Treat form feed as valid whitespace before a line continuation (astral-sh#19220)

Co-authored-by: Micha Reiser <[email protected]>

Author: soundsonacid

crates/ruff_linter/resources/test/fixtures/flake8_type_checking/whitespace.py

@@ -0,0 +1,6 @@
+# Regression test for: https://github.com/astral-sh/ruff/issues/19175
+# there is a (potentially invisible) unicode formfeed character (000C) between `TYPE_CHECKING` and the backslash
+from typing import TYPE_CHECKING\
+
+if TYPE_CHECKING: import builtins
+builtins.print("!")

crates/ruff_linter/src/importer/insertion.rs

@@ -5,6 +5,7 @@ use ruff_python_ast::Stmt;
 use ruff_python_ast::helpers::is_docstring_stmt;
 use ruff_python_codegen::Stylist;
 use ruff_python_parser::{TokenKind, Tokens};
+use ruff_python_trivia::is_python_whitespace;
 use ruff_python_trivia::{PythonWhitespace, textwrap::indent};
 use ruff_source_file::{LineRanges, UniversalNewlineIterator};
 use ruff_text_size::{Ranged, TextSize};
@@ -306,7 +307,7 @@ fn match_semicolon(s: &str) -> Option<TextSize> {
 fn match_continuation(s: &str) -> Option<TextSize> {
     for (offset, c) in s.char_indices() {
         match c {
-            ' ' | '\t' => continue,
+            _ if is_python_whitespace(c) => continue,
             '\\' => return Some(TextSize::try_from(offset).unwrap()),
             _ => break,
         }

crates/ruff_linter/src/rules/flake8_type_checking/mod.rs

@@ -36,6 +36,7 @@ mod tests {
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_8.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_9.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("quote.py"))]
+    #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("whitespace.py"))]
     #[test_case(Rule::RuntimeStringUnion, Path::new("TC010_1.py"))]
     #[test_case(Rule::RuntimeStringUnion, Path::new("TC010_2.py"))]
     #[test_case(Rule::TypingOnlyFirstPartyImport, Path::new("TC001.py"))]

crates/ruff_linter/src/rules/flake8_type_checking/snapshots/ruff_linter__rules__flake8_type_checking__tests__runtime-import-in-type-checking-block_whitespace.py.snap

@@ -0,0 +1,22 @@
+---
+source: crates/ruff_linter/src/rules/flake8_type_checking/mod.rs
+---
+whitespace.py:5:26: TC004 [*] Move import `builtins` out of type-checking block. Import is used for more than type hinting.
+  |
+3 | from typing import TYPE_CHECKING\
+4 |
+5 | if TYPE_CHECKING: import builtins
+  |                          ^^^^^^^^ TC004
+6 | builtins.print("!")
+  |
+  = help: Move out of type-checking block
+
+ℹ Unsafe fix
+1 1 | # Regression test for: https://github.com/astral-sh/ruff/issues/19175
+2 2 | # there is a (potentially invisible) unicode formfeed character (000C) between `TYPE_CHECKING` and the backslash
+3   |-from typing import TYPE_CHECKING\
+  3 |+from typing import TYPE_CHECKING; import builtins\
+4 4 | 
+5   |-if TYPE_CHECKING: import builtins
+  5 |+if TYPE_CHECKING: pass
+6 6 | builtins.print("!")