Change W605 autofix to use raw strings if possible (#5352)

Fixes #5061.

crates/ruff/resources/test/fixtures/pycodestyle/W605_0.py

@@ -19,6 +19,9 @@ with \_ somewhere
 in the middle
 """
 
+#: W605:1:38
+value = 'new line\nand invalid escape \_ here'
+
 #: Okay
 regex = r'\.png$'
 regex = '\\.png$'

crates/ruff/src/rules/pycodestyle/rules/invalid_escape_sequence.rs

@@ -79,6 +79,8 @@ pub(crate) fn invalid_escape_sequence(
 
         let mut chars_iter = body.char_indices().peekable();
 
+        let mut contains_valid_escape_sequence = false;
+
         while let Some((i, c)) = chars_iter.next() {
             if c != '\\' {
                 continue;
@@ -101,20 +103,35 @@ pub(crate) fn invalid_escape_sequence(
 
             // If the next character is a valid escape sequence, skip.
             if VALID_ESCAPE_SEQUENCES.contains(next_char) {
+                contains_valid_escape_sequence = true;
                 continue;
             }
 
             let location = start_offset + TextSize::try_from(i).unwrap();
             let range = TextRange::at(location, next_char.text_len() + TextSize::from(1));
-            let mut diagnostic = Diagnostic::new(InvalidEscapeSequence(*next_char), range);
+            let diagnostic = Diagnostic::new(InvalidEscapeSequence(*next_char), range);
-            if autofix {
-                diagnostic.set_fix(Fix::automatic(Edit::insertion(
-                    r"\".to_string(),
-                    range.start() + TextSize::from(1),
-                )));
-            }
             diagnostics.push(diagnostic);
         }
+
+        if autofix {
+            if contains_valid_escape_sequence {
+                // Escape with backslash
+                for diagnostic in &mut diagnostics {
+                    diagnostic.set_fix(Fix::automatic(Edit::insertion(
+                        r"\".to_string(),
+                        diagnostic.range().start() + TextSize::from(1),
+                    )));
+                }
+            } else {
+                // Turn into raw string
+                for diagnostic in &mut diagnostics {
+                    diagnostic.set_fix(Fix::automatic(Edit::insertion(
+                        "r".to_string(),
+                        range.start() + TextSize::try_from(quote_pos).unwrap(),
+                    )));
+                }
+            }
+        }
     }
 
     diagnostics

crates/ruff/src/rules/pycodestyle/snapshots/ruff__rules__pycodestyle__tests__W605_W605_0.py.snap

@@ -14,7 +14,7 @@ W605_0.py:2:10: W605 [*] Invalid escape sequence: `\.`
 ℹ Fix
 1 1 | #: W605:1:10
 2   |-regex = '\.png$'
-  2 |+regex = '\\.png$'
+  2 |+regex = r'\.png$'
 3 3 | 
 4 4 | #: W605:2:1
 5 5 | regex = '''
@@ -30,14 +30,14 @@ W605_0.py:6:1: W605 [*] Invalid escape sequence: `\.`
   = help: Add backslash to escape sequence
 
 ℹ Fix
+2 2 | regex = '\.png$'
 3 3 | 
 4 4 | #: W605:2:1
-5 5 | regex = '''
+5   |-regex = '''
-6   |-\.png$
+  5 |+regex = r'''
-  6 |+\\.png$
+6 6 | \.png$
 7 7 | '''
 8 8 | 
-9 9 | #: W605:2:6
 
 W605_0.py:11:6: W605 [*] Invalid escape sequence: `\_`
    |
@@ -54,7 +54,7 @@ W605_0.py:11:6: W605 [*] Invalid escape sequence: `\_`
 9  9  | #: W605:2:6
 10 10 | f(
 11    |-    '\_'
-   11 |+    '\\_'
+   11 |+    r'\_'
 12 12 | )
 13 13 | 
 14 14 | #: W605:4:6
@@ -71,13 +71,33 @@ W605_0.py:18:6: W605 [*] Invalid escape sequence: `\_`
    = help: Add backslash to escape sequence
 
 ℹ Fix
-15 15 | """
+12 12 | )
+13 13 | 
+14 14 | #: W605:4:6
+15    |-"""
+   15 |+r"""
 16 16 | multi-line
 17 17 | literal
-18    |-with \_ somewhere
+18 18 | with \_ somewhere
-   18 |+with \\_ somewhere
+
-19 19 | in the middle
+W605_0.py:23:39: W605 [*] Invalid escape sequence: `\_`
+   |
+22 | #: W605:1:38
+23 | value = 'new line\nand invalid escape \_ here'
+   |                                       ^^ W605
+24 | 
+25 | #: Okay
+   |
+   = help: Add backslash to escape sequence
+
+ℹ Fix
 20 20 | """
 21 21 | 
+22 22 | #: W605:1:38
+23    |-value = 'new line\nand invalid escape \_ here'
+   23 |+value = 'new line\nand invalid escape \\_ here'
+24 24 | 
+25 25 | #: Okay
+26 26 | regex = r'\.png$'
 
 

crates/ruff/src/rules/pycodestyle/snapshots/ruff__rules__pycodestyle__tests__W605_W605_1.py.snap

@@ -14,7 +14,7 @@ W605_1.py:2:10: W605 [*] Invalid escape sequence: `\.`
 ℹ Fix
 1 1 | #: W605:1:10
 2   |-regex = '\.png$'
-  2 |+regex = '\\.png$'
+  2 |+regex = r'\.png$'
 3 3 | 
 4 4 | #: W605:2:1
 5 5 | regex = '''
@@ -30,14 +30,14 @@ W605_1.py:6:1: W605 [*] Invalid escape sequence: `\.`
   = help: Add backslash to escape sequence
 
 ℹ Fix
+2 2 | regex = '\.png$'
 3 3 | 
 4 4 | #: W605:2:1
-5 5 | regex = '''
+5   |-regex = '''
-6   |-\.png$
+  5 |+regex = r'''
-  6 |+\\.png$
+6 6 | \.png$
 7 7 | '''
 8 8 | 
-9 9 | #: W605:2:6
 
 W605_1.py:11:6: W605 [*] Invalid escape sequence: `\_`
    |
@@ -54,7 +54,7 @@ W605_1.py:11:6: W605 [*] Invalid escape sequence: `\_`
 9  9  | #: W605:2:6
 10 10 | f(
 11    |-    '\_'
-   11 |+    '\\_'
+   11 |+    r'\_'
 12 12 | )
 13 13 | 
 14 14 | #: W605:4:6
@@ -71,13 +71,13 @@ W605_1.py:18:6: W605 [*] Invalid escape sequence: `\_`
    = help: Add backslash to escape sequence
 
 ℹ Fix
-15 15 | """
+12 12 | )
+13 13 | 
+14 14 | #: W605:4:6
+15    |-"""
+   15 |+r"""
 16 16 | multi-line
 17 17 | literal
-18    |-with \_ somewhere
+18 18 | with \_ somewhere
-   18 |+with \\_ somewhere
-19 19 | in the middle
-20 20 | """
-21 21 |