[CS] Quick workaround for rdar://160135085

Temporarily disable the checking requirements for typealias types,
and desugar the typealias since the constraint system does not
currently correctly handle type variables in the underlying type.

lib/Sema/TypeOfReference.cpp

@@ -268,9 +268,7 @@ public:
     auto substTy = TypeAliasType::get(
         aliasTy->getDecl(), transform(aliasTy->getParent()), genericArgs,
         transform(aliasTy->getSinglyDesugaredType()));
-    openGenericTypeRequirements(substTy->getDecl(),
-                                substTy->getSubstitutionMap());
-    return substTy;
+    return substTy->getSinglyDesugaredType();
   }
 
   Type transformErrorType(ErrorType *errTy) {

test/Constraints/rdar160135085.swift

@@ -0,0 +1,24 @@
+// RUN: %empty-directory(%t/modules)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/modules/A.swiftmodule -module-name A %t/a.swift
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/modules/B.swiftmodule -module-name B -I %t/modules %t/b.swift
+// RUN: %target-swift-frontend -typecheck -I %t/modules %t/c.swift
+
+//--- a.swift
+
+public struct S<T> {
+  public init(_ x: T) {}
+}
+
+//--- b.swift
+
+import A
+public typealias S = A.S
+
+//--- c.swift
+
+import A
+import B
+
+_ = S(0)

test/Constraints/requirement_opening.swift

@@ -1,4 +1,5 @@
 // RUN: %target-typecheck-verify-swift
+// REQUIRES: rdar160135085
 
 struct K<U> {} // expected-note 6{{'U' declared as parameter to type 'K'}}
 protocol Q {}

test/decl/typealias/generic.swift

@@ -465,3 +465,19 @@ func testSugar(_ gx: GX<Int>, _ gy: GX<Int>.GY<Double>, gz: GX<Int>.GY<Double>.E
   let i2: Int = gy  // expected-error{{cannot convert value of type 'GX<Int>.GY<Double>' (aka 'Array<Double>') to specified type 'Int'}}
   let i3: Int = gz // expected-error{{cannot convert value of type 'GX<Int>.GY<Double>.Element' (aka 'Double') to specified type 'Int'}}
 }
+
+func testLocalRequirementInference<T>(_ x: T, y: Int, s: S) {
+  typealias X<U: P> = (T, U) where T == U.A
+  func foo<V>(_ x: X<V>) {} // expected-note {{where 'V' = 'Int'}} expected-note {{where 'T' = 'T', 'V.A' = 'S.A' (aka 'Float')}}
+  foo((x, y)) // expected-error {{local function 'foo' requires that 'Int' conform to 'P'}}
+  foo((x, s)) // expected-error {{local function 'foo' requires the types 'T' and 'S.A' (aka 'Float') be equivalent}}
+}
+
+struct TestNestedRequirementInference<T> {
+  typealias X<U: P> = (T, U) where T == U.A
+  func foo<V>(_ x: X<V>) {} // expected-note {{where 'V' = 'Int'}} expected-note {{where 'T' = 'T', 'V.A' = 'S.A' (aka 'Float')}}
+  func bar(_ x: T, y: Int, s: S) {
+    foo((x, y)) // expected-error {{instance method 'foo' requires that 'Int' conform to 'P'}}
+    foo((x, s)) // expected-error {{instance method 'foo' requires the types 'T' and 'S.A' (aka 'Float') be equivalent}}
+  }
+}

validation-test/compiler_crashers_2_fixed/078aab8ab466b66a.swift

@@ -0,0 +1,6 @@
+// {"kind":"typecheck","signature":"swift::constraints::ConstraintSystem::openGenericParameters(swift::DeclContext*, swift::GenericSignature, llvm::SmallVectorImpl<std::__1::pair<swift::GenericTypeParamType*, swift::TypeVariableType*>>&, swift::constraints::ConstraintLocatorBuilder, swift::constraints::PreparedOverloadBuilder*)","signatureAssert":"Assertion failed: (sig), function openGenericParameters"}
+// RUN: not %target-swift-frontend -typecheck %s
+class a<b
+  func c -> d
+  typealias c  :  a
+c

validation-test/compiler_crashers_2_fixed/b31917ad9b8e4fe4.swift

@@ -0,0 +1,8 @@
+// {"kind":"typecheck","original":"0df5dc82","signature":"swift::constraints::ConstraintSystem::typeVarOccursInType(swift::TypeVariableType*, swift::Type, bool*)","signatureAssert":"Assertion failed: ((!typeVariables.empty() || hasError()) && \"Did not find type variables!\"), function getTypeVariables"}
+// RUN: not %target-swift-frontend -typecheck %s
+struct a<each b {
+  typealias d<c> = (
+  >  func  1 {
+    typealias e = f
+    e
+    typealias e = d