Fix for crash when methods with default private type params in remote packages are called

.release-notes/4167.md

@@ -0,0 +1,22 @@
+## Fix for compiler segfault #4130
+
+The compiler crash described in #4130 happened with code that attempted to call a method in a different package when this remote method used a package-private type as a default parameter.
+
+```pony
+// In the "lib" pacakge
+
+primitive _Private
+
+primitive Public
+  fun apply[T](v: (T | _Private) = _Private): None => None
+
+// In main
+use lib = "lib"
+
+actor Main
+  new create(env: Env) =>
+    let p = lib.Public.apply[U8]()
+    env.out.print(p.string())
+```
+
+It was decided that this code is valid Pony code, and this PR fixes the crash so that code like the above compiles.

src/libponyc/verify/call.c

@@ -28,8 +28,8 @@ static bool check_partial_function_call(pass_opt_t* opt, ast_t* ast)
     ast_id(call_error) == TK_NONE || ast_id(call_error) == TK_DONTCARE);
 
   // Look up the original method definition for this method call.
-  deferred_reification_t* method_def = lookup(opt, receiver, ast_type(receiver),
-    ast_name(method));
+  deferred_reification_t* method_def = lookup_try(opt, receiver, ast_type(receiver),
+    ast_name(method), true); // allow private types
   ast_t* method_ast = method_def->ast;
   deferred_reify_free(method_def);
 

test/libponyc-run/private-type-as-default-argument-in-public-function/lib/lib.pony

@@ -0,0 +1,4 @@
+primitive _Private
+
+primitive Public
+  fun apply[T](v: (T | _Private) = _Private): None => None

test/libponyc-run/private-type-as-default-argument-in-public-function/main.pony

@@ -0,0 +1,6 @@
+use lib = "lib"
+
+actor Main
+  new create(env: Env) =>
+    let p = lib.Public.apply[U8]()
+    env.out.print(p.string())