help / completion: make "git help" do the hard work

The "help" builtin has been able to emit configuration variables since
e17ca92637 (completion: drop the hard coded list of config vars,
2018-05-26), but it hasn't produced exactly the format the completion
script wanted. Let's do that.

We got partway there in 2675ea1cc0 (completion: use 'sort -u' to
deduplicate config variable names, 2019-08-13) and
d9438873c4 (completion: deduplicate configuration sections,
2019-08-13), but after both we still needed some sorting,
de-duplicating and awk post-processing of the list.

We can instead simply do the relevant parsing ourselves (we were doing
most of it already), and call string_list_remove_duplicates() after
already sorting the list, so the caller doesn't need to invoke "sort
-u". The "--config-for-completion" output is the same as before after
being passed through "sort -u".

Then add a new "--config-sections-for-completion" option. Under that
output we'll emit config sections like "alias" (instead of "alias." in
the --config-for-completion output).

We need to be careful to leave the "--config-for-completion" option
compatible with users git, but are still running a shell with an older
git-completion.bash. If we e.g. changed the option name they'd see
messages about git-completion.bash being unable to find the
"--config-for-completion" option.

Such backwards compatibility isn't something we should bend over
backwards for, it's only helping users who:

 * Upgrade git
 * Are in an old shell
 * The git-completion.bash in that shell hasn't cached the old
   "--config-for-completion" output already.

But since it's easy in this case to retain compatibility, let's do it,
the older versions of git-completion.bash won't care that the input
they get doesn't change after a "sort -u".

While we're at it let's make "--config-for-completion" die if there's
anything left over in "argc", and do the same in the new
"--config-sections-for-completion" option.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/help.c

@@ -34,11 +34,18 @@ enum help_format {
 	HELP_FORMAT_WEB
 };
 
+enum show_config_type {
+	SHOW_CONFIG_HUMAN,
+	SHOW_CONFIG_VARS,
+	SHOW_CONFIG_SECTIONS,
+};
+
 static enum help_action {
 	HELP_ACTION_ALL = 1,
 	HELP_ACTION_GUIDES,
 	HELP_ACTION_CONFIG,
 	HELP_ACTION_CONFIG_FOR_COMPLETION,
+	HELP_ACTION_CONFIG_SECTIONS_FOR_COMPLETION,
 } cmd_mode;
 
 static const char *html_path;
@@ -63,6 +70,8 @@ static struct option builtin_help_options[] = {
 		    HELP_ACTION_CONFIG),
 	OPT_CMDMODE_F(0, "config-for-completion", &cmd_mode, "",
 		    HELP_ACTION_CONFIG_FOR_COMPLETION, PARSE_OPT_HIDDEN),
+	OPT_CMDMODE_F(0, "config-sections-for-completion", &cmd_mode, "",
+		    HELP_ACTION_CONFIG_SECTIONS_FOR_COMPLETION, PARSE_OPT_HIDDEN),
 
 	OPT_END(),
 };
@@ -82,7 +91,7 @@ struct slot_expansion {
 	int found;
 };
 
-static void list_config_help(int for_human)
+static void list_config_help(enum show_config_type type)
 {
 	struct slot_expansion slot_expansions[] = {
 		{ "advice", "*", list_config_advices },
@@ -100,6 +109,8 @@ static void list_config_help(int for_human)
 	const char **p;
 	struct slot_expansion *e;
 	struct string_list keys = STRING_LIST_INIT_DUP;
+	struct string_list keys_uniq = STRING_LIST_INIT_DUP;
+	struct string_list_item *item;
 	int i;
 
 	for (p = config_name_list; *p; p++) {
@@ -130,34 +141,46 @@ static void list_config_help(int for_human)
 	for (i = 0; i < keys.nr; i++) {
 		const char *var = keys.items[i].string;
 		const char *wildcard, *tag, *cut;
+		const char *dot = NULL;
+		struct strbuf sb = STRBUF_INIT;
 
-		if (for_human) {
+		switch (type) {
+		case SHOW_CONFIG_HUMAN:
 			puts(var);
 			continue;
+		case SHOW_CONFIG_SECTIONS:
+			dot = strchr(var, '.');
+			break;
+		case SHOW_CONFIG_VARS:
+			break;
 		}
-
 		wildcard = strchr(var, '*');
 		tag = strchr(var, '<');
 
-		if (!wildcard && !tag) {
-			puts(var);
+		if (!dot && !wildcard && !tag) {
+			string_list_append(&keys_uniq, var);
 			continue;
 		}
 
-		if (wildcard && !tag)
+		if (dot)
+			cut = dot;
+		else if (wildcard && !tag)
 			cut = wildcard;
 		else if (!wildcard && tag)
 			cut = tag;
 		else
 			cut = wildcard < tag ? wildcard : tag;
 
-		/*
-		 * We may produce duplicates, but that's up to
-		 * git-completion.bash to handle
-		 */
-		printf("%.*s\n", (int)(cut - var), var);
+		strbuf_add(&sb, var, cut - var);
+		string_list_append(&keys_uniq, sb.buf);
+		strbuf_release(&sb);
+
 	}
 	string_list_clear(&keys, 0);
+	string_list_remove_duplicates(&keys_uniq, 0);
+	for_each_string_list_item(item, &keys_uniq)
+		puts(item->string);
+	string_list_clear(&keys_uniq, 0);
 }
 
 static enum help_format parse_help_format(const char *format)
@@ -589,12 +612,17 @@ int cmd_help(int argc, const char **argv, const char *prefix)
 		printf("%s\n", _(git_more_info_string));
 		return 0;
 	case HELP_ACTION_CONFIG_FOR_COMPLETION:
-		list_config_help(0);
+		no_extra_argc(argc);
+		list_config_help(SHOW_CONFIG_VARS);
+		return 0;
+	case HELP_ACTION_CONFIG_SECTIONS_FOR_COMPLETION:
+		no_extra_argc(argc);
+		list_config_help(SHOW_CONFIG_SECTIONS);
 		return 0;
 	case HELP_ACTION_CONFIG:
 		no_extra_argc(argc);
 		setup_pager();
-		list_config_help(1);
+		list_config_help(SHOW_CONFIG_HUMAN);
 		printf("\n%s\n", _("'git help config' for more information"));
 		return 0;
 	}

contrib/completion/git-completion.bash

@@ -2503,7 +2503,14 @@ __git_config_vars=
 __git_compute_config_vars ()
 {
 	test -n "$__git_config_vars" ||
-	__git_config_vars="$(git help --config-for-completion | sort -u)"
+	__git_config_vars="$(git help --config-for-completion)"
+}
+
+__git_config_sections=
+__git_compute_config_sections ()
+{
+	test -n "$__git_config_sections" ||
+	__git_config_sections="$(git help --config-sections-for-completion)"
 }
 
 # Completes possible values of various configuration variables.
@@ -2717,16 +2724,8 @@ __git_complete_config_variable_name ()
 		__gitcomp "$__git_config_vars" "" "$cur_" "$sfx"
 		;;
 	*)
-		__git_compute_config_vars
-		__gitcomp "$(echo "$__git_config_vars" |
-				awk -F . '{
-					sections[$1] = 1
-				}
-				END {
-					for (s in sections)
-						print s "."
-				}
-				')" "" "$cur_"
+		__git_compute_config_sections
+		__gitcomp "$__git_config_sections" "" "$cur_" "."
 		;;
 	esac
 }

t/t0012-help.sh

@@ -42,7 +42,8 @@ test_expect_success 'invalid usage' '
 	test_expect_code 129 git help -a -g &&
 
 	test_expect_code 129 git help -g -c &&
-	test_expect_code 0 git help --config-for-completion add
+	test_expect_code 129 git help --config-for-completion add &&
+	test_expect_code 129 git help --config-sections-for-completion add
 '
 
 test_expect_success "works for commands and guides by default" '
@@ -106,11 +107,21 @@ test_expect_success 'git help --config-for-completion' '
 	     sort -u >human.munged &&
 
 	git help --config-for-completion >vars &&
-	sort -u <vars >vars.new &&
-	mv vars.new vars &&
 	test_cmp human.munged vars
 '
 
+test_expect_success 'git help --config-sections-for-completion' '
+	git help -c >human &&
+	grep -E \
+	     -e "^[^.]+\.[^.]+$" \
+	     -e "^[^.]+\.[^.]+\.[^.]+$" human |
+	     sed -e "s/\..*//" |
+	     sort -u >human.munged &&
+
+	git help --config-sections-for-completion >sections &&
+	test_cmp human.munged sections
+'
+
 test_expect_success 'generate builtin list' '
 	git --list-cmds=builtins >builtins
 '