[PATCH] ucm: Allow empty strings in "${var:...}" substitutions

[Hans de Goede <hdegoede@xxxxxxxxxx>]

Recent ucm-conf changes introduce checks like this one in various places:

If.mspk {
        Condition {
                Type String
                Empty "${var:MonoSpeaker}"
        }
        True ...
        False ...
}

The 'Empty "${var:MonoSpeaker}"' part can only every succeed if we do:

Define.MonoSpeaker ""

But so far that would result in an error like this one:

ALSA lib ucm_subs.c:367:(uc_mgr_get_substituted_value) variable '${var:MonoSpeaker}' is not defined in this context!
ALSA lib main.c:983:(snd_use_case_mgr_open) error: failed to import cht-bsw-rt5672 use case configuration -22
alsaucm: error failed to open sound card cht-bsw-rt5672: Invalid argument

This commit fixes this by allowing empty values for "${var:...}"
substitutions.

Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
Note besides the mentioned error, this also fixes similar errors I have
been seeing on every board since alsa-ucm-conf commit d001c8de287f
("ucm.conf: add support for the kernel module name tree")
---
 src/ucm/ucm_subs.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/ucm/ucm_subs.c b/src/ucm/ucm_subs.c
index 293426f2..a154aa51 100644
--- a/src/ucm/ucm_subs.c
+++ b/src/ucm/ucm_subs.c
@@ -262,9 +262,10 @@ static char *rval_var(snd_use_case_mgr_t *uc_mgr, const char *id)
 		goto __rval;						\
 	}
 
-#define MATCH_VARIABLE2(name, id, fcn)					\
+#define MATCH_VARIABLE2(name, id, fcn, empty_ok)			\
 	if (strncmp((name), (id), sizeof(id) - 1) == 0) {		\
 		idsize = sizeof(id) - 1;				\
+		allow_empty = (empty_ok);				\
 		fcn2 = (fcn);						\
 		goto __match2;						\
 	}
@@ -314,11 +315,11 @@ __std:
 		MATCH_VARIABLE(value, "${CardName}", rval_card_name, false);
 		MATCH_VARIABLE(value, "${CardLongName}", rval_card_longname, false);
 		MATCH_VARIABLE(value, "${CardComponents}", rval_card_components, true);
-		MATCH_VARIABLE2(value, "${env:", rval_env);
-		MATCH_VARIABLE2(value, "${sys:", rval_sysfs);
-		MATCH_VARIABLE2(value, "${var:", rval_var);
-		MATCH_VARIABLE2(value, "${CardNumberByName:", rval_card_number_by_name);
-		MATCH_VARIABLE2(value, "${CardIdByName:", rval_card_id_by_name);
+		MATCH_VARIABLE2(value, "${env:", rval_env, false);
+		MATCH_VARIABLE2(value, "${sys:", rval_sysfs, false);
+		MATCH_VARIABLE2(value, "${var:", rval_var, true);
+		MATCH_VARIABLE2(value, "${CardNumberByName:", rval_card_number_by_name, false);
+		MATCH_VARIABLE2(value, "${CardIdByName:", rval_card_id_by_name, false);
 __merr:
 		err = -EINVAL;
 		tmp = strchr(value, '}');
-- 
2.26.2