[pyflakes] Fix infinite loop with unused local import in `__init__.…

…py` (`F401`) (#15517)

## Summary

This fixes the infinite loop reported in #12897, where an
`unused-import` that is undefined at the scope of `__all__` is "fixed"
by adding it to `__all__` repeatedly. These changes make it so that only
imports in the global scope will be suggested to add to `__all__` and
the unused local import is simply removed.

## Test Plan

Added a CLI integration test that sets up the same module structure as
the original report

Closes #12897

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_33/__init__.py

@@ -0,0 +1,8 @@
+"""Regression test for https://github.com/astral-sh/ruff/issues/12897"""
+
+__all__ = ('Spam',)
+
+
+class Spam:
+    def __init__(self) -> None:
+        from F401_33.other import Ham

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_33/other.py

@@ -0,0 +1 @@
+Ham = 1

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

@@ -286,6 +286,35 @@ mod tests {
         assert_messages!(snapshot, diagnostics);
     }
 
+    // Regression test for https://github.com/astral-sh/ruff/issues/12897
+    #[test_case(Rule::UnusedImport, Path::new("F401_33/__init__.py"))]
+    fn f401_preview_local_init_import(rule_code: Rule, path: &Path) -> Result<()> {
+        let snapshot = format!(
+            "preview__{}_{}",
+            rule_code.noqa_code(),
+            path.to_string_lossy()
+        );
+        let settings = LinterSettings {
+            preview: PreviewMode::Enabled,
+            isort: isort::settings::Settings {
+                // Like `f401_preview_first_party_submodule`, this test requires the input module to
+                // be first-party
+                known_modules: isort::categorize::KnownModules::new(
+                    vec!["F401_*".parse()?],
+                    vec![],
+                    vec![],
+                    vec![],
+                    FxHashMap::default(),
+                ),
+                ..isort::settings::Settings::default()
+            },
+            ..LinterSettings::for_rule(rule_code)
+        };
+        let diagnostics = test_path(Path::new("pyflakes").join(path).as_path(), &settings)?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
+
     #[test_case(Rule::UnusedImport, Path::new("F401_24/__init__.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_25__all_nonempty/__init__.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_26__all_empty/__init__.py"))]

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

@@ -9,7 +9,8 @@ use ruff_macros::{derive_message_formats, ViolationMetadata};
 use ruff_python_ast::name::QualifiedName;
 use ruff_python_ast::{self as ast, Stmt};
 use ruff_python_semantic::{
-    AnyImport, BindingKind, Exceptions, Imported, NodeId, Scope, SemanticModel, SubmoduleImport,
+    AnyImport, BindingKind, Exceptions, Imported, NodeId, Scope, ScopeId, SemanticModel,
+    SubmoduleImport,
 };
 use ruff_text_size::{Ranged, TextRange};
 
@@ -329,6 +330,7 @@ pub(crate) fn unused_import(checker: &Checker, scope: &Scope, diagnostics: &mut
             import,
             range: binding.range(),
             parent_range: binding.parent_range(checker.semantic()),
+            scope: binding.scope,
         };
 
         if checker.rule_is_ignored(Rule::UnusedImport, import.start())
@@ -366,7 +368,10 @@ pub(crate) fn unused_import(checker: &Checker, scope: &Scope, diagnostics: &mut
             .map(|binding| {
                 let context = if in_except_handler {
                     UnusedImportContext::ExceptHandler
-                } else if in_init && is_first_party(&binding.import, checker) {
+                } else if in_init
+                    && binding.scope.is_global()
+                    && is_first_party(&binding.import, checker)
+                {
                     UnusedImportContext::DunderInitFirstParty {
                         dunder_all_count: DunderAllCount::from(dunder_all_exprs.len()),
                         submodule_import: binding.import.is_submodule_import(),
@@ -460,6 +465,8 @@ struct ImportBinding<'a> {
     range: TextRange,
     /// The range of the import's parent statement.
     parent_range: Option<TextRange>,
+    /// The [`ScopeId`] of the scope in which the [`ImportBinding`] was defined.
+    scope: ScopeId,
 }
 
 impl ImportBinding<'_> {

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__preview__F401_F401_33____init__.py.snap

@@ -0,0 +1,19 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+snapshot_kind: text
+---
+__init__.py:8:35: F401 [*] `F401_33.other.Ham` imported but unused
+  |
+6 | class Spam:
+7 |     def __init__(self) -> None:
+8 |         from F401_33.other import Ham
+  |                                   ^^^ F401
+  |
+  = help: Remove unused import: `F401_33.other.Ham`
+
+ℹ Unsafe fix
+5 5 | 
+6 6 | class Spam:
+7 7 |     def __init__(self) -> None:
+8   |-        from F401_33.other import Ham
+  8 |+        pass