[`ruff_linter`] - Use LibCST in `adjust_indentation` for mixed whitespace (#12740)

crates/ruff_linter/resources/test/fixtures/flake8_return/RET505.py

@@ -238,3 +238,9 @@ def indent(x, y, w, z):
   # comment
         c = 3
         return z
+
+def f():
+	if True:
+	 return True
+	else:
+	 return False

crates/ruff_linter/src/fix/edits.rs

@@ -300,11 +300,25 @@ pub(crate) fn adjust_indentation(
     indexer: &Indexer,
     stylist: &Stylist,
 ) -> Result<String> {
-    // If the range includes a multi-line string, use LibCST to ensure that we don't adjust the
-    // whitespace _within_ the string.
-    if indexer.multiline_ranges().intersects(range) || indexer.fstring_ranges().intersects(range) {
     let contents = locator.slice(range);
 
+    // If the range includes a multi-line string, use LibCST to ensure that we don't adjust the
+    // whitespace _within_ the string.
+    let contains_multiline_string =
+        indexer.multiline_ranges().intersects(range) || indexer.fstring_ranges().intersects(range);
+
+    // If the range has mixed indentation, we will use LibCST as well.
+    let mixed_indentation = contents.universal_newlines().any(|line| {
+        let trimmed = line.trim_whitespace_start();
+        if trimmed.is_empty() {
+            return false;
+        }
+
+        let line_indentation: &str = &line[..line.len() - trimmed.len()];
+        line_indentation.contains('\t') && line_indentation.contains(' ')
+    });
+
+    if contains_multiline_string || mixed_indentation {
         let module_text = format!("def f():{}{contents}", stylist.line_ending().as_str());
 
         let mut tree = match_statement(&module_text)?;
@@ -322,7 +336,6 @@ pub(crate) fn adjust_indentation(
         Ok(module_text)
     } else {
         // Otherwise, we can do a simple adjustment ourselves.
-        let contents = locator.slice(range);
         Ok(dedent_to(contents, indentation))
     }
 }

crates/ruff_linter/src/rules/flake8_return/snapshots/ruff_linter__rules__flake8_return__tests__RET505_RET505.py.snap

@@ -215,4 +215,12 @@ RET505.py:237:5: RET505 Unnecessary `else` after `return` statement
     |
     = help: Remove unnecessary `else`
 
-
+RET505.py:245:2: RET505 Unnecessary `else` after `return` statement
+    |
+243 |     if True:
+244 |      return True
+245 |     else:
+    |     ^^^^ RET505
+246 |      return False
+    |
+    = help: Remove unnecessary `else`

crates/ruff_linter/src/rules/flake8_return/snapshots/ruff_linter__rules__flake8_return__tests__preview__RET505_RET505.py.snap

@@ -460,5 +460,24 @@ RET505.py:237:5: RET505 [*] Unnecessary `else` after `return` statement
 240     |-        return z
     238 |+    c = 3
     239 |+    return z
+241 240 | 
+242 241 | def f():
+243 242 | 	if True:
 
+RET505.py:245:2: RET505 [*] Unnecessary `else` after `return` statement
+    |
+243 |     if True:
+244 |      return True
+245 |     else:
+    |     ^^^^ RET505
+246 |      return False
+    |
+    = help: Remove unnecessary `else`
 
+ℹ Safe fix
+242 242 | def f():
+243 243 | 	if True:
+244 244 | 	 return True
+245     |-	else:
+246     |-	 return False
+    245 |+	return False