feat: Add ShowMovement Tag

This commit adds the `SHOWMOVEMENT` [tag](https://picard-docs.musicbrainz.org/en/appendices/tag_mapping.html#show-work-movement-4). Historically, this tag originates from iTunes' MP4, but has since become widely used. It is created by Picard's Classical music [plugins](https://picard-docs.musicbrainz.org/en/variables/variables_classical.html) (such as "Classical Extras" or "Work & Movement").

The reasoning behind this tag is to display Work & Movement titles without redundant information and in a more uniform way. Moreover, it additionally serves as an implicit marker denoting classical music tracks (genre tags aren't sufficient).

If the client so chooses to support this tag, they can display `Work` and `Movement` instead of the track title allowing for cleaner display. Other clients can continue to display the `%title%` as before without any fuss.

NEWS

@@ -48,7 +48,7 @@ ver 0.24 (not yet released)
   - add option "mixramp_analyzer" to scan MixRamp tags on-the-fly
   - "one-shot" consume mode
 * tags
-  - new tags "TitleSort", "Mood"
+  - new tags "TitleSort", "Mood", "ShowMovement"
 * output
   - add option "always_off"
   - alsa: require alsa-lib 1.1 or later

doc/protocol.rst

@@ -344,6 +344,7 @@ The following tags are supported by :program:`MPD`:
 * **ensemble**: the ensemble performing this song, e.g. "Wiener Philharmoniker".
 * **movement**: name of the movement, e.g. "Andante con moto".
 * **movementnumber**: movement number, e.g. "2" or "II".
+* **showmovement**: If this tag is set to "1" players supporting this tag will display the `work`, `movement`, and `movementnumber`` instead of the track title.
 * **location**: location of the recording, e.g. "Royal Albert Hall".
 * **grouping**: "used if the sound belongs to a larger category of
   sounds/music" (`from the IDv2.4.0 TIT1 description

src/db/plugins/ProxyDatabasePlugin.cxx

@@ -184,6 +184,9 @@ static constexpr struct {
 	{ TAG_MOOD, MPD_TAG_MOOD },
 	{ TAG_MUSICBRAINZ_RELEASEGROUPID,
 	  MPD_TAG_MUSICBRAINZ_RELEASEGROUPID },
+#endif
+#if LIBMPDCLIENT_CHECK_VERSION(2,23,0)
+	{ TAG_SHOWMOVEMENT, MPD_TAG_SHOWMOVEMENT },
 #endif
 	{ TAG_NUM_OF_ITEM_TYPES, MPD_TAG_COUNT }
 };

src/tag/Names.cxx

@@ -28,6 +28,7 @@ static constexpr struct tag_table tag_item_names_init[] = {
 	{"Work", TAG_WORK},
 	{"Movement", TAG_MOVEMENT},
 	{"MovementNumber", TAG_MOVEMENTNUMBER},
+	{"ShowMovement", TAG_SHOWMOVEMENT},
 	{"Ensemble", TAG_ENSEMBLE},
 	{"Location", TAG_LOCATION},
 	{"Grouping", TAG_GROUPING},

src/tag/Type.hxx

@@ -30,6 +30,7 @@ enum TagType : uint8_t {
 	TAG_WORK,
 	TAG_MOVEMENT,
 	TAG_MOVEMENTNUMBER,
+	TAG_SHOWMOVEMENT,
 	TAG_ENSEMBLE,
 	TAG_LOCATION,
 	TAG_GROUPING,