[pylint] Implement PLR0916 (too-many-boolean-expressions)

crates/ruff_linter/resources/test/fixtures/pylint/too_many_boolean_expressions.py

@@ -0,0 +1,54 @@
+if a:
+    ...
+elif (a and b):
+    ...
+elif (a and b) and c:
+    ...
+elif (a and b) and c and d:
+    ...
+elif (a and b) and c and d and e:
+    ...
+elif (a and b) and c and d and e and f:
+    ...
+elif (a and b) and c and d and e and f and g:
+    ...
+elif (a and b) and c and d and e and f and g and h:
+    ...
+elif (a and b) and c and d and e and f and g and h and i:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u and v:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u and v and w:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u and v and w and x:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u and v and w and x and y:
+    ...
+elif (a and b) and c and d and e and f and g and h and i and j and k and l and m and n and o and p and q and r and s and t and u and v and w and x and y and z:
+    ...
+else:
+    ...

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

@@ -1070,6 +1070,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::CheckAndRemoveFromSet) {
                 refurb::rules::check_and_remove_from_set(checker, if_);
             }
+            if checker.enabled(Rule::TooManyBooleanExpressions) {
+                pylint::rules::too_many_boolean_expressions(checker, if_);
+            }
             if checker.source_type.is_stub() {
                 if checker.any_enabled(&[
                     Rule::UnrecognizedVersionInfoCheck,

crates/ruff_linter/src/codes.rs

@@ -247,6 +247,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "R0912") => (RuleGroup::Stable, rules::pylint::rules::TooManyBranches),
         (Pylint, "R0913") => (RuleGroup::Stable, rules::pylint::rules::TooManyArguments),
         (Pylint, "R0915") => (RuleGroup::Stable, rules::pylint::rules::TooManyStatements),
+        (Pylint, "R0916") => (RuleGroup::Preview, rules::pylint::rules::TooManyBooleanExpressions),
         (Pylint, "R1701") => (RuleGroup::Stable, rules::pylint::rules::RepeatedIsinstanceCalls),
         (Pylint, "R1711") => (RuleGroup::Stable, rules::pylint::rules::UselessReturn),
         (Pylint, "R1714") => (RuleGroup::Stable, rules::pylint::rules::RepeatedEqualityComparison),

crates/ruff_linter/src/rules/pylint/mod.rs

@@ -231,6 +231,22 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn max_boolean_expressions() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("pylint/too_many_boolean_expressions.py"),
+            &LinterSettings {
+                pylint: pylint::settings::Settings {
+                    max_bool_expr: 5,
+                    ..pylint::settings::Settings::default()
+                },
+                ..LinterSettings::for_rule(Rule::TooManyBooleanExpressions)
+            },
+        )?;
+        assert_messages!(diagnostics);
+        Ok(())
+    }
+
     #[test]
     fn max_statements() -> Result<()> {
         let diagnostics = test_path(

crates/ruff_linter/src/rules/pylint/rules/mod.rs

@@ -45,6 +45,7 @@ pub(crate) use subprocess_popen_preexec_fn::*;
 pub(crate) use subprocess_run_without_check::*;
 pub(crate) use sys_exit_alias::*;
 pub(crate) use too_many_arguments::*;
+pub(crate) use too_many_boolean_expressions::*;
 pub(crate) use too_many_branches::*;
 pub(crate) use too_many_public_methods::*;
 pub(crate) use too_many_return_statements::*;
@@ -108,6 +109,7 @@ mod subprocess_popen_preexec_fn;
 mod subprocess_run_without_check;
 mod sys_exit_alias;
 mod too_many_arguments;
+mod too_many_boolean_expressions;
 mod too_many_branches;
 mod too_many_public_methods;
 mod too_many_return_statements;

crates/ruff_linter/src/rules/pylint/rules/too_many_boolean_expressions.rs

@@ -0,0 +1,89 @@
+use ast::{Expr, StmtIf};
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast as ast;
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for too many Boolean expressions in an `if` statement.
+///
+/// By default, this rule allows up to 5 expressions. This can be configured
+/// using the [`pylint.max-bool-expr`] option.
+///
+/// ## Why is this bad?
+/// `if` statements with many Boolean expressions are harder to understand
+/// and maintain. Consider assigning the result of the Boolean expression,
+/// or any of its sub-expressions, to a variable.
+///
+/// ## Example
+/// ```python
+/// if a and b and c and d and e and f and g and h:
+///     ...
+/// ```
+///
+/// ## Options
+/// - `pylint.max-bool-expr`
+#[violation]
+pub struct TooManyBooleanExpressions {
+    expressions: usize,
+    max_expressions: usize,
+}
+
+impl Violation for TooManyBooleanExpressions {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let TooManyBooleanExpressions {
+            expressions,
+            max_expressions,
+        } = self;
+        format!("Too many Boolean expressions ({expressions} > {max_expressions})")
+    }
+}
+
+/// PLR0916
+pub(crate) fn too_many_boolean_expressions(checker: &mut Checker, stmt: &StmtIf) {
+    if let Some(bool_op) = stmt.test.as_bool_op_expr() {
+        let expressions = count_bools(bool_op);
+        if expressions > checker.settings.pylint.max_bool_expr {
+            checker.diagnostics.push(Diagnostic::new(
+                TooManyBooleanExpressions {
+                    expressions,
+                    max_expressions: checker.settings.pylint.max_bool_expr,
+                },
+                bool_op.range(),
+            ));
+        }
+    }
+
+    for elif in &stmt.elif_else_clauses {
+        if let Some(bool_op) = elif.test.as_ref().and_then(Expr::as_bool_op_expr) {
+            let expressions = count_bools(bool_op);
+            if expressions > checker.settings.pylint.max_bool_expr {
+                checker.diagnostics.push(Diagnostic::new(
+                    TooManyBooleanExpressions {
+                        expressions,
+                        max_expressions: checker.settings.pylint.max_bool_expr,
+                    },
+                    bool_op.range(),
+                ));
+            }
+        }
+    }
+}
+
+/// Count the number of Boolean expressions in a `bool_op` expression.
+fn count_bools(bool_op: &ast::ExprBoolOp) -> usize {
+    bool_op
+        .values
+        .iter()
+        .map(|expr| {
+            if let Expr::BoolOp(bool_op) = expr {
+                count_bools(bool_op)
+            } else {
+                1
+            }
+        })
+        .sum::<usize>()
+}

crates/ruff_linter/src/rules/pylint/settings.rs

@@ -40,6 +40,7 @@ pub struct Settings {
     pub allow_magic_value_types: Vec<ConstantType>,
     pub max_args: usize,
     pub max_returns: usize,
+    pub max_bool_expr: usize,
     pub max_branches: usize,
     pub max_statements: usize,
     pub max_public_methods: usize,
@@ -51,6 +52,7 @@ impl Default for Settings {
             allow_magic_value_types: vec![ConstantType::Str, ConstantType::Bytes],
             max_args: 5,
             max_returns: 6,
+            max_bool_expr: 5,
             max_branches: 12,
             max_statements: 50,
             max_public_methods: 20,