[NFC] Add LookupConformancesInContextRequest

Add a request to lookup all implied conformances for use while
typechecking the primary. This provides a cache-point for
evaluator-based dependency tracking.

Author: CodaFi

include/swift/AST/TypeCheckRequests.h

@@ -2160,6 +2160,39 @@ class ClosureHasExplicitResultRequest
   bool isCached() const { return true; }
 };
 
+using ProtocolConformanceLookupResult = SmallVector<ProtocolConformance *, 2>;
+void simple_display(llvm::raw_ostream &out, ConformanceLookupKind kind);
+
+/// Lookup and expand all conformances in the given context.
+///
+/// This request specifically accomodates algorithms for retrieving all
+/// conformances in the primary, even those that are unstated in source but
+/// are implied by other conformances, inherited from other types, or synthesized
+/// by the compiler. A simple case of this is the following:
+///
+/// \code
+/// protocol P {}
+/// protocol Q : P {}
+/// extension T : Q {}
+/// \endcode
+///
+/// Here, a conformance to \c Q has been stated, but a conformance to \c P
+/// must also be reported so it can be checked as well.
+class LookupAllConformancesInContextRequest :
+    public SimpleRequest<LookupAllConformancesInContextRequest,
+                         ProtocolConformanceLookupResult(const DeclContext *),
+                         CacheKind::Uncached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  llvm::Expected<ProtocolConformanceLookupResult>
+  evaluate(Evaluator &evaluator, const DeclContext *DC) const;
+};
+
 // Allow AnyValue to compare two Type values, even though Type doesn't
 // support ==.
 template<>

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -234,3 +234,6 @@ SWIFT_REQUEST(TypeChecker, ScopedImportLookupRequest,
               ArrayRef<ValueDecl *>(ImportDecl *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ClosureHasExplicitResultRequest,
               bool(ClosureExpr *), Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, LookupAllConformancesInContextRequest,
+              ProtocolConformanceLookupResult(const DeclContext *),
+              Uncached, NoLocationInfo)

lib/AST/ProtocolConformance.cpp

@@ -1335,7 +1335,7 @@ DeclContext::getLocalProtocols(ConformanceLookupKind lookupKind) const {
   if (!nominal) {
     return result;
   }
-  
+
   // Update to record all potential conformances.
   nominal->prepareConformanceTable();
   nominal->ConformanceTable->lookupConformances(
@@ -1361,9 +1361,12 @@ DeclContext::getLocalConformances(ConformanceLookupKind lookupKind) const {
 
   // Protocols only have self-conformances.
   if (auto protocol = dyn_cast<ProtocolDecl>(nominal)) {
-    if (protocol->requiresSelfConformanceWitnessTable())
-      return { protocol->getASTContext().getSelfConformance(protocol) };
-    return { };
+    if (protocol->requiresSelfConformanceWitnessTable()) {
+      return SmallVector<ProtocolConformance *, 2>{
+        protocol->getASTContext().getSelfConformance(protocol)
+      };
+    }
+    return SmallVector<ProtocolConformance *, 2>();
   }
 
   // Update to record all potential conformances.

lib/Sema/TypeCheckProtocol.cpp

@@ -5011,6 +5011,12 @@ diagnoseMissingAppendInterpolationMethod(NominalTypeDecl *typeDecl) {
   }
 }
 
+llvm::Expected<SmallVector<ProtocolConformance *, 2>>
+LookupAllConformancesInContextRequest::evaluate(
+    Evaluator &eval, const DeclContext *DC) const {
+  return DC->getLocalConformances(ConformanceLookupKind::All);
+}
+
 void TypeChecker::checkConformancesInContext(DeclContext *dc,
                                              IterableDeclContext *idc) {
   // For anything imported from Clang, lazily check conformances.
@@ -5037,7 +5043,9 @@ void TypeChecker::checkConformancesInContext(DeclContext *dc,
     tracker = SF->getReferencedNameTracker();
 
   // Check each of the conformances associated with this context.
-  auto conformances = dc->getLocalConformances(ConformanceLookupKind::All);
+  auto conformances =
+      evaluateOrDefault(dc->getASTContext().evaluator,
+                        LookupAllConformancesInContextRequest{dc}, {});
 
   // The conformance checker bundle that checks all conformances in the context.
   auto &Context = dc->getASTContext();