[PATCH 2/2] completion: add proper public __git_complete

[Felipe Contreras <felipe.contreras@gmail.com>]

Back in 2012 I argued [1] for the introduction of a helper that would
allow users to specify aliases like:

  git_complete gf git_fetch

Back then there was pushback because there was no clear guideline for
public functions (git_complete vs _git_complete vs _GIT_complete), and
some aliases didn't actually work.

Fast-forward to 2020 and there's still no guideline for public
functions, and those aliases still don't work (even though I sent the
fixes).

This has not prevented people from using this function that is clearly
needed to setup custom aliases [2], and in fact it's the recommended
way. But it is cumbersome that the user must type:

  __git_complete gf _git_fetch

Or worse:

  __git_complete gk __gitk_main

8 years is more than enough time to stop waiting for the perfect to
come; let's define a public function (with the same name) that is
actually user-friendly:

  __git_complete gf git_fetch
  __git_complete gk gitk

While also maintaining backwards compatibility.

The logic is:

 1. If $2 exists, use it directly
 2. If not, check if __$2_main exists
 3. If not, check if _$2 exists
 4. If not, fail

[1] https://lore.kernel.org/git/1334524814-13581-1-git-send-email-felipe.contreras@gmail.com/
[2] https://stackoverflow.com/questions/342969/how-do-i-get-bash-completion-to-work-with-aliases

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
 contrib/completion/git-completion.bash | 31 ++++++++++++++++++++------
 t/t9902-completion.sh                  | 15 ++++++++++++-
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 463a3124da..6b0432a72d 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -3493,10 +3493,7 @@ __git_func_wrap ()
 	$1
 }
 
-# Setup completion for certain functions defined above by setting common
-# variables and workarounds.
-# This is NOT a public function; use at your own risk.
-__git_complete ()
+___git_complete ()
 {
 	local wrapper="__git_wrap${2}"
 	eval "$wrapper () { __git_func_wrap $2 ; }"
@@ -3504,13 +3501,33 @@ __git_complete ()
 		|| complete -o default -o nospace -F $wrapper $1
 }
 
-__git_complete git __git_main
-__git_complete gitk __gitk_main
+# Setup the completion for git commands
+# 1: command or alias
+# 2: function to call (e.g. `git`, `gitk`, `git_fetch`)
+__git_complete ()
+{
+	local func
+
+	if [[ "$(type -t $2)" == function ]]; then
+		func=$2
+	elif [[ "$(type -t __$2_main)" == function ]]; then
+		func=__$2_main
+	elif [[ "$(type -t _$2)" == function ]]; then
+		func=_$2
+	else
+		echo "ERROR: could not find function '$2'" 1>&2
+		return 1
+	fi
+	___git_complete $1 $func
+}
+
+___git_complete git __git_main
+___git_complete gitk __gitk_main
 
 # The following are necessary only for Cygwin, and only are needed
 # when the user has tab-completed the executable name and consequently
 # included the '.exe' suffix.
 #
 if [ "$OSTYPE" = cygwin ]; then
-	__git_complete git.exe __git_main
+	___git_complete git.exe __git_main
 fi
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 2e59fe4de0..53669a36f1 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -2381,10 +2381,23 @@ test_expect_success 'sourcing the completion script clears cached --options' '
 '
 
 test_expect_success '__git_complete' '
+	unset -f __git_wrap__git_main &&
+
 	__git_complete foo __git_main &&
 	test "$(type -t __git_wrap__git_main)" == function &&
+	unset -f __git_wrap__git_main &&
+
 	__git_complete gf _git_fetch &&
-	test "$(type -t __git_wrap_git_fetch)" == function
+	test "$(type -t __git_wrap_git_fetch)" == function &&
+
+	__git_complete foo git &&
+	test "$(type -t __git_wrap__git_main)" == function &&
+	unset -f __git_wrap__git_main &&
+
+	__git_complete gd git_diff &&
+	test "$(type -t __git_wrap_git_diff)" == function &&
+
+	test_must_fail __git_complete ga missing
 '
 
 test_done
-- 
2.30.0.rc2