Avoid adding required imports to stub files (#3940)

crates/ruff/resources/test/fixtures/isort/required_imports/docstring.pyi

@@ -0,0 +1,3 @@
+"""Hello, world!"""
+
+x = 1

crates/ruff/src/checkers/imports.rs

@@ -9,6 +9,7 @@ use ruff_python_ast::helpers::to_module_path;
 use ruff_python_ast::imports::{ImportMap, ModuleImport};
 use ruff_python_ast::source_code::{Indexer, Locator, Stylist};
 use ruff_python_ast::visitor::Visitor;
+use ruff_python_stdlib::path::is_python_stub_file;
 
 use crate::directives::IsortDirectives;
 use crate::registry::Rule;
@@ -88,9 +89,11 @@ pub fn check_imports(
     path: &Path,
     package: Option<&Path>,
 ) -> (Vec<Diagnostic>, Option<ImportMap>) {
+    let is_stub = is_python_stub_file(path);
+
     // Extract all imports from the AST.
     let tracker = {
-        let mut tracker = ImportTracker::new(locator, directives, path);
+        let mut tracker = ImportTracker::new(locator, directives, is_stub);
         tracker.visit_body(python_ast);
         tracker
     };
@@ -111,7 +114,7 @@ pub fn check_imports(
     }
     if settings.rules.enabled(Rule::MissingRequiredImport) {
         diagnostics.extend(isort::rules::add_required_imports(
-            &blocks, python_ast, locator, stylist, settings, autofix,
+            &blocks, python_ast, locator, stylist, settings, autofix, is_stub,
         ));
     }
 

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

@@ -714,6 +714,7 @@ mod tests {
     }
 
     #[test_case(Path::new("docstring.py"))]
+    #[test_case(Path::new("docstring.pyi"))]
     #[test_case(Path::new("docstring_only.py"))]
     #[test_case(Path::new("multiline_docstring.py"))]
     #[test_case(Path::new("empty.py"))]
@@ -737,6 +738,7 @@ mod tests {
     }
 
     #[test_case(Path::new("docstring.py"))]
+    #[test_case(Path::new("docstring.pyi"))]
     #[test_case(Path::new("docstring_only.py"))]
     #[test_case(Path::new("empty.py"))]
     fn required_imports(path: &Path) -> Result<()> {
@@ -760,6 +762,7 @@ mod tests {
     }
 
     #[test_case(Path::new("docstring.py"))]
+    #[test_case(Path::new("docstring.pyi"))]
     #[test_case(Path::new("docstring_only.py"))]
     #[test_case(Path::new("empty.py"))]
     fn combined_required_imports(path: &Path) -> Result<()> {
@@ -782,6 +785,7 @@ mod tests {
     }
 
     #[test_case(Path::new("docstring.py"))]
+    #[test_case(Path::new("docstring.pyi"))]
     #[test_case(Path::new("docstring_only.py"))]
     #[test_case(Path::new("empty.py"))]
     fn straight_required_import(path: &Path) -> Result<()> {

crates/ruff/src/rules/isort/rules/add_required_imports.rs

@@ -5,7 +5,7 @@ use rustpython_parser::ast::{Location, StmtKind, Suite};
 use ruff_diagnostics::{AlwaysAutofixableViolation, Diagnostic};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::is_docstring_stmt;
-use ruff_python_ast::imports::{Alias, AnyImport, Import, ImportFrom};
+use ruff_python_ast::imports::{Alias, AnyImport, FutureImport, Import, ImportFrom};
 use ruff_python_ast::source_code::{Locator, Stylist};
 use ruff_python_ast::types::Range;
 
@@ -84,6 +84,7 @@ fn contains(block: &Block, required_import: &AnyImport) -> bool {
     })
 }
 
+#[allow(clippy::too_many_arguments)]
 fn add_required_import(
     required_import: &AnyImport,
     blocks: &[&Block],
@@ -92,6 +93,7 @@ fn add_required_import(
     stylist: &Stylist,
     settings: &Settings,
     autofix: flags::Autofix,
+    is_stub: bool,
 ) -> Option<Diagnostic> {
     // If the import is already present in a top-level block, don't add it.
     if blocks
@@ -107,6 +109,11 @@ fn add_required_import(
         return None;
     }
 
+    // We don't need to add `__future__` imports to stubs.
+    if is_stub && required_import.is_future_import() {
+        return None;
+    }
+
     // Always insert the diagnostic at top-of-file.
     let mut diagnostic = Diagnostic::new(
         MissingRequiredImport(required_import.to_string()),
@@ -126,6 +133,7 @@ pub fn add_required_imports(
     stylist: &Stylist,
     settings: &Settings,
     autofix: flags::Autofix,
+    is_stub: bool,
 ) -> Vec<Diagnostic> {
     settings
         .isort
@@ -167,6 +175,7 @@ pub fn add_required_imports(
                             stylist,
                             settings,
                             autofix,
+                            is_stub,
                         )
                     })
                     .collect(),
@@ -186,6 +195,7 @@ pub fn add_required_imports(
                             stylist,
                             settings,
                             autofix,
+                            is_stub,
                         )
                     })
                     .collect(),

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__combined_required_imports_docstring.pyi.snap

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

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__required_import_docstring.pyi.snap

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

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__required_imports_docstring.pyi.snap

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

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__straight_required_import_docstring.pyi.snap

@@ -0,0 +1,19 @@
+---
+source: crates/ruff/src/rules/isort/mod.rs
+---
+docstring.pyi:1:1: I002 [*] Missing required import: `import os`
+  |
+1 | """Hello, world!"""
+  |  I002
+2 | 
+3 | x = 1
+  |
+  = help: Insert required import: `import os`
+
+ℹ Suggested fix
+1 1 | """Hello, world!"""
+  2 |+import os
+2 3 | 
+3 4 | x = 1
+
+

crates/ruff/src/rules/isort/track.rs

@@ -1,5 +1,3 @@
-use std::path::Path;
-
 use rustpython_parser::ast::{
     Alias, Arg, Arguments, Boolop, Cmpop, Comprehension, Constant, Excepthandler,
     ExcepthandlerKind, Expr, ExprContext, Keyword, MatchCase, Operator, Pattern, Stmt, StmtKind,
@@ -8,11 +6,9 @@ use rustpython_parser::ast::{
 
 use ruff_python_ast::source_code::Locator;
 use ruff_python_ast::visitor::Visitor;
-use ruff_python_stdlib::path::is_python_stub_file;
 
 use crate::directives::IsortDirectives;
-
-use super::helpers;
+use crate::rules::isort::helpers;
 
 #[derive(Debug, Copy, Clone)]
 pub enum Trailer {
@@ -38,11 +34,11 @@ pub struct ImportTracker<'a> {
 }
 
 impl<'a> ImportTracker<'a> {
-    pub fn new(locator: &'a Locator<'a>, directives: &'a IsortDirectives, path: &'a Path) -> Self {
+    pub fn new(locator: &'a Locator<'a>, directives: &'a IsortDirectives, is_stub: bool) -> Self {
         Self {
             locator,
             directives,
-            is_stub: is_python_stub_file(path),
+            is_stub,
             blocks: vec![Block::default()],
             split_index: 0,
             nested: false,

crates/ruff_python_ast/src/imports.rs

@@ -75,6 +75,32 @@ impl std::fmt::Display for ImportFrom<'_> {
     }
 }
 
+pub trait FutureImport {
+    /// Returns `true` if this import is from the `__future__` module.
+    fn is_future_import(&self) -> bool;
+}
+
+impl FutureImport for Import<'_> {
+    fn is_future_import(&self) -> bool {
+        self.name.name == "__future__"
+    }
+}
+
+impl FutureImport for ImportFrom<'_> {
+    fn is_future_import(&self) -> bool {
+        self.module == Some("__future__")
+    }
+}
+
+impl FutureImport for AnyImport<'_> {
+    fn is_future_import(&self) -> bool {
+        match self {
+            AnyImport::Import(import) => import.is_future_import(),
+            AnyImport::ImportFrom(import_from) => import_from.is_future_import(),
+        }
+    }
+}
+
 /// A representation of a module reference in an import statement.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct ModuleImport {