config: improve error message for boolean config

Currently invalid boolean config values return messages about 'bad
numeric', which is slightly misleading when the error was due to a
boolean value. We can improve the developer experience by returning a
boolean error message when we know the value is neither a bool text or
int.

before with an invalid boolean value of `non-boolean`, its unclear what
numeric is referring to:
  fatal: bad numeric config value 'non-boolean' for 'commit.gpgsign': invalid unit

now the error message mentions `non-boolean` is a bad boolean value:
  fatal: bad boolean config value 'non-boolean' for 'commit.gpgsign'

Signed-off-by: Andrew Klotz <agc.klotz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -1030,6 +1030,20 @@ static void die_bad_number(const char *name, const char *value)
 	}
 }
 
+NORETURN
+static void die_bad_bool(const char *name, const char *value)
+{
+	if (!strcmp(name, "GIT_TEST_GETTEXT_POISON"))
+		/*
+		 * We explicitly *don't* use _() here since it would
+		 * cause an infinite loop with _() needing to call
+		 * use_gettext_poison().
+		 */
+		die("bad boolean config value '%s' for '%s'", value, name);
+	else
+		die(_("bad boolean config value '%s' for '%s'"), value, name);
+}
+
 int git_config_int(const char *name, const char *value)
 {
 	int ret;
@@ -1102,8 +1116,10 @@ int git_config_bool_or_int(const char *name, const char *value, int *is_bool)
 
 int git_config_bool(const char *name, const char *value)
 {
-	int discard;
-	return !!git_config_bool_or_int(name, value, &discard);
+	int v = git_parse_maybe_bool(value);
+	if (v < 0)
+		die_bad_bool(name, value);
+	return v;
 }
 
 int git_config_string(const char **dest, const char *var, const char *value)

t/t1300-config.sh

@@ -672,6 +672,13 @@ 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 'invalid unit boolean' '
+	git config commit.gpgsign "1true" &&
+	test_cmp_config 1true commit.gpgsign &&
+	test_must_fail git config --bool --get commit.gpgsign 2>actual &&
+	test_i18ngrep "bad boolean config value .1true. for .commit.gpgsign." 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 &&