[PATCH] config: fix case sensitive subsection names on writing

[Stefan Beller <sbeller@google.com>]

A use reported a submodule issue regarding strange case indentation
issues, but it could be boiled down to the following test case:

  $ git init test  && cd test
  $ git config foo."Bar".key test
  $ git config foo."bar".key test
  $ tail -n 3 .git/config
  [foo "Bar"]
        key = test
        key = test

Sub sections are case sensitive and we have a test for correctly reading
them. However we do not have a test for writing out config correctly with
case sensitive subsection names, which is why this went unnoticed in
6ae996f2acf (git_config_set: make use of the config parser's event
stream, 2018-04-09)

Make the subsection case sensitive and provide a test for both reading
and writing.

Reported-by: JP Sugarbroad <jpsugar@google.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
---
 config.c          |  2 +-
 t/t1300-config.sh | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/config.c b/config.c
index 3aacddfec4b..3ded92b678b 100644
--- a/config.c
+++ b/config.c
@@ -2374,7 +2374,7 @@ static int store_aux_event(enum config_event_t type,
 		store->is_keys_section =
 			store->parsed[store->parsed_nr].is_keys_section =
 			cf->var.len - 1 == store->baselen &&
-			!strncasecmp(cf->var.buf, store->key, store->baselen);
+			!strncmp(cf->var.buf, store->key, store->baselen);
 		if (store->is_keys_section) {
 			store->section_seen = 1;
 			ALLOC_GROW(store->seen, store->seen_nr + 1,
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index 03c223708eb..8325d4495f4 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -1218,6 +1218,24 @@ test_expect_success 'last one wins: three level vars' '
 	test_cmp expect actual
 '
 
+test_expect_success 'setting different case subsections ' '
+	test_when_finished "rm -f caseSens caseSens_actual caseSens_expect" &&
+
+	# v.a.r and v.A.r are not the same variable, as the middle
+	# level of a three-level configuration variable name is
+	# case sensitive.
+	git config -f caseSens v."A".r VAL &&
+	git config -f caseSens v."a".r val &&
+
+	echo VAL >caseSens_expect &&
+	git config -f caseSens v."A".r >caseSens_actual &&
+	test_cmp caseSens_expect caseSens_actual &&
+
+	echo val >caseSens_expect &&
+	git config -f caseSens v."a".r >caseSens_actual &&
+	test_cmp caseSens_expect caseSens_actual
+'
+
 for VAR in a .a a. a.0b a."b c". a."b c".0d
 do
 	test_expect_success "git -c $VAR=VAL rejects invalid '$VAR'" '
-- 
2.18.0.345.g5c9ce644c3-goog