fix: Initialize additional fields in the AST (#4930)

Fixes #4893

Source/DafnyCore/AST/TypeDeclarations/NewtypeDecl.cs

@@ -30,6 +30,7 @@ public NewtypeDecl(RangeToken rangeToken, Name name, ModuleDefinition module, Ty
     Contract.Requires(isRefining ^ (baseType != null));
     Contract.Requires(members != null);
     BaseType = baseType;
+    this.NewSelfSynonym();
   }
   public NewtypeDecl(RangeToken rangeToken, Name name, ModuleDefinition module, BoundVar bv, Expression constraint,
     SubsetTypeDecl.WKind witnessKind, Expression witness, List<Type> parentTraits, List<MemberDecl> members, Attributes attributes, bool isRefining)

Source/IntegrationTests/TestFiles/LitTests/LitTest/git-issues/git-issue-4893.dfy

@@ -0,0 +1,15 @@
+// RUN: %testDafnyForEachResolver --expect-exit-code=0 "%s"
+
+module A
+{
+  export
+    provides T
+
+  newtype T = int
+}
+
+module B
+{
+  import A
+  type X = A.T
+}

Source/IntegrationTests/TestFiles/LitTests/LitTest/git-issues/git-issue-4893.dfy.expect

@@ -0,0 +1,2 @@
+
+Dafny program verifier finished with 0 verified, 0 errors

docs/dev/news/4930.fix

@@ -0,0 +1 @@
+Initialize additional fields in the AST