conf: fix the device parsing when arguments has no defaults

The commit bf528b90 sets the value to an empty string which causes
these errors:

   pcm_hw.c: Invalid type for device
   pcm_hw.c: Invalid type for subdevice

When device arguments (@args) have no default values set,
the field must be skipped to keep the compatibility.

BugLink: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues/1246
Fixes: https://github.com/alsa-project/alsa-lib/issues/199
Fixes: bf528b90 ("conf: add possibility to evaluate simple integer math expressions")
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

2 files changed, 11 insertions, 2 deletions

diff --git a/src/conf.c b/src/conf.c
index 0f6d2ba8..d3597cbc 100644
--- a/src/conf.c
+++ b/src/conf.c
@@ -4994,8 +4994,10 @@ int snd_config_copy(snd_config_t **dst,
 static int _snd_config_expand_vars(snd_config_t **dst, const char *s, void *private_data)
 {
 	snd_config_t *val, *vars = private_data;
-	if (snd_config_search(vars, s, &val) < 0)
-		return snd_config_make_string(dst, "");
+	if (snd_config_search(vars, s, &val) < 0) {
+		*dst = NULL;
+		return 0;
+	}
 	return snd_config_copy(dst, val);
 }
 
@@ -5060,6 +5062,8 @@ static int _snd_config_expand(snd_config_t *src,
 				err = snd_config_evaluate_string(dst, s, fcn, vars);
 				if (err < 0)
 					return err;
+				if (*dst == NULL)
+					return 0;
 				err = snd_config_set_id(*dst, id);
 				if (err < 0) {
 					snd_config_delete(*dst);
diff --git a/src/confeval.c b/src/confeval.c
index be9ac874..4a6f8c2e 100644
--- a/src/confeval.c
+++ b/src/confeval.c
@@ -203,6 +203,11 @@ int _snd_eval_string(snd_config_t **dst, const char *s,
 				free(m);
 				if (err < 0)
 					return err;
+				if (tmp == NULL) {
+					err = snd_config_imake_integer(&tmp, NULL, 0);
+					if (err < 0)
+						return err;
+				}
 				s = e;
 			}
 			err = _to_integer(op == LEFT ? &left : &right, tmp);