git_config_set: reuse empty sections

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.

Now that we use the `event_fn` callback, it is easy to add support for
re-using empty sections, so let's do that.

Note: t5512-ls-remote requires that this change is applied *after* the
patch "git config --unset: remove empty sections (in the common case)":
without that patch, there would be empty `transfer` and `uploadpack`
sections ready for reuse, but in the *wrong* order (and sconsequently,
t5512's "overrides work between mixed transfer/upload-pack hideRefs"
would fail).

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

config.c

@@ -2336,6 +2336,12 @@ static int store_aux_event(enum config_event_t type,
 			store->parsed[store->parsed_nr].is_keys_section =
 			cf->var.len - 1 == store->baselen &&
 			!strncasecmp(cf->var.buf, store->key, store->baselen);
+		if (store->is_keys_section) {
+			store->section_seen = 1;
+			ALLOC_GROW(store->seen, store->seen_nr + 1,
+				   store->seen_alloc);
+			store->seen[store->seen_nr] = store->parsed_nr;
+		}
 	}
 
 	store->parsed_nr++;
@@ -2770,7 +2776,13 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 
 			new_line = 0;
 			if (!store.key_seen) {
-				replace_end = copy_end = store.parsed[j].end;
+				copy_end = store.parsed[j].end;
+				/* include '\n' when copying section header */
+				if (copy_end > 0 && copy_end < contents_sz &&
+				    contents[copy_end - 1] != '\n' &&
+				    contents[copy_end] == '\n')
+					copy_end++;
+				replace_end = copy_end;
 			} else {
 				replace_end = store.parsed[j].end;
 				copy_end = store.parsed[j].begin;

t/t1300-config.sh

@@ -1483,7 +1483,7 @@ 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