[PATCH/RFC 0/5] add "unset.variable" for unsetting previously set variables

@@ -1214,7 +1214,7 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 	return ret == 0 ? found : ret;
 }
 
-int git_config_with_options(config_fn_t fn, void *data,
+static int git_config_with_options_raw(config_fn_t fn, void *data,
 			    struct git_config_source *config_source,
 			    int respect_includes)
 {

@@ -1247,9 +1247,26 @@ int git_config_with_options(config_fn_t fn, void *data,
 	return ret;
 }
 
+static int config_set_callback(const char *key, const char *value, void *cb);
+
+int git_config_with_options(config_fn_t fn, void *data,
+			    struct git_config_source *config_source,
+			    int respect_includes)
+{
+	int ret;
+	struct config_set options_config;
+	git_configset_init(&options_config);
+	ret = git_config_with_options_raw(config_set_callback, &options_config,
+					  config_source, respect_includes);
+	if (ret >= 0)
+		configset_iter(&options_config, fn, data);
+	git_configset_clear(&options_config);
+	return ret;
+}
+
 static void git_config_raw(config_fn_t fn, void *data)
 {
-	if (git_config_with_options(fn, data, NULL, 1) < 0)
+	if (git_config_with_options_raw(fn, data, NULL, 1) < 0)
 		/*
 		 * git_config_with_options() normally returns only
 		 * positive values, as most errors are fatal, and

@@ -678,7 +678,7 @@ test_expect_success 'invalid unit' '
 	git config aninvalid.unit >actual &&
 	test_cmp expect actual &&
 	cat >expect <<-\EOF
-	fatal: bad numeric config value '\''1auto'\'' for '\''aninvalid.unit'\'' in .git/config: invalid unit
+	fatal: bad numeric config value '\''1auto'\'' for '\''aninvalid.unit'\'': invalid unit
 	EOF
 	test_must_fail git config --int --get aninvalid.unit 2>actual &&
 	test_i18ncmp expect actual

@@ -1150,6 +1150,25 @@ int git_config_system(void)
 	return !git_env_bool("GIT_CONFIG_NOSYSTEM", 0);
 }
 
+static void configset_iter(struct config_set *cs, config_fn_t fn, void *data)
+{
+	int i, value_index;
+	struct string_list *values;
+	struct config_set_element *entry;
+	struct configset_list *list = &cs->list;
+	struct key_value_info *kv_info;
+
+	for (i = 0; i < list->nr; i++) {
+		entry = list->items[i].e;
+		value_index = list->items[i].value_index;
+		values = &entry->value_list;
+		if (fn(entry->key, values->items[value_index].string, data) < 0) {
+			kv_info = values->items[value_index].util;
+			git_die_config_linenr(entry->key, kv_info->filename, kv_info->linenr);
+		}
+	}
+}
+
 int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 {
 	int ret = 0, found = 0;

@@ -1245,25 +1264,6 @@ static void git_config_raw(config_fn_t fn, void *data)
 		die(_("unknown error occured while reading the configuration files"));
 }
 
-static void configset_iter(struct config_set *cs, config_fn_t fn, void *data)
-{
-	int i, value_index;
-	struct string_list *values;
-	struct config_set_element *entry;
-	struct configset_list *list = &cs->list;
-	struct key_value_info *kv_info;
-
-	for (i = 0; i < list->nr; i++) {
-		entry = list->items[i].e;
-		value_index = list->items[i].value_index;
-		values = &entry->value_list;
-		if (fn(entry->key, values->items[value_index].string, data) < 0) {
-			kv_info = values->items[value_index].util;
-			git_die_config_linenr(entry->key, kv_info->filename, kv_info->linenr);
-		}
-	}
-}
-
 static void git_config_check_init(void);
 
 void git_config(config_fn_t fn, void *data)

@@ -1311,6 +1311,38 @@ static struct config_set_element *configset_find_element(struct config_set *cs,
 	return found_entry;
 }
 
+static void delete_config_variable(struct config_set *cs, const char *key, const char *value)
+{
+	char *normalized_value;
+	struct config_set_element *e = NULL;
+	int ret, current = 0, updated = 0;
+	struct configset_list *list = &cs->list;
+	/*
+	 * if we find a key value pair with key as "unset.variable", unset all variables
+	 * in the configset with keys equivalent to the value in "unset.variable".
+	 * unsetting a variable means that the variable is permanently deleted from the
+	 * configset.
+	 */
+	ret = git_config_parse_key(value, &normalized_value, NULL);
+	if (!ret) {
+		/* first remove matching variables from the configset_list */
+		while (current < list->nr) {
+			if (!strcmp(list->items[current].e->key, normalized_value))
+				current++;
+			else
+				list->items[updated++] = list->items[current++];
+		}
+		list->nr = updated;
+		/* then delete the matching entry from the configset hashmap */
+		e = configset_find_element(cs, normalized_value);
+		if (e) {
+			free(e->key);
+			string_list_clear(&e->value_list, 1);
+			hashmap_remove(&cs->config_hash, e, NULL);
+		}
+	}
+}
+
 static int configset_add_value(struct config_set *cs, const char *key, const char *value)
 {
 	struct config_set_element *e;

@@ -1331,6 +1363,8 @@ static int configset_add_value(struct config_set *cs, const char *key, const cha
 		hashmap_add(&cs->config_hash, e);
 	}
 	si = string_list_append_nodup(&e->value_list, value ? xstrdup(value) : NULL);
+	if (!strcmp(key, "unset.variable"))
+		delete_config_variable(cs, key, value);
 
 	ALLOC_GROW(cs->list.items, cs->list.nr + 1, cs->list.alloc);
 	l_item = &cs->list.items[cs->list.nr++];

@@ -2382,6 +2382,18 @@ transfer.unpackLimit::
 	not set, the value of this variable is used instead.
 	The default value is 100.
 
+unset.variable::
+	This variable can be used to unset previously set variables
+	which had been already declared in files of lower priority
+	or declared before in the same file. It does not unset
+	matching variables declared after its position in the file
+	or in files of higher priority. It can be used to unset
+	pesky variables declared in files which the user might not
+	be able to open due to not having the required security
+	privileges, for example, system wide configuration file
+	`/etc/gitconfig` which may be accessible to the system
+	administrator only.
+
 uploadarchive.allowUnreachable::
 	If true, allow clients to use `git archive --remote` to request
 	any tree, whether reachable from the ref tips or not. See the

@@ -1179,4 +1179,58 @@ test_expect_success POSIXPERM,PERL 'preserves existing permissions' '
 	  "die q(badrename) if ((stat(q(.git/config)))[2] & 07777) != 0600"
 '
 
+test_expect_success 'unset.variable unsets all previous matching keys' '
+	cat >.git/config <<-\EOF &&
+	[alias]
+		checkconfig = -c foo.check=baz config foo.check
+		checkconfig = -c foo.check=bar config foo.check
+	[unset]
+		variable = alias.checkconfig
+	EOF
+
+	test_expect_code 1 git checkconfig
+'
+
+test_expect_success 'unset.variable does not touch all matching keys after it' '
+	cat >.git/config <<-\EOF &&
+	[alias]
+		checkconfig = -c foo.check=foo config foo.check
+	[unset]
+		variable = alias.checkconfig
+	[alias]
+		checkconfig = -c foo.check=baz config foo.check
+		checkconfig = -c foo.check=bar config foo.check
+	EOF
+
+	cat >expect <<-\EOF &&
+	bar
+	EOF
+
+	test_expect_code 0 git checkconfig >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'document how unset.variable will behave in shell scripts' '
+	rm -f .git/config &&
+	cat >expect <<-\EOF &&
+	EOF
+	git config foo.bar boz1 &&
+	git config --add foo.bar boz2 &&
+	git config unset.variable foo.bar &&
+	git config --add foo.bar boz3 &&
+	test_must_fail git config --get-all foo.bar >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'unset.variable declared after in shell scripts' '
+	rm -f .git/config &&
+	cat >expect <<-\EOF &&
+	EOF
+	git config foo.bar boz1 &&
+	git config --add foo.bar boz2 &&
+	git config unset.variable foo.bar &&
+	test_must_fail git config --get-all foo.bar >actual &&
+	test_cmp expect actual
+'
+
 test_done