Sema: Remove useBridgedNSErrorConformances()

The walker in SILGenLazyConformance.cpp should be sufficient to catch
any conformances needed at runtime, and after all the recent changes
SILGen is now able to trigger lazy conformance checking and synthesis
of fully-checked function bodies for accessors, which is enough to
remove the explicit conformance checks from Sema in this case.

Author: slavapestov

lib/Sema/CSApply.cpp

@@ -285,18 +285,6 @@ namespace {
     const Solution &solution;
     bool SuppressDiagnostics;
 
-    /// Recognize used conformances from an imported type when we must emit
-    /// the witness table.
-    ///
-    /// This arises in _BridgedStoredNSError, where we wouldn't
-    /// otherwise pull in the witness table, causing dynamic casts to
-    /// perform incorrectly, and _ErrorCodeProtocol, where we need to
-    /// check for _BridgedStoredNSError conformances on the
-    /// corresponding ErrorType.
-    void checkForImportedUsedConformances(Type toType) {
-      cs.getTypeChecker().useBridgedNSErrorConformances(dc, toType);
-    }
-
     /// Coerce the given tuple to another tuple type.
     ///
     /// \param expr The expression we're converting.
@@ -3189,7 +3177,6 @@ namespace {
       auto toType = simplifyType(cs.getType(expr->getCastTypeLoc()));
       auto sub = cs.coerceToRValue(expr->getSubExpr());
 
-      checkForImportedUsedConformances(toType);
       expr->setSubExpr(sub);
 
       // Set the type we checked against.
@@ -3557,7 +3544,6 @@ namespace {
       // Simplify the type we're casting to.
       auto toType = simplifyType(cs.getType(expr->getCastTypeLoc()));
       expr->getCastTypeLoc().setType(toType);
-      checkForImportedUsedConformances(toType);
 
       auto &tc = cs.getTypeChecker();
 
@@ -3650,7 +3636,6 @@ namespace {
         toType = toType->getOptionalObjectType();
 
       expr->getCastTypeLoc().setType(toType);
-      checkForImportedUsedConformances(toType);
 
       // The subexpression is always an rvalue.
       auto &tc = cs.getTypeChecker();
@@ -3729,7 +3714,6 @@ namespace {
                                            bool isInsideIsExpr = false) {
       // Simplify the type we're casting to.
       auto toType = simplifyType(cs.getType(expr->getCastTypeLoc()));
-      checkForImportedUsedConformances(toType);
       expr->getCastTypeLoc().setType(toType);
 
       // The subexpression is always an rvalue.
@@ -7449,11 +7433,7 @@ namespace {
     }
 
     Expr *walkToExprPost(Expr *expr) override {
-      Expr *result = Rewriter.walkToExprPost(expr);
-      auto &cs = Rewriter.getConstraintSystem();
-      if (result && cs.hasType(result))
-        Rewriter.checkForImportedUsedConformances(cs.getType(result));
-      return result;
+      return Rewriter.walkToExprPost(expr);
     }
 
     /// Ignore statements.

lib/Sema/TypeCheckPattern.cpp

@@ -1292,9 +1292,6 @@ bool TypeChecker::coercePatternToType(Pattern *&P, TypeResolution resolution,
 
     auto castType = IP->getCastTypeLoc().getType();
 
-    // Make sure we use any bridged NSError-related conformances.
-    useBridgedNSErrorConformances(dc, castType);
-
     // Determine whether we have an imbalance in the number of optionals.
     SmallVector<Type, 2> inputTypeOptionals;
     type->lookThroughAllOptionalTypes(inputTypeOptionals);

lib/Sema/TypeCheckProtocol.cpp

@@ -4299,55 +4299,6 @@ TypeChecker::LookUpConformance::operator()(
                           ConformanceCheckFlags::SkipConditionalRequirements));
 }
 
-void TypeChecker::useBridgedNSErrorConformances(DeclContext *dc, Type type) {
-  auto errorProto = Context.getProtocol(KnownProtocolKind::Error);
-  auto bridgedStoredNSError = Context.getProtocol(
-                                    KnownProtocolKind::BridgedStoredNSError);
-  auto errorCodeProto = Context.getProtocol(
-                              KnownProtocolKind::ErrorCodeProtocol);
-  auto rawProto = Context.getProtocol(
-                        KnownProtocolKind::RawRepresentable);
-
-  if (!errorProto || !bridgedStoredNSError || !errorCodeProto || !rawProto)
-    return;
-
-  // The NSError: Error conformance.
-  if (auto nsError = Context.getNSErrorDecl()) {
-    validateDecl(nsError);
-    (void)conformsToProtocol(nsError->TypeDecl::getDeclaredInterfaceType(),
-                             errorProto, dc, ConformanceCheckFlags::Used);
-  }
-
-  // _BridgedStoredNSError.
-  auto conformance = conformsToProtocol(type, bridgedStoredNSError, dc,
-                                        ConformanceCheckFlags::Used);
-  if (conformance && conformance->isConcrete()) {
-    // Hack: If we've used a conformance to the _BridgedStoredNSError
-    // protocol, also use the RawRepresentable and _ErrorCodeProtocol
-    // conformances on the Code associated type witness.
-    if (auto codeType = conformance->getTypeWitnessByName(
-                          type, Context.Id_Code)) {
-      (void)conformsToProtocol(codeType, errorCodeProto, dc,
-                               ConformanceCheckFlags::Used);
-      (void)conformsToProtocol(codeType, rawProto, dc,
-                               ConformanceCheckFlags::Used);
-    }
-  }
-
-  // _ErrorCodeProtocol.
-  conformance =
-  conformsToProtocol(type, errorCodeProto, dc,
-                     (ConformanceCheckFlags::SuppressDependencyTracking|
-                      ConformanceCheckFlags::Used));
-  if (conformance && conformance->isConcrete()) {
-    if (Type errorType = conformance->getTypeWitnessByName(
-          type, Context.Id_ErrorType)) {
-      (void)conformsToProtocol(errorType, bridgedStoredNSError, dc,
-                               ConformanceCheckFlags::Used);
-    }
-  }
-}
-
 void TypeChecker::checkConformance(NormalProtocolConformance *conformance) {
   MultiConformanceChecker checker(*this);
   checker.addConformance(conformance);

lib/Sema/TypeChecker.h

@@ -1690,10 +1690,6 @@ class TypeChecker final : public LazyResolver {
   /// Check that the type of the given property conforms to NSCopying.
   Optional<ProtocolConformanceRef> checkConformanceToNSCopying(VarDecl *var);
 
-  /// Mark any _BridgedNSError/_BridgedStoredNSError/related
-  /// conformances in the given type as "used".
-  void useBridgedNSErrorConformances(DeclContext *dc, Type type);
-
   /// Derive an implicit declaration to satisfy a requirement of a derived
   /// protocol conformance.
   ///