Preserve raw string prefix and escapes (#15694)

## Summary

Fixes #9663 and also improves the fixes for
[RUF055](https://docs.astral.sh/ruff/rules/unnecessary-regular-expression/)
since regular expressions are often written as raw strings.

This doesn't include raw f-strings.

## Test Plan

Existing snapshots for RUF055 and PT009, plus a new `Generator` test and
a regression test for the reported `PIE810` issue.

crates/ruff_linter/resources/test/fixtures/flake8_pie/PIE810.py

@@ -76,3 +76,9 @@ def func():
 
     if msg.startswith(y) or msg.endswith(x) or msg.startswith("h"): # OK
         print("yes")
+
+
+def func():
+    "Regression test for https://github.com/astral-sh/ruff/issues/9663"
+    if x.startswith("a") or x.startswith("b") or re.match(r"a\.b", x):
+        print("yes")

crates/ruff_linter/src/rules/flake8_pie/snapshots/ruff_linter__rules__flake8_pie__tests__PIE810_PIE810.py.snap

@@ -142,3 +142,21 @@ PIE810.py:25:8: PIE810 [*] Call `startswith` once with a `tuple`
 26 26 |         print("yes") 
 27 27 | 
 28 28 | # ok
+
+PIE810.py:83:8: PIE810 [*] Call `startswith` once with a `tuple`
+   |
+81 | def func():
+82 |     "Regression test for https://github.com/astral-sh/ruff/issues/9663"
+83 |     if x.startswith("a") or x.startswith("b") or re.match(r"a\.b", x):
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PIE810
+84 |         print("yes")
+   |
+   = help: Merge into a single `startswith` call
+
+ℹ Unsafe fix
+80 80 | 
+81 81 | def func():
+82 82 |     "Regression test for https://github.com/astral-sh/ruff/issues/9663"
+83    |-    if x.startswith("a") or x.startswith("b") or re.match(r"a\.b", x):
+   83 |+    if x.startswith(("a", "b")) or re.match(r"a\.b", x):
+84 84 |         print("yes")

crates/ruff_linter/src/rules/flake8_pytest_style/snapshots/ruff_linter__rules__flake8_pytest_style__tests__PT009.snap

@@ -498,7 +498,7 @@ PT009.py:73:9: PT009 [*] Use a regular `assert` instead of unittest-style `asser
 71 71 | 
 72 72 |     def test_assert_regex(self):
 73    |-        self.assertRegex("abc", r"def")  # Error
-   73 |+        assert re.search("def", "abc")  # Error
+   73 |+        assert re.search(r"def", "abc")  # Error
 74 74 | 
 75 75 |     def test_assert_not_regex(self):
 76 76 |         self.assertNotRegex("abc", r"abc")  # Error
@@ -518,7 +518,7 @@ PT009.py:76:9: PT009 [*] Use a regular `assert` instead of unittest-style `asser
 74 74 | 
 75 75 |     def test_assert_not_regex(self):
 76    |-        self.assertNotRegex("abc", r"abc")  # Error
-   76 |+        assert not re.search("abc", "abc")  # Error
+   76 |+        assert not re.search(r"abc", "abc")  # Error
 77 77 | 
 78 78 |     def test_assert_regexp_matches(self):
 79 79 |         self.assertRegexpMatches("abc", r"def")  # Error
@@ -538,7 +538,7 @@ PT009.py:79:9: PT009 [*] Use a regular `assert` instead of unittest-style `asser
 77 77 | 
 78 78 |     def test_assert_regexp_matches(self):
 79    |-        self.assertRegexpMatches("abc", r"def")  # Error
-   79 |+        assert re.search("def", "abc")  # Error
+   79 |+        assert re.search(r"def", "abc")  # Error
 80 80 | 
 81 81 |     def test_assert_not_regexp_matches(self):
 82 82 |         self.assertNotRegex("abc", r"abc")  # Error
@@ -558,7 +558,7 @@ PT009.py:82:9: PT009 [*] Use a regular `assert` instead of unittest-style `asser
 80 80 | 
 81 81 |     def test_assert_not_regexp_matches(self):
 82    |-        self.assertNotRegex("abc", r"abc")  # Error
-   82 |+        assert not re.search("abc", "abc")  # Error
+   82 |+        assert not re.search(r"abc", "abc")  # Error
 83 83 | 
 84 84 |     def test_fail_if(self):
 85 85 |         self.failIf("abc")  # Error

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__preview__RUF055_RUF055_0.py.snap

@@ -142,14 +142,14 @@ RUF055_0.py:89:1: RUF055 [*] Plain string pattern passed to `re` function
 90 | re.sub(r"a", r"\n", "a")
 91 | re.sub(r"a", "\a", "a")
    |
-   = help: Replace with `"a".replace("a", "\n")`
+   = help: Replace with `"a".replace(r"a", "\n")`
 
 ℹ Safe fix
 86 86 | # `re.sub(r"a", r"\n", some_string)` is fixed to `some_string.replace("a", "\n")`
 87 87 | # *not* `some_string.replace("a", "\\n")`.
 88 88 | # We currently emit diagnostics for some of these without fixing them.
 89    |-re.sub(r"a", "\n", "a")
-   89 |+"a".replace("a", "\n")
+   89 |+"a".replace(r"a", "\n")
 90 90 | re.sub(r"a", r"\n", "a")
 91 91 | re.sub(r"a", "\a", "a")
 92 92 | re.sub(r"a", r"\a", "a")
@@ -172,14 +172,14 @@ RUF055_0.py:91:1: RUF055 [*] Plain string pattern passed to `re` function
    | ^^^^^^^^^^^^^^^^^^^^^^^ RUF055
 92 | re.sub(r"a", r"\a", "a")
    |
-   = help: Replace with `"a".replace("a", "\x07")`
+   = help: Replace with `"a".replace(r"a", "\x07")`
 
 ℹ Safe fix
 88 88 | # We currently emit diagnostics for some of these without fixing them.
 89 89 | re.sub(r"a", "\n", "a")
 90 90 | re.sub(r"a", r"\n", "a")
 91    |-re.sub(r"a", "\a", "a")
-   91 |+"a".replace("a", "\x07")
+   91 |+"a".replace(r"a", "\x07")
 92 92 | re.sub(r"a", r"\a", "a")
 93 93 | 
 94 94 | re.sub(r"a", "\?", "a")
@@ -202,14 +202,14 @@ RUF055_0.py:94:1: RUF055 [*] Plain string pattern passed to `re` function
    | ^^^^^^^^^^^^^^^^^^^^^^^ RUF055
 95 | re.sub(r"a", r"\?", "a")
    |
-   = help: Replace with `"a".replace("a", "\\?")`
+   = help: Replace with `"a".replace(r"a", "\\?")`
 
 ℹ Safe fix
 91 91 | re.sub(r"a", "\a", "a")
 92 92 | re.sub(r"a", r"\a", "a")
 93 93 | 
 94    |-re.sub(r"a", "\?", "a")
-   94 |+"a".replace("a", "\\?")
+   94 |+"a".replace(r"a", "\\?")
 95 95 | re.sub(r"a", r"\?", "a")
 
 RUF055_0.py:95:1: RUF055 [*] Plain string pattern passed to `re` function
@@ -218,11 +218,11 @@ RUF055_0.py:95:1: RUF055 [*] Plain string pattern passed to `re` function
 95 | re.sub(r"a", r"\?", "a")
    | ^^^^^^^^^^^^^^^^^^^^^^^^ RUF055
    |
-   = help: Replace with `"a".replace("a", "\\?")`
+   = help: Replace with `"a".replace(r"a", r"\?")`
 
 ℹ Safe fix
 92 92 | re.sub(r"a", r"\a", "a")
 93 93 | 
 94 94 | re.sub(r"a", "\?", "a")
 95    |-re.sub(r"a", r"\?", "a")
-   95 |+"a".replace("a", "\\?")
+   95 |+"a".replace(r"a", r"\?")

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__preview__RUF055_RUF055_1.py.snap

@@ -29,11 +29,11 @@ RUF055_1.py:17:1: RUF055 [*] Plain string pattern passed to `re` function
 17 | re.sub(r"abc", repl, haystack)
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ RUF055
    |
-   = help: Replace with `haystack.replace("abc", repl)`
+   = help: Replace with `haystack.replace(r"abc", repl)`
 
 ℹ Safe fix
 14 14 | 
 15 15 | # also works for the `repl` argument in sub
 16 16 | repl = "new"
 17    |-re.sub(r"abc", repl, haystack)
-   17 |+haystack.replace("abc", repl)
+   17 |+haystack.replace(r"abc", repl)

crates/ruff_python_ast/src/str.rs

@@ -24,6 +24,14 @@ impl Quote {
         }
     }
 
+    #[inline]
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::Single => "'",
+            Self::Double => "\"",
+        }
+    }
+
     #[must_use]
     #[inline]
     pub const fn opposite(self) -> Self {

crates/ruff_python_codegen/src/generator.rs

@@ -1284,10 +1284,19 @@ impl<'a> Generator<'a> {
 
     fn unparse_string_literal(&mut self, string_literal: &ast::StringLiteral) {
         let ast::StringLiteral { value, flags, .. } = string_literal;
-        if flags.prefix().is_unicode() {
+        // for raw strings, we don't want to perform the UnicodeEscape in `p_str_repr`, so build the
-            self.p("u");
+        // replacement here
+        if flags.prefix().is_raw() {
+            self.p(flags.prefix().as_str());
+            self.p(self.quote.as_str());
+            self.p(value);
+            self.p(self.quote.as_str());
+        } else {
+            if flags.prefix().is_unicode() {
+                self.p("u");
+            }
+            self.p_str_repr(value);
         }
-        self.p_str_repr(value);
     }
 
     fn unparse_string_literal_value(&mut self, value: &ast::StringLiteralValue) {
@@ -1712,7 +1721,7 @@ class Foo:
         assert_eq!(round_trip(r#""hello""#), r#""hello""#);
         assert_eq!(round_trip(r"'hello'"), r#""hello""#);
         assert_eq!(round_trip(r"u'hello'"), r#"u"hello""#);
-        assert_eq!(round_trip(r"r'hello'"), r#""hello""#);
+        assert_eq!(round_trip(r"r'hello'"), r#"r"hello""#);
         assert_eq!(round_trip(r"b'hello'"), r#"b"hello""#);
         assert_eq!(round_trip(r#"("abc" "def" "ghi")"#), r#""abc" "def" "ghi""#);
         assert_eq!(round_trip(r#""he\"llo""#), r#"'he"llo'"#);
@@ -1720,6 +1729,12 @@ class Foo:
         assert_eq!(round_trip(r#"f'abc{"def"}{1}'"#), r#"f"abc{'def'}{1}""#);
     }
 
+    #[test]
+    fn raw() {
+        assert_round_trip!(r#"r"a\.b""#); // https://github.com/astral-sh/ruff/issues/9663
+        assert_round_trip!(r#"R"a\.b""#);
+    }
+
     #[test]
     fn self_documenting_fstring() {
         assert_round_trip!(r#"f"{ chr(65)  =   }""#);