handle multiline fstrings in 3.12

src/flake8/_compat.py

@@ -0,0 +1,11 @@
+from __future__ import annotations
+
+import sys
+import tokenize
+
+if sys.version_info >= (3, 12):
+    FSTRING_START = tokenize.FSTRING_START
+    FSTRING_MIDDLE = tokenize.FSTRING_MIDDLE
+    FSTRING_END = tokenize.FSTRING_END
+else:
+    FSTRING_START = FSTRING_MIDDLE = FSTRING_END = -1

src/flake8/checker.py

@@ -20,6 +20,7 @@ from flake8 import defaults
 from flake8 import exceptions
 from flake8 import processor
 from flake8 import utils
+from flake8._compat import FSTRING_START
 from flake8.discover_files import expand_paths
 from flake8.options.parse_args import parse_args
 from flake8.plugins.finder import Checkers
@@ -551,15 +552,17 @@ class FileChecker:
     ) -> None:
         """Run physical checks if and only if it is at the end of the line."""
         assert self.processor is not None
+        if token.type == FSTRING_START:  # pragma: >=3.12 cover
+            self.processor.fstring_start(token.start[0])
         # a newline token ends a single physical line.
-        if processor.is_eol_token(token):
+        elif processor.is_eol_token(token):
             # if the file does not end with a newline, the NEWLINE
             # token is inserted by the parser, but it does not contain
             # the previous physical line in `token[4]`
-            if token[4] == "":
+            if token.line == "":
                 self.run_physical_checks(prev_physical)
             else:
-                self.run_physical_checks(token[4])
+                self.run_physical_checks(token.line)
         elif processor.is_multiline_string(token):
             # Less obviously, a string that contains newlines is a
             # multiline string, either triple-quoted or with internal
@@ -572,10 +575,8 @@ class FileChecker:
             # - have to wind self.line_number back because initially it
             #   points to the last line of the string, and we want
             #   check_physical() to give accurate feedback
-            line_no = token[2][0]
-            with self.processor.inside_multiline(line_number=line_no):
-                for line in self.processor.split_line(token):
-                    self.run_physical_checks(line)
+            for line in self.processor.multiline_string(token):
+                self.run_physical_checks(line)
 
 
 def _try_initialize_processpool(

src/flake8/processor.py

@@ -3,9 +3,7 @@ from __future__ import annotations
 
 import argparse
 import ast
-import contextlib
 import logging
-import sys
 import tokenize
 from typing import Any
 from typing import Generator
@@ -14,6 +12,8 @@ from typing import Tuple
 
 from flake8 import defaults
 from flake8 import utils
+from flake8._compat import FSTRING_END
+from flake8._compat import FSTRING_MIDDLE
 from flake8.plugins.finder import LoadedPlugin
 
 LOG = logging.getLogger(__name__)
@@ -117,6 +117,7 @@ class FileProcessor:
         self._file_tokens: list[tokenize.TokenInfo] | None = None
         # map from line number to the line we'll search for `noqa` in
         self._noqa_line_mapping: dict[int, str] | None = None
+        self._fstring_start = -1
 
     @property
     def file_tokens(self) -> list[tokenize.TokenInfo]:
@@ -129,14 +130,26 @@ class FileProcessor:
 
         return self._file_tokens
 
-    @contextlib.contextmanager
-    def inside_multiline(
-        self, line_number: int
-    ) -> Generator[None, None, None]:
-        """Context-manager to toggle the multiline attribute."""
-        self.line_number = line_number
+    def fstring_start(self, lineno: int) -> None:
+        """Signal the beginning of an fstring."""
+        self._fstring_start = lineno
+
+    def multiline_string(
+        self, token: tokenize.TokenInfo
+    ) -> Generator[str, None, None]:
+        """Iterate through the lines of a multiline string."""
+        if token.type == FSTRING_END:
+            start = self._fstring_start
+        else:
+            start = token.start[0]
+
         self.multiline = True
-        yield
+        self.line_number = start
+        # intentionally don't include the last line, that line will be
+        # terminated later by a future end-of-line
+        for _ in range(start, token.end[0]):
+            yield self.lines[self.line_number - 1]
+            self.line_number += 1
         self.multiline = False
 
     def reset_blank_before(self) -> None:
@@ -196,10 +209,7 @@ class FileProcessor:
                 continue
             if token_type == tokenize.STRING:
                 text = mutate_string(text)
-            elif (
-                sys.version_info >= (3, 12)
-                and token_type == tokenize.FSTRING_MIDDLE
-            ):
+            elif token_type == FSTRING_MIDDLE:
                 text = "x" * len(text)
             if previous_row:
                 (start_row, start_column) = start
@@ -231,19 +241,6 @@ class FileProcessor:
         self.statistics["logical lines"] += 1
         return joined_comments, self.logical_line, mapping_list
 
-    def split_line(
-        self, token: tokenize.TokenInfo
-    ) -> Generator[str, None, None]:
-        """Split a physical line's line based on new-lines.
-
-        This also auto-increments the line number for the caller.
-        """
-        # intentionally don't include the last line, that line will be
-        # terminated later by a future end-of-line
-        for line_no in range(token.start[0], token.end[0]):
-            yield self.lines[line_no - 1]
-            self.line_number += 1
-
     def keyword_arguments_for(
         self,
         parameters: dict[str, bool],
@@ -398,7 +395,9 @@ def is_eol_token(token: tokenize.TokenInfo) -> bool:
 
 def is_multiline_string(token: tokenize.TokenInfo) -> bool:
     """Check if this is a multiline string."""
-    return token[0] == tokenize.STRING and "\n" in token[1]
+    return token.type == FSTRING_END or (
+        token.type == tokenize.STRING and "\n" in token.string
+    )
 
 
 def token_is_newline(token: tokenize.TokenInfo) -> bool:

tests/integration/test_plugins.py

@@ -199,6 +199,38 @@ t.py:3:1: T001 '"""\\n'
     assert out == expected
 
 
+def test_physical_line_plugin_multiline_fstring(tmpdir, capsys):
+    cfg_s = f"""\
+[flake8:local-plugins]
+extension =
+    T = {yields_physical_line.__module__}:{yields_physical_line.__name__}
+"""
+
+    cfg = tmpdir.join("tox.ini")
+    cfg.write(cfg_s)
+
+    src = '''\
+y = 1
+x = f"""
+hello {y}
+"""
+'''
+    t_py = tmpdir.join("t.py")
+    t_py.write_binary(src.encode())
+
+    with tmpdir.as_cwd():
+        assert main(("t.py", "--config", str(cfg))) == 1
+
+    expected = '''\
+t.py:1:1: T001 'y = 1\\n'
+t.py:2:1: T001 'x = f"""\\n'
+t.py:3:1: T001 'hello {y}\\n'
+t.py:4:1: T001 '"""\\n'
+'''
+    out, err = capsys.readouterr()
+    assert out == expected
+
+
 def yields_logical_line(logical_line):
     yield 0, f"T001 {logical_line!r}"
 

tests/unit/test_file_processor.py

@@ -275,13 +275,15 @@ def test_processor_split_line(default_options):
         (3, 3),
         'x = """\ncontents\n"""\n',
     )
-    expected = [('x = """\n', 0), ("contents\n", 1)]
+    expected = [('x = """\n', 1, True), ("contents\n", 2, True)]
+    assert file_processor.multiline is False
     actual = [
-        (line, file_processor.line_number)
-        for line in file_processor.split_line(token)
+        (line, file_processor.line_number, file_processor.multiline)
+        for line in file_processor.multiline_string(token)
     ]
+    assert file_processor.multiline is False
     assert expected == actual
-    assert file_processor.line_number == 2
+    assert file_processor.line_number == 3
 
 
 def test_build_ast(default_options):
@@ -321,21 +323,6 @@ def test_visited_new_blank_line(default_options):
     assert file_processor.blank_lines == 1
 
 
-def test_inside_multiline(default_options):
-    """Verify we update the line number and reset multiline."""
-    file_processor = processor.FileProcessor(
-        "-", default_options, lines=["a = 1\n"]
-    )
-
-    assert file_processor.multiline is False
-    assert file_processor.line_number == 0
-    with file_processor.inside_multiline(10):
-        assert file_processor.multiline is True
-        assert file_processor.line_number == 10
-
-    assert file_processor.multiline is False
-
-
 @pytest.mark.parametrize(
     "string, expected",
     [