ASTDemangler: Remove overly-zealous validation check when demangling constrained existential types

Author: slavapestov

lib/AST/ASTDemangler.cpp

@@ -674,8 +674,7 @@ Type ASTBuilder::createConstrainedExistentialType(
 
     case RequirementKind::SameType:
       if (auto *DMT = req.getFirstType()->getAs<DependentMemberType>())
-        if (baseDecl->getAssociatedType(DMT->getName()))
-          cmap[DMT->getName()] = req.getSecondType();
+        cmap[DMT->getName()] = req.getSecondType();
     }
   }
   llvm::SmallVector<Type, 4> args;

test/TypeDecoder/constrained_existentials.swift

@@ -0,0 +1,45 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-build-swift -emit-executable %s -g -o %t/constrained_existentials -emit-module -Xfrontend -disable-availability-checking
+// RUN: sed -ne '/\/\/ *DEMANGLE: /s/\/\/ *DEMANGLE: *//p' < %s > %t/input
+// RUN: %lldb-moduleimport-test %t/constrained_existentials -type-from-mangled=%t/input | %FileCheck %s
+
+func blackHole(_: Any...) {}
+
+protocol BaseProto<A, B> {
+  associatedtype A
+  associatedtype B
+}
+
+protocol DerivedProto<A, B>: BaseProto {}
+
+protocol OtherProto {}
+
+struct S<A, B>: DerivedProto, OtherProto {}
+
+// We should lift the artificial ban on compositions involving constrained protocol types
+typealias BaseProtoIntStringAndOtherProto = BaseProto<Int, String> & OtherProto
+
+do {
+  let e0: any BaseProto<Int, String> = S<Int, String>()
+  let e1: any BaseProto<Int, String>.Type = S<Int, String>.self
+  let e2: (any BaseProto<Int, String>).Type = (any BaseProto<Int, String>).self
+
+  blackHole(e0, e1, e2)
+}
+
+// DEMANGLE: $s24constrained_existentials9BaseProto_pSi1AAaBPRts_SS1BADRtsXPD
+// DEMANGLE: $s24constrained_existentials9BaseProto_pSi1AAaBPRts_SS1BADRtsXPXmTD
+// DEMANGLE: $s24constrained_existentials9BaseProto_pSi1AAaBPRts_SS1BADRtsXPXMtD
+
+// CHECK: BaseProto<Int, String>
+// CHECK: @thick BaseProto<Int, String>.Type
+// CHECK: @thin BaseProto<Int, String>.Protocol
+
+do {
+  let e0: any DerivedProto<Int, String> = S<Int, String>()
+  let e1: any DerivedProto<Int, String>.Type = S<Int, String>.self
+  let e2: (any DerivedProto<Int, String>).Type = (any DerivedProto<Int, String>).self
+
+  blackHole(e0, e1, e2)
+}