Fix another f-string regression (#4339)

CHANGES.md

@@ -26,6 +26,9 @@
 
 <!-- Changes to the parser or to version autodetection -->
 
+- Fix regression where Black failed to parse a multiline f-string containing another
+  multiline string (#4339)
+
 ### Performance
 
 <!-- Changes that improve Black's performance. -->

src/blib2to3/pgen2/tokenize.py

@@ -622,10 +622,10 @@ def generate_tokens(
                 spos = strstart
                 epos = (lnum, end)
                 tokenline = contline + line
-                if (
-                    fstring_state.current() == STATE_NOT_FSTRING
-                    and not is_fstring_start(token)
-                ):
+                if fstring_state.current() in (
+                    STATE_NOT_FSTRING,
+                    STATE_IN_BRACES,
+                ) and not is_fstring_start(token):
                     yield (STRING, token, spos, epos, tokenline)
                     endprog_stack.pop()
                     parenlev = parenlev_stack.pop()

tests/data/cases/pep_701.py

@@ -125,6 +125,9 @@
 
 f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'
 
+f"""{'''
+'''}"""
+
 # output
 
 x = f"foo"
@@ -252,3 +255,6 @@
 f"{1:{2}d}"
 
 f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'
+
+f"""{'''
+'''}"""