[`flake8-self`] Add Plugin and Rule `SLF001` (#2470)

LICENSE

@@ -1030,3 +1030,8 @@ are:
     OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
     SOFTWARE.
   """
+
+- flake8-self, licensed as follows:
+  """
+    Freely Distributable
+  """

README.md

@@ -158,6 +158,7 @@ This README is also available as [documentation](https://beta.ruff.rs/docs/).
    1. [Pylint (PL)](#pylint-pl)
    1. [tryceratops (TRY)](#tryceratops-try)
    1. [flake8-raise (RSE)](#flake8-raise-rse)
+   1. [flake8-self (SLF)](#flake8-self-slf)
    1. [Ruff-specific rules (RUF)](#ruff-specific-rules-ruf)<!-- End auto-generated table of contents. -->
 1. [Editor Integrations](#editor-integrations)
 1. [FAQ](#faq)
@@ -1368,6 +1369,14 @@ For more, see [flake8-raise](https://pypi.org/project/flake8-raise/) on PyPI.
 | ---- | ---- | ------- | --- |
 | RSE102 | unnecessary-paren-on-raise-exception | Unnecessary parentheses on raised exception |  |
 
+### flake8-self (SLF)
+
+For more, see [flake8-self](https://pypi.org/project/flake8-self/) on PyPI.
+
+| Code | Name | Message | Fix |
+| ---- | ---- | ------- | --- |
+| SLF001 | private-member-access | Private member accessed: `{access}` |  |
+
 ### Ruff-specific rules (RUF)
 
 | Code | Name | Message | Fix |
@@ -1661,6 +1670,7 @@ natively, including:
 - [flake8-quotes](https://pypi.org/project/flake8-quotes/)
 - [flake8-raise](https://pypi.org/project/flake8-raise/)
 - [flake8-return](https://pypi.org/project/flake8-return/)
+- [flake8-self](https://pypi.org/project/flake8-self/)
 - [flake8-simplify](https://pypi.org/project/flake8-simplify/) ([#998](https://github.com/charliermarsh/ruff/issues/998))
 - [flake8-super](https://pypi.org/project/flake8-super/)
 - [flake8-tidy-imports](https://pypi.org/project/flake8-tidy-imports/)
@@ -1750,6 +1760,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [flake8-quotes](https://pypi.org/project/flake8-quotes/)
 - [flake8-raise](https://pypi.org/project/flake8-raise/)
 - [flake8-return](https://pypi.org/project/flake8-return/)
+- [flake8-self](https://pypi.org/project/flake8-self/)
 - [flake8-simplify](https://pypi.org/project/flake8-simplify/) ([#998](https://github.com/charliermarsh/ruff/issues/998))
 - [flake8-super](https://pypi.org/project/flake8-super/)
 - [flake8-tidy-imports](https://pypi.org/project/flake8-tidy-imports/)

resources/test/fixtures/flake8_self/SLF001.py

@@ -0,0 +1,31 @@
+class Foo:
+
+    def __init__(self):
+        self.public_thing = "foo"
+        self._private_thing = "bar"
+        self.__really_private_thing = "baz"
+
+    def __str__(self):
+        return "foo"
+
+    def public_func(self):
+        pass
+
+    def _private_func(self):
+        pass
+
+    def __really_private_func(self, arg):
+        pass
+
+
+foo = Foo()
+
+print(foo.public_thing)
+print(foo.public_func())
+print(foo.__dict__)
+print(foo.__str__())
+
+print(foo._private_thing)  # SLF001
+print(foo.__really_private_thing)  # SLF001
+print(foo._private_func())  # SLF001
+print(foo.__really_private_func(1))  # SLF001

ruff.schema.json

@@ -1828,6 +1828,10 @@
         "SIM4",
         "SIM40",
         "SIM401",
+        "SLF",
+        "SLF0",
+        "SLF00",
+        "SLF001",
         "T",
         "T1",
         "T10",

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_simplify,
+    flake8_pie, flake8_print, flake8_pytest_style, flake8_raise, flake8_return, flake8_self,
-    flake8_tidy_imports, flake8_type_checking, flake8_unused_arguments, flake8_use_pathlib, mccabe,
+    flake8_simplify, flake8_tidy_imports, flake8_type_checking, flake8_unused_arguments,
-    pandas_vet, pep8_naming, pycodestyle, pydocstyle, pyflakes, pygrep_hooks, pylint, pyupgrade,
+    flake8_use_pathlib, mccabe, pandas_vet, pep8_naming, pycodestyle, pydocstyle, pyflakes,
-    ruff, tryceratops,
+    pygrep_hooks, pylint, pyupgrade, ruff, tryceratops,
 };
 use crate::settings::types::PythonVersion;
 use crate::settings::{flags, Settings};
@@ -2148,6 +2148,9 @@ where
                 if self.settings.rules.enabled(&Rule::BannedApi) {
                     flake8_tidy_imports::banned_api::banned_attribute_access(self, expr);
                 }
+                if self.settings.rules.enabled(&Rule::PrivateMemberAccess) {
+                    flake8_self::rules::private_member_access(self, expr);
+                }
                 pandas_vet::rules::check_attr(self, attr, value, expr);
             }
             ExprKind::Call {

src/registry.rs

@@ -484,6 +484,8 @@ ruff_macros::define_rule_mapping!(
     G202 => rules::flake8_logging_format::violations::LoggingRedundantExcInfo,
     // flake8-raise
     RSE102 => rules::flake8_raise::rules::UnnecessaryParenOnRaiseException,
+    // flake8-self
+    SLF001 => rules::flake8_self::rules::PrivateMemberAccess,
     // ruff
     RUF001 => violations::AmbiguousUnicodeCharacterString,
     RUF002 => violations::AmbiguousUnicodeCharacterDocstring,
@@ -616,6 +618,9 @@ pub enum Linter {
     /// [flake8-raise](https://pypi.org/project/flake8-raise/)
     #[prefix = "RSE"]
     Flake8Raise,
+    /// [flake8-self](https://pypi.org/project/flake8-self/)
+    #[prefix = "SLF"]
+    Flake8Self,
     /// Ruff-specific rules
     #[prefix = "RUF"]
     Ruff,

src/rules/flake8_self/mod.rs

@@ -0,0 +1,26 @@
+//! Rules from [flake8-self](https://pypi.org/project/flake8-self/).
+pub(crate) mod rules;
+
+#[cfg(test)]
+mod tests {
+    use std::convert::AsRef;
+    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::PrivateMemberAccess, Path::new("SLF001.py"); "SLF001")]
+    fn rules(rule_code: Rule, path: &Path) -> Result<()> {
+        let snapshot = format!("{}_{}", rule_code.as_ref(), path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("flake8_self").join(path).as_path(),
+            &settings::Settings::for_rule(rule_code),
+        )?;
+        assert_yaml_snapshot!(snapshot, diagnostics);
+        Ok(())
+    }
+}

src/rules/flake8_self/rules/mod.rs

@@ -0,0 +1,3 @@
+pub use private_member_access::{private_member_access, PrivateMemberAccess};
+
+mod private_member_access;

src/rules/flake8_self/rules/private_member_access.rs

@@ -0,0 +1,43 @@
+use ruff_macros::derive_message_formats;
+
+use crate::ast::types::Range;
+use crate::checkers::ast::Checker;
+use crate::define_violation;
+use crate::registry::Diagnostic;
+use crate::violation::Violation;
+use rustpython_ast::{Expr, ExprKind};
+
+define_violation!(
+    pub struct PrivateMemberAccess {
+        pub access: String,
+    }
+);
+impl Violation for PrivateMemberAccess {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let PrivateMemberAccess { access } = self;
+        format!("Private member accessed: `{access}`")
+    }
+}
+
+const VALID_IDS: [&str; 3] = ["self", "cls", "mcs"];
+
+/// SLF001
+pub fn private_member_access(checker: &mut Checker, expr: &Expr) {
+    if let ExprKind::Attribute { value, attr, .. } = &expr.node {
+        if !attr.ends_with("__") && (attr.starts_with('_') || attr.starts_with("__")) {
+            let ExprKind::Name { id, .. } = &value.node else {
+                return;
+            };
+
+            if !VALID_IDS.contains(&id.as_str()) {
+                checker.diagnostics.push(Diagnostic::new(
+                    PrivateMemberAccess {
+                        access: format!("{}.{}", id, attr),
+                    },
+                    Range::from_located(expr),
+                ));
+            }
+        }
+    }
+}

src/rules/flake8_self/snapshots/ruff__rules__flake8_self__tests__private-member-access_SLF001.py.snap

@@ -0,0 +1,45 @@
+---
+source: src/rules/flake8_self/mod.rs
+expression: diagnostics
+---
+- kind:
+    PrivateMemberAccess: ~
+  location:
+    row: 28
+    column: 6
+  end_location:
+    row: 28
+    column: 24
+  fix: ~
+  parent: ~
+- kind:
+    PrivateMemberAccess: ~
+  location:
+    row: 29
+    column: 6
+  end_location:
+    row: 29
+    column: 32
+  fix: ~
+  parent: ~
+- kind:
+    PrivateMemberAccess: ~
+  location:
+    row: 30
+    column: 6
+  end_location:
+    row: 30
+    column: 23
+  fix: ~
+  parent: ~
+- kind:
+    PrivateMemberAccess: ~
+  location:
+    row: 31
+    column: 6
+  end_location:
+    row: 31
+    column: 31
+  fix: ~
+  parent: ~
+

src/rules/mod.rs

@@ -23,6 +23,7 @@ pub mod flake8_pytest_style;
 pub mod flake8_quotes;
 pub mod flake8_raise;
 pub mod flake8_return;
+pub mod flake8_self;
 pub mod flake8_simplify;
 pub mod flake8_tidy_imports;
 pub mod flake8_type_checking;