[SourceKit] Move the cancellation flag from TypeCheckerOptions to ASTContext

We need to modify the pointer pointing to the cancellation flag when reusing an ASTContext for code completion. This is not possible by the previous design because `TypeCheckerOptions` was `const`. Moving the cancellation flag to `ASTContext` will also allow other stages of the compiler to honor a cancellation request.

Author: ahoppen

include/swift/AST/ASTContext.h

@@ -273,6 +273,15 @@ class ASTContext final {
   /// Diags - The diagnostics engine.
   DiagnosticEngine &Diags;
 
+  /// If the shared pointer is not a \c nullptr and the pointee is \c true,
+  /// all operations working on this ASTContext should be aborted at the next
+  /// possible opportunity.
+  /// This is used by SourceKit to cancel requests for which the result is no
+  /// longer of interest.
+  /// The returned result will be discarded, so the operation that acknowledges
+  /// the cancellation might return with any result.
+  std::shared_ptr<std::atomic<bool>> CancellationFlag = nullptr;
+
   TypeCheckCompletionCallback *CompletionCallback = nullptr;
 
   /// The request-evaluator that is used to process various requests.

include/swift/Basic/LangOptions.h

@@ -606,12 +606,6 @@ namespace swift {
     /// than this many seconds.
     unsigned ExpressionTimeoutThreshold = 600;
 
-    /// If the shared pointer is not a \c nullptr and the pointee is \c true,
-    /// typechecking should be aborted at the next possible opportunity.
-    /// This is used by SourceKit to cancel requests for which the result is no
-    /// longer of interest.
-    std::shared_ptr<std::atomic<bool>> CancellationFlag = nullptr;
-
     /// If non-zero, abort the switch statement exhaustiveness checker if
     /// the Space::minus function is called more than this many times.
     ///

include/swift/Sema/ConstraintSystem.h

@@ -5176,7 +5176,7 @@ class ConstraintSystem {
     if (isExpressionAlreadyTooComplex)
       return true;
 
-    auto CancellationFlag = getASTContext().TypeCheckerOpts.CancellationFlag;
+    auto CancellationFlag = getASTContext().CancellationFlag;
     if (CancellationFlag && CancellationFlag->load(std::memory_order_relaxed))
       return true;
 

tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp

@@ -1079,7 +1079,6 @@ ASTUnitRef ASTBuildOperation::buildASTUnit(std::string &Error) {
       Invocation, convertFileContentsToInputs(Contents));
 
   Invocation.getLangOptions().CollectParsedToken = true;
-  Invocation.getTypeCheckerOptions().CancellationFlag = CancellationFlag;
 
   if (FileSystem != llvm::vfs::getRealFileSystem()) {
     CompIns.getSourceMgr().setFileSystem(FileSystem);
@@ -1091,6 +1090,7 @@ ASTUnitRef ASTBuildOperation::buildASTUnit(std::string &Error) {
     Error = "compilation setup failed";
     return nullptr;
   }
+  CompIns.getASTContext().CancellationFlag = CancellationFlag;
   if (CompIns.loadStdlibIfNeeded()) {
     LOG_WARN_FUNC("Loading the stdlib failed");
     Error = "Loading the stdlib failed";