AST: Preserve sugar in TypeMatcher::visitBoundGenericType()

Author: slavapestov

include/swift/AST/TypeMatcher.h

@@ -419,9 +419,8 @@ class TypeMatcher {
 
     bool visitBoundGenericType(CanBoundGenericType firstBGT,
                                Type secondType, Type sugaredFirstType) {
-      auto _secondBGT = secondType->getCanonicalType();
-      if (firstBGT->getKind() == _secondBGT->getKind()) {
-        auto secondBGT = cast<BoundGenericType>(_secondBGT);
+      if (firstBGT->getKind() == secondType->getDesugaredType()->getKind()) {
+        auto secondBGT = secondType->castTo<BoundGenericType>();
         if (firstBGT->getDecl() != secondBGT->getDecl())
           return mismatch(firstBGT.getPointer(), secondBGT, sugaredFirstType);
 

test/Generics/requirement_machine_diagnostics.swift

@@ -194,3 +194,7 @@ func inferred3<T : P11>(_: T) where T.X : Hashable, T.Z == Set<T.Y>, T.X == T.Y
 func inferred4<T : P11>(_: T) where T.Z == Set<T.Y>, T.X : Hashable, T.X == T.Y {}
 func inferred5<T : P11>(_: T) where T.Z == Set<T.X>, T.Y : Hashable, T.X == T.Y {}
 func inferred6<T : P11>(_: T) where T.Y : Hashable, T.Z == Set<T.X>, T.X == T.Y {}
+
+func typeMatcherSugar<T>(_: T) where Array<Int> == Array<T>, Array<Int> == Array<T> {}
+// expected-warning@-1 2{{redundant same-type constraint 'Array<Int>' == 'Array<T>'}}
+// expected-warning@-2{{redundant same-type constraint 'T' == 'Int'}}