[Request-evaluator] Disable cycle diagnostics when used in the type checker.

The type checker has *lots* cycles, and producing diagnostics for them
at this point in the development of the request-evaluator is not
productive because it breaks currently-working code. Disable cycle
diagnostics for now when using the request-evaluator in the type
checker. We'll enable it later as things improve, or as a separate
logging mode in the interim.

Author: DougGregor

include/swift/AST/Evaluator.h

@@ -107,6 +107,9 @@ class Evaluator {
   /// diagnostics will be emitted.
   DiagnosticEngine &diags;
 
+  /// Whether to diagnose cycles or ignore them completely.
+  bool shouldDiagnoseCycles;
+
   /// A vector containing all of the active evaluation requests, which
   /// is treated as a stack and is used to detect cycles.
   llvm::SetVector<AnyRequest> activeRequests;
@@ -128,7 +131,7 @@ class Evaluator {
 public:
   /// Construct a new evaluator that can emit cyclic-dependency
   /// diagnostics through the given diagnostics engine.
-  Evaluator(DiagnosticEngine &diags);
+  Evaluator(DiagnosticEngine &diags, bool shouldDiagnoseCycles);
 
   /// Evaluate the given request and produce its result,
   /// consulting/populating the cache as required.

lib/AST/ASTContext.cpp

@@ -463,7 +463,7 @@ ASTContext::ASTContext(LangOptions &langOpts, SearchPathOptions &SearchPathOpts,
     SearchPathOpts(SearchPathOpts),
     SourceMgr(SourceMgr),
     Diags(Diags),
-    evaluator(Diags),
+    evaluator(Diags, /*shouldDiagnoseCycles=*/false),
     TheBuiltinModule(createBuiltinModule(*this)),
     StdlibModuleName(getIdentifier(STDLIB_NAME)),
     SwiftShimsModuleName(getIdentifier(SWIFT_SHIMS_NAME)),

lib/AST/Evaluator.cpp

@@ -32,7 +32,8 @@ std::string AnyRequest::getAsString() const {
   return result;
 }
 
-Evaluator::Evaluator(DiagnosticEngine &diags) : diags(diags) { }
+Evaluator::Evaluator(DiagnosticEngine &diags, bool shouldDiagnoseCycles)
+  : diags(diags), shouldDiagnoseCycles(shouldDiagnoseCycles) { }
 
 bool Evaluator::checkDependency(const AnyRequest &request) {
   // If there is an active request, record it's dependency on this request.
@@ -44,7 +45,9 @@ bool Evaluator::checkDependency(const AnyRequest &request) {
     return false;
   }
 
-  diagnoseCycle(request);
+  if (shouldDiagnoseCycles)
+    diagnoseCycle(request);
+
   return true;
 }
 

unittests/AST/ArithmeticEvaluator.cpp

@@ -200,7 +200,7 @@ TEST(ArithmeticEvaluator, Simple) {
 
   SourceManager sourceMgr;
   DiagnosticEngine diags(sourceMgr);
-  Evaluator evaluator(diags);
+  Evaluator evaluator(diags, /*shouldDiagnoseCycles=*/true);
 
   const double expectedResult = (3.14159 + 2.71828) * 42.0;
   EXPECT_EQ(evaluator(InternallyCachedEvaluationRule(product)),
@@ -320,7 +320,7 @@ TEST(ArithmeticEvaluator, Cycle) {
 
   SourceManager sourceMgr;
   DiagnosticEngine diags(sourceMgr);
-  Evaluator evaluator(diags);
+  Evaluator evaluator(diags, /*shouldDiagnoseCycles=*/true);
 
   // Evaluate when there is a cycle.
   UncachedEvaluationRule::brokeCycle = false;