De-register temporary buffer 'SourceFile's created during availability attribute argument parsing

Otherwise these source file objects linger in the source manager but they refer to a fully-temporary 'ASTContext' which does not exist after parsing is complete, which means they cannot be used in any way and attempting to do so would lead to a crash.

Author: artemcm

include/swift/Basic/SourceManager.h

@@ -381,6 +381,9 @@ class SourceManager {
   /// Record the source file as having the given buffer ID.
   void recordSourceFile(unsigned bufferID, SourceFile *sourceFile);
 
+  /// Remove the source file for the given buffer ID from records.
+  void deleteSourceFile(unsigned bufferID);
+
   /// Retrieve the source files for the given buffer ID.
   llvm::TinyPtrVector<SourceFile *>
   getSourceFilesForBufferID(unsigned bufferID) const;

lib/Basic/SourceLoc.cpp

@@ -219,6 +219,10 @@ void SourceManager::recordSourceFile(unsigned bufferID, SourceFile *sourceFile){
   bufferIDToSourceFiles[bufferID].push_back(sourceFile);
 }
 
+void SourceManager::deleteSourceFile(unsigned bufferID){
+  bufferIDToSourceFiles.erase(bufferID);
+}
+
 llvm::TinyPtrVector<SourceFile *>
 SourceManager::getSourceFilesForBufferID(unsigned bufferID) const {
   auto found = bufferIDToSourceFiles.find(bufferID);

lib/Parse/Parser.cpp

@@ -1199,6 +1199,8 @@ struct ParserUnit::Implementation {
   SerializationOptions SerializationOpts;
   DiagnosticEngine Diags;
   ASTContext &Ctx;
+  SourceManager &SM;
+  unsigned BufferID;
   SourceFile *SF;
   std::unique_ptr<Parser> TheParser;
 
@@ -1208,7 +1210,8 @@ struct ParserUnit::Implementation {
         SILOpts(SILOptions()), Diags(SM),
         Ctx(*ASTContext::get(LangOpts, TypeCheckerOpts, SILOpts, SearchPathOpts,
                              clangImporterOpts, symbolGraphOpts, CASOpts,
-                             SerializationOpts, SM, Diags)) {
+                             SerializationOpts, SM, Diags)),
+        SM(SM), BufferID(BufferID) {
     registerParseRequestFunctions(Ctx.evaluator);
 
     auto parsingOpts = SourceFile::getDefaultParsingOptions(LangOpts);
@@ -1222,6 +1225,7 @@ struct ParserUnit::Implementation {
 
   ~Implementation() {
     TheParser.reset();
+    SM.deleteSourceFile(BufferID);
     delete &Ctx;
   }
 };