[Serialization] Intro the DESERIALIZATION_SAFETY record format

The DESERIALIZATION_SAFETY record will be used by the deserialization
safety feature to identify decls that are unsafe to read so they can be
skipped.

Author: xymus

lib/Serialization/DeclTypeRecordNodes.def

@@ -182,6 +182,8 @@ OTHER(LOCAL_DISCRIMINATOR, 127)
 OTHER(PRIVATE_DISCRIMINATOR, 128)
 OTHER(FILENAME_FOR_PRIVATE, 129)
 
+OTHER(DESERIALIZATION_SAFETY, 130)
+
 // 140 is unused; was ABSTRACT_PROTOCOL_CONFORMANCE
 OTHER(NORMAL_PROTOCOL_CONFORMANCE, 141)
 OTHER(SPECIALIZED_PROTOCOL_CONFORMANCE, 142)

lib/Serialization/Deserialization.cpp

@@ -5411,6 +5411,9 @@ llvm::Error DeclDeserializer::deserializeDeclCommon() {
       IdentifierID filenameID;
       decls_block::FilenameForPrivateLayout::readRecord(scratch, filenameID);
       filenameForPrivate = MF.getIdentifierText(filenameID);
+    } else if (recordID == decls_block::DESERIALIZATION_SAFETY) {
+      IdentifierID declID;
+      decls_block::DeserializationSafetyLayout::readRecord(scratch, declID);
     } else {
       return llvm::Error::success();
     }

lib/Serialization/ModuleFormat.h

@@ -58,7 +58,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 731; // macro definition
+const uint16_t SWIFTMODULE_VERSION_MINOR = 732; // deserialization safety
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
@@ -1809,6 +1809,11 @@ namespace decls_block {
     IdentifierIDField  // the file name, as an identifier
   >;
 
+  using DeserializationSafetyLayout = BCRecordLayout<
+    DESERIALIZATION_SAFETY,
+    IdentifierIDField // name to debug access to unsafe decl
+  >;
+
   using NormalProtocolConformanceLayout = BCRecordLayout<
     NORMAL_PROTOCOL_CONFORMANCE,
     DeclIDField, // the protocol

lib/Serialization/Serialization.cpp

@@ -5336,6 +5336,7 @@ void Serializer::writeAllDeclsAndTypes() {
   registerDeclTypeAbbr<LocalDiscriminatorLayout>();
   registerDeclTypeAbbr<PrivateDiscriminatorLayout>();
   registerDeclTypeAbbr<FilenameForPrivateLayout>();
+  registerDeclTypeAbbr<DeserializationSafetyLayout>();
   registerDeclTypeAbbr<MembersLayout>();
   registerDeclTypeAbbr<XRefLayout>();