config: report correct line number upon error

When get_value() parses a key/value pair, it is possible that the line
number is decreased (because the \n has been consumed already) before the
key/value pair is passed to the callback function, to allow for the
correct line to be attributed in case of an error.

However, when git_parse_source() asks get_value() to parse the key/value
pair, the error reporting is performed *after* get_value() returns.

Which means that we have to be careful not to increase the line number
in get_value() after the callback function returned an error.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -588,6 +588,7 @@ static int get_value(config_fn_t fn, void *data, struct strbuf *name)
 	 */
 	cf->linenr--;
 	ret = fn(name->buf, value, data);
+	if (ret >= 0)
 		cf->linenr++;
 	return ret;
 }

t/t1300-repo-config.sh

@@ -703,6 +703,12 @@ test_expect_success 'invalid unit' '
 	test_i18ngrep "bad numeric config value .1auto. for .aninvalid.unit. in file .git/config: invalid unit" actual
 '
 
+test_expect_success 'line number is reported correctly' '
+	printf "[bool]\n\tvar\n" >invalid &&
+	test_must_fail git config -f invalid --path bool.var 2>actual &&
+	test_i18ngrep "line 2" actual
+'
+
 test_expect_success 'invalid stdin config' '
 	echo "[broken" | test_must_fail git config --list --file - >output 2>&1 &&
 	test_i18ngrep "bad config line 1 in standard input" output