Sema: Fix re-entrant call to ensureRequirementsAreSatisfied() when resolving associated conformances

ConformanceChecker::ensureRequirementsAreSatisfied() modifies the
conformance as it resolves each one of its associated conformances,
so a re-entrant call can end up corrupting state by adding too
many elements to the buffer, or adding elements at the wrong
offsets.

If TypeChecker::checkConformanceRequirements() was called before
ConformanceChecker::resolveTypeWitnesses(), we could re-entrantly call
ConformanceChecker::ensureRequirementsAreSatisfied():

TypeChecker::checkConformanceRequirements()
=> ConformanceChecker::ensureRequirementsAreSatisfied()
   => Type::subst(), etc
      => ConformanceChecker::resolveTypeWitnesses()
         => ConformanceChecker::ensureRequirementsAreSatisfied()

The code in SubstitutionMap::lookupConformance() worked around
this by checking the failure condition and calling
resolveTypeWitness() first, before calling getAssociatedConformance().

Instead, remove this and call resolveTypeWitness() from inside
NormalProtocolConformance::getAssociatedConformance().

Author: slavapestov

include/swift/AST/LazyResolver.h

@@ -78,10 +78,6 @@ class LazyResolver {
   /// Mark the given conformance as "used" from the given declaration context.
   virtual void markConformanceUsed(ProtocolConformanceRef conformance,
                                    DeclContext *dc) = 0;
-
-  /// Fill in the signature conformances of the given protocol conformance.
-  virtual void checkConformanceRequirements(
-                                    NormalProtocolConformance *conformance) = 0;
 };
 
 class LazyMemberLoader;

lib/AST/ProtocolConformance.cpp

@@ -904,8 +904,9 @@ NormalProtocolConformance::getAssociatedConformance(Type assocType,
   // Fill in the signature conformances, if we haven't done so yet.
   if (getSignatureConformances().empty()) {
     assocType->getASTContext().getLazyResolver()
-      ->checkConformanceRequirements(
-        const_cast<NormalProtocolConformance *>(this));
+      ->resolveTypeWitness(
+        const_cast<NormalProtocolConformance *>(this),
+        nullptr);
   }
 
   assert(!getSignatureConformances().empty() &&

lib/AST/SubstitutionMap.cpp

@@ -416,17 +416,6 @@ SubstitutionMap::lookupConformance(CanType type, ProtocolDecl *proto) const {
       // to use that.
       if (normal->getState() == ProtocolConformanceState::CheckingTypeWitnesses)
         return None;
-
-      auto lazyResolver = type->getASTContext().getLazyResolver();
-      if (lazyResolver == nullptr)
-        return None;
-
-      lazyResolver->resolveTypeWitness(normal, nullptr);
-
-      // Error case: the conformance is broken, so we cannot handle this
-      // substitution.
-      if (normal->getSignatureConformances().empty())
-        return None;
     }
 
     // Get the associated conformance.

lib/Sema/TypeChecker.h

@@ -1676,8 +1676,7 @@ class TypeChecker final : public LazyResolver {
   void checkConformance(NormalProtocolConformance *conformance);
 
   /// Check the requirement signature of the given conformance.
-  void checkConformanceRequirements(NormalProtocolConformance *conformance)
-         override ;
+  void checkConformanceRequirements(NormalProtocolConformance *conformance);
 
   /// Check all of the conformances in the given context.
   void checkConformancesInContext(DeclContext *dc,

test/IRGen/Inputs/signature_conformances_other.swift

@@ -0,0 +1,11 @@
+protocol Q {
+  associatedtype T
+}
+
+protocol P : Q {
+  associatedtype U
+}
+
+struct Conforms<T, U> : P {}
+
+func takesP<T : P>(_: T) {}

test/IRGen/signature_conformances_multifile.swift

@@ -0,0 +1,16 @@
+// RUN: %target-swift-frontend -emit-ir -primary-file %s %S/Inputs/signature_conformances_other.swift | %FileCheck %s
+
+// Make sure we correctly determine the witness table is dependent, even though
+// it was defined in a different file.
+
+// CHECK-LABEL: define hidden swiftcc void @"$s32signature_conformances_multifile5passPyyF"()
+func passP() {
+  // CHECK: call swiftcc void @"$s32signature_conformances_multifile8ConformsVACyxq_GycfC"(%swift.type* @"$sSiN", %swift.type* @"$sSSN")
+  // CHECK: %0 = call swiftcc %swift.metadata_response @"$s32signature_conformances_multifile8ConformsVySiSSGMa"
+  // CHECK: %1 = extractvalue %swift.metadata_response %0
+  // CHECK: %2 = call i8** @"$s32signature_conformances_multifile8ConformsVySiSSGACyxq_GAA1PAAWl"()
+  // CHECK: call swiftcc void @"$s32signature_conformances_multifile6takesPyyxAA1PRzlF"(%swift.opaque* noalias nocapture undef, %swift.type* %1, i8** %2)
+  takesP(Conforms<Int, String>())
+
+  // CHECK: ret void
+}