Rewrote RCow to make it covariant instead of invariant.

Fixing the lifetime issues (WRT RCow) in
#75

Changed how `RCow` is represented, requiring uses of the `RCow` type to be updated.

Added `RCowVal`, `RCowStr`, and `RCowSlice` type aliases to make `RCow` usable.

Updated uses of `RCow` in `abi_stable` to make it compile,
the repository will be fixed in a latter commit.

Updated RCow tests.

Added tests for comparison traits, conversion traits.

Added `IntoOwned` trait.

Made the comparison traits accept RCows with different type arguments.

Added these conversion impls:
- `From<&'a RVec<T>> for RCowSlice<'a, T>`
- `From<&'a Vec<T>> for RCowSlice<'a, T>`

Now the conversion impls between `Cow` and `RCow` are non-trivial,
using the new `RCowCompatibleRef` trait to simplify some bounds.

Now `RCow` only implements `IntoReprRust`/`AsRef`/`Borrow` for
`RCowVal`, `RCowSlice`, and `RCowStr`.

Removed `BorrowOwned` trait.

abi_stable/src/abi_stability/extra_checks.rs

@@ -63,7 +63,7 @@
 //!     marker_type::UnsafeIgnoredType,
 //!     sabi_extern_fn,
 //!     sabi_trait::prelude::TD_Opaque,
-//!     std_types::{RCow, ROption, RResult, RSome, RStr},
+//!     std_types::{RCowSlice, ROption, RResult, RSome, RStr},
 //!     type_layout::TypeLayout,
 //!     GetStaticEquivalent, StableAbi,
 //! };
@@ -219,8 +219,8 @@
 //!         })
 //!     }
 //!
-//!     fn nested_type_layouts(&self) -> RCow<'_, [&'static TypeLayout]> {
-//!         RCow::from_slice(&[])
+//!     fn nested_type_layouts(&self) -> RCowSlice<'_, &'static TypeLayout> {
+//!         RCowSlice::from(&[])
 //!     }
 //!
 //!     fn combine(
@@ -292,7 +292,7 @@
 //!     },
 //!     sabi_extern_fn,
 //!     sabi_trait::prelude::TD_Opaque,
-//!     std_types::{RCow, RDuration, ROption, RResult, RStr, RString},
+//!     std_types::{RCowSlice, RDuration, ROption, RResult, RStr, RString},
 //!     type_layout::TypeLayout,
 //!     StableAbi,
 //! };
@@ -374,8 +374,8 @@
 //!         })
 //!     }
 //!
-//!     fn nested_type_layouts(&self) -> RCow<'_, [&'static TypeLayout]> {
-//!         RCow::from_slice(&[])
+//!     fn nested_type_layouts(&self) -> RCowSlice<'_, &'static TypeLayout> {
+//!         RCowSlice::from(&[])
 //!     }
 //! }
 //!
@@ -421,7 +421,7 @@
 //!     marker_type::UnsafeIgnoredType,
 //!     sabi_extern_fn,
 //!     sabi_trait::prelude::TD_Opaque,
-//!     std_types::{RCow, RDuration, RResult, RStr, RString},
+//!     std_types::{RCowSlice, RDuration, RResult, RStr, RString},
 //!     type_layout::TypeLayout,
 //!     GetStaticEquivalent, StableAbi,
 //! };
@@ -558,8 +558,8 @@
 //!         })
 //!     }
 //!
-//!     fn nested_type_layouts(&self) -> RCow<'_, [&'static TypeLayout]> {
-//!         RCow::from_slice(&[])
+//!     fn nested_type_layouts(&self) -> RCowSlice<'_, &'static TypeLayout> {
+//!         RCowSlice::from(&[])
 //!     }
 //! }
 //!
@@ -592,7 +592,7 @@
 use crate::{
     rtry, sabi_trait,
     sabi_types::{RMut, RRef},
-    std_types::{RBox, RBoxError, RCow, RNone, ROk, ROption, RResult},
+    std_types::{RBox, RBoxError, RCowSlice, RNone, ROk, ROption, RResult},
     traits::IntoReprC,
     type_layout::TypeLayout,
     StableAbi,
@@ -706,7 +706,7 @@ pub unsafe trait ExtraChecks: 'static + Debug + Display + Clone + Send + Sync {
     /// Returns the `TypeLayout`s owned or referenced by `self`.
     ///
     /// This is necessary for the Debug implementation of `TypeLayout`.
-    fn nested_type_layouts(&self) -> RCow<'_, [&'static TypeLayout]>;
+    fn nested_type_layouts(&self) -> RCowSlice<'_, &'static TypeLayout>;
 
     /// Combines this ExtraChecks trait object with another one.
     ///

abi_stable/src/erased_types/enabled_traits_macro.rs

@@ -29,7 +29,7 @@ macro_rules! declare_enabled_traits {
                 ForExtraChecksImplementor,ExtraChecksError,
             },
             type_layout::TypeLayout,
-            std_types::{RCow,RResult},
+            std_types::{RCowSlice,RResult},
             StableAbi,
         };
 
@@ -129,8 +129,8 @@ macro_rules! declare_enabled_traits {
                 })
             }
 
-            fn nested_type_layouts(&self)->RCow<'_,[&'static TypeLayout]>{
-                RCow::from_slice(&[])
+            fn nested_type_layouts(&self)->RCowSlice<'_, &'static TypeLayout>{
+                RCowSlice::from_slice(&[])
             }
         }
 

abi_stable/src/multikey_map.rs

@@ -472,15 +472,15 @@ mod tests {
 
         let (ret, ret_discr) = map.get_or_insert(10, 1).split();
         *ret.value = 1234;
-        assert_matches!(InsertionTime::Now { .. } = ret_discr);
+        assert_matches!(ret_discr, InsertionTime::Now { .. });
 
         assert_matches!(
-            (&mut 1234, InsertionTime::Before { .. }) =
-                map.get_or_insert(10, 2).map(|x| x.value).split()
+            map.get_or_insert(10, 2).map(|x| x.value).split(),
+            (&mut 1234, InsertionTime::Before { .. })
         );
         assert_matches!(
-            (&mut 1234, InsertionTime::Before { .. }) =
-                map.get_or_insert(10, 3).map(|x| x.value).split()
+            map.get_or_insert(10, 3).map(|x| x.value).split(),
+            (&mut 1234, InsertionTime::Before { .. })
         );
     }
 
@@ -491,7 +491,7 @@ mod tests {
         let (ret, ret_discr) = map.get_or_insert(100, 1).split();
         let index0 = ret.index;
         *ret.value = 1234;
-        assert_matches!(InsertionTime::Now { .. } = ret_discr);
+        assert_matches!(ret_discr, InsertionTime::Now { .. });
 
         let index1 = map.get_or_insert(200, 200).into_inner().index;
         let index2 = map.get_or_insert(300, 300).into_inner().index;

abi_stable/src/std_types.rs

@@ -39,7 +39,7 @@ pub use self::{
     arc::RArc,
     boxed::RBox,
     cmp_ordering::RCmpOrdering,
-    cow::RCow,
+    cow::{RCow, RCowSlice, RCowStr, RCowVal},
     map::RHashMap,
     option::{RNone, ROption, RSome},
     result::{RErr, ROk, RResult},