completion: add a helper function to get config variables

Currently there are a few completion functions that perform similar 'git
config' queries and filtering to get config variable names: the completion
of pretty aliases, aliases, and remote groups for 'git remote update'.

Unify those 'git config' queries in a helper function to eliminate code
duplication.

Though the helper functions to get pretty aliases and alieses are reduced
to mere one-liner wrappers around the newly added function, keep these
helpers still, because users' completion functions out there might depend
on them.  And they keep their callers a tad easier to read, too.

Add tests for the pretty alias and alias helper to show that they work
as before; not for the remote groups query, though, because that's not
extracted into a helper function and it's not worth the effort to do so
for a sole callsite.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -739,30 +739,29 @@ __git_compute_porcelain_commands ()
 	__git_porcelain_commands=$(__git_list_porcelain_commands)
 }
 
-__git_pretty_aliases ()
+# Lists all set config variables starting with the given section prefix,
+# with the prefix removed.
+__git_get_config_variables ()
 {
-	local i IFS=$'\n'
-	for i in $(git --git-dir="$(__gitdir)" config --get-regexp "pretty\..*" 2>/dev/null); do
+	local section="$1" i IFS=$'\n'
+	for i in $(git --git-dir="$(__gitdir)" config --get-regexp "$section\..*" 2>/dev/null); do
 		case "$i" in
-		pretty.*)
-			i="${i#pretty.}"
+		$section.*)
+			i="${i#$section.}"
 			echo "${i/ */}"
 			;;
 		esac
 	done
 }
 
+__git_pretty_aliases ()
+{
+	__git_get_config_variables "pretty"
+}
+
 __git_aliases ()
 {
-	local i IFS=$'\n'
-	for i in $(git --git-dir="$(__gitdir)" config --get-regexp "alias\..*" 2>/dev/null); do
-		case "$i" in
-		alias.*)
-			i="${i#alias.}"
-			echo "${i/ */}"
-			;;
-		esac
-	done
+	__git_get_config_variables "alias"
 }
 
 # __git_aliased_command requires 1 argument
@@ -2259,12 +2258,7 @@ _git_remote ()
 		__git_complete_remote_or_refspec
 		;;
 	update)
-		local i c='' IFS=$'\n'
-		for i in $(git --git-dir="$(__gitdir)" config --get-regexp "remotes\..*" 2>/dev/null); do
-			i="${i#remotes.}"
-			c="$c ${i/ */}"
-		done
-		__gitcomp "$c"
+		__gitcomp "$(__git_get_config_variables "remotes")"
 		;;
 	*)
 		;;

t/t9902-completion.sh

@@ -370,6 +370,28 @@ test_expect_success '__git_remotes - list remotes from $GIT_DIR/remotes and from
 	test_cmp expect actual
 '
 
+test_expect_success '__git_pretty_aliases' '
+	cat >expect <<-EOF &&
+	author
+	hash
+	EOF
+	test_config pretty.author "%an %ae" &&
+	test_config pretty.hash %H &&
+	__git_pretty_aliases >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '__git_aliases' '
+	cat >expect <<-EOF &&
+	ci
+	co
+	EOF
+	test_config alias.ci commit &&
+	test_config alias.co checkout &&
+	__git_aliases >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'basic' '
 	run_completion "git " &&
 	# built-in