Do proper error recover for fstrings and fix another issue there.

parso/python/errors.py

@@ -840,11 +840,11 @@ class _TryStmtRule(SyntaxRule):
 class _FStringRule(SyntaxRule):
     _fstring_grammar = None
     message_empty = "f-string: empty expression not allowed"  # f'{}'
-    "f-string: single '}' is not allowed"  # f'}'
+    message_single_closing = "f-string: single '}' is not allowed"  # f'}'
     message_nested = "f-string: expressions nested too deeply"
     message_backslash = "f-string expression part cannot include a backslash"  # f'{"\"}' or f'{"\\"}'
     message_comment = "f-string expression part cannot include '#'"  # f'{#}'
-    "f-string: unterminated string"  # f'{"}'
+    message_string = "f-string: unterminated string"  # f'{"}'
     message_conversion = "f-string: invalid conversion character: expected 's', 'r', or 'a'"
     message_incomplete = "f-string: expecting '}'"  # f'{'
 
@@ -866,6 +866,8 @@ class _FStringRule(SyntaxRule):
                 self._check_expression(child)
             elif child.type == 'error_node':
                 self.add_issue(child, message=self.message_incomplete)
+            elif child.type == 'error_leaf':
+                self.add_issue(child, message=self.message_single_closing)
 
     def _check_python_expr(self, python_expr):
         value = python_expr.value

parso/python/fstring.py

@@ -198,9 +198,17 @@ class Parser(parser.BaseParser):
                 add_token_callback
             )
 
-        dfa, state, (type_, nodes) = stack[1]
-        stack[0][2][1].append(ErrorNode(nodes))
-        stack[1:] = []
-        #error_leaf = tree.PythonErrorLeaf(tok_name[typ].lower(), value, start_pos, prefix)
+        if len(stack) == 1:
+            error_leaf = ErrorLeaf(
+                TokenNamespace.token_map[typ].lower(),
+                value,
+                start_pos,
+                prefix
+            )
+            stack[0][2][1].append(error_leaf)
+        else:
+            dfa, state, (type_, nodes) = stack[1]
+            stack[0][2][1].append(ErrorNode(nodes))
+            stack[1:] = []
 
-        add_token_callback(typ, value, start_pos, prefix)
+            add_token_callback(typ, value, start_pos, prefix)

test/failing_examples.py

@@ -147,6 +147,8 @@ FAILING_EXAMPLES = [
     "f'{1!b}'",
     "f'{1:{5:{3}}}'",
     "f'{'",
+    "f'{'",
+    "f'}'",
 ]
 
 GLOBAL_NONLOCAL_ERROR = [