Incremental migration of message.cc to Emit

PiperOrigin-RevId: 532314829

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

@@ -3640,36 +3640,52 @@ void MessageGenerator::GenerateSerializeOneField(io::Printer* p,
                                                  const FieldDescriptor* field,
                                                  int cached_has_bits_index) {
   auto v = p->WithVars(FieldVars(field, options_));
-  Formatter format(p);
-  if (!field->options().weak()) {
-    // For weakfields, PrintFieldComment is called during iteration.
-    PrintFieldComment(format, field);
-  }
+  auto emit_body = [&] {
+    field_generators_.get(field).GenerateSerializeWithCachedSizesToArray(p);
+  };
 
-  bool have_enclosing_if = false;
   if (field->options().weak()) {
-  } else if (HasHasbit(field)) {
-    // Attempt to use the state of cached_has_bits, if possible.
-    int has_bit_index = HasBitIndex(field);
-    auto v = p->WithVars(HasBitVars(field));
-    if (cached_has_bits_index == has_bit_index / 32) {
-      format("if (cached_has_bits & $has_mask$) {\n");
-    } else {
-      format("if (($has_bits$[$has_array_index$] & $has_mask$) != 0) {\n");
-    }
-
-    have_enclosing_if = true;
-  } else if (field->is_optional() && !HasHasbit(field)) {
-    have_enclosing_if = EmitFieldNonDefaultCondition(p, "this->", field);
+    emit_body();
+    p->Emit("\n");
+    return;
   }
 
-  if (have_enclosing_if) format.Indent();
-  field_generators_.get(field).GenerateSerializeWithCachedSizesToArray(p);
-  if (have_enclosing_if) {
-    format.Outdent();
-    format("}\n");
+  PrintFieldComment(Formatter{p}, field);
+  if (HasHasbit(field)) {
+    p->Emit(
+        {
+            {"body", emit_body},
+            {"cond",
+             [&] {
+               int has_bit_index = HasBitIndex(field);
+               auto v = p->WithVars(HasBitVars(field));
+               // Attempt to use the state of cached_has_bits, if possible.
+               if (cached_has_bits_index == has_bit_index / 32) {
+                 p->Emit("cached_has_bits & $has_mask$");
+               } else {
+                 p->Emit("($has_bits$[$has_array_index$] & $has_mask$) != 0");
+               }
+             }},
+        },
+        R"cc(
+          if ($cond$) {
+            $body$;
+          }
+        )cc");
+  } else if (field->is_optional()) {
+    bool have_enclosing_if = EmitFieldNonDefaultCondition(p, "this->", field);
+    if (have_enclosing_if) p->Indent();
+    emit_body();
+    if (have_enclosing_if) {
+      p->Outdent();
+      p->Emit(R"cc(
+        }
+      )cc");
+    }
+  } else {
+    emit_body();
   }
-  format("\n");
+  p->Emit("\n");
 }
 
 void MessageGenerator::GenerateSerializeOneExtensionRange(io::Printer* p,