[PATCH v1] config: fix case-insensitive match for old-style [section.subsection]

[RISHAV DEWAN <rishavdewan10@gmail.com>]

When writing to an old-style "[section.subsection]" header, the
config file parser always folds the subsection to lower case
(get_base_var() lowercases unconditionally), while the key given on
the command line keeps whatever case the caller typed
(do_parse_config_key() deliberately leaves the subsection segment
untouched). matches() compared these two forms with a plain strcmp(),
so a caller passing an upper-cased subsection (e.g. 'git config
section.Subsection.key value2' against a file containing
'[section.subsection]') never matched the existing key and a
duplicate line was appended instead of replacing the value. This was
a known, documented limitation (see the now-removed BUGS section of
git-config.adoc).

Track whether the currently active section was parsed case-
insensitively (old-style) or case-sensitively (new-style, quoted) in
struct config_store_data, and have matches() use that information to
compare the subsection segment of the key accordingly, instead of an
unconditional case-sensitive strcmp().

Signed-off-by: RISHAV DEWAN <rishavdewan10@gmail.com>
---
 Documentation/git-config.adoc | 21 ---------------------
 config.c                      | 18 +++++++++++++++++-
 t/t1300-config.sh             |  2 --
 3 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/Documentation/git-config.adoc b/Documentation/git-config.adoc
index 57af010ade..11dfd802b4 100644
--- a/Documentation/git-config.adoc
+++ b/Documentation/git-config.adoc
@@ -634,27 +634,6 @@ http.sslverify false
 
 include::config.adoc[]
 
-BUGS
-----
-When using the deprecated `[section.subsection]` syntax, changing a value
-will result in adding a multi-line key instead of a change, if the subsection
-is given with at least one uppercase character. For example when the config
-looks like
-
---------
-  [section.subsection]
-    key = value1
---------
-
-and running `git config section.Subsection.key value2` will result in
-
---------
-  [section.subsection]
-    key = value1
-    key = value2
---------
-
-
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/config.c b/config.c
index 6a0de86e3a..7f086fcd75 100644
--- a/config.c
+++ b/config.c
@@ -2594,6 +2594,7 @@ struct config_store_data {
 	} *parsed;
 	unsigned int parsed_nr, parsed_alloc, *seen, seen_nr, seen_alloc;
 	unsigned int key_seen:1, section_seen:1, is_keys_section:1;
+	unsigned int subsection_case_sensitive:1;
 };
 #define CONFIG_STORE_INIT { 0 }
 
@@ -2613,7 +2614,21 @@ static void config_store_data_clear(struct config_store_data *store)
 static int matches(const char *key, const char *value,
 		   const struct config_store_data *store)
 {
-	if (strcmp(key, store->key))
+	/*
+	 * The subsection part of "key" (key[0..store->baselen)) was parsed
+	 * out of the config file using the case sensitivity of whichever
+	 * section header it came from (see store_aux_event()): old-style
+	 * "[section.subsection]" headers are folded to lower case while
+	 * parsing, so they must be compared case-insensitively against
+	 * store->key, which preserves whatever case the caller passed on
+	 * the command line. New-style "[section "Subsection"]" headers keep
+	 * their case, so they need an exact, case-sensitive comparison.
+	 */
+	int (*cmpfn)(const char *, const char *, size_t) =
+		store->subsection_case_sensitive ? strncasecmp : strncmp;
+
+	if (cmpfn(key, store->key, store->baselen) ||
+	    strcmp(key + store->baselen, store->key + store->baselen))
 		return 0; /* not ours */
 	if (store->fixed_value && value)
 		return !strcmp(store->fixed_value, value);
@@ -2654,6 +2669,7 @@ static int store_aux_event(enum config_event_t type, size_t begin, size_t end,
 			!cmpfn(cs->var.buf, store->key, store->baselen);
 		if (store->is_keys_section) {
 			store->section_seen = 1;
+			store->subsection_case_sensitive = cs->subsection_case_sensitive;
 			ALLOC_GROW(store->seen, store->seen_nr + 1,
 				   store->seen_alloc);
 			store->seen[store->seen_nr] = store->parsed_nr;
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index 87ca11a127..eaa3b83990 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -1499,7 +1499,6 @@ test_expect_success 'old-fashioned settings are case insensitive' '
 	EOF
 	q_to_tab >testConfig_expect <<-EOF &&
 	[V.A]
-	r = value1
 	Qr = value2
 	EOF
 	git config -f testConfig_actual "V.A.r" value2 &&
@@ -1511,7 +1510,6 @@ test_expect_success 'old-fashioned settings are case insensitive' '
 	EOF
 	q_to_tab >testConfig_expect <<-EOF &&
 	[V.A]
-	r = value1
 	Qr = value2
 	EOF
 	git config -f testConfig_actual "v.A.r" value2 &&
-- 
2.50.1 (Apple Git-155)