[pyupgrade] Fix syntax error on string with newline escape and comment (UP037) (#22968)

## Summary

Fixes a syntax error introduced by `UP037` when a quoted annotation
contains a trailing comment.

Fixes #19835.

## Problem
The logic for detecting trailing comments in quoted annotations was
brittle, relying on a fixed offset (`len() - 2`) from the end of the
token stream. This failed to correctly identify comments in strings like
`"A\n#"`, leading to invalid code generation where the closing
parenthesis of the function definition was commented out.

## Approach
Updated the logic in
`crates/ruff_linter/src/rules/pyupgrade/rules/quoted_annotation.rs` to
detect trailing comments. It now iterates backwards through the tokens
of the annotation string, skipping any newline tokens, to find if the
last significant token is a comment.

## Test Plan
Added regression tests to
`crates/ruff_linter/resources/test/fixtures/pyupgrade/UP037_0.py`.
Verified with:
`cargo test -p ruff_linter pyupgrade::tests`

Author: danparizher

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP037_0.py

@@ -120,3 +120,7 @@ def f() -> """Literal[0]
     
     """:
     return 0
+
+# https://github.com/astral-sh/ruff/issues/19835
+def foo(bar: "A\n#"): ...
+def foo(bar: "A\n#\n"): ...

crates/ruff_linter/src/rules/pyupgrade/rules/quoted_annotation.rs

@@ -115,9 +115,8 @@ pub(crate) fn quoted_annotation(checker: &Checker, annotation: &str, range: Text
 
     let last_token_is_comment = checker
         .tokens()
-        // The actual last token will always be a logical newline,
-        // so we check the second to last
-        .get(checker.tokens().len().saturating_sub(2))
+        .iter()
+        .rfind(|tok| !tok.kind().is_any_newline())
         .is_some_and(|tok| tok.kind() == TokenKind::Comment);
 
     let new_content = match (spans_multiple_lines, last_token_is_comment) {

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP037_0.py.snap

@@ -590,5 +590,44 @@ help: Remove quotes
 119 |     #
 120 |     
     -     """:
-121 +     ):
+121 +     
+122 + ):
+123 |     return 0
+124 | 
+125 | # https://github.com/astral-sh/ruff/issues/19835
+
+UP037 [*] Remove quotes from type annotation
+   --> UP037_0.py:125:14
+    |
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+    |              ^^^^^^
+126 | def foo(bar: "A\n#\n"): ...
+    |
+help: Remove quotes
 122 |     return 0
+123 | 
+124 | # https://github.com/astral-sh/ruff/issues/19835
+    - def foo(bar: "A\n#"): ...
+125 + def foo(bar: (A
+126 + #
+127 + )): ...
+128 | def foo(bar: "A\n#\n"): ...
+
+UP037 [*] Remove quotes from type annotation
+   --> UP037_0.py:126:14
+    |
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+126 | def foo(bar: "A\n#\n"): ...
+    |              ^^^^^^^^
+    |
+help: Remove quotes
+123 | 
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+    - def foo(bar: "A\n#\n"): ...
+126 + def foo(bar: (A
+127 + #
+128 + 
+129 + )): ...

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__add_future_annotation_UP037_0.py.snap

@@ -590,5 +590,44 @@ help: Remove quotes
 119 |     #
 120 |     
     -     """:
-121 +     ):
+121 +     
+122 + ):
+123 |     return 0
+124 | 
+125 | # https://github.com/astral-sh/ruff/issues/19835
+
+UP037 [*] Remove quotes from type annotation
+   --> UP037_0.py:125:14
+    |
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+    |              ^^^^^^
+126 | def foo(bar: "A\n#\n"): ...
+    |
+help: Remove quotes
 122 |     return 0
+123 | 
+124 | # https://github.com/astral-sh/ruff/issues/19835
+    - def foo(bar: "A\n#"): ...
+125 + def foo(bar: (A
+126 + #
+127 + )): ...
+128 | def foo(bar: "A\n#\n"): ...
+
+UP037 [*] Remove quotes from type annotation
+   --> UP037_0.py:126:14
+    |
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+126 | def foo(bar: "A\n#\n"): ...
+    |              ^^^^^^^^
+    |
+help: Remove quotes
+123 | 
+124 | # https://github.com/astral-sh/ruff/issues/19835
+125 | def foo(bar: "A\n#"): ...
+    - def foo(bar: "A\n#\n"): ...
+126 + def foo(bar: (A
+127 + #
+128 + 
+129 + )): ...