Caps: serde: use a placeholder for `CapsFeature`

`CapsFeature` is not available in `gstreamer-rs` yet. Use a placeholder
with a `None` value for now.

gstreamer/src/caps_serde.rs

@@ -6,23 +6,38 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use serde::de;
 use serde::de::{Deserialize, Deserializer, SeqAccess, Visitor};
-use serde::ser::{Serialize, Serializer, SerializeSeq};
+use serde::ser::{Serialize, Serializer, SerializeSeq, SerializeTuple};
 
 use std::fmt;
 
 use Caps;
 use CapsRef;
 use Structure;
+use StructureRef;
 
-impl<'a> Serialize for CapsRef {
+// `CapsFeature` is not available in `gstreamer-rs` yet
+struct CapsItemSe<'a>(&'a StructureRef);
+impl<'a> Serialize for CapsItemSe<'a> {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        let mut tup = serializer.serialize_tuple(2)?;
+        tup.serialize_element(self.0)?;
+        // `CapsFeature` is not available in `gstreamer-rs` yet
+        // Fake the type for now and use `None` as a value
+        tup.serialize_element::<Option<Structure>>(&None)?;
+        tup.end()
+    }
+}
+
+impl Serialize for CapsRef {
     fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
         let iter = self.iter();
         let size = iter.size_hint().0;
         if size > 0 {
             let mut seq = serializer.serialize_seq(Some(size))?;
             for structure in iter {
-                seq.serialize_element(structure)?;
+                seq.serialize_element(&CapsItemSe(structure))?;
             }
             seq.end()
         } else {
@@ -32,26 +47,65 @@ impl<'a> Serialize for CapsRef {
     }
 }
 
-impl<'a> Serialize for Caps {
+impl Serialize for Caps {
     fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
         self.as_ref().serialize(serializer)
     }
 }
 
+// `CapsFeature` is not available in `gstreamer-rs` yet
+struct CapsItemDe(Structure);
+impl From<CapsItemDe> for Structure {
+    fn from(caps_item: CapsItemDe) -> Structure {
+        caps_item.0
+    }
+}
+
+struct CapsItemVisitor;
+impl<'de> Visitor<'de> for CapsItemVisitor {
+    type Value = CapsItemDe;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a tuple `(Structure, Option<CapsFeature>)`")
+    }
+
+    fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
+        let structure = seq.next_element::<Structure>()?
+            .ok_or(de::Error::custom("Expected a `Structure` for `Caps` item"))?;
+        // `CapsFeature` is not available in `gstreamer-rs` yet
+        // Fake the type for now and expect `None` as a value
+        let feature_option = seq.next_element::<Option<Structure>>()?
+            .ok_or(de::Error::custom("Expected an `Option<CapsFeature>` for `Caps` item"))?;
+        if feature_option.is_some() {
+            Err(de::Error::custom(
+                "Found a value for `CapsFeature`, expected `None` (not implemented yet)"
+            ))
+        } else {
+            Ok(CapsItemDe(structure))
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for CapsItemDe {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<CapsItemDe, D::Error> {
+        deserializer.deserialize_tuple(2, CapsItemVisitor)
+    }
+}
+
 struct CapsVisitor;
 impl<'de> Visitor<'de> for CapsVisitor {
     type Value = Caps;
 
     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        formatter.write_str("a sequence of `Structure`s")
+        formatter.write_str("a sequence of `(Structure, Option<CapsFeature>)`")
     }
 
     fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
         let mut caps = Caps::new_empty();
         {
             let caps = caps.get_mut().unwrap();
-            while let Some(structure) = seq.next_element::<Structure>()? {
-                caps.append_structure(structure);
+            while let Some(caps_item) = seq.next_element::<CapsItemDe>()? {
+                caps.append_structure(caps_item.into());
             }
         }
         Ok(caps)
@@ -92,7 +146,7 @@ mod tests {
             Ok(
                 concat!(
                     "[",
-                    "    (\"foo/bar\", [",
+                    "    ((\"foo/bar\", [",
                     "        (\"int\", \"i32\", 12),",
                     "        (\"bool\", \"bool\", true),",
                     "        (\"string\", \"String\", \"bla\"),",
@@ -101,7 +155,7 @@ mod tests {
                     "            (\"i32\", 1),",
                     "            (\"i32\", 2),",
                     "        ]),",
-                    "    ]),",
+                    "    ]), None),",
                     "]"
                 )
                     .to_owned()
@@ -118,16 +172,19 @@ mod tests {
 
         let caps_ron = r#"
             [
-                ("foo/bar", [
-                    ("int", "i32", 12),
-                    ("bool", "bool", true),
-                    ("string", "String", "bla"),
-                    ("fraction", "Fraction", (1, 2)),
-                    ("array", "Array", [
-                        ("i32", 1),
-                        ("i32", 2),
+                (
+                    ("foo/bar", [
+                        ("int", "i32", 12),
+                        ("bool", "bool", true),
+                        ("string", "String", "bla"),
+                        ("fraction", "Fraction", (1, 2)),
+                        ("array", "Array", [
+                            ("i32", 1),
+                            ("i32", 2),
+                        ]),
                     ]),
-                ]),
+                    None,
+                ),
             ]"#;
         let caps: Caps = ron::de::from_str(caps_ron).unwrap();
         let s = caps.get_structure(0).unwrap();

gstreamer/src/sample_serde.rs

@@ -152,10 +152,10 @@ mod tests {
                     "    )),",
                     "    buffer_list: None,",
                     "    caps: Some([",
-                    "        (\"sample/caps\", [",
+                    "        ((\"sample/caps\", [",
                     "            (\"int\", \"i32\", 12),",
                     "            (\"bool\", \"bool\", true),",
-                    "        ]),",
+                    "        ]), None),",
                     "    ]),",
                     "    segment: Some((",
                     "        flags: (",
@@ -257,10 +257,10 @@ mod tests {
                 )),
                 buffer_list: None,
                 caps: Some([
-                    ("sample/caps", [
+                    (("sample/caps", [
                         ("int", "i32", 12),
                         ("bool", "bool", true),
-                    ]),
+                    ]), None),
                 ]),
                 segment: Some((
                     flags: (