f-string syntax in Python 3.8 was enhanced

See e.g. https://twitter.com/raymondh/status/1135253771846471680

parso/python/grammar38.txt

@@ -153,5 +153,5 @@ strings: (STRING | fstring)+
 fstring: FSTRING_START fstring_content* FSTRING_END
 fstring_content: FSTRING_STRING | fstring_expr
 fstring_conversion: '!' NAME
-fstring_expr: '{' testlist [ fstring_conversion ] [ fstring_format_spec ] '}'
+fstring_expr: '{' testlist ['='] [ fstring_conversion ] [ fstring_format_spec ] '}'
 fstring_format_spec: ':' fstring_content*

test/failing_examples.py

@@ -146,7 +146,7 @@ FAILING_EXAMPLES = [
     # Now nested parsing
     "f'{continue}'",
     "f'{1;1}'",
-    "f'{a=3}'",
+    "f'{a*=3}'",
     "f'{b\"\" \"\"}'",
 ]
 

test/test_fstring.py

@@ -7,7 +7,7 @@ from parso.python.tokenize import tokenize
 
 @pytest.fixture
 def grammar():
-    return load_grammar(version='3.6')
+    return load_grammar(version='3.8')
 
 
 @pytest.mark.parametrize(
@@ -31,6 +31,10 @@ def grammar():
         '{{{1}',
         '1{{2{{3',
         '}}',
+
+        # New Python 3.8 syntax f'{a=}'
+        '{a=}',
+        '{a()=}',
     ]
 )
 def test_valid(code, grammar):