@ -1120,26 +1120,44 @@ __git_pretty_aliases ()
 # __git_aliased_command requires 1 argument
 __git_aliased_command ()
 {
-	local word cmdline=$(__git config --get "alias.$1")
-	for word in $cmdline; do
-		case "$word" in
-		\!gitk|gitk)
-			echo "gitk"
+	local cur=$1 last list word cmdline
+
+	while [[ -n "$cur" ]]; do
+		if [[ "$list" == *" $cur "* ]]; then
+			# loop detected
 			return
-			;;
-		\!*)	: shell command alias ;;
-		-*)	: option ;;
-		*=*)	: setting env ;;
-		git)	: git itself ;;
-		\(\))   : skip parens of shell function definition ;;
-		{)	: skip start of shell helper function ;;
-		:)	: skip null command ;;
-		\'*)	: skip opening quote after sh -c ;;
-		*)
-			echo "$word"
-			return
-		esac
+		fi
+
+		cmdline=$(__git config --get "alias.$cur")
+		list=" $cur $list"
+		last=$cur
+		cur=
+
+		for word in $cmdline; do
+			case "$word" in
+			\!gitk|gitk)
+				cur="gitk"
+				break
+				;;
+			\!*)	: shell command alias ;;
+			-*)	: option ;;
+			*=*)	: setting env ;;
+			git)	: git itself ;;
+			\(\))   : skip parens of shell function definition ;;
+			{)	: skip start of shell helper function ;;
+			:)	: skip null command ;;
+			\'*)	: skip opening quote after sh -c ;;
+			*)
+				cur="$word"
+				break
+			esac
+		done
 	done
+
+	cur=$last
+	if [[ "$cur" != "$1" ]]; then
+		echo "$cur"
+	fi
 }
 
 # Check whether one of the given words is present on the command line,

t/t9902-completion.sh

@@ -2195,6 +2195,25 @@ test_expect_success 'complete files' '
 	test_completion "git add mom" "momified"
 '
 
+test_expect_success "simple alias" '
+	test_config alias.co checkout &&
+	test_completion "git co m" <<-\EOF
+	master Z
+	mybranch Z
+	mytag Z
+	EOF
+'
+
+test_expect_success "recursive alias" '
+	test_config alias.co checkout &&
+	test_config alias.cod "co --detached" &&
+	test_completion "git cod m" <<-\EOF
+	master Z
+	mybranch Z
+	mytag Z
+	EOF
+'
+
 test_expect_success "completion uses <cmd> completion for alias: !sh -c 'git <cmd> ...'" '
 	test_config alias.co "!sh -c '"'"'git checkout ...'"'"'" &&
 	test_completion "git co m" <<-\EOF