[PATCH 9/9] git_config_set: reuse empty sections

[Johannes Schindelin <johannes.schindelin@gmx.de>]

It can happen quite easily that the last setting in a config section is
removed, and to avoid confusion when there are comments in the config
about that section, we keep a lone section header, i.e. an empty
section.

The code to add new entries in the config tries to be cute by reusing
the parsing code that is used to retrieve config settings, but that
poses the problem that the latter use case does *not* care about empty
sections, therefore even the former user case won't see them.

Fix this by introducing a mode where the parser reports also empty
sections (with a trailing '.' as tell-tale), and then using that when
adding new config entries.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 config.c          | 32 +++++++++++++++++++++++---------
 t/t1300-config.sh |  2 +-
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/config.c b/config.c
index eb1e0d335fc..b04c40f76bc 100644
--- a/config.c
+++ b/config.c
@@ -653,13 +653,15 @@ static int get_base_var(struct strbuf *name)
 	}
 }
 
-static int git_parse_source(config_fn_t fn, void *data)
+static int git_parse_source(config_fn_t fn, void *data,
+			    int include_section_headers)
 {
 	int comment = 0;
 	int baselen = 0;
 	struct strbuf *var = &cf->var;
 	int error_return = 0;
 	char *error_msg = NULL;
+	int saw_section_header = 0;
 
 	/* U+FEFF Byte Order Mark in UTF8 */
 	const char *bomptr = utf8_bom;
@@ -685,6 +687,16 @@ static int git_parse_source(config_fn_t fn, void *data)
 			if (cf->eof)
 				return 0;
 			comment = 0;
+			if (saw_section_header) {
+				if (include_section_headers) {
+					cf->linenr--;
+					error_return = fn(var->buf, NULL, data);
+					if (error_return < 0)
+						break;
+					cf->linenr++;
+				}
+				saw_section_header = 0;
+			}
 			continue;
 		}
 		if (comment || isspace(c))
@@ -700,6 +712,7 @@ static int git_parse_source(config_fn_t fn, void *data)
 				break;
 			strbuf_addch(var, '.');
 			baselen = var->len;
+			saw_section_header = 1;
 			continue;
 		}
 		if (!isalpha(c))
@@ -1398,7 +1411,8 @@ int git_default_config(const char *var, const char *value, void *dummy)
  * fgetc, ungetc, ftell of top need to be initialized before calling
  * this function.
  */
-static int do_config_from(struct config_source *top, config_fn_t fn, void *data)
+static int do_config_from(struct config_source *top, config_fn_t fn, void *data,
+			  int include_section_headers)
 {
 	int ret;
 
@@ -1410,7 +1424,7 @@ static int do_config_from(struct config_source *top, config_fn_t fn, void *data)
 	strbuf_init(&top->var, 1024);
 	cf = top;
 
-	ret = git_parse_source(fn, data);
+	ret = git_parse_source(fn, data, include_section_headers);
 
 	/* pop config-file parsing state stack */
 	strbuf_release(&top->value);
@@ -1423,7 +1437,7 @@ static int do_config_from(struct config_source *top, config_fn_t fn, void *data)
 static int do_config_from_file(config_fn_t fn,
 		const enum config_origin_type origin_type,
 		const char *name, const char *path, FILE *f,
-		void *data)
+		void *data, int include_section_headers)
 {
 	struct config_source top;
 
@@ -1436,12 +1450,12 @@ static int do_config_from_file(config_fn_t fn,
 	top.do_ungetc = config_file_ungetc;
 	top.do_ftell = config_file_ftell;
 
-	return do_config_from(&top, fn, data);
+	return do_config_from(&top, fn, data, include_section_headers);
 }
 
 static int git_config_from_stdin(config_fn_t fn, void *data)
 {
-	return do_config_from_file(fn, CONFIG_ORIGIN_STDIN, "", NULL, stdin, data);
+	return do_config_from_file(fn, CONFIG_ORIGIN_STDIN, "", NULL, stdin, data, 0);
 }
 
 int git_config_from_file(config_fn_t fn, const char *filename, void *data)
@@ -1452,7 +1466,7 @@ int git_config_from_file(config_fn_t fn, const char *filename, void *data)
 	f = fopen_or_warn(filename, "r");
 	if (f) {
 		flockfile(f);
-		ret = do_config_from_file(fn, CONFIG_ORIGIN_FILE, filename, filename, f, data);
+		ret = do_config_from_file(fn, CONFIG_ORIGIN_FILE, filename, filename, f, data, 0);
 		funlockfile(f);
 		fclose(f);
 	}
@@ -1475,7 +1489,7 @@ int git_config_from_mem(config_fn_t fn, const enum config_origin_type origin_typ
 	top.do_ungetc = config_buf_ungetc;
 	top.do_ftell = config_buf_ftell;
 
-	return do_config_from(&top, fn, data);
+	return do_config_from(&top, fn, data, 0);
 }
 
 int git_config_from_blob_oid(config_fn_t fn,
@@ -2743,7 +2757,7 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		f = fopen_or_warn(config_filename, "r");
 		if (!f || do_config_from_file(store_aux, CONFIG_ORIGIN_FILE,
 					      config_filename, config_filename,
-					      f, NULL)) {
+					      f, NULL, 1)) {
 			error("invalid config file %s", config_filename);
 			if (store.value_regex != NULL &&
 			    store.value_regex != CONFIG_REGEX_NONE) {
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index ecbcc9cf3d0..867397ae930 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -1463,7 +1463,7 @@ test_expect_success '--unset-all removes section if empty & uncommented' '
 	test_line_count = 0 .git/config
 '
 
-test_expect_failure 'adding a key into an empty section reuses header' '
+test_expect_success 'adding a key into an empty section reuses header' '
 	cat >.git/config <<-\EOF &&
 	[section]
 	EOF
-- 
2.16.2.windows.1.26.g2cc3565eb4b