[incrParse] Support incremental parsing for edited files

include/swift/Frontend/Frontend.h

@@ -34,6 +34,7 @@
 #include "swift/Migrator/MigratorOptions.h"
 #include "swift/Parse/CodeCompletionCallbacks.h"
 #include "swift/Parse/Parser.h"
+#include "swift/Parse/SyntaxParsingCache.h"
 #include "swift/Sema/SourceLoader.h"
 #include "swift/Serialization/Validation.h"
 #include "swift/Subsystems.h"
@@ -68,6 +69,9 @@ class CompilerInvocation {
   MigratorOptions MigratorOpts;
   SILOptions SILOpts;
   IRGenOptions IRGenOpts;
+  /// The \c SyntaxParsingCache to use when parsing the main file of this
+  /// invocation
+  SyntaxParsingCache *MainFileSyntaxParsingCache = nullptr;
 
   llvm::MemoryBuffer *CodeCompletionBuffer = nullptr;
 
@@ -217,6 +221,14 @@ public:
   IRGenOptions &getIRGenOptions() { return IRGenOpts; }
   const IRGenOptions &getIRGenOptions() const { return IRGenOpts; }
 
+  void setMainFileSyntaxParsingCache(SyntaxParsingCache *Cache) {
+    MainFileSyntaxParsingCache = Cache;
+  }
+
+  SyntaxParsingCache *getMainFileSyntaxParsingCache() const {
+    return MainFileSyntaxParsingCache;
+  }
+
   void setParseStdlib() {
     FrontendOpts.ParseStdlib = true;
   }