Add a fix for redefinition-while-unused (#9419)

## Summary

This PR enables Ruff to remove redefined imports, as in:

```python
import os
import os

print(os)
```

Previously, Ruff would flag `F811` on the second `import os`, but
couldn't fix it.

For now, this fix is marked as safe, but only available in preview.

Closes #3477.

crates/ruff_linter/src/checkers/ast/analyze/deferred_scopes.rs

@@ -1,10 +1,11 @@
-use ruff_diagnostics::Diagnostic;
+use ruff_diagnostics::{Diagnostic, Fix};
 use ruff_python_semantic::analyze::visibility;
-use ruff_python_semantic::{Binding, BindingKind, ScopeKind};
+use ruff_python_semantic::{Binding, BindingKind, Imported, ScopeKind};
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
 use crate::codes::Rule;
+use crate::fix;
 use crate::rules::{
     flake8_pyi, flake8_type_checking, flake8_unused_arguments, pyflakes, pylint, ruff,
 };
@@ -247,9 +248,33 @@ pub(crate) fn deferred_scopes(checker: &mut Checker) {
                         },
                         binding.range(),
                     );
+
                     if let Some(range) = binding.parent_range(&checker.semantic) {
                         diagnostic.set_parent(range.start());
                     }
+
+                    if checker.settings.preview.is_enabled() {
+                        if let Some(import) = binding.as_any_import() {
+                            if let Some(source) = binding.source {
+                                diagnostic.try_set_fix(|| {
+                                    let statement = checker.semantic().statement(source);
+                                    let parent = checker.semantic().parent_statement(source);
+                                    let edit = fix::edits::remove_unused_imports(
+                                        std::iter::once(import.member_name().as_ref()),
+                                        statement,
+                                        parent,
+                                        checker.locator(),
+                                        checker.stylist(),
+                                        checker.indexer(),
+                                    )?;
+                                    Ok(Fix::safe_edit(edit).isolate(Checker::isolation(
+                                        checker.semantic().parent_statement_id(source),
+                                    )))
+                                });
+                            }
+                        }
+                    }
+
                     diagnostics.push(diagnostic);
                 }
             }

crates/ruff_linter/src/rules/pyflakes/mod.rs

@@ -168,6 +168,34 @@ mod tests {
         Ok(())
     }
 
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_0.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_1.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_10.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_11.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_12.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_13.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_14.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_15.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_16.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_17.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_18.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_19.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_2.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_20.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_21.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_22.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_23.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_24.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_25.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_26.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_27.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_3.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_4.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_5.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_6.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_7.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_8.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_9.py"))]
     #[test_case(Rule::UnusedVariable, Path::new("F841_4.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(

crates/ruff_linter/src/rules/pyflakes/rules/redefined_while_unused.rs

@@ -1,4 +1,4 @@
-use ruff_diagnostics::Violation;
+use ruff_diagnostics::{FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_source_file::SourceRow;
 
@@ -29,9 +29,16 @@ pub struct RedefinedWhileUnused {
 }
 
 impl Violation for RedefinedWhileUnused {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
     #[derive_message_formats]
     fn message(&self) -> String {
         let RedefinedWhileUnused { name, row } = self;
         format!("Redefinition of unused `{name}` from {row}")
     }
+
+    fn fix_title(&self) -> Option<String> {
+        let RedefinedWhileUnused { name, .. } = self;
+        Some(format!("Remove definition: `{name}`"))
+    }
 }

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_0.py.snap

@@ -7,5 +7,6 @@ F811_0.py:10:5: F811 Redefinition of unused `bar` from line 6
    |     ^^^ F811
 11 |     pass
    |
+   = help: Remove definition: `bar`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_1.py.snap

@@ -6,5 +6,6 @@ F811_1.py:1:25: F811 Redefinition of unused `FU` from line 1
 1 | import fu as FU, bar as FU
   |                         ^^ F811
   |
+  = help: Remove definition: `FU`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_12.py.snap

@@ -9,5 +9,6 @@ F811_12.py:6:20: F811 Redefinition of unused `mixer` from line 2
   |                    ^^^^^ F811
 7 | mixer(123)
   |
+  = help: Remove definition: `mixer`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_15.py.snap

@@ -7,5 +7,6 @@ F811_15.py:4:5: F811 Redefinition of unused `fu` from line 1
   |     ^^ F811
 5 |     pass
   |
+  = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_16.py.snap

@@ -9,5 +9,6 @@ F811_16.py:8:13: F811 Redefinition of unused `fu` from line 3
   |             ^^ F811
 9 |             pass
   |
+  = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_17.py.snap

@@ -9,6 +9,7 @@ F811_17.py:6:12: F811 Redefinition of unused `fu` from line 2
 7 | 
 8 |     def baz():
   |
+  = help: Remove definition: `fu`
 
 F811_17.py:9:13: F811 Redefinition of unused `fu` from line 6
    |
@@ -17,5 +18,6 @@ F811_17.py:9:13: F811 Redefinition of unused `fu` from line 6
    |             ^^ F811
 10 |             pass
    |
+   = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_2.py.snap

@@ -6,5 +6,6 @@ F811_2.py:1:34: F811 Redefinition of unused `FU` from line 1
 1 | from moo import fu as FU, bar as FU
   |                                  ^^ F811
   |
+  = help: Remove definition: `FU`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_21.py.snap

@@ -9,5 +9,6 @@ F811_21.py:32:5: F811 Redefinition of unused `Sequence` from line 26
    |     ^^^^^^^^ F811
 33 | )
    |
+   = help: Remove definition: `Sequence`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_23.py.snap

@@ -7,5 +7,6 @@ F811_23.py:4:15: F811 Redefinition of unused `foo` from line 3
 4 | import bar as foo
   |               ^^^ F811
   |
+  = help: Remove definition: `foo`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_26.py.snap

@@ -9,5 +9,6 @@ F811_26.py:5:9: F811 Redefinition of unused `func` from line 2
   |         ^^^^ F811
 6 |         pass
   |
+  = help: Remove definition: `func`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_3.py.snap

@@ -6,5 +6,6 @@ F811_3.py:1:12: F811 Redefinition of unused `fu` from line 1
 1 | import fu; fu = 3
   |            ^^ F811
   |
+  = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_4.py.snap

@@ -6,5 +6,6 @@ F811_4.py:1:12: F811 Redefinition of unused `fu` from line 1
 1 | import fu; fu, bar = 3
   |            ^^ F811
   |
+  = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_5.py.snap

@@ -6,5 +6,6 @@ F811_5.py:1:13: F811 Redefinition of unused `fu` from line 1
 1 | import fu; [fu, bar] = 3
   |             ^^ F811
   |
+  = help: Remove definition: `fu`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_6.py.snap

@@ -9,5 +9,6 @@ F811_6.py:6:12: F811 Redefinition of unused `os` from line 5
   |            ^^ F811
 7 | os.path
   |
+  = help: Remove definition: `os`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_8.py.snap

@@ -10,5 +10,6 @@ F811_8.py:5:12: F811 Redefinition of unused `os` from line 4
 6 | except:
 7 |     pass
   |
+  = help: Remove definition: `os`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__del_shadowed_global_import_in_local_scope.snap

@@ -25,5 +25,6 @@ source: crates/ruff_linter/src/rules/pyflakes/mod.rs
 6 | 
 7 |     # Despite this `del`, `import os` in `f` should still be flagged as shadowing an unused
   |
+  = help: Remove definition: `os`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__del_shadowed_import_shadow_in_local_scope.snap

@@ -24,5 +24,6 @@ source: crates/ruff_linter/src/rules/pyflakes/mod.rs
   |     ^^ F811
 6 |     print(os)
   |
+  = help: Remove definition: `os`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__del_shadowed_local_import_in_local_scope.snap

@@ -10,5 +10,6 @@ source: crates/ruff_linter/src/rules/pyflakes/mod.rs
 5 | 
 6 |     # Despite this `del`, `import os` should still be flagged as shadowing an unused
   |
+  = help: Remove definition: `os`
 
 

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_0.py.snap

@@ -0,0 +1,12 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_0.py:10:5: F811 Redefinition of unused `bar` from line 6
+   |
+10 | def bar():
+   |     ^^^ F811
+11 |     pass
+   |
+   = help: Remove definition: `bar`
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_1.py.snap

@@ -0,0 +1,15 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_1.py:1:25: F811 [*] Redefinition of unused `FU` from line 1
+  |
+1 | import fu as FU, bar as FU
+  |                         ^^ F811
+  |
+  = help: Remove definition: `FU`
+
+ℹ Safe fix
+1   |-import fu as FU, bar as FU
+  1 |+import fu as FU
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_10.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_11.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_12.py.snap

@@ -0,0 +1,22 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_12.py:6:20: F811 [*] Redefinition of unused `mixer` from line 2
+  |
+4 |     pass
+5 | else:
+6 |     from bb import mixer
+  |                    ^^^^^ F811
+7 | mixer(123)
+  |
+  = help: Remove definition: `mixer`
+
+ℹ Safe fix
+3 3 | except ImportError:
+4 4 |     pass
+5 5 | else:
+6   |-    from bb import mixer
+  6 |+    pass
+7 7 | mixer(123)
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_13.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_14.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_15.py.snap

@@ -0,0 +1,12 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_15.py:4:5: F811 Redefinition of unused `fu` from line 1
+  |
+4 | def fu():
+  |     ^^ F811
+5 |     pass
+  |
+  = help: Remove definition: `fu`
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_16.py.snap

@@ -0,0 +1,14 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_16.py:8:13: F811 Redefinition of unused `fu` from line 3
+  |
+6 | def bar():
+7 |     def baz():
+8 |         def fu():
+  |             ^^ F811
+9 |             pass
+  |
+  = help: Remove definition: `fu`
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_17.py.snap

@@ -0,0 +1,32 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_17.py:6:12: F811 [*] Redefinition of unused `fu` from line 2
+  |
+5 | def bar():
+6 |     import fu
+  |            ^^ F811
+7 | 
+8 |     def baz():
+  |
+  = help: Remove definition: `fu`
+
+ℹ Safe fix
+3 3 | 
+4 4 | 
+5 5 | def bar():
+6   |-    import fu
+7 6 | 
+8 7 |     def baz():
+9 8 |         def fu():
+
+F811_17.py:9:13: F811 Redefinition of unused `fu` from line 6
+   |
+ 8 |     def baz():
+ 9 |         def fu():
+   |             ^^ F811
+10 |             pass
+   |
+   = help: Remove definition: `fu`
+
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_18.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_19.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F811_F811_2.py.snap

@@ -0,0 +1,15 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F811_2.py:1:34: F811 [*] Redefinition of unused `FU` from line 1
+  |
+1 | from moo import fu as FU, bar as FU
+  |                                  ^^ F811
+  |
+  = help: Remove definition: `FU`
+
+ℹ Safe fix
+1   |-from moo import fu as FU, bar as FU
+  1 |+from moo import fu as FU
+
+