Revert "Sema: Don't resolve protocol typealiases to DependentMemberTypes"

This reverts commit 1dd79ae.

Fixes rdar://problem/88230388.

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -431,18 +431,17 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
 
     if (selfType->is<GenericTypeParamType>()) {
       if (typeDecl->getDeclContext()->getSelfProtocolDecl()) {
-        auto *aliasDecl = dyn_cast<TypeAliasDecl>(typeDecl);
-        if (getStage() == TypeResolutionStage::Structural &&
-            aliasDecl && !aliasDecl->isGeneric()) {
-          return aliasDecl->getStructuralType();
-        }
-
-        if (auto assocType = dyn_cast<AssociatedTypeDecl>(typeDecl)) {
-          typeDecl = assocType->getAssociatedTypeAnchor();
+        if (isa<AssociatedTypeDecl>(typeDecl) ||
+            (isa<TypeAliasDecl>(typeDecl) &&
+             !cast<TypeAliasDecl>(typeDecl)->isGeneric())) {
+          if (getStage() == TypeResolutionStage::Structural) {
+            return DependentMemberType::get(selfType, typeDecl->getName());
+          } else if (auto assocType = dyn_cast<AssociatedTypeDecl>(typeDecl)) {
+            typeDecl = assocType->getAssociatedTypeAnchor();
+          }
         }
       }
 
-      // FIXME: Remove this once the above FIXME is addressed.
       if (typeDecl->getDeclContext()->getSelfClassDecl()) {
         // We found a member of a class from a protocol or protocol
         // extension.
@@ -2638,7 +2637,14 @@ TypeResolver::resolveAttributedType(TypeAttributes &attrs, TypeRepr *repr,
   // context, and then set isNoEscape if @escaping is not present.
   if (!ty) ty = resolveType(repr, instanceOptions);
   if (!ty || ty->hasError()) return ty;
-  
+
+  // Type aliases inside protocols are not yet resolved in the structural
+  // stage of type resolution
+  if (ty->is<DependentMemberType>() &&
+      resolution.getStage() == TypeResolutionStage::Structural) {
+    return ty;
+  }
+
   // Handle @escaping
   if (ty->is<FunctionType>()) {
     if (attrs.has(TAK_escaping)) {

test/Generics/infinite_concrete_type.swift

@@ -3,7 +3,7 @@
 class G<T> {}
 
 protocol P1 { // expected-error {{cannot build rewrite system for protocol; concrete nesting limit exceeded}}
-// expected-note@-1 {{failed rewrite rule is [P1:A].[concrete: G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<[P1:A]>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>] => [P1:A]}}
+// expected-note@-1 {{failed rewrite rule is [P1:A].[concrete: G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<G<[P1].A>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>] => [P1:A]}}
   associatedtype A where A == G<B>
   associatedtype B where B == G<A>
 }

test/Generics/protocol_typealias_cycle_1.swift

@@ -0,0 +1,20 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol P {
+  func invoke()
+
+  associatedtype X
+  associatedtype Y where Y : Q
+}
+
+protocol Q {
+  associatedtype T
+}
+
+struct S: Q {
+  typealias T = Int
+}
+
+extension P where X == () {
+  typealias Y = S
+}

test/Generics/protocol_typealias_cycle_2.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol P {
+  associatedtype T where T == Self
+  static func f() -> T
+}
+
+extension P {
+  typealias T = Self
+}

test/decl/protocol/req/associated_type_ambiguity.swift

@@ -1,17 +1,17 @@
 // RUN: %target-typecheck-verify-swift -requirement-machine-inferred-signatures=on -requirement-machine-protocol-signatures=on
-// RUN: not %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-inferred-signatures=on -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-inferred-signatures=on -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
 
 protocol P1 {
-  typealias T = Int // expected-note {{found this candidate}}
+  typealias T = Int
 }
 
 protocol P2 {
-  associatedtype T // expected-note {{found this candidate}}
+  associatedtype T
 }
 
 // CHECK: ExtensionDecl line={{.*}} base=P1
 // CHECK-NEXT: Generic signature: <Self where Self : P1, Self : P2>
-extension P1 where Self : P2, T == Int { // expected-error {{'T' is ambiguous for type lookup in this context}}
+extension P1 where Self : P2, T == Int {
   func takeT11(_: T) {}
   func takeT12(_: Self.T) {}
 }

test/decl/typealias/protocol.swift

@@ -268,7 +268,7 @@ extension P10 {
   typealias U = Float
 }
 
-extension P10 where T == Int { } // expected-warning{{neither type in same-type constraint ('Int' or 'Int') refers to a generic parameter or associated type}}
+extension P10 where T == Int { } // expected-warning{{neither type in same-type constraint ('Self.T' (aka 'Int') or 'Int') refers to a generic parameter or associated type}}
 
 extension P10 where A == X<T> { }
 
@@ -277,7 +277,7 @@ extension P10 where A == X<U> { }
 extension P10 where A == X<Self.U> { }
 
 extension P10 where V == Int { } // expected-warning {{'V' is deprecated: just use Int, silly}}
-// expected-warning@-1{{neither type in same-type constraint ('Int' or 'Int') refers to a generic parameter or associated type}}
+// expected-warning@-1{{neither type in same-type constraint ('Self.V' (aka 'Int') or 'Int') refers to a generic parameter or associated type}}
 
 // rdar://problem/36003312
 protocol P11 {

validation-test/compiler_crashers_2_fixed/sr11639.swift

@@ -1,4 +1,6 @@
-// RUN: %target-swift-frontend -emit-ir -primary-file %s -debug-generic-signatures -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
+// RUN: %target-swift-frontend -emit-ir -primary-file %s -debug-generic-signatures -requirement-machine-protocol-signatures=off 2>&1 | %FileCheck %s
+
+// FIXME: Get this working with -requirement-machine-protocol-signatures=on again
 
 public protocol FooProtocol {
   associatedtype Bar