Add fix for future-required-type-annotation (#8711)

## Summary

We already support inserting imports for `I002` -- this PR just adds the
same fix for `FA102`, which is explicitly about `from __future__ import
annotations`.

Closes https://github.com/astral-sh/ruff/issues/8682.

crates/ruff_linter/src/importer/mod.rs

@@ -7,7 +7,7 @@ use std::error::Error;
 
 use anyhow::Result;
 use libcst_native::{ImportAlias, Name, NameOrAttribute};
-use ruff_python_ast::{self as ast, PySourceType, Stmt, Suite};
+use ruff_python_ast::{self as ast, PySourceType, Stmt};
 use ruff_text_size::{Ranged, TextSize};
 
 use ruff_diagnostics::Edit;
@@ -26,7 +26,7 @@ mod insertion;
 
 pub(crate) struct Importer<'a> {
     /// The Python AST to which we are adding imports.
-    python_ast: &'a Suite,
+    python_ast: &'a [Stmt],
     /// The [`Locator`] for the Python AST.
     locator: &'a Locator<'a>,
     /// The [`Stylist`] for the Python AST.
@@ -39,7 +39,7 @@ pub(crate) struct Importer<'a> {
 
 impl<'a> Importer<'a> {
     pub(crate) fn new(
-        python_ast: &'a Suite,
+        python_ast: &'a [Stmt],
         locator: &'a Locator<'a>,
         stylist: &'a Stylist<'a>,
     ) -> Self {

crates/ruff_linter/src/rules/flake8_future_annotations/rules/future_required_type_annotation.rs

@@ -1,11 +1,13 @@
-use ruff_python_ast::Expr;
 use std::fmt;
 
-use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Fix};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_text_size::Ranged;
+use ruff_python_ast::imports::{AnyImport, ImportFrom};
+use ruff_python_ast::Expr;
+use ruff_text_size::{Ranged, TextSize};
 
 use crate::checkers::ast::Checker;
+use crate::importer::Importer;
 
 /// ## What it does
 /// Checks for uses of PEP 585- and PEP 604-style type annotations in Python
@@ -42,6 +44,10 @@ use crate::checkers::ast::Checker;
 ///     ...
 /// ```
 ///
+/// ## Fix safety
+/// This rule's fix is marked as unsafe, as adding `from __future__ import annotations`
+/// may change the semantics of the program.
+///
 /// ## Options
 /// - `target-version`
 #[violation]
@@ -66,18 +72,28 @@ impl fmt::Display for Reason {
     }
 }
 
-impl Violation for FutureRequiredTypeAnnotation {
+impl AlwaysFixableViolation for FutureRequiredTypeAnnotation {
     #[derive_message_formats]
     fn message(&self) -> String {
         let FutureRequiredTypeAnnotation { reason } = self;
         format!("Missing `from __future__ import annotations`, but uses {reason}")
     }
+
+    fn fix_title(&self) -> String {
+        format!("Add `from __future__ import annotations`")
+    }
 }
 
 /// FA102
 pub(crate) fn future_required_type_annotation(checker: &mut Checker, expr: &Expr, reason: Reason) {
-    checker.diagnostics.push(Diagnostic::new(
-        FutureRequiredTypeAnnotation { reason },
-        expr.range(),
-    ));
+    let mut diagnostic = Diagnostic::new(FutureRequiredTypeAnnotation { reason }, expr.range());
+    if let Some(python_ast) = checker.semantic().definitions.python_ast() {
+        let required_import =
+            AnyImport::ImportFrom(ImportFrom::member("__future__", "annotations"));
+        diagnostic.set_fix(Fix::unsafe_edit(
+            Importer::new(python_ast, checker.locator(), checker.stylist())
+                .add_import(&required_import, TextSize::default()),
+        ));
+    }
+    checker.diagnostics.push(diagnostic);
 }

crates/ruff_linter/src/rules/flake8_future_annotations/snapshots/ruff_linter__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_lowercase.py.snap

@@ -1,19 +1,33 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_future_annotations/mod.rs
 ---
-no_future_import_uses_lowercase.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+no_future_import_uses_lowercase.py:2:13: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 1 | def main() -> None:
 2 |     a_list: list[str] = []
   |             ^^^^^^^^^ FA102
 3 |     a_list.append("hello")
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_lowercase.py:6:14: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_lowercase.py:6:14: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 6 | def hello(y: dict[str, int]) -> None:
   |              ^^^^^^^^^^^^^^ FA102
 7 |     del y
   |
+  = help: Add `from __future__ import annotations`
+
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] = []
+3 4 |     a_list.append("hello")
 
 

crates/ruff_linter/src/rules/flake8_future_annotations/snapshots/ruff_linter__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_union.py.snap

@@ -1,34 +1,62 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_future_annotations/mod.rs
 ---
-no_future_import_uses_union.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+no_future_import_uses_union.py:2:13: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 1 | def main() -> None:
 2 |     a_list: list[str] | None = []
   |             ^^^^^^^^^ FA102
 3 |     a_list.append("hello")
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] | None = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union.py:2:13: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 604 union
   |
 1 | def main() -> None:
 2 |     a_list: list[str] | None = []
   |             ^^^^^^^^^^^^^^^^ FA102
 3 |     a_list.append("hello")
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union.py:6:14: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] | None = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union.py:6:14: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 6 | def hello(y: dict[str, int] | None) -> None:
   |              ^^^^^^^^^^^^^^ FA102
 7 |     del y
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union.py:6:14: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] | None = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union.py:6:14: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 604 union
   |
 6 | def hello(y: dict[str, int] | None) -> None:
   |              ^^^^^^^^^^^^^^^^^^^^^ FA102
 7 |     del y
   |
+  = help: Add `from __future__ import annotations`
+
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str] | None = []
+3 4 |     a_list.append("hello")
 
 

crates/ruff_linter/src/rules/flake8_future_annotations/snapshots/ruff_linter__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_union_inner.py.snap

@@ -1,52 +1,94 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_future_annotations/mod.rs
 ---
-no_future_import_uses_union_inner.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+no_future_import_uses_union_inner.py:2:13: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 1 | def main() -> None:
 2 |     a_list: list[str | None] = []
   |             ^^^^^^^^^^^^^^^^ FA102
 3 |     a_list.append("hello")
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union_inner.py:2:18: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union_inner.py:2:18: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 604 union
   |
 1 | def main() -> None:
 2 |     a_list: list[str | None] = []
   |                  ^^^^^^^^^^ FA102
 3 |     a_list.append("hello")
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union_inner.py:6:14: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union_inner.py:6:14: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 6 | def hello(y: dict[str | None, int]) -> None:
   |              ^^^^^^^^^^^^^^^^^^^^^ FA102
 7 |     z: tuple[str, str | None, str] = tuple(y)
 8 |     del z
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union_inner.py:6:19: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union_inner.py:6:19: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 604 union
   |
 6 | def hello(y: dict[str | None, int]) -> None:
   |                   ^^^^^^^^^^ FA102
 7 |     z: tuple[str, str | None, str] = tuple(y)
 8 |     del z
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union_inner.py:7:8: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union_inner.py:7:8: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 585 collection
   |
 6 | def hello(y: dict[str | None, int]) -> None:
 7 |     z: tuple[str, str | None, str] = tuple(y)
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ FA102
 8 |     del z
   |
+  = help: Add `from __future__ import annotations`
 
-no_future_import_uses_union_inner.py:7:19: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
+
+no_future_import_uses_union_inner.py:7:19: FA102 [*] Missing `from __future__ import annotations`, but uses PEP 604 union
   |
 6 | def hello(y: dict[str | None, int]) -> None:
 7 |     z: tuple[str, str | None, str] = tuple(y)
   |                   ^^^^^^^^^^ FA102
 8 |     del z
   |
+  = help: Add `from __future__ import annotations`
+
+ℹ Unsafe fix
+  1 |+from __future__ import annotations
+1 2 | def main() -> None:
+2 3 |     a_list: list[str | None] = []
+3 4 |     a_list.append("hello")
 
 

crates/ruff_linter/src/rules/refurb/rules/repeated_append.rs

@@ -6,7 +6,7 @@ use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::{self as ast, Expr, Stmt};
 use ruff_python_codegen::Generator;
 use ruff_python_semantic::analyze::typing::is_list;
-use ruff_python_semantic::{Binding, BindingId, DefinitionId, SemanticModel};
+use ruff_python_semantic::{Binding, BindingId, SemanticModel};
 use ruff_text_size::{Ranged, TextRange};
 
 use crate::checkers::ast::Checker;
@@ -183,8 +183,7 @@ fn match_consecutive_appends<'a>(
     let siblings: &[Stmt] = if semantic.at_top_level() {
         // If the statement is at the top level, we should go to the parent module.
         // Module is available in the definitions list.
-        let module = semantic.definitions[DefinitionId::module()].as_module()?;
-        module.python_ast
+        semantic.definitions.python_ast()?
     } else {
         // Otherwise, go to the parent, and take its body as a sequence of siblings.
         semantic

crates/ruff_python_semantic/src/definition.rs

@@ -248,6 +248,12 @@ impl<'a> Definitions<'a> {
 
         ContextualizedDefinitions(definitions.raw)
     }
+
+    /// Returns a reference to the Python AST.
+    pub fn python_ast(&self) -> Option<&'a [Stmt]> {
+        let module = self[DefinitionId::module()].as_module()?;
+        Some(module.python_ast)
+    }
 }
 
 impl<'a> Deref for Definitions<'a> {