[flake8-tidy-imports] Add TID253 (#6378)

## Summary

Add a new rule `TID253` (`banned-module-level-imports`), to ban a
user-specified list of imports from appearing at module level. This rule
doesn't exist in `flake8-tidy-imports`, so it's unique to Ruff. The
implementation is pretty similar to `TID251`.

Briefly discussed
[here](https://github.com/astral-sh/ruff/discussions/6370).

## Test Plan

Added a new test case, checking that inline imports are allowed and that
non-inline imports from the banned list are disallowed.

crates/ruff/resources/test/fixtures/flake8_tidy_imports/TID253.py

@@ -0,0 +1,31 @@
+## Banned modules ##
+import torch
+
+from torch import *
+
+from tensorflow import a, b, c
+
+import torch as torch_wearing_a_trenchcoat
+
+# this should count as module level
+x = 1; import tensorflow
+
+# banning a module also bans any submodules
+import torch.foo.bar
+
+from tensorflow.foo import bar
+
+from torch.foo.bar import *
+
+# unlike TID251, inline imports are *not* banned
+def my_cool_function():
+    import tensorflow.foo.bar
+
+def another_cool_function():
+    from torch.foo import bar
+
+def import_alias():
+    from torch.foo import bar
+
+if TYPE_CHECKING:
+    import torch

crates/ruff/src/checkers/ast/analyze/statement.rs

@@ -566,6 +566,15 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                         alias,
                     );
                 }
+
+                if checker.enabled(Rule::BannedModuleLevelImports) {
+                    flake8_tidy_imports::rules::name_or_parent_is_banned_at_module_level(
+                        checker,
+                        &alias.name,
+                        alias.range(),
+                    );
+                }
+
                 if !checker.source_type.is_stub() {
                     if checker.enabled(Rule::UselessImportAlias) {
                         pylint::rules::useless_import_alias(checker, alias);
@@ -734,6 +743,28 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                     }
                 }
             }
+            if checker.enabled(Rule::BannedModuleLevelImports) {
+                if let Some(module) =
+                    helpers::resolve_imported_module_path(level, module, checker.module_path)
+                {
+                    flake8_tidy_imports::rules::name_or_parent_is_banned_at_module_level(
+                        checker,
+                        &module,
+                        stmt.range(),
+                    );
+
+                    for alias in names {
+                        if &alias.name == "*" {
+                            continue;
+                        }
+                        flake8_tidy_imports::rules::name_is_banned_at_module_level(
+                            checker,
+                            &format!("{module}.{}", alias.name),
+                            alias.range(),
+                        );
+                    }
+                }
+            }
             if checker.enabled(Rule::PytestIncorrectPytestImport) {
                 if let Some(diagnostic) =
                     flake8_pytest_style::rules::import_from(stmt, module, level)

crates/ruff/src/codes.rs

@@ -311,6 +311,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         // flake8-tidy-imports
         (Flake8TidyImports, "251") => (RuleGroup::Unspecified, rules::flake8_tidy_imports::rules::BannedApi),
         (Flake8TidyImports, "252") => (RuleGroup::Unspecified, rules::flake8_tidy_imports::rules::RelativeImports),
+        (Flake8TidyImports, "253") => (RuleGroup::Unspecified, rules::flake8_tidy_imports::rules::BannedModuleLevelImports),
 
         // flake8-return
         (Flake8Return, "501") => (RuleGroup::Unspecified, rules::flake8_return::rules::UnnecessaryReturnNone),

crates/ruff/src/rules/flake8_tidy_imports/mod.rs

@@ -124,4 +124,23 @@ mod tests {
         assert_messages!(diagnostics);
         Ok(())
     }
+
+    #[test]
+    fn banned_module_level_imports() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("flake8_tidy_imports/TID253.py"),
+            &Settings {
+                flake8_tidy_imports: flake8_tidy_imports::settings::Settings {
+                    banned_module_level_imports: vec![
+                        "torch".to_string(),
+                        "tensorflow".to_string(),
+                    ],
+                    ..Default::default()
+                },
+                ..Settings::for_rules(vec![Rule::BannedModuleLevelImports])
+            },
+        )?;
+        assert_messages!(diagnostics);
+        Ok(())
+    }
 }

crates/ruff/src/rules/flake8_tidy_imports/options.rs

@@ -41,6 +41,19 @@ pub struct Options {
     /// Note that this rule is only meant to flag accidental uses,
     /// and can be circumvented via `eval` or `importlib`.
     pub banned_api: Option<FxHashMap<String, ApiBan>>,
+    #[option(
+        default = r#"[]"#,
+        value_type = r#"list[str]"#,
+        example = r#"
+            # Ban certain modules from being imported at module level, instead requiring
+            # that they're imported lazily (e.g., within a function definition).
+            banned-module-level-imports = ["torch", "tensorflow"]
+        "#
+    )]
+    /// List of specific modules that may not be imported at module level, and should instead be
+    /// imported lazily (e.g., within a function definition, or an `if TYPE_CHECKING:`
+    /// block, or some other nested context).
+    pub banned_module_level_imports: Option<Vec<String>>,
 }
 
 impl From<Options> for Settings {
@@ -48,6 +61,7 @@ impl From<Options> for Settings {
         Self {
             ban_relative_imports: options.ban_relative_imports.unwrap_or(Strictness::Parents),
             banned_api: options.banned_api.unwrap_or_default(),
+            banned_module_level_imports: options.banned_module_level_imports.unwrap_or_default(),
         }
     }
 }
@@ -57,6 +71,7 @@ impl From<Settings> for Options {
         Self {
             ban_relative_imports: Some(settings.ban_relative_imports),
             banned_api: Some(settings.banned_api),
+            banned_module_level_imports: Some(settings.banned_module_level_imports),
         }
     }
 }

crates/ruff/src/rules/flake8_tidy_imports/rules/banned_module_level_imports.rs

@@ -0,0 +1,111 @@
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_text_size::TextRange;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for module-level imports that should instead be imported lazily
+/// (e.g., within a function definition, or an `if TYPE_CHECKING:` block, or
+/// some other nested context).
+///
+/// ## Why is this bad?
+/// Some modules are expensive to import. For example, importing `torch` or
+/// `tensorflow` can introduce a noticeable delay in the startup time of a
+/// Python program.
+///
+/// In such cases, you may want to enforce that the module is imported lazily
+/// as needed, rather than at the top of the file. This could involve inlining
+/// the import into the function that uses it, rather than importing it
+/// unconditionally, to ensure that the module is only imported when necessary.
+///
+/// ## Example
+/// ```python
+/// import tensorflow as tf
+///
+///
+/// def show_version():
+///     print(tf.__version__)
+/// ```
+///
+/// Use instead:
+/// ```python
+/// def show_version():
+///     import tensorflow as tf
+///
+///     print(tf.__version__)
+/// ```
+///
+/// ## Options
+/// - `flake8-tidy-imports.banned-module-level-imports`
+#[violation]
+pub struct BannedModuleLevelImports {
+    name: String,
+}
+
+impl Violation for BannedModuleLevelImports {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let BannedModuleLevelImports { name } = self;
+        format!("`{name}` is banned at the module level")
+    }
+}
+
+/// TID253
+pub(crate) fn name_is_banned_at_module_level(
+    checker: &mut Checker,
+    name: &str,
+    text_range: TextRange,
+) {
+    banned_at_module_level_with_policy(checker, name, text_range, &NameMatchPolicy::ExactOnly);
+}
+
+/// TID253
+pub(crate) fn name_or_parent_is_banned_at_module_level(
+    checker: &mut Checker,
+    name: &str,
+    text_range: TextRange,
+) {
+    banned_at_module_level_with_policy(checker, name, text_range, &NameMatchPolicy::ExactOrParents);
+}
+
+#[derive(Debug)]
+enum NameMatchPolicy {
+    /// Only match an exact module name (e.g., given `import foo.bar`, only match `foo.bar`).
+    ExactOnly,
+    /// Match an exact module name or any of its parents (e.g., given `import foo.bar`, match
+    /// `foo.bar` or `foo`).
+    ExactOrParents,
+}
+
+fn banned_at_module_level_with_policy(
+    checker: &mut Checker,
+    name: &str,
+    text_range: TextRange,
+    policy: &NameMatchPolicy,
+) {
+    if !checker.semantic().at_top_level() {
+        return;
+    }
+    let banned_module_level_imports = &checker
+        .settings
+        .flake8_tidy_imports
+        .banned_module_level_imports;
+    for banned_module_name in banned_module_level_imports {
+        let name_is_banned = match policy {
+            NameMatchPolicy::ExactOnly => name == banned_module_name,
+            NameMatchPolicy::ExactOrParents => {
+                name == banned_module_name || name.starts_with(&format!("{banned_module_name}."))
+            }
+        };
+        if name_is_banned {
+            checker.diagnostics.push(Diagnostic::new(
+                BannedModuleLevelImports {
+                    name: banned_module_name.to_string(),
+                },
+                text_range,
+            ));
+            return;
+        }
+    }
+}

crates/ruff/src/rules/flake8_tidy_imports/rules/mod.rs

@@ -1,5 +1,7 @@
 pub(crate) use banned_api::*;
+pub(crate) use banned_module_level_imports::*;
 pub(crate) use relative_imports::*;
 
 mod banned_api;
+mod banned_module_level_imports;
 mod relative_imports;

crates/ruff/src/rules/flake8_tidy_imports/settings.rs

@@ -26,4 +26,5 @@ pub enum Strictness {
 pub struct Settings {
     pub ban_relative_imports: Strictness,
     pub banned_api: FxHashMap<String, ApiBan>,
+    pub banned_module_level_imports: Vec<String>,
 }

crates/ruff/src/rules/flake8_tidy_imports/snapshots/ruff__rules__flake8_tidy_imports__tests__banned_module_level_imports.snap

@@ -0,0 +1,81 @@
+---
+source: crates/ruff/src/rules/flake8_tidy_imports/mod.rs
+---
+TID253.py:2:8: TID253 `torch` is banned at the module level
+  |
+1 | ## Banned modules ##
+2 | import torch
+  |        ^^^^^ TID253
+3 | 
+4 | from torch import *
+  |
+
+TID253.py:4:1: TID253 `torch` is banned at the module level
+  |
+2 | import torch
+3 | 
+4 | from torch import *
+  | ^^^^^^^^^^^^^^^^^^^ TID253
+5 | 
+6 | from tensorflow import a, b, c
+  |
+
+TID253.py:6:1: TID253 `tensorflow` is banned at the module level
+  |
+4 | from torch import *
+5 | 
+6 | from tensorflow import a, b, c
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TID253
+7 | 
+8 | import torch as torch_wearing_a_trenchcoat
+  |
+
+TID253.py:8:8: TID253 `torch` is banned at the module level
+   |
+ 6 | from tensorflow import a, b, c
+ 7 | 
+ 8 | import torch as torch_wearing_a_trenchcoat
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TID253
+ 9 | 
+10 | # this should count as module level
+   |
+
+TID253.py:11:15: TID253 `tensorflow` is banned at the module level
+   |
+10 | # this should count as module level
+11 | x = 1; import tensorflow
+   |               ^^^^^^^^^^ TID253
+12 | 
+13 | # banning a module also bans any submodules
+   |
+
+TID253.py:14:8: TID253 `torch` is banned at the module level
+   |
+13 | # banning a module also bans any submodules
+14 | import torch.foo.bar
+   |        ^^^^^^^^^^^^^ TID253
+15 | 
+16 | from tensorflow.foo import bar
+   |
+
+TID253.py:16:1: TID253 `tensorflow` is banned at the module level
+   |
+14 | import torch.foo.bar
+15 | 
+16 | from tensorflow.foo import bar
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TID253
+17 | 
+18 | from torch.foo.bar import *
+   |
+
+TID253.py:18:1: TID253 `torch` is banned at the module level
+   |
+16 | from tensorflow.foo import bar
+17 | 
+18 | from torch.foo.bar import *
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ TID253
+19 | 
+20 | # unlike TID251, inline imports are *not* banned
+   |
+
+