Add flake8-pyi with one rule (#2682)

Add basic scaffold for [flake8-pyi](https://github.com/PyCQA/flake8-pyi) and the first rule, Y001

rel: https://github.com/charliermarsh/ruff/issues/848

LICENSE

@@ -245,6 +245,31 @@ are:
     SOFTWARE.
   """
 
+- flake8-pyi, licensed as follows:
+  """
+    The MIT License (MIT)
+
+    Copyright (c) 2016 Łukasz Langa
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE.
+  """
+
 - flake8-print, licensed as follows:
   """
     MIT License

README.md

@@ -145,6 +145,7 @@ This README is also available as [documentation](https://beta.ruff.rs/docs/).
    1. [flake8-no-pep420 (INP)](#flake8-no-pep420-inp)
    1. [flake8-pie (PIE)](#flake8-pie-pie)
    1. [flake8-print (T20)](#flake8-print-t20)
+   1. [flake8-pyi (PYI)](#flake8-pyi-pyi)
    1. [flake8-pytest-style (PT)](#flake8-pytest-style-pt)
    1. [flake8-quotes (Q)](#flake8-quotes-q)
    1. [flake8-return (RET)](#flake8-return-ret)
@@ -1142,6 +1143,14 @@ For more, see [flake8-print](https://pypi.org/project/flake8-print/) on PyPI.
 | T201 | print-found | `print` found |  |
 | T203 | p-print-found | `pprint` found |  |
 
+### flake8-pyi (PYI)
+
+For more, see [flake8-pyi](https://pypi.org/project/flake8-pyi/) on PyPI.
+
+| Code | Name | Message | Fix |
+| ---- | ---- | ------- | --- |
+| [PYI001](https://github.com/charliermarsh/ruff/blob/main/docs/rules/prefix-type-params.md) | [prefix-type-params](https://github.com/charliermarsh/ruff/blob/main/docs/rules/prefix-type-params.md) | Name of private `{kind}` must start with _ |  |
+
 ### flake8-pytest-style (PT)
 
 For more, see [flake8-pytest-style](https://pypi.org/project/flake8-pytest-style/) on PyPI.
@@ -1701,6 +1710,7 @@ natively, including:
 * [flake8-no-pep420](https://pypi.org/project/flake8-no-pep420)
 * [flake8-pie](https://pypi.org/project/flake8-pie/)
 * [flake8-print](https://pypi.org/project/flake8-print/)
+* [flake8-pyi](https://pypi.org/project/flake8-pyi/)
 * [flake8-pytest-style](https://pypi.org/project/flake8-pytest-style/)
 * [flake8-quotes](https://pypi.org/project/flake8-quotes/)
 * [flake8-raise](https://pypi.org/project/flake8-raise/)

crates/ruff/resources/test/fixtures/flake8_pyi/PYI001.py

@@ -0,0 +1,13 @@
+from typing import ParamSpec, TypeVar, TypeVarTuple
+
+T = TypeVar("T")  # OK
+
+TTuple = TypeVarTuple("TTuple")  # OK
+
+P = ParamSpec("P")  # OK
+
+_T = TypeVar("_T")  # OK
+
+_TTuple = TypeVarTuple("_TTuple")  # OK
+
+_P = ParamSpec("_P")  # OK

crates/ruff/resources/test/fixtures/flake8_pyi/PYI001.pyi

@@ -0,0 +1,13 @@
+from typing import ParamSpec, TypeVar, TypeVarTuple
+
+T = TypeVar("T")  # Error: TypeVars in stubs must start with _
+
+TTuple = TypeVarTuple("TTuple")  # Error: TypeVarTuples must also start with _
+
+P = ParamSpec("P")  # Error: ParamSpecs must start with _
+
+_T = TypeVar("_T")  # OK
+
+_TTuple = TypeVarTuple("_TTuple")  # OK
+
+_P = ParamSpec("_P")  # OK

crates/ruff/src/checkers/ast.rs

@@ -36,10 +36,10 @@ use crate::rules::{
     flake8_2020, flake8_annotations, flake8_bandit, flake8_blind_except, flake8_boolean_trap,
     flake8_bugbear, flake8_builtins, flake8_comprehensions, flake8_datetimez, flake8_debugger,
     flake8_errmsg, flake8_implicit_str_concat, flake8_import_conventions, flake8_logging_format,
-    flake8_pie, flake8_print, flake8_pytest_style, flake8_raise, flake8_return, flake8_self,
-    flake8_simplify, flake8_tidy_imports, flake8_type_checking, flake8_unused_arguments,
-    flake8_use_pathlib, mccabe, pandas_vet, pep8_naming, pycodestyle, pydocstyle, pyflakes,
-    pygrep_hooks, pylint, pyupgrade, ruff, tryceratops,
+    flake8_pie, flake8_print, flake8_pyi, flake8_pytest_style, flake8_raise, flake8_return,
+    flake8_self, flake8_simplify, flake8_tidy_imports, flake8_type_checking,
+    flake8_unused_arguments, flake8_use_pathlib, mccabe, pandas_vet, pep8_naming, pycodestyle,
+    pydocstyle, pyflakes, pygrep_hooks, pylint, pyupgrade, ruff, tryceratops,
 };
 use crate::settings::types::PythonVersion;
 use crate::settings::{flags, Settings};
@@ -1713,6 +1713,12 @@ where
                     }
                 }
 
+                if self.settings.rules.enabled(&Rule::PrefixTypeParams) {
+                    if self.path.extension().map_or(false, |ext| ext == "pyi") {
+                        flake8_pyi::rules::prefix_type_params(self, value, targets);
+                    }
+                }
+
                 if self.settings.rules.enabled(&Rule::UselessMetaclassType) {
                     pyupgrade::rules::useless_metaclass_type(self, stmt, value, targets);
                 }

crates/ruff/src/registry.rs

@@ -442,6 +442,8 @@ ruff_macros::define_rule_mapping!(
     EM101 => rules::flake8_errmsg::rules::RawStringInException,
     EM102 => rules::flake8_errmsg::rules::FStringInException,
     EM103 => rules::flake8_errmsg::rules::DotFormatInException,
+    // flake8-pyi
+    PYI001 => rules::flake8_pyi::rules::PrefixTypeParams,
     // flake8-pytest-style
     PT001 => rules::flake8_pytest_style::rules::IncorrectFixtureParenthesesStyle,
     PT002 => rules::flake8_pytest_style::rules::FixturePositionalArgs,
@@ -632,6 +634,9 @@ pub enum Linter {
     /// [flake8-print](https://pypi.org/project/flake8-print/)
     #[prefix = "T20"]
     Flake8Print,
+    /// [flake8-pyi](https://pypi.org/project/flake8-pyi/)
+    #[prefix = "PYI"]
+    Flake8Pyi,
     /// [flake8-pytest-style](https://pypi.org/project/flake8-pytest-style/)
     #[prefix = "PT"]
     Flake8PytestStyle,

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

@@ -0,0 +1,26 @@
+//! Rules from [flake8-pyi](https://pypi.org/project/flake8-pyi/).
+pub(crate) mod rules;
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+
+    use anyhow::Result;
+    use test_case::test_case;
+
+    use crate::registry::Rule;
+    use crate::test::test_path;
+    use crate::{assert_yaml_snapshot, settings};
+
+    #[test_case(Rule::PrefixTypeParams, Path::new("PYI001.pyi"))]
+    #[test_case(Rule::PrefixTypeParams, Path::new("PYI001.py"))]
+    fn rules(rule_code: Rule, path: &Path) -> Result<()> {
+        let snapshot = format!("{}_{}", rule_code.code(), path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("flake8_pyi").join(path).as_path(),
+            &settings::Settings::for_rule(rule_code),
+        )?;
+        assert_yaml_snapshot!(snapshot, diagnostics);
+        Ok(())
+    }
+}

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

@@ -0,0 +1,92 @@
+use ruff_macros::{define_violation, derive_message_formats};
+use rustpython_parser::ast::{Expr, ExprKind};
+use serde::{Deserialize, Serialize};
+use std::fmt;
+
+use crate::ast::types::Range;
+use crate::checkers::ast::Checker;
+use crate::registry::Diagnostic;
+use crate::violation::Violation;
+
+#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum VarKind {
+    TypeVar,
+    ParamSpec,
+    TypeVarTuple,
+}
+
+impl fmt::Display for VarKind {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            VarKind::TypeVar => fmt.write_str("TypeVar"),
+            VarKind::ParamSpec => fmt.write_str("ParamSpec"),
+            VarKind::TypeVarTuple => fmt.write_str("TypeVarTuple"),
+        }
+    }
+}
+
+define_violation!(
+    /// ### What it does
+    /// Checks that type `TypeVar`, `ParamSpec`, and `TypeVarTuple` definitions in
+    /// stubs are prefixed with `_`.
+    ///
+    /// ### Why is this bad?
+    /// By prefixing type parameters with `_`, we can avoid accidentally exposing
+    /// names internal to the stub.
+    ///
+    /// ### Example
+    /// ```python
+    /// from typing import TypeVar
+    ///
+    /// T = TypeVar("T")
+    /// ```
+    ///
+    /// Use instead:
+    /// ```python
+    /// from typing import TypeVar
+    ///
+    /// _T = TypeVar("_T")
+    /// ```
+    pub struct PrefixTypeParams {
+        pub kind: VarKind,
+    }
+);
+impl Violation for PrefixTypeParams {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let PrefixTypeParams { kind } = self;
+        format!("Name of private `{kind}` must start with _")
+    }
+}
+
+/// PYI001
+pub fn prefix_type_params(checker: &mut Checker, value: &Expr, targets: &[Expr]) {
+    if targets.len() != 1 {
+        return;
+    }
+    if let ExprKind::Name { id, .. } = &targets[0].node {
+        if id.starts_with('_') {
+            return;
+        }
+    };
+
+    if let ExprKind::Call { func, .. } = &value.node {
+        let Some(kind) = checker.resolve_call_path(func).and_then(|call_path| {
+            if checker.match_typing_call_path(&call_path, "ParamSpec") {
+                Some(VarKind::ParamSpec)
+            } else if checker.match_typing_call_path(&call_path, "TypeVar") {
+                Some(VarKind::TypeVar)
+            } else if checker.match_typing_call_path(&call_path, "TypeVarTuple") {
+                Some(VarKind::TypeVarTuple)
+            } else {
+                None
+            }
+        }) else {
+            return;
+        };
+        checker.diagnostics.push(Diagnostic::new(
+            PrefixTypeParams { kind },
+            Range::from_located(value),
+        ));
+    }
+}

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI001_PYI001.py.snap

@@ -0,0 +1,6 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+expression: diagnostics
+---
+[]
+

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI001_PYI001.pyi.snap

@@ -0,0 +1,38 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+expression: diagnostics
+---
+- kind:
+    PrefixTypeParams:
+      kind: TypeVar
+  location:
+    row: 3
+    column: 4
+  end_location:
+    row: 3
+    column: 16
+  fix: ~
+  parent: ~
+- kind:
+    PrefixTypeParams:
+      kind: TypeVarTuple
+  location:
+    row: 5
+    column: 9
+  end_location:
+    row: 5
+    column: 31
+  fix: ~
+  parent: ~
+- kind:
+    PrefixTypeParams:
+      kind: ParamSpec
+  location:
+    row: 7
+    column: 4
+  end_location:
+    row: 7
+    column: 18
+  fix: ~
+  parent: ~
+

crates/ruff/src/rules/mod.rs

@@ -19,6 +19,7 @@ pub mod flake8_logging_format;
 pub mod flake8_no_pep420;
 pub mod flake8_pie;
 pub mod flake8_print;
+pub mod flake8_pyi;
 pub mod flake8_pytest_style;
 pub mod flake8_quotes;
 pub mod flake8_raise;

docs/rules/prefix-type-params.md

@@ -0,0 +1,25 @@
+# prefix-type-params (PYI001)
+
+Derived from the **flake8-pyi** linter.
+
+### What it does
+Checks that type `TypeVar`, `ParamSpec`, and `TypeVarTuple` definitions in
+stubs are prefixed with `_`.
+
+### Why is this bad?
+By prefixing type parameters with `_`, we can avoid accidentally exposing
+names internal to the stub.
+
+### Example
+```python
+from typing import TypeVar
+
+T = TypeVar("T")
+```
+
+Use instead:
+```python
+from typing import TypeVar
+
+_T = TypeVar("_T")
+```

ruff.schema.json

@@ -1790,6 +1790,10 @@
         "PTH122",
         "PTH123",
         "PTH124",
+        "PYI",
+        "PYI0",
+        "PYI00",
+        "PYI001",
         "Q",
         "Q0",
         "Q00",