SILGen: Avoid crashing for invalid conformances.

Force resolution of value witnesses and check the conformance for validity
before proceeding to witness table emission in SILGen to avoid crashing because
of unexpected errors in the AST.

Resolves rdar://123027739

Author: tshortli

include/swift/AST/ProtocolConformance.h

@@ -747,6 +747,9 @@ class NormalProtocolConformance : public RootProtocolConformance,
   /// Override the witness for a given requirement.
   void overrideWitness(ValueDecl *requirement, Witness newWitness);
 
+  /// Triggers a request that resolves all of the conformance's value witnesses.
+  void resolveValueWitnesses() const;
+
   /// Determine whether the witness for the given type requirement
   /// is the default definition.
   bool usesDefaultDefinition(AssociatedTypeDecl *requirement) const {

lib/AST/ProtocolConformance.cpp

@@ -706,6 +706,13 @@ void NormalProtocolConformance::overrideWitness(ValueDecl *requirement,
   Mapping[requirement] = witness;
 }
 
+void NormalProtocolConformance::resolveValueWitnesses() const {
+  auto mutableThis = const_cast<NormalProtocolConformance *>(this);
+  evaluateOrDefault(getProtocol()->getASTContext().evaluator,
+                    ResolveValueWitnessesRequest{mutableThis},
+                    evaluator::SideEffect());
+}
+
 SpecializedProtocolConformance::SpecializedProtocolConformance(
     Type conformingType,
     NormalProtocolConformance *genericConformance,

lib/SILGen/SILGen.cpp

@@ -2106,7 +2106,7 @@ class SILGenModuleRAII {
         SGM.pendingForcedFunctions.pop_front();
       }
       while (!SGM.pendingConformances.empty()) {
-        SGM.getWitnessTable(SGM.pendingConformances.front());
+        (void)SGM.getWitnessTable(SGM.pendingConformances.front());
         SGM.pendingConformances.pop_front();
       }
     }

lib/SILGen/SILGenType.cpp

@@ -23,9 +23,9 @@
 #include "Scope.h"
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/GenericEnvironment.h"
-#include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/PropertyWrappers.h"
+#include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/SourceFile.h"
 #include "swift/AST/SubstitutionMap.h"
 #include "swift/AST/TypeMemberVisitor.h"
@@ -529,6 +529,11 @@ class SILGenConformance : public SILGenWitnessTable<SILGenConformance> {
     PrettyStackTraceConformance trace("generating SIL witness table",
                                       Conformance);
 
+    // Check whether the conformance is valid first.
+    Conformance->resolveValueWitnesses();
+    if (Conformance->isInvalid())
+      return nullptr;
+
     auto *proto = Conformance->getProtocol();
     visitProtocolDecl(proto);
 
@@ -1150,7 +1155,7 @@ class SILGenType : public TypeMemberVisitor<SILGenType> {
     for (auto *conformance : theType->getLocalConformances(
                                ConformanceLookupKind::NonInherited)) {
       if (auto *normal = dyn_cast<NormalProtocolConformance>(conformance))
-        SGM.getWitnessTable(normal);
+        (void)SGM.getWitnessTable(normal);
     }
   }
 
@@ -1309,7 +1314,7 @@ class SILGenExtension : public TypeMemberVisitor<SILGenExtension> {
       for (auto *conformance : e->getLocalConformances(
                                  ConformanceLookupKind::All)) {
         if (auto *normal =dyn_cast<NormalProtocolConformance>(conformance))
-          SGM.getWitnessTable(normal);
+          (void)SGM.getWitnessTable(normal);
       }
     }
   }

lib/Sema/CSDiagnostics.cpp

@@ -3473,9 +3473,7 @@ bool ContextualFailure::tryProtocolConformanceFixIt(
       evaluateOrDefault(getASTContext().evaluator,
                         ResolveTypeWitnessesRequest{conformance},
                         evaluator::SideEffect());
-      evaluateOrDefault(getASTContext().evaluator,
-                        ResolveValueWitnessesRequest{conformance},
-                        evaluator::SideEffect());
+      conformance->resolveValueWitnesses();
 
       fakeConformances.push_back(conformance);
     }

lib/Sema/CodeSynthesis.cpp

@@ -1401,9 +1401,7 @@ ResolveImplicitMemberRequest::evaluate(Evaluator &evaluator,
       // FIXME: This should be more fine-grained to avoid having to check
       // for a cycle here.
       if (!evaluator.hasActiveRequest(ResolveValueWitnessesRequest{conformance})) {
-        evaluateOrDefault(evaluator,
-                          ResolveValueWitnessesRequest{conformance},
-                          evaluator::SideEffect());
+        conformance->resolveValueWitnesses();
       }
     }
 

lib/Sema/TypeCheckDecl.cpp

@@ -2870,9 +2870,7 @@ static ArrayRef<Decl *> evaluateMembersRequest(
     }
 
     if (isDerivable) {
-      evaluateOrDefault(ctx.evaluator,
-                        ResolveValueWitnessesRequest{normal},
-                        evaluator::SideEffect());
+      normal->resolveValueWitnesses();
     }
   }
 

lib/Sema/TypeCheckProtocol.cpp

@@ -2472,9 +2472,7 @@ checkIndividualConformance(NormalProtocolConformance *conformance) {
   ensureRequirementsAreSatisfied(Context, conformance);
 
   // Check non-type requirements.
-  evaluateOrDefault(Context.evaluator,
-                    ResolveValueWitnessesRequest{conformance},
-                    evaluator::SideEffect());
+  conformance->resolveValueWitnesses();
 }
 
 /// Add the next associated type deduction to the string representation

lib/Sema/TypeCheckStorage.cpp

@@ -169,9 +169,7 @@ static void computeLoweredProperties(NominalTypeDecl *decl,
             evaluateOrDefault(ctx.evaluator,
                               ResolveTypeWitnessesRequest{normal},
                               evaluator::SideEffect());
-            evaluateOrDefault(ctx.evaluator,
-                              ResolveValueWitnessesRequest{normal},
-                              evaluator::SideEffect());
+            normal->resolveValueWitnesses();
           }
         }
       };

test/SILGen/lazy_typecheck_errors.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-frontend -emit-silgen %s -parse-as-library -module-name Test -enable-library-evolution -experimental-lazy-typecheck -verify
+
+public protocol Proto {
+  func req()
+}
+
+public struct ConformsToProtoMissingRequirement: Proto {
+  // expected-error@-1 {{type 'ConformsToProtoMissingRequirement' does not conform to protocol 'Proto'}}
+}
+
+public struct ConformsToProtoNearMiss: Proto {
+  // expected-error@-1 {{type 'ConformsToProtoNearMiss' does not conform to protocol 'Proto'}}
+
+  public func req(x: Int) {}
+}
+
+public protocol ProtoWithAssociatedType {
+  associatedtype A
+}
+
+public struct ConformsToProtoProtoWithAssociatedType: ProtoWithAssociatedType {
+  // expected-error@-1 {{type 'ConformsToProtoProtoWithAssociatedType' does not conform to protocol 'ProtoWithAssociatedType'}}
+}