fix the one failing test

src/blib2to3/Grammar.txt

@@ -256,7 +256,6 @@ patterns: pattern (',' pattern)* [',']
 pattern: (expr|star_expr) ['as' expr]
 
 fstring: FSTRING_START fstring_middle* FSTRING_END
-# TODO making these FSTRING_MIDDLE makes them unformattable so maybe put a new token here?
 fstring_middle: fstring_replacement_field | FSTRING_MIDDLE
 fstring_replacement_field: '{' (yield_expr | testlist_star_expr) ['='] [ "!" NAME ] [ ':' fstring_format_spec* ] '}'
 fstring_format_spec: FSTRING_MIDDLE | fstring_replacement_field

src/blib2to3/pgen2/tokenize.py

@@ -665,7 +665,6 @@ def generate_tokens(
                 if endmatch:  # all on one line
                     start, end = endmatch.span(0)
                     token = line[start:end]
-                    # TODO: check if the token will ever have any whitespace around?
                     if token.endswith(('"""', "'''")):
                         middle_token, end_token = token[:-3], token[-3:]
                         middle_epos = end_spos = (lnum, end - 3)
@@ -707,8 +706,6 @@ def generate_tokens(
                     contline = line
                     break
 
-            # TODO: fstring_level > 0 is redundant in both cases here,
-            # remove it and ensure nothing breaks
             if inside_fstring_colon:
                 match = fstring_middle_after_colon.match(line, pos)
                 if match is None:
@@ -982,6 +979,10 @@ def generate_tokens(
                 else:
                     if parenlev == 0 and bracelev > 0 and initial == "}":
                         bracelev -= 1
+                        # if we're still inside fstrings, we're still part of the format spec
+                        if inside_fstring_braces:
+                            inside_fstring_colon = True
+                            formatspec_start = (lnum, pos)
                     elif initial in "([{":
                         parenlev += 1
                     elif initial in ")]}":

tests/data/cases/pep_701.py

@@ -67,8 +67,11 @@
 rf'foo'
 rf'{foo}'
 
+f"{x:{y}d}"
+
 x = f"a{2+2:=^{x}}b"
 x = f"a{2+2:=^{foo(x+y**2):something else}}b"
+x = f"a{2+2:=^{foo(x+y**2):something else}one more}b"
 f'{(abc:=10)}'
 
 f"This is a really long string, but just make sure that you reflow fstrings {
@@ -164,8 +167,11 @@
 rf"foo"
 rf"{foo}"
 
+f"{x:{y}d}"
+
 x = f"a{2 + 2:=^{x}}b"
 x = f"a{2 + 2:=^{foo(x + y**2):something else}}b"
+x = f"a{2 + 2:=^{foo(x + y**2):something else}one more}b"
 f"{(abc := 10)}"
 
 f"This is a really long string, but just make sure that you reflow fstrings {2 + 2:d}"