Sema: Change a getInterfaceType() to hasInterfaceType() in a couple of places

ValueDecl::getInterfaceType() asserts if the decl has no interface
type; to check if the declaration has been type checked yet, use
hasInterfaceType().

Fixes <https://bugs.swift.org/browse/SR-4743>.

Author: slavapestov

lib/Sema/CSSimplify.cpp

@@ -2957,7 +2957,7 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
         return result.markErrorAlreadyDiagnosed();
 
       // FIXME: Deal with broken recursion
-      if (!ctor->getInterfaceType())
+      if (!ctor->hasInterfaceType())
         continue;
 
       // If the argument labels for this result are incompatible with
@@ -3054,7 +3054,7 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
     }
 
     // FIXME: Deal with broken recursion
-    if (!cand->getInterfaceType())
+    if (!cand->hasInterfaceType())
       return;
 
     // If the argument labels for this result are incompatible with
@@ -3241,7 +3241,11 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
         result.markErrorAlreadyDiagnosed();
         return result;
       }
-      
+
+      // FIXME: Deal with broken recursion
+      if (!cand->hasInterfaceType())
+        continue;
+
       result.addUnviable(cand, MemberLookupResult::UR_Inaccessible);
     }
   }

validation-test/compiler_crashers_2_fixed/0103-sr4743.swift

@@ -0,0 +1,19 @@
+// RUN: not %target-swift-frontend -typecheck -primary-file %s
+
+public struct _UIntBuffer<Storage, Element> {
+  var _storage: Storage
+  var _bitCount: UInt8
+}
+
+protocol _UTFDecoder {
+  associatedtype BufferStorage
+  associatedtype CodeUnit
+
+  var buffer: _UIntBuffer<BufferStorage, CodeUnit> { get set }
+}
+
+public struct ReverseDecoder : _UTFDecoder {
+  public typealias Buffer = _UIntBuffer<BufferStorage, UInt8>
+  public var buffer = Buffer()
+  public init() {}
+}