Move the Parse trait out of gencode and into the runtime

As part of this, I also removed the inherent methods `parse` and
`parse_dont_enforce_required` from generated messages. This changes the API in
a way that requires fixes for code that's not using our prelude (requires
adding `use protobuf::Parse`).

The blanket implementation of the trait is the same for both the C++ and upb
kernels, so I just put it directly in codegen_traits.rs.

PiperOrigin-RevId: 804967515

Author: Adam Cozzette

rust/codegen_traits.rs

@@ -75,6 +75,22 @@ pub(crate) mod create {
         fn parse(serialized: &[u8]) -> Result<Self, crate::ParseError>;
         fn parse_dont_enforce_required(serialized: &[u8]) -> Result<Self, crate::ParseError>;
     }
+
+    impl<T> Parse for T
+    where
+        Self: Default + crate::ClearAndParse,
+    {
+        fn parse(serialized: &[u8]) -> Result<Self, crate::ParseError> {
+            let mut msg = Self::default();
+            crate::ClearAndParse::clear_and_parse(&mut msg, serialized).map(|_| msg)
+        }
+
+        fn parse_dont_enforce_required(serialized: &[u8]) -> Result<Self, crate::ParseError> {
+            let mut msg = Self::default();
+            crate::ClearAndParse::clear_and_parse_dont_enforce_required(&mut msg, serialized)
+                .map(|_| msg)
+        }
+    }
 }
 
 /// Operations related to reading some aspect of a message (methods that would

src/google/protobuf/compiler/rust/message.cc

@@ -591,16 +591,6 @@ void GenerateRs(Context& ctx, const Descriptor& msg, const upb::DefPool& pool) {
           }
         }
 
-        impl $pb$::Parse for $Msg$ {
-          fn parse(serialized: &[u8]) -> $Result$<Self, $pb$::ParseError> {
-            Self::parse(serialized)
-          }
-
-          fn parse_dont_enforce_required(serialized: &[u8]) -> $Result$<Self, $pb$::ParseError> {
-            Self::parse_dont_enforce_required(serialized)
-          }
-        }
-
         impl $std$::fmt::Debug for $Msg$ {
           fn fmt(&self, f: &mut $std$::fmt::Formatter<'_>) -> $std$::fmt::Result {
             $Msg::debug$
@@ -808,16 +798,6 @@ void GenerateRs(Context& ctx, const Descriptor& msg, const upb::DefPool& pool) {
 
           $raw_arena_getter_for_message$
 
-          pub fn parse(data: &[u8]) -> $Result$<Self, $pb$::ParseError> {
-            let mut msg = Self::new();
-            $pb$::ClearAndParse::clear_and_parse(&mut msg, data).map(|_| msg)
-          }
-
-          pub fn parse_dont_enforce_required(data: &[u8]) -> $Result$<Self, $pb$::ParseError> {
-            let mut msg = Self::new();
-            $pb$::ClearAndParse::clear_and_parse_dont_enforce_required(&mut msg, data).map(|_| msg)
-          }
-
           pub fn as_view(&self) -> $Msg$View<'_> {
             $pbr$::MessageViewInner::view_of_owned(&self.inner).into()
           }