[flake8-pyi]: add rules for unrecognized platform check (PYI007, PYI008) (#2805)

Add two [flake8-pyi](https://github.com/PyCQA/flake8-pyi) rules (Y007, Y008). ref: #848

The specifications are described in [PEP 484 - Version and platform checking](https://peps.python.org/pep-0484/#version-and-platform-checking)

The original implementation in flake8-pyi is shown below.

- Implemention: 66f28a4407/pyi.py (L1429-L1443)
- Tests: 66f28a4407/tests/sysplatform.pyi

crates/ruff/resources/test/fixtures/flake8_pyi/PYI007.py

@@ -0,0 +1,11 @@
+import sys
+
+if sys.platform == "platform_name_1": ...  # OK
+
+if sys.platform != "platform_name_2": ...  # OK
+
+if sys.platform in ["linux"]: ...  # OK
+
+if sys.platform > 3: ...  # OK
+
+if sys.platform == 10.12: ...  # OK

crates/ruff/resources/test/fixtures/flake8_pyi/PYI007.pyi

@@ -0,0 +1,11 @@
+import sys
+
+if sys.platform == "platform_name_1": ...  # OK
+
+if sys.platform != "platform_name_2": ...  # OK
+
+if sys.platform in ["linux"]: ...  # Error: PYI007 Unrecognized sys.platform check
+
+if sys.platform > 3: ...  # Error: PYI007 Unrecognized sys.platform check
+
+if sys.platform == 10.12: ...  # Error: PYI007 Unrecognized sys.platform check

crates/ruff/resources/test/fixtures/flake8_pyi/PYI008.py

@@ -0,0 +1,11 @@
+import sys
+
+if sys.platform == "linus": ...  # OK
+
+if sys.platform != "linux": ...  # OK
+
+if sys.platform == "win32": ...  # OK
+
+if sys.platform != "darwin": ...  # OK
+
+if sys.platform == "cygwin": ...  # OK

crates/ruff/resources/test/fixtures/flake8_pyi/PYI008.pyi

@@ -0,0 +1,11 @@
+import sys
+
+if sys.platform == "linus": ...  # Error: PYI008 Unrecognized platform `linus`
+
+if sys.platform != "linux": ...  # OK
+
+if sys.platform == "win32": ...  # OK
+
+if sys.platform != "darwin": ...  # OK
+
+if sys.platform == "cygwin": ...  # OK

crates/ruff/src/checkers/ast.rs

@@ -3155,6 +3155,23 @@ where
                 if self.settings.rules.enabled(&Rule::YodaConditions) {
                     flake8_simplify::rules::yoda_conditions(self, expr, left, ops, comparators);
                 }
+
+                if self
+                    .settings
+                    .rules
+                    .enabled(&Rule::UnrecognizedPlatformCheck)
+                    || self.settings.rules.enabled(&Rule::UnrecognizedPlatformName)
+                {
+                    if self.path.extension().map_or(false, |ext| ext == "pyi") {
+                        flake8_pyi::rules::unrecognized_platform(
+                            self,
+                            expr,
+                            left,
+                            ops,
+                            comparators,
+                        );
+                    }
+                }
             }
             ExprKind::Constant {
                 value: Constant::Str(value),

crates/ruff/src/registry.rs

@@ -446,6 +446,8 @@ ruff_macros::define_rule_mapping!(
     EM103 => rules::flake8_errmsg::rules::DotFormatInException,
     // flake8-pyi
     PYI001 => rules::flake8_pyi::rules::PrefixTypeParams,
+    PYI007 => rules::flake8_pyi::rules::UnrecognizedPlatformCheck,
+    PYI008 => rules::flake8_pyi::rules::UnrecognizedPlatformName,
     // flake8-pytest-style
     PT001 => rules::flake8_pytest_style::rules::IncorrectFixtureParenthesesStyle,
     PT002 => rules::flake8_pytest_style::rules::FixturePositionalArgs,

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

@@ -14,6 +14,10 @@ mod tests {
 
     #[test_case(Rule::PrefixTypeParams, Path::new("PYI001.pyi"))]
     #[test_case(Rule::PrefixTypeParams, Path::new("PYI001.py"))]
+    #[test_case(Rule::UnrecognizedPlatformCheck, Path::new("PYI007.pyi"))]
+    #[test_case(Rule::UnrecognizedPlatformCheck, Path::new("PYI007.py"))]
+    #[test_case(Rule::UnrecognizedPlatformName, Path::new("PYI008.pyi"))]
+    #[test_case(Rule::UnrecognizedPlatformName, Path::new("PYI008.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.code(), path.to_string_lossy());
         let diagnostics = test_path(

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

@@ -0,0 +1,7 @@
+pub use prefix_type_params::{prefix_type_params, PrefixTypeParams};
+pub use unrecognized_platform::{
+    unrecognized_platform, UnrecognizedPlatformCheck, UnrecognizedPlatformName,
+};
+
+mod prefix_type_params;
+mod unrecognized_platform;

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

@@ -0,0 +1,154 @@
+use rustpython_parser::ast::{Cmpop, Constant, Expr, ExprKind};
+
+use ruff_macros::{define_violation, derive_message_formats};
+
+use crate::ast::types::Range;
+use crate::checkers::ast::Checker;
+use crate::registry::{Diagnostic, Rule};
+use crate::violation::Violation;
+
+define_violation!(
+    /// ## What it does
+    /// Check for unrecognized `sys.platform` checks. Platform checks should be
+    /// simple string comparisons.
+    ///
+    /// **Note**: this rule is only enabled in `.pyi` stub files.
+    ///
+    /// ## Why is this bad?
+    /// Some `sys.platform` checks are too complex for type checkers to
+    /// understand, and thus result in false positives. `sys.platform` checks
+    /// should be simple string comparisons, like `sys.platform == "linux"`.
+    ///
+    /// ## Example
+    /// ```python
+    /// if sys.platform.startswith("linux"):
+    ///    # Linux specific definitions
+    /// else:
+    ///   # Posix specific definitions
+    /// ```
+    ///
+    /// Instead, use a simple string comparison, such as `==` or `!=`:
+    /// ```python
+    /// if sys.platform == "linux":
+    ///     # Linux specific definitions
+    /// else:
+    ///     # Posix specific definitions
+    /// ```
+    ///
+    /// ## References
+    /// - [PEP 484](https://peps.python.org/pep-0484/#version-and-platform-checking)
+    pub struct UnrecognizedPlatformCheck;
+);
+impl Violation for UnrecognizedPlatformCheck {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Unrecognized sys.platform check")
+    }
+}
+
+define_violation!(
+    /// ## What it does
+    /// Check for unrecognized platform names in `sys.platform` checks.
+    ///
+    /// **Note**: this rule is only enabled in `.pyi` stub files.
+    ///
+    /// ## Why is this bad?
+    /// If a `sys.platform` check compares to a platform name outside of a
+    /// small set of known platforms (e.g. "linux", "win32", etc.), it's likely
+    /// a typo or a platform name that is not recognized by type checkers.
+    ///
+    /// The list of known platforms is: "linux", "win32", "cygwin", "darwin".
+    ///
+    /// ## Example
+    /// ```python
+    /// if sys.platform == "linus":
+    ///     ...
+    /// ```
+    ///
+    /// Use instead:
+    /// ```python
+    /// if sys.platform == "linux":
+    ///    ...
+    /// ```
+    ///
+    /// ## References
+    /// - [PEP 484](https://peps.python.org/pep-0484/#version-and-platform-checking)
+    pub struct UnrecognizedPlatformName {
+        pub platform: String,
+    }
+);
+impl Violation for UnrecognizedPlatformName {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let UnrecognizedPlatformName { platform } = self;
+        format!("Unrecognized platform `{platform}`")
+    }
+}
+
+/// PYI007, PYI008
+pub fn unrecognized_platform(
+    checker: &mut Checker,
+    expr: &Expr,
+    left: &Expr,
+    ops: &[Cmpop],
+    comparators: &[Expr],
+) {
+    let ([op], [right]) = (ops, comparators) else {
+        return;
+    };
+
+    let diagnostic_unrecognized_platform_check =
+        Diagnostic::new(UnrecognizedPlatformCheck, Range::from_located(expr));
+    if !checker.resolve_call_path(left).map_or(false, |call_path| {
+        call_path.as_slice() == ["sys", "platform"]
+    }) {
+        return;
+    }
+
+    // "in" might also make sense but we don't currently have one.
+    if !matches!(op, Cmpop::Eq | Cmpop::NotEq)
+        && checker
+            .settings
+            .rules
+            .enabled(&Rule::UnrecognizedPlatformCheck)
+    {
+        checker
+            .diagnostics
+            .push(diagnostic_unrecognized_platform_check);
+        return;
+    }
+
+    match &right.node {
+        ExprKind::Constant {
+            value: Constant::Str(value),
+            ..
+        } => {
+            // Other values are possible but we don't need them right now.
+            // This protects against typos.
+            if !["linux", "win32", "cygwin", "darwin"].contains(&value.as_str())
+                && checker
+                    .settings
+                    .rules
+                    .enabled(&Rule::UnrecognizedPlatformName)
+            {
+                checker.diagnostics.push(Diagnostic::new(
+                    UnrecognizedPlatformName {
+                        platform: value.clone(),
+                    },
+                    Range::from_located(right),
+                ));
+            }
+        }
+        _ => {
+            if checker
+                .settings
+                .rules
+                .enabled(&Rule::UnrecognizedPlatformCheck)
+            {
+                checker
+                    .diagnostics
+                    .push(diagnostic_unrecognized_platform_check);
+            }
+        }
+    }
+}

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI007_PYI007.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__PYI007_PYI007.pyi.snap

@@ -0,0 +1,35 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+expression: diagnostics
+---
+- kind:
+    UnrecognizedPlatformCheck: ~
+  location:
+    row: 7
+    column: 3
+  end_location:
+    row: 7
+    column: 28
+  fix: ~
+  parent: ~
+- kind:
+    UnrecognizedPlatformCheck: ~
+  location:
+    row: 9
+    column: 3
+  end_location:
+    row: 9
+    column: 19
+  fix: ~
+  parent: ~
+- kind:
+    UnrecognizedPlatformCheck: ~
+  location:
+    row: 11
+    column: 3
+  end_location:
+    row: 11
+    column: 24
+  fix: ~
+  parent: ~
+

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI008_PYI008.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__PYI008_PYI008.pyi.snap

@@ -0,0 +1,16 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+expression: diagnostics
+---
+- kind:
+    UnrecognizedPlatformName:
+      platform: linus
+  location:
+    row: 3
+    column: 19
+  end_location:
+    row: 3
+    column: 26
+  fix: ~
+  parent: ~
+