improve traceback of import errors

src/parser.pyj

@@ -746,7 +746,7 @@ def parse($TEXT, options):
     def do_import(key):
         if key in IMPORTED: return  # we'll reuse the original imported code
         if IMPORTING[key]:          # cyclical import
-            raise ImportError('Detected a recursive import of: ' + key + ' while importing: ' + module_id)
+            raise ImportError('Detected a recursive import of: ' + key + ' while importing: ' + module_id, options.filename)
 
         # Ensure that the package containing this module is also imported
         package_module_id = key.split('.')[:-1].join('.')
@@ -761,20 +761,29 @@ def parse($TEXT, options):
                     if e.code is 'ENOENT' or e.code is 'EPERM' or e.code is 'EACCESS':
                         if i is 1:
                             return None, None
-                    if i is 1:
+                    else:
                         raise
 
         src_code = filename = None
         modpath = key.replace(/\./g, '/')
 
         for location in import_dirs:
             if location:
-                data, filename = safe_read(location + '/' + modpath)
+                try:
+                    data, filename = safe_read(location + '/' + modpath)
+                except as e:
+                    if isinstance(e, ImportError):
+                        raise e
+                    msg = "Failed Import: '" + key + "', due to an error: " + e.message
+                    raise ImportError(msg, options.filename, e)
                 if data is not None:
                     src_code = data
                     break
         if src_code is None:
-            raise "Failed Import: '" + key + "' module doesn't exist in any of the import directories: " + import_dirs.join(', ')
+            raise ImportError(
+              "Failed Import: '" + key + "' module doesn't exist in any of the import directories: " + import_dirs.join(', '),
+               options.filename
+            )
         contents = parse(src_code, {
             filename: filename,
             toplevel: None,

src/utils.pyj

@@ -48,8 +48,12 @@ def DefaultsError(msg, defs):
     this.defs = defs
 
 class ImportError(Error):
-    def __init__(self, message):
+    def __init__(self, message, filename, readfile_error):
+        # readfile_error - optional container for underlying error while reading module file
+        # it is may be useful when custom `readfile` is used
         self.message = message
+        self.filename = filename
+        self.readfile_error = readfile_error
 
 class ParseError(Error):
     def __init__(self, message, line, col, pos, is_eof, filename):

test/basic/imports.pyj

@@ -61,3 +61,17 @@ assert.equal(b, this)
 
 # Test global symbol declared in other module
 assert.equal(GLOBAL_SYMBOL, 'i am global')
+
+# Test custom error while reading module file
+try:
+    rapydscript.parse(
+        'import abc\n',
+        {
+            readfile: def(fp): raise Error('custom_error');, 
+            basedir: '/' 
+        }
+    )
+except as e: # e is the instance of ImportError that should contain readfile_error
+    assert.ok(isinstance(e, rapydscript.ImportError))
+    assert.ok(e.readfile_error)
+    assert(e.readfile_error.message is 'custom_error')