builtin/grep.c: respect 'submodule.recurse' option

In builtin/grep.c we parse the config before evaluating the command line
options. This makes the task of teaching grep to respect the new config
option 'submodule.recurse' very easy by just parsing that option.

As an alternative I had implemented a similar structure to treat
submodules as the fetch/push command have, including
* aligning the meaning of the 'recurse_submodules' to possible submodule
  values RECURSE_SUBMODULES_* as defined in submodule.h.
* having a callback to parse the value and
* reacting to the RECURSE_SUBMODULES_DEFAULT state that was the initial
  state.

However all this is not needed for a true boolean value, so let's keep
it simple. However this adds another place where "submodule.recurse" is
parsed.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/grep.c

@@ -302,6 +302,9 @@ static int grep_cmd_config(const char *var, const char *value, void *cb)
 #endif
 	}
 
+	if (!strcmp(var, "submodule.recurse"))
+		recurse_submodules = git_config_bool(var, value);
+
 	return st;
 }
 

t/t7814-grep-recurse-submodules.sh

@@ -33,6 +33,24 @@ test_expect_success 'grep correctly finds patterns in a submodule' '
 	test_cmp expect actual
 '
 
+test_expect_success 'grep finds patterns in a submodule via config' '
+	test_config submodule.recurse true &&
+	# expect from previous test
+	git grep -e "(3|4)" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'grep --no-recurse-submodules overrides config' '
+	test_config submodule.recurse true &&
+	cat >expect <<-\EOF &&
+	a:(1|2)d(3|4)
+	b/b:(3|4)
+	EOF
+
+	git grep -e "(3|4)" --no-recurse-submodules >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'grep and basic pathspecs' '
 	cat >expect <<-\EOF &&
 	submodule/a:(1|2)d(3|4)