F401 - Distinguish between imports we wish to remove and those we wis…

…h to make explicit-exports (#11168)

Resolves #10390 and starts to address #10391

# Changes to behavior

* In `__init__.py` we now offer some fixes for unused imports.
* If the import binding is first-party this PR suggests a fix to turn it
into a redundant alias.
* If the import binding is not first-party, this PR suggests a fix to
remove it from the `__init__.py`.
* The fix-titles are specific to these new suggested fixes.
* `checker.settings.ignore_init_module_imports` setting is
deprecated/ignored. There is probably a documentation change to make
that complete which I haven't done.

---

<details><summary>Old description of implementation changes</summary>

# Changes to the implementation

* In the body of the loop over import statements that contain unused
bindings, the bindings are partitioned into `to_reexport` and
`to_remove` (according to how we want to resolve the fact they're
unused) with the following predicate:
  ```rust
in_init && is_first_party(checker, &import.qualified_name().to_string())
// true means make it a reexport
  ```
* Instead of generating a single fix per import statement, we now
generate up to two fixes per import statement:
  ```rust
  (fix_by_removing_imports(checker, node_id, &to_remove, in_init).ok(),
   fix_by_reexporting(checker, node_id, &to_reexport, dunder_all).ok())
  ```
* The `to_remove` fixes are unsafe when `in_init`.
* The `to_explicit` fixes are safe. Currently, until a future PR, we
make them redundant aliases (e.g. `import a` would become `import a as
a`).

## Other changes

* `checker.settings.ignore_init_module_imports` is deprecated/ignored.
Instead, all fixes are gated on `checker.settings.preview.is_enabled()`.
* Got rid of the pattern match on the import-binding bound by the inner
loop because it seemed less readable than referencing fields on the
binding.
* [x] `// FIXME: rename "imports" to "bindings"` if reviewer agrees (see
code)
* [x] `// FIXME: rename "node_id" to "import_statement"` if reviewer
agrees (see code)

<details>
<summary><h2>Scope cut until a future PR</h2></summary>

* (Not implemented) The `to_explicit` fixes will be added to `__all__`
unless it doesn't exist. When `__all__` doesn't exist they're resolved
by converting to redundant aliases (e.g. `import a` would become `import
a as a`).
 
---

</details>

# Test plan

* [x] `crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24`
contains an `__init__.py` with*out* `__all__` that exercises the
features in this PR, but it doesn't pass.
* [x]
`crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25_dunder_all`
contains an `__init__.py` *with* `__all__` that exercises the features
in this PR, but it doesn't pass.
* [x] Write unit tests for the new edit functions in
`fix::edits::make_redundant_alias`.

</details>

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24/__init__.py

@@ -0,0 +1,36 @@
+"""__init__.py without __all__
+
+Unused stdlib and third party imports are unsafe removals
+
+Unused first party imports get changed to redundant aliases
+"""
+
+
+# stdlib
+
+import os  # Ok: is used
+
+_ = os
+
+
+import argparse as argparse  # Ok: is redundant alias
+
+
+import sys  # F401: remove unused
+
+
+# first-party
+
+
+from . import used  # Ok: is used
+
+_ = used
+
+
+from . import aliased as aliased  # Ok: is redundant alias
+
+
+from . import unused  # F401: change to redundant alias
+
+
+from . import renamed as bees  # F401: no fix

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24/aliased.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24/renamed.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24/unused.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_24/used.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/__init__.py

@@ -0,0 +1,42 @@
+"""__init__.py with __all__
+
+Unused stdlib and third party imports are unsafe removals
+
+Unused first party imports get added to __all__
+"""
+
+
+# stdlib
+
+import os  # Ok: is used
+
+_ = os
+
+
+import argparse  # Ok: is exported in __all__
+
+
+import sys  # F401: remove unused
+
+
+# first-party
+
+
+from . import used  # Ok: is used
+
+_ = used
+
+
+from . import aliased as aliased  # Ok: is redundant alias
+
+
+from . import exported  # Ok: is exported in __all__
+
+
+# from . import unused # F401: add to __all__
+
+
+# from . import renamed as bees # F401: add to __all__
+
+
+__all__ = ["argparse", "exported"]

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/aliased.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/exported.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/renamed.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/unused.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_25__all/used.py

@@ -0,0 +1 @@
+# empty module imported by __init__.py for test fixture

crates/ruff_linter/src/fix/edits.rs

@@ -122,6 +122,28 @@ pub(crate) fn remove_unused_imports<'a>(
     }
 }
 
+/// Edits to make the specified imports explicit, e.g. change `import x` to `import x as x`.
+pub(crate) fn make_redundant_alias<'a>(
+    member_names: impl Iterator<Item = &'a str>,
+    stmt: &Stmt,
+) -> Vec<Edit> {
+    let aliases = match stmt {
+        Stmt::Import(ast::StmtImport { names, .. }) => names,
+        Stmt::ImportFrom(ast::StmtImportFrom { names, .. }) => names,
+        _ => {
+            return Vec::new();
+        }
+    };
+    member_names
+        .filter_map(|name| {
+            aliases
+                .iter()
+                .find(|alias| alias.asname.is_none() && name == alias.name.id)
+                .map(|alias| Edit::range_replacement(format!("{name} as {name}"), alias.range))
+        })
+        .collect()
+}
+
 #[derive(Debug, Copy, Clone)]
 pub(crate) enum Parentheses {
     /// Remove parentheses, if the removed argument is the only argument left.
@@ -457,11 +479,12 @@ fn all_lines_fit(
 mod tests {
     use anyhow::Result;
 
+    use ruff_diagnostics::Edit;
     use ruff_python_parser::parse_suite;
     use ruff_source_file::Locator;
-    use ruff_text_size::{Ranged, TextSize};
+    use ruff_text_size::{Ranged, TextRange, TextSize};
 
-    use crate::fix::edits::{next_stmt_break, trailing_semicolon};
+    use crate::fix::edits::{make_redundant_alias, next_stmt_break, trailing_semicolon};
 
     #[test]
     fn find_semicolon() -> Result<()> {
@@ -532,4 +555,35 @@ x = 1 \
             TextSize::from(12)
         );
     }
+
+    #[test]
+    fn redundant_alias() {
+        let contents = "import x, y as y, z as bees";
+        let program = parse_suite(contents).unwrap();
+        let stmt = program.first().unwrap();
+        assert_eq!(
+            make_redundant_alias(["x"].into_iter(), stmt),
+            vec![Edit::range_replacement(
+                String::from("x as x"),
+                TextRange::new(TextSize::new(7), TextSize::new(8)),
+            )],
+            "make just one item redundant"
+        );
+        assert_eq!(
+            make_redundant_alias(vec!["x", "y"].into_iter(), stmt),
+            vec![Edit::range_replacement(
+                String::from("x as x"),
+                TextRange::new(TextSize::new(7), TextSize::new(8)),
+            )],
+            "the second item is already a redundant alias"
+        );
+        assert_eq!(
+            make_redundant_alias(vec!["x", "z"].into_iter(), stmt),
+            vec![Edit::range_replacement(
+                String::from("x as x"),
+                TextRange::new(TextSize::new(7), TextSize::new(8)),
+            )],
+            "the third item is already aliased to something else"
+        );
+    }
 }

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

@@ -205,6 +205,9 @@ mod tests {
     }
 
     #[test_case(Rule::UnusedVariable, Path::new("F841_4.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("__init__.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("F401_24/__init__.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("F401_25__all/__init__.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(
             "preview__{}_{}",
@@ -249,19 +252,6 @@ mod tests {
         Ok(())
     }
 
-    #[test]
-    fn init_unused_import_opt_in_to_fix() -> Result<()> {
-        let diagnostics = test_path(
-            Path::new("pyflakes/__init__.py"),
-            &LinterSettings {
-                ignore_init_module_imports: false,
-                ..LinterSettings::for_rules(vec![Rule::UnusedImport])
-            },
-        )?;
-        assert_messages!(diagnostics);
-        Ok(())
-    }
-
     #[test]
     fn default_builtins() -> Result<()> {
         let diagnostics = test_path(