[PATCH] completion: add and use the __git_get_config_subsection helper function

[PATCH] completion: add and use the __git_get_config_subsection helper function

[SZEDER Gábor]

Our Bash completion script recently learned to complete configured
trailer key aliases for 'git config --trailer=<TAB>', but the helper
function extracting the key alias from 'git config's output, i.e. the
subsection from 'trailer.*.key', ended up more complex than necessary,
with considerable overhead from executing four external processes in a
pipe.

Replace those commands in the pipe with a simple shell loop using only
a pair of parameter expansions and a builtin 'echo', which is easier
to understand and should perform better (I assume that users don't
have that many subsections in any particular section to make the
processing with an external process (let alone four) worth it).

And while at it, let's extract this loop into a generic
__git_get_config_subsections() helper function, as it might be useful
elsewhere in the future as well (at the moment it isn't, AFAICT).

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 contrib/completion/git-completion.bash | 14 +++++++++++++-
 t/t9902-completion.sh                  | 13 +++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 13a39ebd2e..34bbb66f85 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1148,6 +1148,18 @@ __git_get_config_variables ()
 	done
 }
 
+# Lists all subsections in the given section which contain the given
+# config variable, with the section and variable names removed.
+__git_get_config_subsections ()
+{
+	local section="$1" var="$2" i IFS=$'\n'
+	for i in $(__git config --name-only --get-regexp "^$section\..*\.$var$"); do
+		i=${i#$section.}
+		i=${i%.$var}
+		echo "$i"
+	done
+}
+
 __git_pretty_aliases ()
 {
 	__git_get_config_variables "pretty"
@@ -1681,7 +1693,7 @@ __git_untracked_file_modes="all no normal"
 
 __git_trailer_tokens ()
 {
-	__git config --name-only --get-regexp '^trailer\..*\.key$' | cut -d. -f 2- | rev | cut -d. -f2- | rev
+	__git_get_config_subsections trailer key
 }
 
 _git_commit ()
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index a7c3b4eb63..11ed83d0ed 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -2130,6 +2130,19 @@ test_expect_success '__git_get_config_variables' '
 	test_cmp expect actual
 '
 
+test_expect_success '__git_get_config_subsections' '
+	cat >expect <<-\EOF &&
+	subsection-1
+	SubSection-2
+	sub.section.3
+	EOF
+	test_config interesting.subsection-1.name good &&
+	test_config Interesting.SubSection-2.Name good &&
+	test_config interesting.sub.section.3.name good &&
+	__git_get_config_subsections interesting name >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success '__git_pretty_aliases' '
 	cat >expect <<-EOF &&
 	author
-- 
2.43.0.rc1.528.g8f9d60d041

Re: [PATCH] completion: add and use the __git_get_config_subsection helper function

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> +# Lists all subsections in the given section which contain the given
> +# config variable, with the section and variable names removed.
> +__git_get_config_subsections ()
> +{
> +	local section="$1" var="$2" i IFS=$'\n'
> +	for i in $(__git config --name-only --get-regexp "^$section\..*\.$var$"); do
> +		i=${i#$section.}
> +		i=${i%.$var}

As this script is allowed bash-isms, I wondered if we can use
a single pattern substitution instead of two remove pre/suffix
pattern substitution, but I guess it would not work, and the above
is perfectly readable.

> +		echo "$i"

As the subsection is designed to contain unbounded set of end-user
controlled names, we probably should do

		printf "%s\n" "$i"

instead to protect us from interesting names (e.g. ones that begin
with a dash).

> +	done
> +}

Interesting to see that we do not need to bother deduplicating the
output from here.

> diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> index a7c3b4eb63..11ed83d0ed 100755
> --- a/t/t9902-completion.sh
> +++ b/t/t9902-completion.sh
> @@ -2130,6 +2130,19 @@ test_expect_success '__git_get_config_variables' '
>  	test_cmp expect actual
>  '
>  
> +test_expect_success '__git_get_config_subsections' '
> +	cat >expect <<-\EOF &&
> +	subsection-1
> +	SubSection-2
> +	sub.section.3
> +	EOF
> +	test_config interesting.subsection-1.name good &&
> +	test_config Interesting.SubSection-2.Name good &&
> +	test_config interesting.sub.section.3.name good &&
> +	__git_get_config_subsections interesting name >actual &&
> +	test_cmp expect actual
> +'

Good to see an uppercase character is used here ;-).

Thanks.

Re: [PATCH] completion: add and use the __git_get_config_subsection helper function

[SZEDER Gábor]

On Tue, Nov 14, 2023 at 10:08:46AM +0900, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@gmail.com> writes:
> 
> > +# Lists all subsections in the given section which contain the given
> > +# config variable, with the section and variable names removed.
> > +__git_get_config_subsections ()
> > +{
> > +	local section="$1" var="$2" i IFS=$'\n'
> > +	for i in $(__git config --name-only --get-regexp "^$section\..*\.$var$"); do
> > +		i=${i#$section.}
> > +		i=${i%.$var}
> 
> As this script is allowed bash-isms, I wondered if we can use
> a single pattern substitution instead of two remove pre/suffix
> pattern substitution, but I guess it would not work, and the above
> is perfectly readable.

Yeah, I don't think it's possible to remove the prefix and suffix with
Bash builtins in a single operation.

> > +		echo "$i"
> 
> As the subsection is designed to contain unbounded set of end-user
> controlled names, we probably should do
> 
> 		printf "%s\n" "$i"
> 
> instead to protect us from interesting names (e.g. ones that begin
> with a dash).

Indeed, will do.

> > +	done
> > +}
> 
> Interesting to see that we do not need to bother deduplicating the
> output from here.

Bash will sort and deduplicate the completion words anyway, so we
don't have to.  Sometimes we do deduplicate them, though, but either
to make testing easier or for performance reasons; in this case
neither of them applies.

> > diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> > index a7c3b4eb63..11ed83d0ed 100755
> > --- a/t/t9902-completion.sh
> > +++ b/t/t9902-completion.sh
> > @@ -2130,6 +2130,19 @@ test_expect_success '__git_get_config_variables' '
> >  	test_cmp expect actual
> >  '
> >  
> > +test_expect_success '__git_get_config_subsections' '
> > +	cat >expect <<-\EOF &&
> > +	subsection-1
> > +	SubSection-2
> > +	sub.section.3
> > +	EOF
> > +	test_config interesting.subsection-1.name good &&
> > +	test_config Interesting.SubSection-2.Name good &&
> > +	test_config interesting.sub.section.3.name good &&
> > +	__git_get_config_subsections interesting name >actual &&
> > +	test_cmp expect actual
> > +'
> 
> Good to see an uppercase character is used here ;-).

That's just for good measure, but not really necessasry here, as that
primarily tests that 'git config' lists the section and variable names
(but not the subsection!) normalized to lowercase, no matter what
CaMeLCase the user might have written them.