fix source name of built-in modules

Closes PR 12051

 Merge to 5.1.2

collects/tests/racket/module.rktl

@@ -518,6 +518,14 @@
   (print (module->namespace ''n) s)
   (test #t regexp-match? #rx"<namespace:'" (get-output-string s)))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check "source" name of built-in module:
+
+(parameterize ([current-namespace (module->namespace ''#%network)])
+  (test '#%network 
+        variable-reference->module-source
+        (eval (datum->syntax #'here '(#%variable-reference)))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

src/racket/src/module.c

@@ -4769,6 +4769,8 @@ Scheme_Env *scheme_primitive_module(Scheme_Object *name, Scheme_Env *for_env)
       src = prefix;
     else
       src = scheme_intern_resolved_module_path(src);
+    if (SCHEME_FALSEP(src))
+      src = name;
     insp = scheme_get_param(config, MZCONFIG_CODE_INSPECTOR);
   }
   else {