[flake8-pyi] Implement PYI044 (#5021)

## Summary

This implements PYI044. This rule checks if `from __future__ import
annotations` is used in stub files as it has no effect in stub files, since type
checkers automatically treat stubs as having those semantics.

Updates https://github.com/astral-sh/ruff/issues/848

## Test Plan

Added a test case and snapshots.

crates/ruff/resources/test/fixtures/flake8_pyi/PYI044.py

@@ -0,0 +1,7 @@
+# Bad import.
+from __future__ import annotations # Not PYI044 (not a stubfile).
+
+# Good imports.
+from __future__ import Something
+import sys
+from socket import AF_INET

crates/ruff/resources/test/fixtures/flake8_pyi/PYI044.pyi

@@ -0,0 +1,7 @@
+# Bad import.
+from __future__ import annotations # PYI044.
+
+# Good imports.
+from __future__ import Something
+import sys
+from socket import AF_INET

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

@@ -1121,6 +1121,9 @@ where
                     if self.enabled(Rule::UnaliasedCollectionsAbcSetImport) {
                         flake8_pyi::rules::unaliased_collections_abc_set_import(self, import_from);
                     }
+                    if self.enabled(Rule::FutureAnnotationsInStub) {
+                        flake8_pyi::rules::from_future_import(self, import_from);
+                    }
                 }
                 for alias in names {
                     if let Some("__future__") = module {

crates/ruff/src/codes.rs

@@ -616,6 +616,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Pyi, "035") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::UnassignedSpecialVariableInStub),
         (Flake8Pyi, "042") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::SnakeCaseTypeAlias),
         (Flake8Pyi, "043") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::TSuffixedTypeAlias),
+        (Flake8Pyi, "044") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::FutureAnnotationsInStub),
         (Flake8Pyi, "045") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::IterMethodReturnIterable),
         (Flake8Pyi, "048") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::StubBodyMultipleStatements),
         (Flake8Pyi, "050") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::NoReturnArgumentAnnotationInStub),

crates/ruff/src/rules/flake8_pyi/mod.rs

@@ -54,6 +54,8 @@ mod tests {
     #[test_case(Rule::StubBodyMultipleStatements, Path::new("PYI048.pyi"))]
     #[test_case(Rule::TSuffixedTypeAlias, Path::new("PYI043.py"))]
     #[test_case(Rule::TSuffixedTypeAlias, Path::new("PYI043.pyi"))]
+    #[test_case(Rule::FutureAnnotationsInStub, Path::new("PYI044.py"))]
+    #[test_case(Rule::FutureAnnotationsInStub, Path::new("PYI044.pyi"))]
     #[test_case(Rule::TypeCommentInStub, Path::new("PYI033.py"))]
     #[test_case(Rule::TypeCommentInStub, Path::new("PYI033.pyi"))]
     #[test_case(Rule::TypedArgumentDefaultInStub, Path::new("PYI011.py"))]

crates/ruff/src/rules/flake8_pyi/rules/future_annotations_in_stub.rs

@@ -0,0 +1,33 @@
+use rustpython_parser::ast::StmtImportFrom;
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+
+#[violation]
+pub struct FutureAnnotationsInStub;
+
+impl Violation for FutureAnnotationsInStub {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("`from __future__ import annotations` has no effect in stub files, since type checkers automatically treat stubs as having those semantics")
+    }
+}
+
+/// PYI044
+pub(crate) fn from_future_import(checker: &mut Checker, target: &StmtImportFrom) {
+    if let StmtImportFrom {
+        range,
+        module: Some(name),
+        names,
+        ..
+    } = target
+    {
+        if name == "__future__" && names.iter().any(|alias| &*alias.name == "annotations") {
+            checker
+                .diagnostics
+                .push(Diagnostic::new(FutureAnnotationsInStub, *range));
+        }
+    }
+}

crates/ruff/src/rules/flake8_pyi/rules/mod.rs

@@ -4,6 +4,7 @@ pub(crate) use collections_named_tuple::*;
 pub(crate) use docstring_in_stubs::*;
 pub(crate) use duplicate_union_member::*;
 pub(crate) use ellipsis_in_non_empty_class_body::*;
+pub(crate) use future_annotations_in_stub::*;
 pub(crate) use iter_method_return_iterable::*;
 pub(crate) use no_return_argument_annotation::*;
 pub(crate) use non_empty_stub_body::*;
@@ -28,6 +29,7 @@ mod collections_named_tuple;
 mod docstring_in_stubs;
 mod duplicate_union_member;
 mod ellipsis_in_non_empty_class_body;
+mod future_annotations_in_stub;
 mod iter_method_return_iterable;
 mod no_return_argument_annotation;
 mod non_empty_stub_body;

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI044_PYI044.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI044_PYI044.pyi.snap

@@ -0,0 +1,13 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+PYI044.pyi:2:1: PYI044 `from __future__ import annotations` has no effect in stub files, since type checkers automatically treat stubs as having those semantics
+  |
+1 | # Bad import.
+2 | from __future__ import annotations # PYI044.
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI044
+3 | 
+4 | # Good imports.
+  |
+
+