[refurb] Implement delete-full-slice rule (FURB131)

crates/ruff/resources/test/fixtures/refurb/FURB131.py

@@ -0,0 +1,64 @@
+from typing import Dict, List
+
+names = {"key": "value"}
+nums = [1, 2, 3]
+x = 42
+y = "hello"
+
+# these should match
+
+# FURB131
+del nums[:]
+
+
+# FURB131
+del names[:]
+
+
+# FURB131
+del x, nums[:]
+
+
+# FURB131
+del y, names[:], x
+
+
+def yes_one(x: list[int]):
+    # FURB131
+    del x[:]
+
+
+def yes_two(x: dict[int, str]):
+    # FURB131
+    del x[:]
+
+
+def yes_three(x: List[int]):
+    # FURB131
+    del x[:]
+
+
+def yes_four(x: Dict[int, str]):
+    # FURB131
+    del x[:]
+
+
+# these should not
+
+del names["key"]
+del nums[0]
+
+x = 1
+del x
+
+
+del nums[1:2]
+
+
+del nums[:2]
+del nums[1:]
+del nums[::2]
+
+
+def no_one(param):
+    del param[:]

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

@@ -1460,14 +1460,17 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 }
             }
         }
-        Stmt::Delete(ast::StmtDelete { targets, range: _ }) => {
+        Stmt::Delete(delete @ ast::StmtDelete { targets, range: _ }) => {
             if checker.enabled(Rule::GlobalStatement) {
                 for target in targets {
                     if let Expr::Name(ast::ExprName { id, .. }) = target {
                         pylint::rules::global_statement(checker, id);
                     }
                 }
             }
+            if checker.enabled(Rule::DeleteFullSlice) {
+                refurb::rules::delete_full_slice(checker, delete);
+            }
         }
         Stmt::Expr(ast::StmtExpr { value, range: _ }) => {
             if checker.enabled(Rule::UselessComparison) {

crates/ruff/src/codes.rs

@@ -867,6 +867,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
 
         // refurb
         (Refurb, "113") => (RuleGroup::Unspecified, rules::refurb::rules::RepeatedAppend),
+        (Refurb, "131") => (RuleGroup::Unspecified, rules::refurb::rules::DeleteFullSlice),
 
         _ => return None,
     })

crates/ruff/src/rules/refurb/helpers.rs

@@ -0,0 +1,187 @@
+use ast::{ParameterWithDefault, Parameters};
+use ruff_python_ast::{self as ast, Expr, Stmt};
+use ruff_python_semantic::analyze::type_inference::{PythonType, ResolvedPythonType};
+use ruff_python_semantic::{Binding, BindingKind, SemanticModel};
+
+/// Abstraction for a type checker, conservatively checks for the intended type(s).
+trait TypeChecker {
+    /// Check annotation expression to match the intended type(s).
+    fn match_annotation(semantic: &SemanticModel, annotation: &Expr) -> bool;
+    /// Check initializer expression to match the intended type(s).
+    fn match_initializer(semantic: &SemanticModel, initializer: &Expr) -> bool;
+}
+
+/// Check if the type checker accepts the given binding with the given name.
+///
+/// NOTE: this function doesn't perform more serious type inference, so it won't be able
+///       to understand if the value gets initialized from a call to a function always returning
+///       lists. This also implies no interfile analysis.
+fn check_type<T: TypeChecker>(semantic: &SemanticModel, binding: &Binding, name: &str) -> bool {
+    assert!(binding.source.is_some());
+    let stmt = semantic.statement(binding.source.unwrap());
+
+    match binding.kind {
+        BindingKind::Assignment => match stmt {
+            // ```python
+            // x = init_expr
+            // ```
+            //
+            // The type checker might know how to infer the type based on `init_expr`.
+            Stmt::Assign(ast::StmtAssign { value, .. }) => {
+                T::match_initializer(semantic, value.as_ref())
+            }
+
+            // ```python
+            // x: annotation = some_expr
+            // ```
+            //
+            // In this situation, we check only the annotation.
+            Stmt::AnnAssign(ast::StmtAnnAssign { annotation, .. }) => {
+                T::match_annotation(semantic, annotation.as_ref())
+            }
+            _ => false,
+        },
+
+        BindingKind::Argument => match stmt {
+            // ```python
+            // def foo(x: annotation):
+            //   ...
+            // ```
+            //
+            // We trust the annotation and see if the type checker matches the annotation.
+            Stmt::FunctionDef(ast::StmtFunctionDef { parameters, .. }) => {
+                let Some(parameter) = find_parameter_by_name(parameters.as_ref(), name) else {
+                    return false;
+                };
+                let Some(ref annotation) = parameter.parameter.annotation else {
+                    return false;
+                };
+                T::match_annotation(semantic, annotation.as_ref())
+            }
+            _ => false,
+        },
+
+        BindingKind::Annotation => match stmt {
+            // ```python
+            // x: annotation
+            // ```
+            //
+            // It's a typed declaration, type annotation is the only source of information.
+            Stmt::AnnAssign(ast::StmtAnnAssign { annotation, .. }) => {
+                T::match_annotation(semantic, annotation.as_ref())
+            }
+            _ => false,
+        },
+
+        _ => false,
+    }
+}
+
+/// Type checker for builtin types.
+trait BuiltinTypeChecker {
+    /// Builtin type name.
+    const BUILTIN_TYPE_NAME: &'static str;
+    /// Type name as found in the `Typing` module.
+    const TYPING_NAME: &'static str;
+    /// [`PythonType`] associated with the intended type.
+    const EXPR_TYPE: PythonType;
+
+    /// Check annotation expression to match the intended type.
+    fn match_annotation(semantic: &SemanticModel, annotation: &Expr) -> bool {
+        let Expr::Subscript(ast::ExprSubscript { value, .. }) = annotation else {
+            return false;
+        };
+        Self::match_builtin_type(semantic, value)
+            || semantic.match_typing_expr(value, Self::TYPING_NAME)
+    }
+
+    /// Check initializer expression to match the intended type.
+    fn match_initializer(semantic: &SemanticModel, initializer: &Expr) -> bool {
+        Self::match_expr_type(initializer) || Self::match_builtin_constructor(semantic, initializer)
+    }
+
+    /// Check if the type can be inferred from the given expression.
+    fn match_expr_type(initializer: &Expr) -> bool {
+        let init_type: ResolvedPythonType = initializer.into();
+        match init_type {
+            ResolvedPythonType::Atom(atom) => atom == Self::EXPR_TYPE,
+            _ => false,
+        }
+    }
+
+    /// Check if the given expression corresponds to a constructor call of the builtin type.
+    fn match_builtin_constructor(semantic: &SemanticModel, initializer: &Expr) -> bool {
+        let Expr::Call(ast::ExprCall { func, .. }) = initializer else {
+            return false;
+        };
+        Self::match_builtin_type(semantic, func.as_ref())
+    }
+
+    /// Check if the given expression names the builtin type.
+    fn match_builtin_type(semantic: &SemanticModel, type_expr: &Expr) -> bool {
+        let Expr::Name(ast::ExprName { id, .. }) = type_expr else {
+            return false;
+        };
+        id == Self::BUILTIN_TYPE_NAME && semantic.is_builtin(Self::BUILTIN_TYPE_NAME)
+    }
+}
+
+impl<T: BuiltinTypeChecker> TypeChecker for T {
+    fn match_annotation(semantic: &SemanticModel, annotation: &Expr) -> bool {
+        <Self as BuiltinTypeChecker>::match_annotation(semantic, annotation)
+    }
+
+    fn match_initializer(semantic: &SemanticModel, initializer: &Expr) -> bool {
+        <Self as BuiltinTypeChecker>::match_initializer(semantic, initializer)
+    }
+}
+
+struct ListChecker;
+
+impl BuiltinTypeChecker for ListChecker {
+    const TYPING_NAME: &'static str = "List";
+    const BUILTIN_TYPE_NAME: &'static str = "list";
+    const EXPR_TYPE: PythonType = PythonType::List;
+}
+
+struct DictChecker;
+
+impl BuiltinTypeChecker for DictChecker {
+    const TYPING_NAME: &'static str = "Dict";
+    const BUILTIN_TYPE_NAME: &'static str = "dict";
+    const EXPR_TYPE: PythonType = PythonType::Dict;
+}
+
+/// Test whether the given binding (and the given name) can be considered a list.
+/// For this, we check what value might be associated with it through it's initialization and
+/// what annotation it has (we consider `list` and `typing.List`).
+pub(super) fn is_list<'a>(semantic: &'a SemanticModel, binding: &'a Binding, name: &str) -> bool {
+    check_type::<ListChecker>(semantic, binding, name)
+}
+
+/// Test whether the given binding (and the given name) can be considered a dictionary.
+/// For this, we check what value might be associated with it through it's initialization and
+/// what annotation it has (we consider `dict` and `typing.Dict`).
+pub(super) fn is_dict<'a>(semantic: &'a SemanticModel, binding: &'a Binding, name: &str) -> bool {
+    check_type::<DictChecker>(semantic, binding, name)
+}
+
+#[inline]
+fn find_parameter_by_name<'a>(
+    parameters: &'a Parameters,
+    name: &'a str,
+) -> Option<&'a ParameterWithDefault> {
+    find_parameter_by_name_impl(&parameters.args, name)
+        .or_else(|| find_parameter_by_name_impl(&parameters.posonlyargs, name))
+        .or_else(|| find_parameter_by_name_impl(&parameters.kwonlyargs, name))
+}
+
+#[inline]
+fn find_parameter_by_name_impl<'a>(
+    parameters: &'a [ParameterWithDefault],
+    name: &'a str,
+) -> Option<&'a ParameterWithDefault> {
+    parameters
+        .iter()
+        .find(|arg| arg.parameter.name.as_str() == name)
+}

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

@@ -1,4 +1,5 @@
 //! Rules from [refurb](https://pypi.org/project/refurb/)/
+mod helpers;
 pub(crate) mod rules;
 
 #[cfg(test)]
@@ -13,6 +14,7 @@ mod tests {
     use crate::{assert_messages, settings};
 
     #[test_case(Rule::RepeatedAppend, Path::new("FURB113.py"))]
+    #[test_case(Rule::DeleteFullSlice, Path::new("FURB131.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(