Add various glib::Value trait impls for borrowed versions of types

For SDPMessageRef, StructureRef and CapsFeatureRef this involves the
conversion from and to a glib::Value. Specifically this means that e.g.
a StructureRef can be retrieved from a glib::Value via borrowing, i.e.
without creating a copy of the structure first.

For all mini objects only retrieval from a glib::Value is implemented as
the other direction would allow to get multiple immutable references
from a mutable reference without borrowing, which is not allowed and
would make it possible to observe a mini object changing while having an
immutable reference to it.

gstreamer-sdp/src/sdp_message.rs

@@ -928,6 +928,45 @@ impl ToOwned for SDPMessageRef {
     }
 }
 
+impl glib::types::StaticType for SDPMessageRef {
+    fn static_type() -> glib::types::Type {
+        unsafe { from_glib(gst_sdp_sys::gst_sdp_message_get_type()) }
+    }
+}
+
+impl<'a> glib::value::FromValueOptional<'a> for &'a SDPMessageRef {
+    unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
+        let ptr = gobject_sys::g_value_get_boxed(v.to_glib_none().0);
+        if ptr.is_null() {
+            None
+        } else {
+            Some(&*(ptr as *const SDPMessageRef))
+        }
+    }
+}
+
+impl glib::value::SetValue for SDPMessageRef {
+    unsafe fn set_value(v: &mut glib::Value, s: &Self) {
+        gobject_sys::g_value_set_boxed(
+            v.to_glib_none_mut().0,
+            s as *const SDPMessageRef as glib_sys::gpointer,
+        );
+    }
+}
+
+impl glib::value::SetValueOptional for SDPMessageRef {
+    unsafe fn set_value_optional(v: &mut glib::Value, s: Option<&Self>) {
+        if let Some(s) = s {
+            gobject_sys::g_value_set_boxed(
+                v.to_glib_none_mut().0,
+                s as *const SDPMessageRef as glib_sys::gpointer,
+            );
+        } else {
+            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, ptr::null_mut());
+        }
+    }
+}
+
 macro_rules! define_iter(
     ($name:ident, $typ:ty, $get_item:expr, $get_len:expr) => {
     #[derive(Debug)]

gstreamer/src/caps_features.rs

@@ -19,8 +19,8 @@ use once_cell::sync::Lazy;
 
 use glib;
 use glib::translate::{
-    from_glib, from_glib_full, from_glib_none, FromGlibPtrFull, FromGlibPtrNone, GlibPtrDefault,
-    Stash, StashMut, ToGlibPtr, ToGlibPtrMut,
+    from_glib, from_glib_full, FromGlibPtrFull, FromGlibPtrNone, GlibPtrDefault, Stash, StashMut,
+    ToGlibPtr, ToGlibPtrMut,
 };
 use glib_sys::gpointer;
 use gobject_sys;
@@ -247,24 +247,23 @@ impl FromGlibPtrFull<*mut gst_sys::GstCapsFeatures> for CapsFeatures {
 
 impl<'a> glib::value::FromValueOptional<'a> for CapsFeatures {
     unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
-        let ptr = gobject_sys::g_value_get_boxed(v.to_glib_none().0);
-        from_glib_none(ptr as *const gst_sys::GstCapsFeatures)
+        <&'a CapsFeaturesRef as glib::value::FromValueOptional<'a>>::from_value_optional(v)
+            .map(ToOwned::to_owned)
     }
 }
 
 impl glib::value::SetValue for CapsFeatures {
     unsafe fn set_value(v: &mut glib::Value, s: &Self) {
-        gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.0.as_ptr() as gpointer);
+        <CapsFeaturesRef as glib::value::SetValue>::set_value(v, s.as_ref())
     }
 }
 
 impl glib::value::SetValueOptional for CapsFeatures {
     unsafe fn set_value_optional(v: &mut glib::Value, s: Option<&Self>) {
-        if let Some(s) = s {
-            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
-        } else {
-            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, ptr::null_mut());
-        }
+        <CapsFeaturesRef as glib::value::SetValueOptional>::set_value_optional(
+            v,
+            s.map(|s| s.as_ref()),
+        )
     }
 }
 
@@ -359,6 +358,41 @@ impl CapsFeaturesRef {
     }
 }
 
+impl glib::types::StaticType for CapsFeaturesRef {
+    fn static_type() -> glib::types::Type {
+        unsafe { from_glib(gst_sys::gst_structure_get_type()) }
+    }
+}
+
+impl<'a> glib::value::FromValueOptional<'a> for &'a CapsFeaturesRef {
+    unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
+        let ptr = gobject_sys::g_value_get_boxed(v.to_glib_none().0);
+        if ptr.is_null() {
+            None
+        } else {
+            Some(CapsFeaturesRef::from_glib_borrow(
+                ptr as *const gst_sys::GstCapsFeatures,
+            ))
+        }
+    }
+}
+
+impl glib::value::SetValue for CapsFeaturesRef {
+    unsafe fn set_value(v: &mut glib::Value, s: &Self) {
+        gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
+    }
+}
+
+impl glib::value::SetValueOptional for CapsFeaturesRef {
+    unsafe fn set_value_optional(v: &mut glib::Value, s: Option<&Self>) {
+        if let Some(s) = s {
+            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
+        } else {
+            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, ptr::null_mut());
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct Iter<'a> {
     caps_features: &'a CapsFeaturesRef,

gstreamer/src/miniobject.rs

@@ -851,6 +851,22 @@ macro_rules! gst_define_mini_object_wrapper(
             }
         }
 
+        impl<'a> $crate::glib::value::FromValueOptional<'a>
+            for &'a $ref_name
+        {
+            unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
+                let ptr = gobject_sys::g_value_get_boxed($crate::glib::translate::ToGlibPtr::to_glib_none(v).0);
+                if ptr.is_null() {
+                    None
+                } else {
+                    Some(&*(ptr as *const $ref_name))
+                }
+            }
+        }
+
+        // Can't have SetValue/SetValueOptional impls as otherwise one could use it to get
+        // immutable references from a mutable reference without borrowing via the value
+
         impl ToOwned for $ref_name {
             type Owned = $name;
 

gstreamer/src/structure.rs

@@ -21,8 +21,8 @@ use Fraction;
 
 use glib;
 use glib::translate::{
-    from_glib, from_glib_full, from_glib_none, FromGlibPtrFull, FromGlibPtrNone, GlibPtrDefault,
-    Stash, StashMut, ToGlib, ToGlibPtr, ToGlibPtrMut,
+    from_glib, from_glib_full, FromGlibPtrFull, FromGlibPtrNone, GlibPtrDefault, Stash, StashMut,
+    ToGlib, ToGlibPtr, ToGlibPtrMut,
 };
 use glib::value::{FromValue, FromValueOptional, SendValue, ToSendValue};
 use glib_sys::gpointer;
@@ -309,24 +309,23 @@ impl FromGlibPtrFull<*mut gst_sys::GstStructure> for Structure {
 
 impl<'a> glib::value::FromValueOptional<'a> for Structure {
     unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
-        let ptr = gobject_sys::g_value_get_boxed(v.to_glib_none().0);
-        from_glib_none(ptr as *const gst_sys::GstStructure)
+        <&'a StructureRef as glib::value::FromValueOptional<'a>>::from_value_optional(v)
+            .map(ToOwned::to_owned)
     }
 }
 
 impl glib::value::SetValue for Structure {
     unsafe fn set_value(v: &mut glib::Value, s: &Self) {
-        gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.0.as_ptr() as gpointer);
+        <StructureRef as glib::value::SetValue>::set_value(v, s.as_ref())
     }
 }
 
 impl glib::value::SetValueOptional for Structure {
     unsafe fn set_value_optional(v: &mut glib::Value, s: Option<&Self>) {
-        if let Some(s) = s {
-            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
-        } else {
-            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, ptr::null_mut());
-        }
+        <StructureRef as glib::value::SetValueOptional>::set_value_optional(
+            v,
+            s.map(|s| s.as_ref()),
+        )
     }
 }
 
@@ -599,6 +598,41 @@ impl PartialEq for StructureRef {
 
 impl Eq for StructureRef {}
 
+impl glib::types::StaticType for StructureRef {
+    fn static_type() -> glib::types::Type {
+        unsafe { from_glib(gst_sys::gst_structure_get_type()) }
+    }
+}
+
+impl<'a> glib::value::FromValueOptional<'a> for &'a StructureRef {
+    unsafe fn from_value_optional(v: &'a glib::Value) -> Option<Self> {
+        let ptr = gobject_sys::g_value_get_boxed(v.to_glib_none().0);
+        if ptr.is_null() {
+            None
+        } else {
+            Some(StructureRef::from_glib_borrow(
+                ptr as *const gst_sys::GstStructure,
+            ))
+        }
+    }
+}
+
+impl glib::value::SetValue for StructureRef {
+    unsafe fn set_value(v: &mut glib::Value, s: &Self) {
+        gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
+    }
+}
+
+impl glib::value::SetValueOptional for StructureRef {
+    unsafe fn set_value_optional(v: &mut glib::Value, s: Option<&Self>) {
+        if let Some(s) = s {
+            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, s.as_ptr() as gpointer);
+        } else {
+            gobject_sys::g_value_set_boxed(v.to_glib_none_mut().0, ptr::null_mut());
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct FieldIterator<'a> {
     structure: &'a StructureRef,