[PATCH 07/12] completion: let 'for-each-ref' and 'ls-remote' filter matching refs

["SZEDER Gábor" <szeder.dev@gmail.com>]

When completing refs, several __git_refs() code paths list all the
refs from the refs/{heads,tags,remotes}/ hierarchy and then
__gitcomp_nl() iterates over those refs in a shell loop to filter out
refs not matching the current word to be completed.  This comes with a
considerable performance penalty when a repository contains a lot of
refs but the current word can be uniquely completed or when only a
handful of refs match the current word.

Specify appropriate globbing patterns to 'git for-each-ref' and 'git
ls-remote' to list only those refs that match the current word to be
completed.  This reduces the number of iterations in __gitcomp_nl()
from the number of refs to the number of matching refs.

This speeds up refs completion considerably when there are a lot of
non-matching refs to be filtered out.  Uniquely completing a branch in
a repository with 100k local branches, all packed, best of five:

  On Linux, before:

    $ time __git_complete_refs --cur=maste

    real    0m0.831s
    user    0m0.808s
    sys     0m0.028s

  After:

    real    0m0.119s
    user    0m0.104s
    sys     0m0.008s

  On Windows, before:

    real    0m1.480s
    user    0m1.031s
    sys     0m0.060s

  After:

    real    0m0.377s
    user    0m0.015s
    sys     0m0.030s

Strictly speaking this is a fundamental behavior change in
__git_refs(), a helper function that is likely used in users' custom
completion scriptlets.  However, arguably this change should be
harmless, because:

  - __git_refs() was only ever intended to feed refs to Bash's
    completion machinery, for which non-matching refs have to be
    filtered out anyway.

  - There were already code paths that list only matching refs
    (listing unique remote branches for 'git checkout's tracking
    DWIMery and listing full remote refs via 'git ls-remote').

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 contrib/completion/git-completion.bash |  14 +++--
 t/t9902-completion.sh                  | 102 +++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+), 5 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index d55eadfd1..615292f8b 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -394,7 +394,7 @@ __git_refs ()
 		case "$cur_" in
 		refs|refs/*)
 			format="refname"
-			refs="${cur_%/*}"
+			refs=("$cur_*" "$cur_*/**")
 			track=""
 			;;
 		*)
@@ -402,11 +402,13 @@ __git_refs ()
 				if [ -e "$dir/$i" ]; then echo $pfx$i; fi
 			done
 			format="refname:strip=2"
-			refs="refs/tags refs/heads refs/remotes"
+			refs=("refs/tags/$cur_*" "refs/tags/$cur_*/**"
+				"refs/heads/$cur_*" "refs/heads/$cur_*/**"
+				"refs/remotes/$cur_*" "refs/remotes/$cur_*/**")
 			;;
 		esac
 		__git_dir="$dir" __git for-each-ref --format="$pfx%($format)" \
-			$refs
+			"${refs[@]}"
 		if [ -n "$track" ]; then
 			# employ the heuristic used by git checkout
 			# Try to find a remote branch that matches the completion word
@@ -438,10 +440,12 @@ __git_refs ()
 		if [ "$list_refs_from" = remote ]; then
 			echo "HEAD"
 			__git for-each-ref --format="%(refname:strip=2)" \
-				"refs/remotes/$remote/" | sed -e "s#^$remote/##"
+				"refs/remotes/$remote/$cur_*" \
+				"refs/remotes/$remote/$cur_*/**" | sed -e "s#^$remote/##"
 		else
 			__git ls-remote "$remote" HEAD \
-				"refs/tags/*" "refs/heads/*" "refs/remotes/*" |
+				"refs/tags/$cur_*" "refs/heads/$cur_*" \
+				"refs/remotes/$cur_*" |
 			while read -r hash i; do
 				case "$i" in
 				*^{})	;;
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 7b42a686c..499be5879 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -837,6 +837,108 @@ test_expect_success '__git refs - exluding full refs' '
 	test_cmp expected "$actual"
 '
 
+test_expect_success 'setup for filtering matching refs' '
+	git branch matching/branch &&
+	git tag matching/tag &&
+	git -C otherrepo branch matching/branch-in-other &&
+	git fetch --no-tags other &&
+	rm -f .git/FETCH_HEAD
+'
+
+test_expect_success '__git_refs - only matching refs' '
+	cat >expected <<-EOF &&
+	HEAD
+	matching-branch
+	matching/branch
+	matching-tag
+	matching/tag
+	EOF
+	(
+		cur=mat &&
+		__git_refs >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - only matching refs - full refs' '
+	cat >expected <<-EOF &&
+	refs/heads/matching-branch
+	refs/heads/matching/branch
+	EOF
+	(
+		cur=refs/heads/mat &&
+		__git_refs >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - only matching refs - remote on local file system' '
+	cat >expected <<-EOF &&
+	HEAD
+	master-in-other
+	matching/branch-in-other
+	EOF
+	(
+		cur=ma &&
+		__git_refs otherrepo >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - only matching refs - configured remote' '
+	cat >expected <<-EOF &&
+	HEAD
+	master-in-other
+	matching/branch-in-other
+	EOF
+	(
+		cur=ma &&
+		__git_refs other >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - only matching refs - remote - full refs' '
+	cat >expected <<-EOF &&
+	refs/heads/master-in-other
+	refs/heads/matching/branch-in-other
+	EOF
+	(
+		cur=refs/heads/ma &&
+		__git_refs other >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - only matching refs - checkout DWIMery' '
+	cat >expected <<-EOF &&
+	HEAD
+	matching-branch
+	matching/branch
+	matching-tag
+	matching/tag
+	matching/branch-in-other
+	EOF
+	for remote_ref in refs/remotes/other/ambiguous \
+		refs/remotes/remote/ambiguous \
+		refs/remotes/remote/branch-in-remote
+	do
+		git update-ref $remote_ref master &&
+		test_when_finished "git update-ref -d $remote_ref"
+	done &&
+	(
+		cur=mat &&
+		__git_refs "" 1 >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success 'teardown after filtering matching refs' '
+	git branch -d matching/branch &&
+	git tag -d matching/tag &&
+	git update-ref -d refs/remotes/other/matching/branch-in-other
+'
+
 test_expect_success '__git_complete_refs - simple' '
 	sed -e "s/Z$//g" >expected <<-EOF &&
 	HEAD Z
-- 
2.11.0.555.g967c1bcb3