[`flake8-future-annotations`] Implement `FA102` (#4702)

crates/ruff/src/checkers/ast/mod.rs

@@ -2184,19 +2184,19 @@ where
             Expr::Subscript(ast::ExprSubscript { value, slice, .. }) => {
                 // Ex) Optional[...], Union[...]
                 if self.any_enabled(&[
-                    Rule::MissingFutureAnnotationsImport,
+                    Rule::MissingFutureAnnotationsImportOldStyle,
                     Rule::NonPEP604Annotation,
                 ]) {
                     if let Some(operator) =
                         analyze::typing::to_pep604_operator(value, slice, &self.semantic_model)
                     {
-                        if self.enabled(Rule::MissingFutureAnnotationsImport) {
+                        if self.enabled(Rule::MissingFutureAnnotationsImportOldStyle) {
                             if self.settings.target_version < PythonVersion::Py310
                                 && self.settings.target_version >= PythonVersion::Py37
                                 && !self.semantic_model.future_annotations()
                                 && self.semantic_model.in_annotation()
                             {
-                                flake8_future_annotations::rules::missing_future_annotations(
+                                flake8_future_annotations::rules::missing_future_annotations_old_style(
                                     self, value,
                                 );
                             }
@@ -2215,6 +2215,21 @@ where
                     }
                 }
 
+                // Ex) list[...]
+                if self.enabled(Rule::MissingFutureAnnotationsImportNewStyle) {
+                    if self.settings.target_version < PythonVersion::Py39
+                        && !self.semantic_model.future_annotations()
+                        && self.semantic_model.in_annotation()
+                        && analyze::typing::is_pep585_generic(value, &self.semantic_model)
+                    {
+                        flake8_future_annotations::rules::missing_future_annotations_new_style(
+                            self,
+                            expr,
+                            flake8_future_annotations::rules::Reason::PEP585,
+                        );
+                    }
+                }
+
                 if self.semantic_model.match_typing_expr(value, "Literal") {
                     self.semantic_model.flags |= SemanticModelFlags::LITERAL;
                 }
@@ -2271,19 +2286,19 @@ where
 
                         // Ex) List[...]
                         if self.any_enabled(&[
-                            Rule::MissingFutureAnnotationsImport,
+                            Rule::MissingFutureAnnotationsImportOldStyle,
                             Rule::NonPEP585Annotation,
                         ]) {
                             if let Some(replacement) =
                                 analyze::typing::to_pep585_generic(expr, &self.semantic_model)
                             {
-                                if self.enabled(Rule::MissingFutureAnnotationsImport) {
+                                if self.enabled(Rule::MissingFutureAnnotationsImportOldStyle) {
                                     if self.settings.target_version < PythonVersion::Py39
                                         && self.settings.target_version >= PythonVersion::Py37
                                         && !self.semantic_model.future_annotations()
                                         && self.semantic_model.in_annotation()
                                     {
-                                        flake8_future_annotations::rules::missing_future_annotations(
+                                        flake8_future_annotations::rules::missing_future_annotations_old_style(
                                             self, expr,
                                         );
                                     }
@@ -2349,19 +2364,19 @@ where
             Expr::Attribute(ast::ExprAttribute { attr, value, .. }) => {
                 // Ex) typing.List[...]
                 if self.any_enabled(&[
-                    Rule::MissingFutureAnnotationsImport,
+                    Rule::MissingFutureAnnotationsImportOldStyle,
                     Rule::NonPEP585Annotation,
                 ]) {
                     if let Some(replacement) =
                         analyze::typing::to_pep585_generic(expr, &self.semantic_model)
                     {
-                        if self.enabled(Rule::MissingFutureAnnotationsImport) {
+                        if self.enabled(Rule::MissingFutureAnnotationsImportOldStyle) {
                             if self.settings.target_version < PythonVersion::Py39
                                 && self.settings.target_version >= PythonVersion::Py37
                                 && !self.semantic_model.future_annotations()
                                 && self.semantic_model.in_annotation()
                             {
-                                flake8_future_annotations::rules::missing_future_annotations(
+                                flake8_future_annotations::rules::missing_future_annotations_old_style(
                                     self, expr,
                                 );
                             }
@@ -3198,6 +3213,20 @@ where
                 op: Operator::BitOr,
                 ..
             }) => {
+                // Ex) `str | None`
+                if self.enabled(Rule::MissingFutureAnnotationsImportNewStyle) {
+                    if self.settings.target_version < PythonVersion::Py310
+                        && !self.semantic_model.future_annotations()
+                        && self.semantic_model.in_annotation()
+                    {
+                        flake8_future_annotations::rules::missing_future_annotations_new_style(
+                            self,
+                            expr,
+                            flake8_future_annotations::rules::Reason::PEP604,
+                        );
+                    }
+                }
+
                 if self.is_stub {
                     if self.enabled(Rule::DuplicateUnionMember)
                         && self.semantic_model.in_type_definition()

crates/ruff/src/codes.rs

@@ -318,7 +318,8 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Annotations, "401") => (RuleGroup::Unspecified, Rule::AnyType),
 
         // flake8-future-annotations
-        (Flake8FutureAnnotations, "100") => (RuleGroup::Unspecified, Rule::MissingFutureAnnotationsImport),
+        (Flake8FutureAnnotations, "100") => (RuleGroup::Unspecified, Rule::MissingFutureAnnotationsImportOldStyle),
+        (Flake8FutureAnnotations, "102") => (RuleGroup::Unspecified, Rule::MissingFutureAnnotationsImportNewStyle),
 
         // flake8-2020
         (Flake82020, "101") => (RuleGroup::Unspecified, Rule::SysVersionSlice3),

crates/ruff/src/registry.rs

@@ -267,7 +267,8 @@ ruff_macros::register_rules!(
     rules::flake8_annotations::rules::MissingReturnTypeClassMethod,
     rules::flake8_annotations::rules::AnyType,
     // flake8-future-annotations
-    rules::flake8_future_annotations::rules::MissingFutureAnnotationsImport,
+    rules::flake8_future_annotations::rules::MissingFutureAnnotationsImportOldStyle,
+    rules::flake8_future_annotations::rules::MissingFutureAnnotationsImportNewStyle,
     // flake8-2020
     rules::flake8_2020::rules::SysVersionSlice3,
     rules::flake8_2020::rules::SysVersion2,

crates/ruff/src/rules/flake8_future_annotations/mod.rs

@@ -25,13 +25,31 @@ mod tests {
     #[test_case(Path::new("ok_non_simplifiable_types.py"))]
     #[test_case(Path::new("ok_uses_future.py"))]
     #[test_case(Path::new("ok_variable_name.py"))]
-    fn rules(path: &Path) -> Result<()> {
+    fn fa100(path: &Path) -> Result<()> {
         let snapshot = path.to_string_lossy().into_owned();
         let diagnostics = test_path(
             Path::new("flake8_future_annotations").join(path).as_path(),
             &settings::Settings {
                 target_version: PythonVersion::Py37,
-                ..settings::Settings::for_rule(Rule::MissingFutureAnnotationsImport)
+                ..settings::Settings::for_rule(Rule::MissingFutureAnnotationsImportOldStyle)
+            },
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
+
+    #[test_case(Path::new("no_future_import_uses_lowercase.py"))]
+    #[test_case(Path::new("no_future_import_uses_union.py"))]
+    #[test_case(Path::new("no_future_import_uses_union_inner.py"))]
+    #[test_case(Path::new("ok_no_types.py"))]
+    #[test_case(Path::new("ok_uses_future.py"))]
+    fn fa102(path: &Path) -> Result<()> {
+        let snapshot = format!("fa102_{}", path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("flake8_future_annotations").join(path).as_path(),
+            &settings::Settings {
+                target_version: PythonVersion::Py37,
+                ..settings::Settings::for_rule(Rule::MissingFutureAnnotationsImportNewStyle)
             },
         )?;
         assert_messages!(snapshot, diagnostics);

crates/ruff/src/rules/flake8_future_annotations/rules/missing_future_annotations_new_style.rs

@@ -0,0 +1,77 @@
+use rustpython_parser::ast::{Expr, Ranged};
+use std::fmt;
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for uses of PEP 585- and PEP 604-style type annotations in Python
+/// modules that lack the required `from __future__ import annotations` import
+/// for compatibility with older Python versions.
+///
+/// ## Why is this bad?
+/// Using PEP 585 and PEP 604 style annotations without a `from __future__ import
+/// annotations` import will cause runtime errors on Python versions prior to
+/// 3.9 and 3.10, respectively.
+///
+/// By adding the `__future__` import, the interpreter will no longer interpret
+/// annotations at evaluation time, making the code compatible with both past
+/// and future Python versions.
+///
+/// ## Example
+/// ```python
+/// def func(obj: dict[str, int | None]) -> None:
+///     ...
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from __future__ import annotations
+///
+///
+/// def func(obj: dict[str, int | None]) -> None:
+///     ...
+/// ```
+#[violation]
+pub struct MissingFutureAnnotationsImportNewStyle {
+    reason: Reason,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) enum Reason {
+    /// The type annotation is written in PEP 585 style (e.g., `list[int]`).
+    PEP585,
+    /// The type annotation is written in PEP 604 style (e.g., `int | None`).
+    PEP604,
+}
+
+impl fmt::Display for Reason {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Reason::PEP585 => fmt.write_str("PEP 585 collection"),
+            Reason::PEP604 => fmt.write_str("PEP 604 union"),
+        }
+    }
+}
+
+impl Violation for MissingFutureAnnotationsImportNewStyle {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let MissingFutureAnnotationsImportNewStyle { reason } = self;
+        format!("Missing `from __future__ import annotations`, but uses {reason}")
+    }
+}
+
+/// FA102
+pub(crate) fn missing_future_annotations_new_style(
+    checker: &mut Checker,
+    expr: &Expr,
+    reason: Reason,
+) {
+    checker.diagnostics.push(Diagnostic::new(
+        MissingFutureAnnotationsImportNewStyle { reason },
+        expr.range(),
+    ));
+}

crates/ruff/src/rules/flake8_future_annotations/rules/missing_future_annotations_old_style.rs

@@ -26,9 +26,8 @@ use crate::checkers::ast::Checker;
 /// from typing import List, Dict, Optional
 ///
 ///
-/// def function(a_dict: Dict[str, Optional[int]]) -> None:
+/// def func(obj: Dict[str, Optional[int]]) -> None:
-///     a_list: List[str] = []
+///     ...
-///     a_list.append("hello")
 /// ```
 ///
 /// Use instead:
@@ -38,9 +37,8 @@ use crate::checkers::ast::Checker;
 /// from typing import List, Dict, Optional
 ///
 ///
-/// def function(a_dict: Dict[str, Optional[int]]) -> None:
+/// def func(obj: Dict[str, Optional[int]]) -> None:
-///     a_list: List[str] = []
+///     ...
-///     a_list.append("hello")
 /// ```
 ///
 /// After running the additional pyupgrade rules:
@@ -48,25 +46,24 @@ use crate::checkers::ast::Checker;
 /// from __future__ import annotations
 ///
 ///
-/// def function(a_dict: dict[str, int | None]) -> None:
+/// def func(obj: dict[str, int | None]) -> None:
-///     a_list: list[str] = []
+///     ...
-///     a_list.append("hello")
 /// ```
 #[violation]
-pub struct MissingFutureAnnotationsImport {
+pub struct MissingFutureAnnotationsImportOldStyle {
     name: String,
 }
 
-impl Violation for MissingFutureAnnotationsImport {
+impl Violation for MissingFutureAnnotationsImportOldStyle {
     #[derive_message_formats]
     fn message(&self) -> String {
-        let MissingFutureAnnotationsImport { name } = self;
+        let MissingFutureAnnotationsImportOldStyle { name } = self;
         format!("Missing `from __future__ import annotations`, but uses `{name}`")
     }
 }
 
 /// FA100
-pub(crate) fn missing_future_annotations(checker: &mut Checker, expr: &Expr) {
+pub(crate) fn missing_future_annotations_old_style(checker: &mut Checker, expr: &Expr) {
     let name = checker
         .semantic_model()
         .resolve_call_path(expr)
@@ -74,7 +71,7 @@ pub(crate) fn missing_future_annotations(checker: &mut Checker, expr: &Expr) {
 
     if let Some(name) = name {
         checker.diagnostics.push(Diagnostic::new(
-            MissingFutureAnnotationsImport { name },
+            MissingFutureAnnotationsImportOldStyle { name },
             expr.range(),
         ));
     }

crates/ruff/src/rules/flake8_future_annotations/rules/mod.rs

@@ -1,5 +1,9 @@
-pub(crate) use missing_future_annotations::{
+pub(crate) use missing_future_annotations_new_style::{
-    missing_future_annotations, MissingFutureAnnotationsImport,
+    missing_future_annotations_new_style, MissingFutureAnnotationsImportNewStyle, Reason,
+};
+pub(crate) use missing_future_annotations_old_style::{
+    missing_future_annotations_old_style, MissingFutureAnnotationsImportOldStyle,
 };
 
-mod missing_future_annotations;
+mod missing_future_annotations_new_style;
+mod missing_future_annotations_old_style;

crates/ruff/src/rules/flake8_future_annotations/snapshots/ruff__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_lowercase.py.snap

@@ -0,0 +1,12 @@
+---
+source: crates/ruff/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
+  |
+2 | def main() -> None:
+3 |     a_list: list[str] = []
+  |             ^^^^^^^^^ FA102
+4 |     a_list.append("hello")
+  |
+
+

crates/ruff/src/rules/flake8_future_annotations/snapshots/ruff__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_union.py.snap

@@ -0,0 +1,20 @@
+---
+source: crates/ruff/src/rules/flake8_future_annotations/mod.rs
+---
+no_future_import_uses_union.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+  |
+2 | def main() -> None:
+3 |     a_list: list[str] | None = []
+  |             ^^^^^^^^^^^^^^^^ FA102
+4 |     a_list.append("hello")
+  |
+
+no_future_import_uses_union.py:2:13: FA102 Missing `from __future__ import annotations`, but uses PEP 585 collection
+  |
+2 | def main() -> None:
+3 |     a_list: list[str] | None = []
+  |             ^^^^^^^^^ FA102
+4 |     a_list.append("hello")
+  |
+
+

crates/ruff/src/rules/flake8_future_annotations/snapshots/ruff__rules__flake8_future_annotations__tests__fa102_no_future_import_uses_union_inner.py.snap

@@ -0,0 +1,36 @@
+---
+source: crates/ruff/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
+  |
+2 | def main() -> None:
+3 |     a_list: list[str | None] = []
+  |             ^^^^^^^^^^^^^^^^ FA102
+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
+  |
+2 | def main() -> None:
+3 |     a_list: list[str | None] = []
+  |                  ^^^^^^^^^^ FA102
+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
+  |
+7 | def hello(y: dict[str | None, int]) -> None:
+8 |     z: tuple[str, str | None, str] = tuple(y)
+  |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ FA102
+9 |     del z
+  |
+
+no_future_import_uses_union_inner.py:7:19: FA102 Missing `from __future__ import annotations`, but uses PEP 604 union
+  |
+7 | def hello(y: dict[str | None, int]) -> None:
+8 |     z: tuple[str, str | None, str] = tuple(y)
+  |                   ^^^^^^^^^^ FA102
+9 |     del z
+  |
+
+

crates/ruff/src/rules/flake8_future_annotations/snapshots/ruff__rules__flake8_future_annotations__tests__fa102_ok_no_types.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff/src/rules/flake8_future_annotations/mod.rs
+---
+

crates/ruff/src/rules/flake8_future_annotations/snapshots/ruff__rules__flake8_future_annotations__tests__fa102_ok_uses_future.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff/src/rules/flake8_future_annotations/mod.rs
+---
+

crates/ruff_python_semantic/src/analyze/typing.rs

@@ -101,6 +101,21 @@ pub fn to_pep585_generic(expr: &Expr, model: &SemanticModel) -> Option<ModuleMem
     })
 }
 
+/// Return whether a given expression uses a PEP 585 standard library generic.
+pub fn is_pep585_generic(expr: &Expr, model: &SemanticModel) -> bool {
+    if let Some(call_path) = model.resolve_call_path(expr) {
+        let [module, name] = call_path.as_slice() else {
+            return false;
+        };
+        for (_, (to_module, to_member)) in PEP_585_GENERICS {
+            if module == to_module && name == to_member {
+                return true;
+            }
+        }
+    }
+    false
+}
+
 #[derive(Debug, Copy, Clone)]
 pub enum Pep604Operator {
     /// The union operator, e.g., `Union[str, int]`, expressible as `str | int` after PEP 604.

ruff.schema.json

@@ -1883,6 +1883,7 @@
         "FA1",
         "FA10",
         "FA100",
+        "FA102",
         "FBT",
         "FBT0",
         "FBT00",