[SourceKit] Limit compiler instance reuse count for completions

Author: rintaro

include/swift/IDE/CompletionInstance.h

@@ -37,6 +37,8 @@ makeCodeCompletionMemoryBuffer(const llvm::MemoryBuffer *origBuf,
 class CompletionInstance {
   std::unique_ptr<CompilerInstance> CachedCI = nullptr;
   bool EnableASTCaching = false;
+  unsigned MaxASTReuseCount = 100;
+  unsigned CurrentASTReuseCount = 0;
 
   swift::CompilerInstance *
   getReusingCompilerInstance(const swift::CompilerInvocation &Invocation,

lib/IDE/CompletionInstance.cpp

@@ -202,6 +202,11 @@ CompilerInstance *CompletionInstance::getReusingCompilerInstance(
   if (!EnableASTCaching)
     return nullptr;
 
+  if (CurrentASTReuseCount >= MaxASTReuseCount) {
+    CurrentASTReuseCount = 0;
+    return nullptr;
+  }
+
   if (!CachedCI)
     return nullptr;
 
@@ -296,6 +301,8 @@ CompilerInstance *CompletionInstance::getReusingCompilerInstance(
       SM.getLocForOffset(BufferID, newInfo.StartOffset),
       diag::completion_reusing_astcontext);
 
+  CurrentASTReuseCount += 1;
+
   return CachedCI.get();
 }