Reify our unifying dreams

This CL collapses (strings, bytes) into primitives for message.cc::GetterForViewOrMut.

Strings, bytes, and all primitives have been unified, properly parameterized based on RsType.
Returning $pb$::Mut<$RsType$> and $pb$::View<$RsType$> made this possible.

Note that the vtables for primitives take in an additional type arg, so we've added that.
In addition, strings / bytes (aka stringlikes) require a transform, so that'll be invoked on an as-needed basis.

PiperOrigin-RevId: 592328216

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

@@ -9,6 +9,7 @@
 
 #include "absl/log/absl_check.h"
 #include "absl/log/absl_log.h"
+#include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
 #include "google/protobuf/compiler/cpp/helpers.h"
 #include "google/protobuf/compiler/cpp/names.h"
@@ -163,6 +164,10 @@ void MessageDrop(Context& ctx, const Descriptor& msg) {
   )rs");
 }
 
+bool IsStringOrBytes(FieldDescriptor::Type t) {
+  return t == FieldDescriptor::TYPE_STRING || t == FieldDescriptor::TYPE_BYTES;
+}
+
 void GetterForViewOrMut(Context& ctx, const FieldDescriptor& field,
                         bool is_mut) {
   auto fieldName = field.name();
@@ -218,69 +223,42 @@ void GetterForViewOrMut(Context& ctx, const FieldDescriptor& field,
   }
 
   auto rsType = PrimitiveRsTypeName(field);
-  if (fieldType == FieldDescriptor::TYPE_STRING ||
-      fieldType == FieldDescriptor::TYPE_BYTES) {
-    ctx.Emit({{"field", fieldName},
-              {"self", self},
-              {"getter_thunk", getter_thunk},
-              {"setter_thunk", setter_thunk},
-              {"RsType", rsType},
-              {"maybe_mutator",
-               [&] {
-                 if (is_mut) {
-                   ctx.Emit({}, R"rs(
-                    pub fn r#$field$_mut(&self) -> $pb$::Mut<'_, $RsType$> {
-                       static VTABLE: $pbi$::BytesMutVTable = 
-                        $pbi$::BytesMutVTable::new(
-                          $pbi$::Private,
-                          $getter_thunk$,
-                          $setter_thunk$,
-                        );
-
-                       unsafe {
-                        <$pb$::Mut<$RsType$>>::from_inner(
-                          $pbi$::Private,
-                          $pbi$::RawVTableMutator::new(
-                            $pbi$::Private,
-                            self.inner,
-                            &VTABLE,
-                           )
-                        )
-                      }
-                    }
-                    )rs");
-                 }
-               }}},
-             R"rs(
-              pub fn r#$field$(&self) -> $pb$::View<'_, $RsType$> {
-                let s = unsafe { $getter_thunk$($self$).as_ref() };
-                unsafe { __pb::ProtoStr::from_utf8_unchecked(s).into() }
-              }
+  auto asRef = IsStringOrBytes(fieldType) ? ".as_ref()" : "";
+  auto vtable =
+      IsStringOrBytes(fieldType) ? "BytesMutVTable" : "PrimitiveVTable";
+  // PrimitiveVtable is parameterized based on the underlying primitive, like
+  // u32 so we need to provide this additional type arg
+  auto optionalTypeArgs =
+      IsStringOrBytes(fieldType) ? "" : absl::StrFormat("<%s>", rsType);
+  // need to stuff ProtoStr and [u8] behind a reference since they are DSTs
+  auto stringTransform =
+      IsStringOrBytes(fieldType)
+          ? "unsafe { __pb::ProtoStr::from_utf8_unchecked(res).into() }"
+          : "res";
 
-              $maybe_mutator$
-            )rs");
-  } else {
   ctx.Emit({{"field", fieldName},
             {"getter_thunk", getter_thunk},
             {"setter_thunk", setter_thunk},
             {"clearer_thunk", clearer_thunk},
             {"self", self},
             {"RsType", rsType},
+            {"as_ref", asRef},
+            {"vtable", vtable},
+            {"optional_type_args", optionalTypeArgs},
+            {"string_transform", stringTransform},
             {"maybe_mutator",
              [&] {
-                 // TODO: once the rust public api is accessible,
-                 // by tooling, ensure that this only appears for the
-                 // mutational pathway
-                 if (is_mut && fieldType) {
+               // TODO: check mutational pathway genn'd correctly
+               if (is_mut) {
                  ctx.Emit({}, R"rs(
                   pub fn r#$field$_mut(&self) -> $pb$::Mut<'_, $RsType$> {
-                      static VTABLE: $pbi$::PrimitiveVTable<$RsType$> =
-                        $pbi$::PrimitiveVTable::new(
+                    static VTABLE: $pbi$::$vtable$$optional_type_args$ =
+                      $pbi$::$vtable$::new(
                         $pbi$::Private,
                         $getter_thunk$,
                         $setter_thunk$);
                     unsafe {
-                        $pb$::PrimitiveMut::from_inner(
+                      <$pb$::Mut<$RsType$>>::from_inner(
                         $pbi$::Private,
                         $pbi$::RawVTableMutator::new(
                           $pbi$::Private,
@@ -295,12 +273,12 @@ void GetterForViewOrMut(Context& ctx, const FieldDescriptor& field,
              }}},
            R"rs(
           pub fn r#$field$(&self) -> $pb$::View<'_, $RsType$> {
-              unsafe { $getter_thunk$($self$) }
+            let res = unsafe { $getter_thunk$($self$)$as_ref$ };
+            $string_transform$
           }
 
           $maybe_mutator$
         )rs");
-  }
 }
 
 void AccessorsForViewOrMut(Context& ctx, const Descriptor& msg, bool is_mut) {