Consider 2-character EOL before line continuation

Author: dhruvmanila

.gitattributes

@@ -8,6 +8,7 @@ crates/ruff_linter/resources/test/fixtures/pycodestyle/W391_3.py text eol=crlf
 crates/ruff_python_formatter/resources/test/fixtures/ruff/docstring_code_examples_crlf.py text eol=crlf
 crates/ruff_python_formatter/tests/snapshots/format@docstring_code_examples_crlf.py.snap text eol=crlf
 
+crates/ruff_python_parser/resources/invalid/re_lexing/line_continuation_windows_eol.py text eol=crlf
 crates/ruff_python_parser/resources/invalid/re_lex_logical_token_windows_eol.py text eol=crlf
 crates/ruff_python_parser/resources/invalid/re_lex_logical_token_mac_eol.py text eol=cr
 

crates/ruff_python_parser/resources/invalid/re_lexing/line_continuation_windows_eol.py

@@ -0,0 +1,4 @@
+call(a, b, \\\
+
+def bar():
+    pass

crates/ruff_python_parser/src/lexer.rs

@@ -1393,26 +1393,40 @@ impl<'src> Lexer<'src> {
         while let Some(ch) = reverse_chars.next() {
             if is_python_whitespace(ch) {
                 current_position -= ch.text_len();
-            } else if matches!(ch, '\n' | '\r') {
-                current_position -= ch.text_len();
-                // Count the number of backslashes before the newline character.
-                let mut backslash_count = 0;
-                while reverse_chars.next_if_eq(&'\\').is_some() {
-                    backslash_count += 1;
-                }
-                if backslash_count == 0 {
-                    // No escapes: `\n`
-                    newline_position = Some(current_position);
-                } else {
-                    if backslash_count % 2 == 0 {
-                        // Even number of backslashes i.e., all backslashes cancel each other out
-                        // which means the newline character is not being escaped.
-                        newline_position = Some(current_position);
+                continue;
+            }
+
+            match ch {
+                '\n' => {
+                    current_position -= ch.text_len();
+                    if let Some(carriage_return) = reverse_chars.next_if_eq(&'\r') {
+                        current_position -= carriage_return.text_len();
                     }
-                    current_position -= TextSize::new('\\'.text_len().to_u32() * backslash_count);
                 }
+                '\r' => {
+                    current_position -= ch.text_len();
+                }
+                _ => break,
+            }
+
+            debug_assert!(matches!(ch, '\n' | '\r'));
+
+            // Count the number of backslashes before the newline character.
+            let mut backslash_count = 0;
+            while reverse_chars.next_if_eq(&'\\').is_some() {
+                backslash_count += 1;
+            }
+
+            if backslash_count == 0 {
+                // No escapes: `\n`
+                newline_position = Some(current_position);
             } else {
-                break;
+                if backslash_count % 2 == 0 {
+                    // Even number of backslashes i.e., all backslashes cancel each other out
+                    // which means the newline character is not being escaped.
+                    newline_position = Some(current_position);
+                }
+                current_position -= TextSize::new('\\'.text_len().to_u32() * backslash_count);
             }
         }
 

crates/ruff_python_parser/tests/snapshots/invalid_syntax@re_lexing__line_continuation_windows_eol.py.snap

@@ -0,0 +1,105 @@
+---
+source: crates/ruff_python_parser/tests/fixtures.rs
+input_file: crates/ruff_python_parser/resources/invalid/re_lexing/line_continuation_windows_eol.py
+---
+## AST
+
+```
+Module(
+    ModModule {
+        range: 0..38,
+        body: [
+            Expr(
+                StmtExpr {
+                    range: 0..14,
+                    value: Call(
+                        ExprCall {
+                            range: 0..14,
+                            func: Name(
+                                ExprName {
+                                    range: 0..4,
+                                    id: "call",
+                                    ctx: Load,
+                                },
+                            ),
+                            arguments: Arguments {
+                                range: 4..14,
+                                args: [
+                                    Name(
+                                        ExprName {
+                                            range: 5..6,
+                                            id: "a",
+                                            ctx: Load,
+                                        },
+                                    ),
+                                    Name(
+                                        ExprName {
+                                            range: 8..9,
+                                            id: "b",
+                                            ctx: Load,
+                                        },
+                                    ),
+                                ],
+                                keywords: [],
+                            },
+                        },
+                    ),
+                },
+            ),
+            FunctionDef(
+                StmtFunctionDef {
+                    range: 18..38,
+                    is_async: false,
+                    decorator_list: [],
+                    name: Identifier {
+                        id: "bar",
+                        range: 22..25,
+                    },
+                    type_params: None,
+                    parameters: Parameters {
+                        range: 25..27,
+                        posonlyargs: [],
+                        args: [],
+                        vararg: None,
+                        kwonlyargs: [],
+                        kwarg: None,
+                    },
+                    returns: None,
+                    body: [
+                        Pass(
+                            StmtPass {
+                                range: 34..38,
+                            },
+                        ),
+                    ],
+                },
+            ),
+        ],
+    },
+)
+```
+## Errors
+
+  |
+1 | call(a, b, \\\
+  |             ^ Syntax Error: unexpected character after line continuation character
+2 | 
+3 | def bar():
+  |
+
+
+  |
+1 | call(a, b, \\\
+  |              ^ Syntax Error: unexpected character after line continuation character
+2 | 
+3 | def bar():
+  |
+
+
+  |
+1 |   call(a, b, \\\
+2 | / 
+3 | | def bar():
+  | |_^ Syntax Error: Expected ')', found newline
+4 |       pass
+  |