[pydoclint] Fix SyntaxError from fixes with line continuations (D201, D202) (#19246)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

This PR fixes #7172 by suppressing the fixes for
[docstring-missing-returns
(DOC201)](https://docs.astral.sh/ruff/rules/docstring-missing-returns/#docstring-missing-returns-doc201)
/ [docstring-extraneous-returns
(DOC202)](https://docs.astral.sh/ruff/rules/docstring-extraneous-returns/#docstring-extraneous-returns-doc202)
if there is a surrounding line continuation character `\` that would
make the fix cause a syntax error.

To do this, the lints are changed from `AlwaysFixableViolation` to
`Violation` with `FixAvailability::Sometimes`.

In the case of `DOC201`, the fix is not given if the non-break line ends
in a line continuation character `\`. Note that lines are iterated in
reverse from the docstring to the function definition.

In the case of `DOC202`, the fix is not given if the docstring ends with
a line continuation character `\`.

## Test Plan

<!-- How was it tested? -->

Added a test case.

crates/ruff_linter/src/rules/pydocstyle/rules/blank_before_after_function.rs

@@ -10,7 +10,7 @@ use ruff_text_size::TextRange;
 use crate::checkers::ast::Checker;
 use crate::docstrings::Docstring;
 use crate::registry::Rule;
-use crate::{AlwaysFixableViolation, Edit, Fix};
+use crate::{Edit, Fix, FixAvailability, Violation};
 
 /// ## What it does
 /// Checks for docstrings on functions that are separated by one or more blank
@@ -42,15 +42,17 @@ pub(crate) struct BlankLineBeforeFunction {
     num_lines: usize,
 }
 
-impl AlwaysFixableViolation for BlankLineBeforeFunction {
+impl Violation for BlankLineBeforeFunction {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
     #[derive_message_formats]
     fn message(&self) -> String {
         let BlankLineBeforeFunction { num_lines } = self;
         format!("No blank lines allowed before function docstring (found {num_lines})")
     }
 
-    fn fix_title(&self) -> String {
-        "Remove blank line(s) before function docstring".to_string()
+    fn fix_title(&self) -> Option<String> {
+        Some("Remove blank line(s) before function docstring".to_string())
     }
 }
 
@@ -86,15 +88,17 @@ pub(crate) struct BlankLineAfterFunction {
     num_lines: usize,
 }
 
-impl AlwaysFixableViolation for BlankLineAfterFunction {
+impl Violation for BlankLineAfterFunction {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
     #[derive_message_formats]
     fn message(&self) -> String {
         let BlankLineAfterFunction { num_lines } = self;
         format!("No blank lines allowed after function docstring (found {num_lines})")
     }
 
-    fn fix_title(&self) -> String {
-        "Remove blank line(s) after function docstring".to_string()
+    fn fix_title(&self) -> Option<String> {
+        Some("Remove blank line(s) after function docstring".to_string())
     }
 }
 
@@ -115,12 +119,14 @@ pub(crate) fn blank_before_after_function(checker: &Checker, docstring: &Docstri
         let mut lines = UniversalNewlineIterator::with_offset(before, function.start()).rev();
         let mut blank_lines_before = 0usize;
         let mut blank_lines_start = lines.next().map(|l| l.end()).unwrap_or_default();
+        let mut start_is_line_continuation = false;
 
         for line in lines {
             if line.trim().is_empty() {
                 blank_lines_before += 1;
                 blank_lines_start = line.start();
             } else {
+                start_is_line_continuation = line.ends_with('\\');
                 break;
             }
         }
@@ -132,11 +138,14 @@ pub(crate) fn blank_before_after_function(checker: &Checker, docstring: &Docstri
                 },
                 docstring.range(),
             );
-            // Delete the blank line before the docstring.
-            diagnostic.set_fix(Fix::safe_edit(Edit::deletion(
-                blank_lines_start,
-                docstring.line_start(),
-            )));
+            // Do not offer fix if a \ would cause it to be a syntax error
+            if !start_is_line_continuation {
+                // Delete the blank line before the docstring.
+                diagnostic.set_fix(Fix::safe_edit(Edit::deletion(
+                    blank_lines_start,
+                    docstring.line_start(),
+                )));
+            }
         }
     }
 
@@ -156,7 +165,9 @@ pub(crate) fn blank_before_after_function(checker: &Checker, docstring: &Docstri
         // Count the number of blank lines after the docstring.
         let mut blank_lines_after = 0usize;
         let mut lines = UniversalNewlineIterator::with_offset(after, docstring.end()).peekable();
-        let first_line_end = lines.next().map(|l| l.end()).unwrap_or_default();
+        let first_line = lines.next();
+        let first_line_line_continuation = first_line.as_ref().is_some_and(|l| l.ends_with('\\'));
+        let first_line_end = first_line.map(|l| l.end()).unwrap_or_default();
         let mut blank_lines_end = first_line_end;
 
         while let Some(line) = lines.peek() {
@@ -185,11 +196,14 @@ pub(crate) fn blank_before_after_function(checker: &Checker, docstring: &Docstri
                 },
                 docstring.range(),
             );
-            // Delete the blank line after the docstring.
-            diagnostic.set_fix(Fix::safe_edit(Edit::deletion(
-                first_line_end,
-                blank_lines_end,
-            )));
+            // Do not offer fix if a \ would cause it to be a syntax error
+            if !first_line_line_continuation {
+                // Delete the blank line after the docstring.
+                diagnostic.set_fix(Fix::safe_edit(Edit::deletion(
+                    first_line_end,
+                    blank_lines_end,
+                )));
+            }
         }
     }
 }

crates/ruff_linter/src/rules/pydocstyle/snapshots/ruff_linter__rules__pydocstyle__tests__D201_D.py.snap

@@ -82,3 +82,14 @@ D.py:568:5: D201 [*] No blank lines allowed before function docstring (found 1)
 568 567 |     """Trailing and leading space.
 569 568 | 
 570 569 |     More content.
+
+D.py:729:5: D201 No blank lines allowed before function docstring (found 1)
+    |
+727 | def line_continuation_chars():\
+728 |
+729 |     """No fix should be offered for D201/D202 because of the line continuation chars."""\
+    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ D201
+730 |
+731 |     ...
+    |
+    = help: Remove blank line(s) before function docstring

crates/ruff_linter/src/rules/pydocstyle/snapshots/ruff_linter__rules__pydocstyle__tests__D202_D.py.snap

@@ -85,4 +85,15 @@ D.py:568:5: D202 [*] No blank lines allowed after function docstring (found 1)
 572     |-
 573 572 |     pass
 574 573 | 
-575 574 |
+575 574 | 
+
+D.py:729:5: D202 No blank lines allowed after function docstring (found 1)
+    |
+727 | def line_continuation_chars():\
+728 |
+729 |     """No fix should be offered for D201/D202 because of the line continuation chars."""\
+    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ D202
+730 |
+731 |     ...
+    |
+    = help: Remove blank line(s) after function docstring

crates/ruff_linter/src/rules/pydocstyle/snapshots/ruff_linter__rules__pydocstyle__tests__D208_D.py.snap

@@ -428,3 +428,5 @@ D.py:723:1: D208 [*] Docstring is over-indented
 723     |-       Returns:
     723 |+    Returns:
 724 724 |     """
+725 725 | 
+726 726 |