Fix for crash involving the use of private types used as default values

This attempts to fix issues #4130 and #4153.

The issue was when a private type in another package was used as a default value in a method call.

Fix to #4130
Since it has been decided to treat this as a bug instead of a missing error, this PR implements the fix suggested by @ergl, namely using `lookup_try()` instead of lookup() in call.c's `check_partial_function_call()` since it allows to permit private types.

Fix to #4153
This is also a simply fix to lookup.c that prevents a potential segfault by a dereferencing of `opt` (`typecheck_t* t = &opt->check;`) *before* `opt != NULL` was checked. As pointed out by @SeanTAllen, opt should not be NULL to begin with when lookup_nominal is called, and instead, an assert should be added and the NULL checks in that function removed.

src/libponyc/type/lookup.c

@@ -57,14 +57,14 @@ static deferred_reification_t* lookup_nominal(pass_opt_t* opt, ast_t* from,
   ast_t* orig, ast_t* type, const char* name, bool errors, bool allow_private)
 {
   pony_assert(ast_id(type) == TK_NOMINAL);
+  pony_assert(opt != NULL);
   typecheck_t* t = &opt->check;
 
   ast_t* def = (ast_t*)ast_data(type);
   AST_GET_CHILDREN(def, type_id, typeparams);
   const char* type_name = ast_name(type_id);
 
-  if(is_name_private(type_name) && (from != NULL) && (opt != NULL)
-    && !allow_private)
+  if(is_name_private(type_name) && (from != NULL) && !allow_private)
   {
     if(ast_nearest(def, TK_PACKAGE) != t->frame->package)
     {
@@ -94,34 +94,31 @@ static deferred_reification_t* lookup_nominal(pass_opt_t* opt, ast_t* from,
       case TK_FUN:
       {
         // Typecheck default args immediately.
-        if(opt != NULL)
+        AST_GET_CHILDREN(find, cap, id, typeparams, params);
+        ast_t* param = ast_child(params);
+
+        while(param != NULL)
         {
-          AST_GET_CHILDREN(find, cap, id, typeparams, params);
-          ast_t* param = ast_child(params);
+          AST_GET_CHILDREN(param, name, type, def_arg);
 
-          while(param != NULL)
+          if((ast_id(def_arg) != TK_NONE) && (ast_type(def_arg) == NULL))
           {
-            AST_GET_CHILDREN(param, name, type, def_arg);
-
-            if((ast_id(def_arg) != TK_NONE) && (ast_type(def_arg) == NULL))
-            {
-              ast_t* child = ast_child(def_arg);
+            ast_t* child = ast_child(def_arg);
 
-              if(ast_id(child) == TK_CALL)
-                ast_settype(child, ast_from(child, TK_INFERTYPE));
+            if(ast_id(child) == TK_CALL)
+              ast_settype(child, ast_from(child, TK_INFERTYPE));
 
-              if(ast_visit_scope(&param, pass_pre_expr, pass_expr, opt,
-                PASS_EXPR) != AST_OK)
-                return NULL;
+            if(ast_visit_scope(&param, pass_pre_expr, pass_expr, opt,
+              PASS_EXPR) != AST_OK)
+              return NULL;
 
-              def_arg = ast_childidx(param, 2);
+            def_arg = ast_childidx(param, 2);
 
-              if(!coerce_literals(&def_arg, type, opt))
-                return NULL;
-            }
-
-            param = ast_sibling(param);
+            if(!coerce_literals(&def_arg, type, opt))
+              return NULL;
           }
+
+          param = ast_sibling(param);
         }
         break;
       }
@@ -140,7 +137,7 @@ static deferred_reification_t* lookup_nominal(pass_opt_t* opt, ast_t* from,
     return NULL;
   }
 
-  if(is_name_private(name) && (from != NULL) && (opt != NULL) && !allow_private)
+  if(is_name_private(name) && (from != NULL) && !allow_private)
   {
     switch(ast_id(find))
     {

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);