[Type checker] Short-circuit uses of concrete typealiases in protocols.

Hack to allow IndexDistance to become a deprecated typealias. The actual
fix here involves deeper surgery into the substitution machinery.

Author: DougGregor

lib/Sema/TypeCheckGeneric.cpp

@@ -202,6 +202,11 @@ Type CompleteGenericTypeResolver::resolveDependentMemberType(
     if (auto proto =
           concrete->getDeclContext()
             ->getAsProtocolOrProtocolExtensionContext()) {
+      // Fast path: if there are no type parameters in the concrete type, just
+      // return it.
+      if (!concrete->getInterfaceType()->hasTypeParameter())
+        return concrete->getInterfaceType();
+
       tc.validateDecl(proto);
       auto subMap = SubstitutionMap::getProtocolSubstitutions(
                       proto, baseTy, ProtocolConformanceRef(proto));

test/decl/typealias/protocol.swift

@@ -245,3 +245,10 @@ struct CandyEdible : Edible {
 // Edible.Snack is witnessed by 'typealias Snack' inside the
 // constrained extension of CandyWrapper above
 extension CandyBar : Edible {}
+
+protocol P9 {
+  typealias A = Int
+}
+
+func testT9a<T: P9, U>(_: T, _: U) where T.A == U { }
+func testT9b<T: P9>(_: T) where T.A == Float { } // expected-error{{'T.A' cannot be equal to both 'Float' and 'P9.A' (aka 'Int')}}

validation-test/compiler_crashers/28779-parent-parent-is-nominaltype-parent-is-boundgenerictype-parent-is-unboundgeneric.swift renamed to validation-test/compiler_crashers_fixed/28779-parent-parent-is-nominaltype-parent-is-boundgenerictype-parent-is-unboundgeneric.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol P{func a:Self.a.a{}class a{class a