ruff_python_ast/

helpers.rs

use std::borrow::Cow;
use std::path::Path;

use rustc_hash::FxHashMap;

use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer, indentation_at_offset};
use ruff_source_file::LineRanges;
use ruff_text_size::{Ranged, TextLen, TextRange, TextSize};

use crate::name::{Name, QualifiedName, QualifiedNameBuilder};
use crate::statement_visitor::StatementVisitor;
use crate::token::Tokens;
use crate::token::parenthesized_range;
use crate::visitor::Visitor;
use crate::{
    self as ast, Arguments, AtomicNodeIndex, CmpOp, ConstantValue, DictItem, ExceptHandler, Expr,
    ExprNoneLiteral, InterpolatedStringElement, MatchCase, Operator, Pattern, Stmt, TypeParam,
};
use crate::{AnyNodeRef, ExprContext};

/// Return `true` if the `Stmt` is a compound statement (as opposed to a simple statement).
pub const fn is_compound_statement(stmt: &Stmt) -> bool {
    matches!(
        stmt,
        Stmt::FunctionDef(_)
            | Stmt::ClassDef(_)
            | Stmt::While(_)
            | Stmt::For(_)
            | Stmt::Match(_)
            | Stmt::With(_)
            | Stmt::If(_)
            | Stmt::Try(_)
    )
}

fn is_iterable_initializer<F>(id: &str, is_builtin: F) -> bool
where
    F: Fn(&str) -> bool,
{
    matches!(id, "list" | "tuple" | "set" | "dict" | "frozenset") && is_builtin(id)
}

/// Whether an expression has no side effects, may have side effects,
/// or is assumed to have side effects.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SideEffect {
    /// The expression is definitely side-effect-free.
    Absent,
    /// The expression may have side effects (e.g., f-string interpolation
    /// may invoke `__format__` or `__str__`).
    Possible,
    /// The expression is assumed to have side effects.
    Present,
}

impl SideEffect {
    pub const fn is_present(self) -> bool {
        matches!(self, Self::Present)
    }

    pub const fn is_absent(self) -> bool {
        matches!(self, Self::Absent)
    }

    #[must_use]
    pub const fn merge(self, other: Self) -> Self {
        match (self, other) {
            (Self::Present, _) | (_, Self::Present) => Self::Present,
            (Self::Possible, _) | (_, Self::Possible) => Self::Possible,
            _ => Self::Absent,
        }
    }

    /// Classify a single expression node's side effect.
    fn from_expr(expr: &Expr, is_builtin: &dyn Fn(&str) -> bool) -> Self {
        match expr {
            // Empty initializers for known builtins are side-effect-free.
            Expr::Call(ast::ExprCall {
                func, arguments, ..
            }) if arguments.is_empty() => {
                if let Expr::Name(ast::ExprName { id, .. }) = func.as_ref() {
                    if is_iterable_initializer(id.as_str(), |id| is_builtin(id)) {
                        return Self::Absent;
                    }
                }
                Self::Present
            }

            // Overloaded operators: only side-effect-free if both sides are literals.
            Expr::BinOp(ast::ExprBinOp { left, right, .. }) => {
                if is_known_safe_binop_operand(left) && is_known_safe_binop_operand(right) {
                    Self::Absent
                } else {
                    Self::Present
                }
            }

            // Non-literal f-string interpolation may invoke `__format__`/`__str__`.
            Expr::FString(ast::ExprFString { value, .. }) => {
                if value.elements().any(has_uncertain_interpolation) {
                    Self::Possible
                } else {
                    Self::Absent
                }
            }
            Expr::TString(ast::ExprTString { value, .. }) => {
                if value.elements().any(has_uncertain_interpolation) {
                    Self::Possible
                } else {
                    Self::Absent
                }
            }

            // Named expressions (walrus operator) are assignments.
            Expr::Named(_) => Self::Present,

            // Complex expressions that are assumed to have side effects.
            Expr::Await(_)
            | Expr::Call(_)
            | Expr::DictComp(_)
            | Expr::Generator(_)
            | Expr::ListComp(_)
            | Expr::SetComp(_)
            | Expr::Subscript(_)
            | Expr::Yield(_)
            | Expr::YieldFrom(_)
            | Expr::IpyEscapeCommand(_) => Self::Present,

            // Side-effect-free expressions — continue walking child nodes.
            Expr::BoolOp(_)
            | Expr::Compare(_)
            | Expr::Dict(_)
            | Expr::If(_)
            | Expr::Lambda(_)
            | Expr::List(_)
            | Expr::Set(_)
            | Expr::Slice(_)
            | Expr::Starred(_)
            | Expr::Tuple(_)
            | Expr::UnaryOp(_)
            | Expr::Attribute(_)
            | Expr::Name(_)
            | Expr::StringLiteral(_)
            | Expr::BytesLiteral(_)
            | Expr::NumberLiteral(_)
            | Expr::Constant(_)
            | Expr::BooleanLiteral(_)
            | Expr::NoneLiteral(_)
            | Expr::EllipsisLiteral(_) => Self::Absent,
        }
    }
}

const fn is_known_safe_binop_operand(expr: &Expr) -> bool {
    match expr {
        Expr::StringLiteral(_)
        | Expr::BytesLiteral(_)
        | Expr::NumberLiteral(_)
        | Expr::Constant(_)
        | Expr::BooleanLiteral(_)
        | Expr::NoneLiteral(_)
        | Expr::EllipsisLiteral(_)
        | Expr::FString(_)
        | Expr::List(_)
        | Expr::Tuple(_)
        | Expr::Set(_)
        | Expr::Dict(_)
        | Expr::ListComp(_)
        | Expr::SetComp(_)
        | Expr::DictComp(_) => true,

        Expr::BoolOp(_)
        | Expr::Named(_)
        | Expr::BinOp(_)
        | Expr::UnaryOp(_)
        | Expr::Lambda(_)
        | Expr::If(_)
        | Expr::Compare(_)
        | Expr::Call(_)
        | Expr::Generator(_)
        | Expr::Await(_)
        | Expr::Yield(_)
        | Expr::YieldFrom(_)
        | Expr::Attribute(_)
        | Expr::Subscript(_)
        | Expr::Starred(_)
        | Expr::Name(_)
        | Expr::Slice(_)
        | Expr::IpyEscapeCommand(_)
        | Expr::TString(_) => false,
    }
}

fn is_definitely_side_effect_free_interpolation_expr(expr: &Expr) -> bool {
    matches!(
        expr,
        Expr::NumberLiteral(_)
            | Expr::Constant(_)
            | Expr::BooleanLiteral(_)
            | Expr::NoneLiteral(_)
            | Expr::EllipsisLiteral(_)
            | Expr::StringLiteral(_)
            | Expr::BytesLiteral(_)
    )
}

fn has_uncertain_interpolation(element: &InterpolatedStringElement) -> bool {
    match element {
        InterpolatedStringElement::Literal(_) => false,
        InterpolatedStringElement::Interpolation(interp) => {
            !is_definitely_side_effect_free_interpolation_expr(&interp.expression)
                || interp
                    .format_spec
                    .as_ref()
                    .is_some_and(|spec| spec.elements.iter().any(has_uncertain_interpolation))
        }
    }
}

/// Return `true` if the `Expr` contains an expression that appears to include a
/// side-effect (like a function call).
///
/// Accepts a closure that determines whether a given name (e.g., `"list"`) is a Python builtin.
pub fn contains_effect<F>(expr: &Expr, is_builtin: F) -> bool
where
    F: Fn(&str) -> bool,
{
    side_effect(expr, is_builtin).is_present()
}

/// Return whether `expr` has no side effects, maybe has side effects, or definitely
/// has side effects.
///
/// Unlike [`contains_effect`], which returns a simple `bool`, this function distinguishes
/// between expressions that are definitely side-effect-free, definitely side-effectful,
/// and those that may invoke user-defined code (e.g., formatting a non-literal f-string
/// interpolation can call `__format__` or `__str__`).
pub fn side_effect<F>(expr: &Expr, is_builtin: F) -> SideEffect
where
    F: Fn(&str) -> bool,
{
    let mut effect = SideEffect::Absent;
    any_over_expr(expr, |expr| {
        match SideEffect::from_expr(expr, &is_builtin) {
            SideEffect::Present => {
                effect = SideEffect::Present;
                true
            }
            SideEffect::Possible => {
                effect = effect.merge(SideEffect::Possible);
                false
            }
            SideEffect::Absent => false,
        }
    });
    effect
}

/// Call `func` over every `Expr` in `expr`, returning `true` if any expression
/// returns `true`..
pub fn any_over_expr<F>(expr: &Expr, mut func: F) -> bool
where
    F: FnMut(&Expr) -> bool,
{
    fn inner(expr: &Expr, func: &mut dyn FnMut(&Expr) -> bool) -> bool {
        if func(expr) {
            return true;
        }
        match expr {
            Expr::BoolOp(ast::ExprBoolOp { values, .. }) => {
                values.iter().any(|expr| any_over_expr(expr, &mut *func))
            }
            Expr::FString(ast::ExprFString { value, .. }) => value
                .elements()
                .any(|expr| any_over_interpolated_string_element(expr, &mut *func)),
            Expr::TString(ast::ExprTString { value, .. }) => value
                .elements()
                .any(|expr| any_over_interpolated_string_element(expr, &mut *func)),
            Expr::Named(ast::ExprNamed {
                target,
                value,
                range: _,
                node_index: _,
            }) => any_over_expr(target, &mut *func) || any_over_expr(value, &mut *func),
            Expr::BinOp(ast::ExprBinOp { left, right, .. }) => {
                any_over_expr(left, &mut *func) || any_over_expr(right, &mut *func)
            }
            Expr::UnaryOp(ast::ExprUnaryOp { operand, .. }) => any_over_expr(operand, func),
            Expr::Lambda(ast::ExprLambda {
                body, parameters, ..
            }) => {
                parameters
                    .iter()
                    .flat_map(|parameters| parameters.iter_non_variadic_params())
                    .filter_map(|parameter| parameter.default.as_deref())
                    .any(|default| any_over_expr(default, &mut *func))
                    || any_over_expr(body, func)
            }
            Expr::If(ast::ExprIf {
                test,
                body,
                orelse,
                range: _,
                node_index: _,
            }) => {
                any_over_expr(test, &mut *func)
                    || any_over_expr(body, &mut *func)
                    || any_over_expr(orelse, &mut *func)
            }
            Expr::Dict(ast::ExprDict { items, .. }) => {
                items.iter().any(|ast::DictItem { key, value }| {
                    any_over_expr(value, &mut *func)
                        || key
                            .as_ref()
                            .is_some_and(|key| any_over_expr(key, &mut *func))
                })
            }
            Expr::Set(ast::ExprSet { elts, .. })
            | Expr::List(ast::ExprList { elts, .. })
            | Expr::Tuple(ast::ExprTuple { elts, .. }) => {
                elts.iter().any(|expr| any_over_expr(expr, &mut *func))
            }
            Expr::ListComp(ast::ExprListComp {
                elt,
                generators,
                range: _,
                node_index: _,
            })
            | Expr::SetComp(ast::ExprSetComp {
                elt,
                generators,
                range: _,
                node_index: _,
            })
            | Expr::Generator(ast::ExprGenerator {
                elt,
                generators,
                range: _,
                node_index: _,
                parenthesized: _,
            }) => {
                any_over_expr(elt, &mut *func)
                    || generators.iter().any(|generator| {
                        any_over_expr(&generator.target, &mut *func)
                            || any_over_expr(&generator.iter, &mut *func)
                            || generator
                                .ifs
                                .iter()
                                .any(|expr| any_over_expr(expr, &mut *func))
                    })
            }
            Expr::DictComp(ast::ExprDictComp {
                key,
                value,
                generators,
                range: _,
                node_index: _,
            }) => {
                key.as_deref()
                    .is_some_and(|key| any_over_expr(key, &mut *func))
                    || any_over_expr(value, &mut *func)
                    || generators.iter().any(|generator| {
                        any_over_expr(&generator.target, &mut *func)
                            || any_over_expr(&generator.iter, &mut *func)
                            || generator
                                .ifs
                                .iter()
                                .any(|expr| any_over_expr(expr, &mut *func))
                    })
            }
            Expr::Await(ast::ExprAwait {
                value,
                range: _,
                node_index: _,
            })
            | Expr::YieldFrom(ast::ExprYieldFrom {
                value,
                range: _,
                node_index: _,
            })
            | Expr::Attribute(ast::ExprAttribute { value, .. })
            | Expr::Starred(ast::ExprStarred { value, .. }) => any_over_expr(value, func),
            Expr::Yield(ast::ExprYield {
                value,
                range: _,
                node_index: _,
            }) => value
                .as_ref()
                .is_some_and(|value| any_over_expr(value, func)),
            Expr::Compare(ast::ExprCompare {
                left, comparators, ..
            }) => {
                any_over_expr(left, &mut *func)
                    || comparators
                        .iter()
                        .any(|expr| any_over_expr(expr, &mut *func))
            }
            Expr::Call(ast::ExprCall {
                func: call_func,
                arguments,
                range_start: _,
                node_index: _,
            }) => {
                // Note that this is the evaluation order but not necessarily the declaration order
                // (e.g. for `f(*args, a=2, *args2, **kwargs)` it's not)
                any_over_expr(call_func, &mut *func)
                    || arguments
                        .args
                        .iter()
                        .any(|expr| any_over_expr(expr, &mut *func))
                    || arguments
                        .keywords
                        .iter()
                        .any(|keyword| any_over_expr(&keyword.value, &mut *func))
            }
            Expr::Subscript(ast::ExprSubscript { value, slice, .. }) => {
                any_over_expr(value, &mut *func) || any_over_expr(slice, &mut *func)
            }
            Expr::Slice(ast::ExprSlice {
                lower,
                upper,
                step,
                range: _,
                node_index: _,
            }) => {
                lower
                    .as_ref()
                    .is_some_and(|value| any_over_expr(value, &mut *func))
                    || upper
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, &mut *func))
                    || step
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, &mut *func))
            }
            Expr::Name(_)
            | Expr::StringLiteral(_)
            | Expr::BytesLiteral(_)
            | Expr::NumberLiteral(_)
            | Expr::Constant(_)
            | Expr::BooleanLiteral(_)
            | Expr::NoneLiteral(_)
            | Expr::EllipsisLiteral(_)
            | Expr::IpyEscapeCommand(_) => false,
        }
    }

    inner(expr, &mut func)
}

fn any_over_type_param(type_param: &TypeParam, func: &mut dyn FnMut(&Expr) -> bool) -> bool {
    match type_param {
        TypeParam::TypeVar(ast::TypeParamTypeVar { bound, default, .. }) => {
            bound
                .as_ref()
                .is_some_and(|value| any_over_expr(value, &mut *func))
                || default
                    .as_ref()
                    .is_some_and(|value| any_over_expr(value, &mut *func))
        }
        TypeParam::TypeVarTuple(ast::TypeParamTypeVarTuple { default, .. }) => default
            .as_ref()
            .is_some_and(|value| any_over_expr(value, &mut *func)),
        TypeParam::ParamSpec(ast::TypeParamParamSpec { default, .. }) => default
            .as_ref()
            .is_some_and(|value| any_over_expr(value, &mut *func)),
    }
}

fn any_over_pattern(pattern: &Pattern, func: &mut dyn FnMut(&Expr) -> bool) -> bool {
    match pattern {
        Pattern::MatchValue(ast::PatternMatchValue {
            value,
            range: _,
            node_index: _,
        }) => any_over_expr(value, func),
        Pattern::MatchSingleton(_) => false,
        Pattern::MatchSequence(ast::PatternMatchSequence { patterns, .. }) => patterns
            .iter()
            .any(|pattern| any_over_pattern(pattern, &mut *func)),
        Pattern::MatchMapping(ast::PatternMatchMapping { keys, patterns, .. }) => {
            keys.iter().any(|key| any_over_expr(key, &mut *func))
                || patterns
                    .iter()
                    .any(|pattern| any_over_pattern(pattern, &mut *func))
        }
        Pattern::MatchClass(ast::PatternMatchClass { cls, arguments, .. }) => {
            any_over_expr(cls, &mut *func)
                || arguments
                    .patterns
                    .iter()
                    .any(|pattern| any_over_pattern(pattern, &mut *func))
                || arguments
                    .keywords
                    .iter()
                    .any(|keyword| any_over_pattern(&keyword.pattern, &mut *func))
        }
        Pattern::MatchStar(_) => false,
        Pattern::MatchAs(ast::PatternMatchAs { pattern, .. }) => pattern
            .as_ref()
            .is_some_and(|pattern| any_over_pattern(pattern, func)),
        Pattern::MatchOr(ast::PatternMatchOr { patterns, .. }) => patterns
            .iter()
            .any(|pattern| any_over_pattern(pattern, &mut *func)),
    }
}

fn any_over_interpolated_string_element(
    element: &ast::InterpolatedStringElement,
    func: &mut dyn FnMut(&Expr) -> bool,
) -> bool {
    match element {
        ast::InterpolatedStringElement::Literal(_) => false,
        ast::InterpolatedStringElement::Interpolation(ast::InterpolatedElement {
            expression,
            format_spec,
            ..
        }) => {
            any_over_expr(expression, &mut *func)
                || format_spec.as_ref().is_some_and(|spec| {
                    spec.elements.iter().any(|spec_element| {
                        any_over_interpolated_string_element(spec_element, &mut *func)
                    })
                })
        }
    }
}

fn any_over_stmt<F>(stmt: &Stmt, mut func: F) -> bool
where
    F: FnMut(&Expr) -> bool,
{
    fn inner(stmt: &Stmt, func: &mut dyn FnMut(&Expr) -> bool) -> bool {
        match stmt {
            Stmt::FunctionDef(ast::StmtFunctionDef {
                parameters,
                type_params,
                body,
                decorator_list,
                returns,
                ..
            }) => {
                parameters.iter().any(|param| {
                    param
                        .default()
                        .is_some_and(|default| any_over_expr(default, &mut *func))
                        || param
                            .annotation()
                            .is_some_and(|annotation| any_over_expr(annotation, &mut *func))
                }) || type_params.as_ref().is_some_and(|type_params| {
                    type_params
                        .iter()
                        .any(|type_param| any_over_type_param(type_param, &mut *func))
                }) || body.iter().any(|stmt| any_over_stmt(stmt, &mut *func))
                    || decorator_list
                        .iter()
                        .any(|decorator| any_over_expr(&decorator.expression, &mut *func))
                    || returns
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, func))
            }
            Stmt::ClassDef(ast::StmtClassDef {
                arguments,
                type_params,
                body,
                decorator_list,
                ..
            }) => {
                // Note that e.g. `class A(*args, a=2, *args2, **kwargs): pass` is a valid class
                // definition
                arguments
                    .as_deref()
                    .is_some_and(|Arguments { args, keywords, .. }| {
                        args.iter().any(|expr| any_over_expr(expr, &mut *func))
                            || keywords
                                .iter()
                                .any(|keyword| any_over_expr(&keyword.value, &mut *func))
                    })
                    || type_params.as_ref().is_some_and(|type_params| {
                        type_params
                            .iter()
                            .any(|type_param| any_over_type_param(type_param, &mut *func))
                    })
                    || body.iter().any(|stmt| any_over_stmt(stmt, &mut *func))
                    || decorator_list
                        .iter()
                        .any(|decorator| any_over_expr(&decorator.expression, &mut *func))
            }
            Stmt::Return(ast::StmtReturn {
                value,
                range: _,
                node_index: _,
            }) => value
                .as_ref()
                .is_some_and(|value| any_over_expr(value, func)),
            Stmt::Delete(ast::StmtDelete { targets, .. }) => {
                targets.iter().any(|expr| any_over_expr(expr, &mut *func))
            }
            Stmt::TypeAlias(ast::StmtTypeAlias {
                name,
                type_params,
                value,
                ..
            }) => {
                any_over_expr(name, &mut *func)
                    || type_params.as_ref().is_some_and(|type_params| {
                        type_params
                            .iter()
                            .any(|type_param| any_over_type_param(type_param, &mut *func))
                    })
                    || any_over_expr(value, func)
            }
            Stmt::Assign(ast::StmtAssign { targets, value, .. }) => {
                targets.iter().any(|expr| any_over_expr(expr, &mut *func))
                    || any_over_expr(value, func)
            }
            Stmt::AugAssign(ast::StmtAugAssign { target, value, .. }) => {
                any_over_expr(target, &mut *func) || any_over_expr(value, &mut *func)
            }
            Stmt::AnnAssign(ast::StmtAnnAssign {
                target,
                annotation,
                value,
                ..
            }) => {
                any_over_expr(target, &mut *func)
                    || any_over_expr(annotation, &mut *func)
                    || value
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, &mut *func))
            }
            Stmt::For(ast::StmtFor {
                target,
                iter,
                body,
                orelse,
                ..
            }) => {
                any_over_expr(target, &mut *func)
                    || any_over_expr(iter, &mut *func)
                    || any_over_body(body, &mut *func)
                    || any_over_body(orelse, &mut *func)
            }
            Stmt::While(ast::StmtWhile {
                test, body, orelse, ..
            }) => {
                any_over_expr(test, &mut *func)
                    || any_over_body(body, &mut *func)
                    || any_over_body(orelse, &mut *func)
            }
            Stmt::If(ast::StmtIf {
                test,
                body,
                elif_else_clauses,
                ..
            }) => {
                any_over_expr(test, &mut *func)
                    || any_over_body(body, &mut *func)
                    || elif_else_clauses.iter().any(|clause| {
                        clause
                            .test
                            .as_ref()
                            .is_some_and(|test| any_over_expr(test, &mut *func))
                            || any_over_body(&clause.body, &mut *func)
                    })
            }
            Stmt::With(ast::StmtWith { items, body, .. }) => {
                items.iter().any(|with_item| {
                    any_over_expr(&with_item.context_expr, &mut *func)
                        || with_item
                            .optional_vars
                            .as_ref()
                            .is_some_and(|expr| any_over_expr(expr, &mut *func))
                }) || any_over_body(body, &mut *func)
            }
            Stmt::Raise(ast::StmtRaise {
                exc,
                cause,
                range: _,
                node_index: _,
            }) => {
                exc.as_ref()
                    .is_some_and(|value| any_over_expr(value, &mut *func))
                    || cause
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, &mut *func))
            }
            Stmt::Try(ast::StmtTry {
                body,
                handlers,
                orelse,
                finalbody,
                ..
            }) => {
                any_over_body(body, &mut *func)
                    || handlers.iter().any(|handler| {
                        let ExceptHandler::ExceptHandler(ast::ExceptHandlerExceptHandler {
                            type_,
                            body,
                            ..
                        }) = handler;
                        type_
                            .as_ref()
                            .is_some_and(|expr| any_over_expr(expr, &mut *func))
                            || any_over_body(body, &mut *func)
                    })
                    || any_over_body(orelse, &mut *func)
                    || any_over_body(finalbody, &mut *func)
            }
            Stmt::Assert(ast::StmtAssert {
                test,
                msg,
                range: _,
                node_index: _,
            }) => {
                any_over_expr(test, &mut *func)
                    || msg
                        .as_ref()
                        .is_some_and(|value| any_over_expr(value, &mut *func))
            }
            Stmt::Match(ast::StmtMatch {
                subject,
                cases,
                range: _,
                node_index: _,
            }) => {
                any_over_expr(subject, &mut *func)
                    || cases.iter().any(|case| {
                        let MatchCase {
                            pattern,
                            guard,
                            body,
                            ..
                        } = case;
                        any_over_pattern(pattern, &mut *func)
                            || guard
                                .as_ref()
                                .is_some_and(|expr| any_over_expr(expr, &mut *func))
                            || any_over_body(body, &mut *func)
                    })
            }
            Stmt::Import(_) => false,
            Stmt::ImportFrom(_) => false,
            Stmt::Global(_) => false,
            Stmt::Nonlocal(_) => false,
            Stmt::Expr(ast::StmtExpr {
                value,
                range: _,
                node_index: _,
            }) => any_over_expr(value, func),
            Stmt::Pass(_) | Stmt::Break(_) | Stmt::Continue(_) => false,
            Stmt::IpyEscapeCommand(_) => false,
        }
    }

    inner(stmt, &mut func)
}

pub fn any_over_body<F>(body: &[Stmt], mut func: F) -> bool
where
    F: FnMut(&Expr) -> bool,
{
    body.iter().any(|stmt| any_over_stmt(stmt, &mut func))
}

pub fn is_dunder(id: &str) -> bool {
    id.starts_with("__") && id.ends_with("__")
}

/// Whether a name starts and ends with a single underscore.
///
/// `_a__` is considered neither a dunder nor a sunder name.
pub fn is_sunder(id: &str) -> bool {
    id.starts_with('_') && id.ends_with('_') && !id.starts_with("__") && !id.ends_with("__")
}

/// Return `true` if the [`Stmt`] is an assignment to a dunder (like `__all__`).
pub fn is_assignment_to_a_dunder(stmt: &Stmt) -> bool {
    // Check whether it's an assignment to a dunder, with or without a type
    // annotation. This is what pycodestyle (as of 2.9.1) does.
    match stmt {
        Stmt::Assign(ast::StmtAssign { targets, .. }) => {
            if let [Expr::Name(ast::ExprName { id, .. })] = targets.as_slice() {
                is_dunder(id)
            } else {
                false
            }
        }
        Stmt::AnnAssign(ast::StmtAnnAssign { target, .. }) => {
            if let Expr::Name(ast::ExprName { id, .. }) = target.as_ref() {
                is_dunder(id)
            } else {
                false
            }
        }
        _ => false,
    }
}

/// Return `true` if the [`Expr`] is a singleton (`None`, `True`, `False`, or
/// `...`).
const fn is_singleton(expr: &Expr) -> bool {
    matches!(
        expr,
        Expr::NoneLiteral(_)
            | Expr::BooleanLiteral(_)
            | Expr::EllipsisLiteral(_)
            | Expr::Constant(ast::ExprConstant {
                value: ConstantValue::None | ConstantValue::Boolean(_) | ConstantValue::Ellipsis,
                ..
            })
    )
}

/// Return `true` if the [`Expr`] is a literal or tuple of literals.
pub fn is_constant(expr: &Expr) -> bool {
    if let Expr::Tuple(tuple) = expr {
        tuple.iter().all(is_constant)
    } else {
        expr.is_literal_expr()
    }
}

/// Return `true` if the [`Expr`] is a non-singleton constant.
pub fn is_constant_non_singleton(expr: &Expr) -> bool {
    is_constant(expr) && !is_singleton(expr)
}

/// Return `true` if an [`Expr`] is a literal `True`.
pub const fn is_const_true(expr: &Expr) -> bool {
    matches!(
        expr,
        Expr::BooleanLiteral(ast::ExprBooleanLiteral { value: true, .. }),
    )
}

/// Return `true` if an [`Expr`] is a literal `False`.
pub const fn is_const_false(expr: &Expr) -> bool {
    matches!(
        expr,
        Expr::BooleanLiteral(ast::ExprBooleanLiteral { value: false, .. }),
    )
}

/// Return `true` if the [`Expr`] is a mutable iterable initializer, like `{}` or `[]`.
pub const fn is_mutable_iterable_initializer(expr: &Expr) -> bool {
    matches!(
        expr,
        Expr::Set(_)
            | Expr::SetComp(_)
            | Expr::List(_)
            | Expr::ListComp(_)
            | Expr::Dict(_)
            | Expr::DictComp(_)
    )
}

/// Extract the names of all handled exceptions.
pub fn extract_handled_exceptions(handlers: &[ExceptHandler]) -> Vec<&Expr> {
    let mut handled_exceptions = Vec::new();
    for handler in handlers {
        match handler {
            ExceptHandler::ExceptHandler(ast::ExceptHandlerExceptHandler { type_, .. }) => {
                if let Some(type_) = type_ {
                    if let Expr::Tuple(tuple) = &**type_ {
                        for type_ in tuple {
                            handled_exceptions.push(type_);
                        }
                    } else {
                        handled_exceptions.push(type_);
                    }
                }
            }
        }
    }
    handled_exceptions
}

/// Given an [`Expr`] that can be callable or not (like a decorator, which could
/// be used with or without explicit call syntax), return the underlying
/// callable.
pub fn map_callable(decorator: &Expr) -> &Expr {
    if let Expr::Call(ast::ExprCall { func, .. }) = decorator {
        // Ex) `@decorator()`
        func
    } else {
        // Ex) `@decorator`
        decorator
    }
}

/// Given an [`Expr`] that can be a [`ExprSubscript`][ast::ExprSubscript] or not
/// (like an annotation that may be generic or not), return the underlying expr.
pub fn map_subscript(expr: &Expr) -> &Expr {
    if let Expr::Subscript(ast::ExprSubscript { value, .. }) = expr {
        // Ex) `Iterable[T]`  => return `Iterable`
        value
    } else {
        // Ex) `Iterable`  => return `Iterable`
        expr
    }
}

/// Given an [`Expr`] that can be starred, return the underlying starred expression.
pub fn map_starred(expr: &Expr) -> &Expr {
    if let Expr::Starred(ast::ExprStarred { value, .. }) = expr {
        // Ex) `*args`
        value
    } else {
        // Ex) `args`
        expr
    }
}

/// Return `true` if the body uses `locals()`, `globals()`, `vars()`, `eval()`.
///
/// Accepts a closure that determines whether a given name (e.g., `"list"`) is a Python builtin.
pub fn uses_magic_variable_access<F>(body: &[Stmt], is_builtin: F) -> bool
where
    F: Fn(&str) -> bool,
{
    any_over_body(body, |expr| {
        if let Expr::Call(ast::ExprCall { func, .. }) = expr {
            if let Expr::Name(ast::ExprName { id, .. }) = func.as_ref() {
                if matches!(id.as_str(), "locals" | "globals" | "vars" | "exec" | "eval") {
                    if is_builtin(id.as_str()) {
                        return true;
                    }
                }
            }
        }
        false
    })
}

/// Format the module reference name for a relative import.
///
/// # Examples
///
/// ```rust
/// # use ruff_python_ast::helpers::format_import_from;
///
/// assert_eq!(format_import_from(0, None), "".to_string());
/// assert_eq!(format_import_from(1, None), ".".to_string());
/// assert_eq!(format_import_from(1, Some("foo")), ".foo".to_string());
/// ```
pub fn format_import_from(level: u32, module: Option<&str>) -> Cow<'_, str> {
    match (level, module) {
        (0, Some(module)) => Cow::Borrowed(module),
        (level, module) => {
            let mut module_name =
                String::with_capacity((level as usize) + module.map_or(0, str::len));
            for _ in 0..level {
                module_name.push('.');
            }
            if let Some(module) = module {
                module_name.push_str(module);
            }
            Cow::Owned(module_name)
        }
    }
}

/// Format the member reference name for a relative import.
///
/// # Examples
///
/// ```rust
/// # use ruff_python_ast::helpers::format_import_from_member;
///
/// assert_eq!(format_import_from_member(0, None, "bar"), "bar".to_string());
/// assert_eq!(format_import_from_member(1, None, "bar"), ".bar".to_string());
/// assert_eq!(format_import_from_member(1, Some("foo"), "bar"), ".foo.bar".to_string());
/// ```
pub fn format_import_from_member(level: u32, module: Option<&str>, member: &str) -> String {
    let mut qualified_name =
        String::with_capacity((level as usize) + module.map_or(0, str::len) + 1 + member.len());
    if level > 0 {
        for _ in 0..level {
            qualified_name.push('.');
        }
    }
    if let Some(module) = module {
        qualified_name.push_str(module);
        qualified_name.push('.');
    }
    qualified_name.push_str(member);
    qualified_name
}

/// Create a module path from a (package, path) pair.
///
/// For example, if the package is `foo/bar` and the path is `foo/bar/baz.py`,
/// the call path is `["baz"]`.
pub fn to_module_path(package: &Path, path: &Path) -> Option<Vec<String>> {
    path.strip_prefix(package.parent()?)
        .ok()?
        .iter()
        .map(Path::new)
        .map(Path::file_stem)
        .map(|path| path.and_then(|path| path.to_os_string().into_string().ok()))
        .collect::<Option<Vec<String>>>()
}

/// Format the call path for a relative import.
///
/// # Examples
///
/// ```rust
/// # use ruff_python_ast::helpers::collect_import_from_member;
///
/// assert_eq!(collect_import_from_member(0, None, "bar").segments(), ["bar"]);
/// assert_eq!(collect_import_from_member(1, None, "bar").segments(), [".", "bar"]);
/// assert_eq!(collect_import_from_member(1, Some("foo"), "bar").segments(), [".", "foo", "bar"]);
/// ```
pub fn collect_import_from_member<'a>(
    level: u32,
    module: Option<&'a str>,
    member: &'a str,
) -> QualifiedName<'a> {
    let mut qualified_name_builder = QualifiedNameBuilder::with_capacity(
        level as usize
            + module
                .map(|module| module.split('.').count())
                .unwrap_or_default()
            + 1,
    );

    // Include the dots as standalone segments.
    if level > 0 {
        for _ in 0..level {
            qualified_name_builder.push(".");
        }
    }

    // Add the remaining segments.
    if let Some(module) = module {
        qualified_name_builder.extend(module.split('.'));
    }

    // Add the member.
    qualified_name_builder.push(member);

    qualified_name_builder.build()
}

/// Format the call path for a relative import, or `None` if the relative import extends beyond
/// the root module.
pub fn from_relative_import<'a>(
    // The path from which the import is relative.
    module: &'a [String],
    // The path of the import itself (e.g., given `from ..foo import bar`, `[".", ".", "foo", "bar]`).
    import: &[&'a str],
    // The remaining segments to the call path (e.g., given `bar.baz`, `["baz"]`).
    tail: &[&'a str],
) -> Option<QualifiedName<'a>> {
    let mut qualified_name_builder =
        QualifiedNameBuilder::with_capacity(module.len() + import.len() + tail.len());

    // Start with the module path.
    qualified_name_builder.extend(module.iter().map(String::as_str));

    // Remove segments based on the number of dots.
    for segment in import {
        if *segment == "." {
            if qualified_name_builder.is_empty() {
                return None;
            }
            qualified_name_builder.pop();
        } else {
            qualified_name_builder.push(segment);
        }
    }

    // Add the remaining segments.
    qualified_name_builder.extend_from_slice(tail);

    Some(qualified_name_builder.build())
}

/// Given an imported module (based on its relative import level and module name), return the
/// fully-qualified module path.
pub fn resolve_imported_module_path<'a>(
    level: u32,
    module: Option<&'a str>,
    module_path: Option<&[String]>,
) -> Option<Cow<'a, str>> {
    if level == 0 {
        return Some(Cow::Borrowed(module.unwrap_or("")));
    }

    let module_path = module_path?;

    if level as usize >= module_path.len() {
        return None;
    }

    let mut qualified_path = module_path[..module_path.len() - level as usize].join(".");
    if let Some(module) = module {
        if !qualified_path.is_empty() {
            qualified_path.push('.');
        }
        qualified_path.push_str(module);
    }
    Some(Cow::Owned(qualified_path))
}

/// A [`Visitor`] to collect all [`Expr::Name`] nodes in an AST.
#[derive(Debug, Default)]
pub struct NameFinder<'a> {
    /// A map from identifier to defining expression.
    pub names: FxHashMap<&'a str, &'a ast::ExprName>,
}

impl<'a> Visitor<'a> for NameFinder<'a> {
    fn visit_expr(&mut self, expr: &'a Expr) {
        if let Expr::Name(name) = expr {
            self.names.insert(&name.id, name);
        }
        crate::visitor::walk_expr(self, expr);
    }
}

/// A [`Visitor`] to collect all stored [`Expr::Name`] nodes in an AST.
#[derive(Debug, Default)]
pub struct StoredNameFinder<'a> {
    /// A map from identifier to defining expression.
    pub names: FxHashMap<&'a str, &'a ast::ExprName>,
}

impl<'a> Visitor<'a> for StoredNameFinder<'a> {
    fn visit_expr(&mut self, expr: &'a Expr) {
        if let Expr::Name(name) = expr {
            if name.ctx.is_store() {
                self.names.insert(&name.id, name);
            }
        }
        crate::visitor::walk_expr(self, expr);
    }
}

/// A [`Visitor`] that collects all `return` statements in a function or method.
#[derive(Default)]
pub struct ReturnStatementVisitor<'a> {
    pub returns: Vec<&'a ast::StmtReturn>,
    pub is_generator: bool,
}

impl<'a> Visitor<'a> for ReturnStatementVisitor<'a> {
    fn visit_stmt(&mut self, stmt: &'a Stmt) {
        match stmt {
            Stmt::FunctionDef(_) | Stmt::ClassDef(_) => {
                // Don't recurse.
            }
            Stmt::Return(stmt) => self.returns.push(stmt),
            _ => crate::visitor::walk_stmt(self, stmt),
        }
    }

    fn visit_expr(&mut self, expr: &'a Expr) {
        if let Expr::Yield(_) | Expr::YieldFrom(_) = expr {
            self.is_generator = true;
        } else {
            crate::visitor::walk_expr(self, expr);
        }
    }
}

/// A [`StatementVisitor`] that collects all `raise` statements in a function or method.
#[derive(Default)]
pub struct RaiseStatementVisitor<'a> {
    pub raises: Vec<(TextRange, Option<&'a Expr>, Option<&'a Expr>)>,
}

impl<'a> StatementVisitor<'a> for RaiseStatementVisitor<'a> {
    fn visit_stmt(&mut self, stmt: &'a Stmt) {
        match stmt {
            Stmt::Raise(ast::StmtRaise {
                exc,
                cause,
                range: _,
                node_index: _,
            }) => {
                self.raises
                    .push((stmt.range(), exc.as_deref(), cause.as_deref()));
            }
            Stmt::ClassDef(_) | Stmt::FunctionDef(_) | Stmt::Try(_) => {}
            Stmt::If(ast::StmtIf {
                body,
                elif_else_clauses,
                ..
            }) => {
                crate::statement_visitor::walk_body(self, body);
                for clause in elif_else_clauses {
                    self.visit_elif_else_clause(clause);
                }
            }
            Stmt::While(ast::StmtWhile { body, .. })
            | Stmt::With(ast::StmtWith { body, .. })
            | Stmt::For(ast::StmtFor { body, .. }) => {
                crate::statement_visitor::walk_body(self, body);
            }
            Stmt::Match(ast::StmtMatch { cases, .. }) => {
                for case in cases {
                    crate::statement_visitor::walk_body(self, &case.body);
                }
            }
            _ => {}
        }
    }
}

/// A [`Visitor`] that detects the presence of `await` expressions in the current scope.
#[derive(Debug, Default)]
pub struct AwaitVisitor {
    pub seen_await: bool,
}

impl Visitor<'_> for AwaitVisitor {
    fn visit_stmt(&mut self, stmt: &Stmt) {
        match stmt {
            Stmt::FunctionDef(_) | Stmt::ClassDef(_) => (),
            Stmt::With(ast::StmtWith { is_async: true, .. }) => {
                self.seen_await = true;
            }
            Stmt::For(ast::StmtFor { is_async: true, .. }) => {
                self.seen_await = true;
            }
            _ => crate::visitor::walk_stmt(self, stmt),
        }
    }

    fn visit_expr(&mut self, expr: &Expr) {
        if let Expr::Await(ast::ExprAwait { .. }) = expr {
            self.seen_await = true;
        } else {
            crate::visitor::walk_expr(self, expr);
        }
    }

    fn visit_comprehension(&mut self, comprehension: &'_ crate::Comprehension) {
        if comprehension.is_async {
            self.seen_await = true;
        } else {
            crate::visitor::walk_comprehension(self, comprehension);
        }
    }
}

/// Return `true` if a `Stmt` is a docstring.
pub fn is_docstring_stmt(stmt: &Stmt) -> bool {
    if let Stmt::Expr(ast::StmtExpr {
        value,
        range: _,
        node_index: _,
    }) = stmt
    {
        value.is_string_literal_expr()
    } else {
        false
    }
}

/// Returns `true` if all statements in `body` are `pass` or `...` (ellipsis)
///
/// An empty body (`[]`) returns `false`
pub fn is_stub_body(body: &[Stmt]) -> bool {
    !body.is_empty()
        && body.iter().all(|stmt| match stmt {
            Stmt::Pass(_) => true,
            Stmt::Expr(ast::StmtExpr { value, .. }) => value.is_ellipsis_literal_expr(),
            _ => false,
        })
}

/// Returns `body` without its leading docstring statement, if present.
pub fn body_without_leading_docstring(body: &[Stmt]) -> &[Stmt] {
    match body.split_first() {
        Some((first, rest)) if is_docstring_stmt(first) => rest,
        _ => body,
    }
}

/// Check if a node is part of a conditional branch.
pub fn on_conditional_branch<'a>(parents: &mut impl Iterator<Item = &'a Stmt>) -> bool {
    parents.any(|parent| {
        if matches!(parent, Stmt::If(_) | Stmt::While(_) | Stmt::Match(_)) {
            return true;
        }
        if let Stmt::Expr(ast::StmtExpr {
            value,
            range: _,
            node_index: _,
        }) = parent
        {
            if value.is_if_expr() {
                return true;
            }
        }
        false
    })
}

/// Check if a node is in a nested block.
pub fn in_nested_block<'a>(mut parents: impl Iterator<Item = &'a Stmt>) -> bool {
    parents.any(|parent| {
        matches!(
            parent,
            Stmt::Try(_) | Stmt::If(_) | Stmt::With(_) | Stmt::Match(_)
        )
    })
}

/// Check if a node represents an unpacking assignment.
pub fn is_unpacking_assignment(parent: &Stmt, child: &Expr) -> bool {
    match parent {
        Stmt::With(ast::StmtWith { items, .. }) => items.iter().any(|item| {
            if let Some(optional_vars) = &item.optional_vars {
                if optional_vars.is_tuple_expr() {
                    if any_over_expr(optional_vars, |expr| expr == child) {
                        return true;
                    }
                }
            }
            false
        }),
        Stmt::Assign(ast::StmtAssign { targets, value, .. }) => {
            // In `(a, b) = (1, 2)`, `(1, 2)` is the target, and it is a tuple.
            let value_is_tuple = matches!(
                value.as_ref(),
                Expr::Set(_) | Expr::List(_) | Expr::Tuple(_)
            );
            // In `(a, b) = coords = (1, 2)`, `(a, b)` and `coords` are the targets, and
            // `(a, b)` is a tuple. (We use "tuple" as a placeholder for any
            // unpackable expression.)
            let targets_are_tuples = targets
                .iter()
                .all(|item| matches!(item, Expr::Set(_) | Expr::List(_) | Expr::Tuple(_)));
            // If we're looking at `a` in `(a, b) = coords = (1, 2)`, then we should
            // identify that the current expression is in a tuple.
            let child_in_tuple = targets_are_tuples
                || targets.iter().any(|item| {
                    matches!(item, Expr::Set(_) | Expr::List(_) | Expr::Tuple(_))
                        && any_over_expr(item, |expr| expr == child)
                });

            // If our child is a tuple, and value is not, it's always an unpacking
            // expression. Ex) `x, y = tup`
            if child_in_tuple && !value_is_tuple {
                return true;
            }

            // If our child isn't a tuple, but value is, it's never an unpacking expression.
            // Ex) `coords = (1, 2)`
            if !child_in_tuple && value_is_tuple {
                return false;
            }

            // If our target and the value are both tuples, then it's an unpacking
            // expression assuming there's at least one non-tuple child.
            // Ex) Given `(x, y) = coords = 1, 2`, `(x, y)` is considered an unpacking
            // expression. Ex) Given `(x, y) = (a, b) = 1, 2`, `(x, y)` isn't
            // considered an unpacking expression.
            if child_in_tuple && value_is_tuple {
                return !targets_are_tuples;
            }

            false
        }
        _ => false,
    }
}

#[derive(Copy, Clone, Debug, PartialEq, is_macro::Is)]
pub enum Truthiness {
    /// The expression is `True`.
    True,
    /// The expression is `False`.
    False,
    /// The expression evaluates to a `False`-like value (e.g., `None`, `0`, `[]`, `""`).
    Falsey,
    /// The expression evaluates to a `True`-like value (e.g., `1`, `"foo"`).
    Truthy,
    /// The expression evaluates to `None`.
    None,
    /// The expression evaluates to an unknown value (e.g., a variable `x` of unknown type).
    Unknown,
}

impl Truthiness {
    /// Return the truthiness of an expression.
    pub fn from_expr<F>(expr: &Expr, is_builtin: F) -> Self
    where
        F: Fn(&str) -> bool,
    {
        match expr {
            Expr::Lambda(_) => Self::Truthy,
            Expr::Generator(_) => Self::Truthy,
            Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => {
                if value.is_empty() {
                    Self::Falsey
                } else {
                    Self::Truthy
                }
            }
            Expr::BytesLiteral(ast::ExprBytesLiteral { value, .. }) => {
                if value.is_empty() {
                    Self::Falsey
                } else {
                    Self::Truthy
                }
            }
            Expr::NumberLiteral(ast::ExprNumberLiteral { value, .. }) => match value {
                ast::Number::Int(int) => {
                    if *int == 0 {
                        Self::Falsey
                    } else {
                        Self::Truthy
                    }
                }
                ast::Number::Float(float) => {
                    if *float == 0.0 {
                        Self::Falsey
                    } else {
                        Self::Truthy
                    }
                }
                ast::Number::Complex { real, imag, .. } => {
                    if *real == 0.0 && *imag == 0.0 {
                        Self::Falsey
                    } else {
                        Self::Truthy
                    }
                }
            },
            Expr::BooleanLiteral(ast::ExprBooleanLiteral { value, .. }) => {
                if *value {
                    Self::True
                } else {
                    Self::False
                }
            }
            Expr::NoneLiteral(_) => Self::None,
            Expr::EllipsisLiteral(_) => Self::Truthy,
            Expr::FString(f_string) => {
                if is_empty_f_string(f_string) {
                    Self::Falsey
                } else if is_non_empty_f_string(f_string) {
                    Self::Truthy
                } else {
                    Self::Unknown
                }
            }
            Expr::TString(_) => Self::Truthy,
            Expr::List(ast::ExprList { elts, .. })
            | Expr::Set(ast::ExprSet { elts, .. })
            | Expr::Tuple(ast::ExprTuple { elts, .. }) => {
                if elts.is_empty() {
                    return Self::Falsey;
                }

                if elts.iter().all(Expr::is_starred_expr) {
                    // [*foo] / [*foo, *bar]
                    Self::Unknown
                } else {
                    Self::Truthy
                }
            }
            Expr::Dict(dict) => {
                if dict.is_empty() {
                    return Self::Falsey;
                }

                // If the dict consists only of double-starred items (e.g., {**x, **y}),
                // consider its truthiness unknown. This matches lists/sets/tuples containing
                // only starred elements, which are also Unknown.
                if dict
                    .items
                    .iter()
                    .all(|item| matches!(item, DictItem { key: None, .. }))
                {
                    // {**foo} / {**foo, **bar}
                    Self::Unknown
                } else {
                    Self::Truthy
                }
            }
            Expr::Call(ast::ExprCall {
                func, arguments, ..
            }) => {
                if let Expr::Name(ast::ExprName { id, .. }) = func.as_ref() {
                    if is_iterable_initializer(id.as_str(), |id| is_builtin(id)) {
                        if arguments.is_empty() {
                            // Ex) `list()`
                            Self::Falsey
                        } else if let [argument] = &*arguments.args
                            && arguments.keywords.is_empty()
                        {
                            // Ex) `list([1, 2, 3])`
                            match argument {
                                // Return Unknown for types with definite truthiness that might
                                // result in empty iterables (t-strings and generators) or will
                                // raise a type error (non-iterable types like numbers, booleans,
                                // None, etc.).
                                Expr::NumberLiteral(_)
                                | Expr::BooleanLiteral(_)
                                | Expr::NoneLiteral(_)
                                | Expr::EllipsisLiteral(_)
                                | Expr::TString(_)
                                | Expr::Lambda(_)
                                | Expr::Generator(_) => Self::Unknown,
                                // Recurse for all other types - collections, comprehensions, variables, etc.
                                // StringLiteral, FString, and BytesLiteral recurse because Self::from_expr
                                // correctly handles their truthiness (checking if empty or not).
                                _ => Self::from_expr(argument, is_builtin),
                            }
                        } else {
                            Self::Unknown
                        }
                    } else {
                        Self::Unknown
                    }
                } else {
                    Self::Unknown
                }
            }
            _ => Self::Unknown,
        }
    }

    pub fn into_bool(self) -> Option<bool> {
        match self {
            Self::True | Self::Truthy => Some(true),
            Self::False | Self::Falsey => Some(false),
            Self::None => Some(false),
            Self::Unknown => None,
        }
    }
}

/// Returns `true` if the expression definitely resolves to a non-empty string, when used as an
/// f-string expression, or `false` if the expression may resolve to an empty string.
fn is_non_empty_f_string(expr: &ast::ExprFString) -> bool {
    fn inner(expr: &Expr) -> bool {
        match expr {
            // When stringified, these expressions are always non-empty.
            Expr::Lambda(_) => true,
            Expr::Dict(_) => true,
            Expr::Set(_) => true,
            Expr::ListComp(_) => true,
            Expr::SetComp(_) => true,
            Expr::DictComp(_) => true,
            Expr::NumberLiteral(_) => true,
            Expr::Constant(_) => true,
            Expr::BooleanLiteral(_) => true,
            Expr::NoneLiteral(_) => true,
            Expr::EllipsisLiteral(_) => true,
            Expr::List(_) => true,
            Expr::Tuple(_) => true,
            Expr::TString(_) => true,

            // These expressions must resolve to the inner expression.
            Expr::If(ast::ExprIf { body, orelse, .. }) => inner(body) && inner(orelse),
            Expr::Named(ast::ExprNamed { value, .. }) => inner(value),

            // These expressions are complex. We can't determine whether they're empty or not.
            Expr::BoolOp(ast::ExprBoolOp { .. }) => false,
            Expr::BinOp(ast::ExprBinOp { .. }) => false,
            Expr::UnaryOp(ast::ExprUnaryOp { .. }) => false,
            // Rich comparison methods can return arbitrary objects.
            Expr::Compare(_) => false,
            Expr::Generator(_) => false,
            Expr::Await(_) => false,
            Expr::Yield(_) => false,
            Expr::YieldFrom(_) => false,
            Expr::Call(_) => false,
            Expr::Attribute(_) => false,
            Expr::Subscript(_) => false,
            Expr::Starred(_) => false,
            Expr::Name(_) => false,
            Expr::Slice(_) => false,
            Expr::IpyEscapeCommand(_) => false,

            // These literals may or may not be empty.
            Expr::FString(f_string) => is_non_empty_f_string(f_string),
            // These literals may or may not be empty.
            Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => !value.is_empty(),
            // Confusingly, f"{b""}" renders as the string 'b""', which is non-empty.
            // Therefore, any bytes interpolation is guaranteed non-empty when stringified.
            Expr::BytesLiteral(_) => true,
        }
    }

    expr.value.iter().any(|part| match part {
        ast::FStringPart::Literal(string_literal) => !string_literal.is_empty(),
        ast::FStringPart::FString(f_string) => {
            // The part is a concatenation of elements, so it's guaranteed non-empty if any element is
            f_string.elements.iter().any(|element| match element {
                InterpolatedStringElement::Literal(string_literal) => !string_literal.is_empty(),
                InterpolatedStringElement::Interpolation(f_string) => {
                    f_string.debug_text.is_some()
                        || (f_string.format_spec.is_none() && inner(&f_string.expression))
                }
            })
        }
    })
}

/// Returns `true` if the expression definitely resolves to the empty string, when used as an f-string
/// expression.
pub fn is_empty_f_string(expr: &ast::ExprFString) -> bool {
    fn inner(expr: &Expr) -> bool {
        match expr {
            Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => value.is_empty(),
            // Confusingly, `bool(f"{b""}") == True` even though
            // `bool(b"") == False`. This is because `f"{b""}"`
            // evaluates as the string `'b""'` of length 3.
            Expr::BytesLiteral(_) => false,
            Expr::FString(ast::ExprFString { value, .. }) => {
                is_empty_interpolated_elements(value.elements())
            }
            _ => false,
        }
    }

    fn is_empty_interpolated_elements<'a>(
        mut elements: impl Iterator<Item = &'a InterpolatedStringElement>,
    ) -> bool {
        elements.all(|element| match element {
            InterpolatedStringElement::Literal(ast::InterpolatedStringLiteralElement {
                value,
                ..
            }) => value.is_empty(),
            InterpolatedStringElement::Interpolation(f_string) => {
                f_string.debug_text.is_none()
                    && f_string.conversion.is_none()
                    && f_string.format_spec.is_none()
                    && inner(&f_string.expression)
            }
        })
    }

    expr.value.iter().all(|part| match part {
        ast::FStringPart::Literal(string_literal) => string_literal.is_empty(),
        ast::FStringPart::FString(f_string) => {
            is_empty_interpolated_elements(f_string.elements.iter())
        }
    })
}

pub fn generate_comparison(
    left: &Expr,
    ops: &[CmpOp],
    comparators: &[Expr],
    parent: AnyNodeRef,
    tokens: &Tokens,
    source: &str,
) -> String {
    let start = left.start();
    let end = comparators.last().map_or_else(|| left.end(), Ranged::end);
    let mut contents = String::with_capacity(usize::from(end - start));

    // Add the left side of the comparison.
    contents.push_str(
        &source[parenthesized_range(left.into(), parent, tokens).unwrap_or(left.range())],
    );

    for (op, comparator) in ops.iter().zip(comparators) {
        // Add the operator.
        contents.push_str(match op {
            CmpOp::Eq => " == ",
            CmpOp::NotEq => " != ",
            CmpOp::Lt => " < ",
            CmpOp::LtE => " <= ",
            CmpOp::Gt => " > ",
            CmpOp::GtE => " >= ",
            CmpOp::In => " in ",
            CmpOp::NotIn => " not in ",
            CmpOp::Is => " is ",
            CmpOp::IsNot => " is not ",
        });

        // Add the right side of the comparison.
        contents.push_str(
            &source[parenthesized_range(comparator.into(), parent, tokens)
                .unwrap_or(comparator.range())],
        );
    }

    contents
}

/// Format the expression as a PEP 604-style optional.
pub fn pep_604_optional(expr: &Expr) -> Expr {
    ast::ExprBinOp {
        left: Box::new(expr.clone()),
        op: Operator::BitOr,
        right: Box::new(Expr::NoneLiteral(ExprNoneLiteral::default())),
        range: TextRange::default(),
        node_index: AtomicNodeIndex::NONE,
    }
    .into()
}

/// Format the expressions as a PEP 604-style union.
pub fn pep_604_union(elts: &[Expr]) -> Expr {
    match elts {
        [] => Expr::Tuple(ast::ExprTuple {
            elts: vec![],
            ctx: ExprContext::Load,
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            parenthesized: true,
            runtime_elts: None,
        }),
        [Expr::Tuple(ast::ExprTuple { elts, .. })] => pep_604_union(elts),
        [elt] => elt.clone(),
        [rest @ .., elt] => Expr::BinOp(ast::ExprBinOp {
            left: Box::new(pep_604_union(rest)),
            op: Operator::BitOr,
            right: Box::new(pep_604_union(std::slice::from_ref(elt))),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        }),
    }
}

/// Format the expression as a `typing.Optional`-style optional.
pub fn typing_optional(elt: Expr, binding: Name) -> Expr {
    Expr::Subscript(ast::ExprSubscript {
        value: Box::new(Expr::Name(ast::ExprName {
            id: binding,
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            ctx: ExprContext::Load,
        })),
        slice: Box::new(elt),
        ctx: ExprContext::Load,
        range: TextRange::default(),
        node_index: AtomicNodeIndex::NONE,
    })
}

/// Format the expressions as a `typing.Union`-style union.
///
/// Note: It is a syntax error to have `Union[]` so the caller
/// should ensure that the `elts` argument is nonempty.
pub fn typing_union(elts: &[Expr], binding: Name) -> Expr {
    Expr::Subscript(ast::ExprSubscript {
        value: Box::new(Expr::Name(ast::ExprName {
            id: binding,
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            ctx: ExprContext::Load,
        })),
        slice: Box::new(Expr::Tuple(ast::ExprTuple {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            elts: elts.to_vec(),
            ctx: ExprContext::Load,
            parenthesized: false,
            runtime_elts: None,
        })),
        ctx: ExprContext::Load,
        range: TextRange::default(),
        node_index: AtomicNodeIndex::NONE,
    })
}

/// Determine the indentation level of an own-line comment, defined as the minimum indentation of
/// all comments between the preceding node and the comment, including the comment itself. In
/// other words, we don't allow successive comments to ident _further_ than any preceding comments.
///
/// For example, given:
/// ```python
/// if True:
///     pass
///     # comment
/// ```
///
/// The indentation would be 4, as the comment is indented by 4 spaces.
///
/// Given:
/// ```python
/// if True:
///     pass
/// # comment
/// else:
///     pass
/// ```
///
/// The indentation would be 0, as the comment is not indented at all.
///
/// Given:
/// ```python
/// if True:
///     pass
///     # comment
///         # comment
/// ```
///
/// Both comments would be marked as indented at 4 spaces, as the indentation of the first comment
/// is used for the second comment.
///
/// This logic avoids pathological cases like:
/// ```python
/// try:
///     if True:
///         if True:
///             pass
///
///         # a
///             # b
///         # c
/// except Exception:
///     pass
/// ```
///
/// If we don't use the minimum indentation of any preceding comments, we would mark `# b` as
/// indented to the same depth as `pass`, which could in turn lead to us treating it as a trailing
/// comment of `pass`, despite there being a comment between them that "resets" the indentation.
pub fn comment_indentation_after(
    preceding: AnyNodeRef,
    comment_range: TextRange,
    source: &str,
) -> TextSize {
    let tokenizer = SimpleTokenizer::new(
        source,
        TextRange::new(source.full_line_end(preceding.end()), comment_range.end()),
    );

    tokenizer
        .filter_map(|token| {
            if token.kind() == SimpleTokenKind::Comment {
                indentation_at_offset(token.start(), source).map(TextLen::text_len)
            } else {
                None
            }
        })
        .min()
        .unwrap_or_default()
}

pub fn is_dotted_name(expr: &ast::Expr) -> bool {
    match expr {
        ast::Expr::Name(_) => true,
        ast::Expr::Attribute(ast::ExprAttribute { value, .. }) => is_dotted_name(value),
        _ => false,
    }
}

#[cfg(test)]
mod tests {
    use std::borrow::Cow;
    use std::cell::RefCell;
    use std::vec;

    use ruff_text_size::TextRange;

    use crate::helpers::{any_over_stmt, any_over_type_param, resolve_imported_module_path};
    use crate::{
        AtomicNodeIndex, Expr, ExprContext, ExprName, ExprNumberLiteral, Identifier, Int, Number,
        Stmt, StmtTypeAlias, TypeParam, TypeParamParamSpec, TypeParamTypeVar,
        TypeParamTypeVarTuple, TypeParams,
    };

    #[test]
    fn resolve_import() {
        // Return the module directly.
        assert_eq!(
            resolve_imported_module_path(0, Some("foo"), None),
            Some(Cow::Borrowed("foo"))
        );

        // Construct the module path from the calling module's path.
        assert_eq!(
            resolve_imported_module_path(
                1,
                Some("foo"),
                Some(&["bar".to_string(), "baz".to_string()])
            ),
            Some(Cow::Owned("bar.foo".to_string()))
        );

        // We can't return the module if it's a relative import, and we don't know the calling
        // module's path.
        assert_eq!(resolve_imported_module_path(1, Some("foo"), None), None);

        // We can't return the module if it's a relative import, and the path goes beyond the
        // calling module's path.
        assert_eq!(
            resolve_imported_module_path(1, Some("foo"), Some(&["bar".to_string()])),
            None,
        );
        assert_eq!(
            resolve_imported_module_path(2, Some("foo"), Some(&["bar".to_string()])),
            None
        );
    }

    #[test]
    fn any_over_stmt_type_alias() {
        let seen = RefCell::new(Vec::new());
        let name = Expr::Name(ExprName {
            id: "x".into(),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            ctx: ExprContext::Load,
        });
        let constant_one = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::from(1u8)),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });
        let constant_two = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::from(2u8)),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });
        let constant_three = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::from(3u8)),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });
        let type_var_one = TypeParam::TypeVar(TypeParamTypeVar {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            bound: Some(Box::new(constant_one.clone())),
            default: None,
            name: Identifier::new("x", TextRange::default()),
        });
        let type_var_two = TypeParam::TypeVar(TypeParamTypeVar {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            bound: None,
            default: Some(Box::new(constant_two.clone())),
            name: Identifier::new("x", TextRange::default()),
        });
        let type_alias = Stmt::TypeAlias(StmtTypeAlias {
            name: Box::new(name.clone()),
            type_params: Some(Box::new(TypeParams {
                type_params: vec![type_var_one, type_var_two],
                range: TextRange::default(),
                node_index: AtomicNodeIndex::NONE,
                runtime_type_params: None,
            })),
            value: Box::new(constant_three.clone()),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });
        assert!(!any_over_stmt(&type_alias, |expr| {
            seen.borrow_mut().push(expr.clone());
            false
        }));
        assert_eq!(
            seen.take(),
            vec![name, constant_one, constant_two, constant_three]
        );
    }

    #[test]
    fn any_over_type_param_type_var() {
        let type_var_no_bound = TypeParam::TypeVar(TypeParamTypeVar {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            bound: None,
            default: None,
            name: Identifier::new("x", TextRange::default()),
        });
        assert!(!any_over_type_param(&type_var_no_bound, &mut |_expr| true));

        let constant = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::ONE),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });

        let type_var_with_bound = TypeParam::TypeVar(TypeParamTypeVar {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            bound: Some(Box::new(constant.clone())),
            default: None,
            name: Identifier::new("x", TextRange::default()),
        });
        assert!(
            any_over_type_param(&type_var_with_bound, &mut |expr| {
                assert_eq!(
                    *expr, constant,
                    "the received expression should be the unwrapped bound"
                );
                true
            }),
            "if true is returned from `func` it should be respected"
        );

        let type_var_with_default = TypeParam::TypeVar(TypeParamTypeVar {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            default: Some(Box::new(constant.clone())),
            bound: None,
            name: Identifier::new("x", TextRange::default()),
        });
        assert!(
            any_over_type_param(&type_var_with_default, &mut |expr| {
                assert_eq!(
                    *expr, constant,
                    "the received expression should be the unwrapped default"
                );
                true
            }),
            "if true is returned from `func` it should be respected"
        );
    }

    #[test]
    fn any_over_type_param_type_var_tuple() {
        let type_var_tuple = TypeParam::TypeVarTuple(TypeParamTypeVarTuple {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            name: Identifier::new("x", TextRange::default()),
            default: None,
        });
        assert!(
            !any_over_type_param(&type_var_tuple, &mut |_expr| true),
            "this TypeVarTuple has no expressions to visit"
        );

        let constant = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::ONE),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });

        let type_var_tuple_with_default = TypeParam::TypeVarTuple(TypeParamTypeVarTuple {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            default: Some(Box::new(constant.clone())),
            name: Identifier::new("x", TextRange::default()),
        });
        assert!(
            any_over_type_param(&type_var_tuple_with_default, &mut |expr| {
                assert_eq!(
                    *expr, constant,
                    "the received expression should be the unwrapped default"
                );
                true
            }),
            "if true is returned from `func` it should be respected"
        );
    }

    #[test]
    fn any_over_type_param_param_spec() {
        let type_param_spec = TypeParam::ParamSpec(TypeParamParamSpec {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            name: Identifier::new("x", TextRange::default()),
            default: None,
        });
        assert!(
            !any_over_type_param(&type_param_spec, &mut |_expr| true),
            "this ParamSpec has no expressions to visit"
        );

        let constant = Expr::NumberLiteral(ExprNumberLiteral {
            value: Number::Int(Int::ONE),
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
        });

        let param_spec_with_default = TypeParam::TypeVarTuple(TypeParamTypeVarTuple {
            range: TextRange::default(),
            node_index: AtomicNodeIndex::NONE,
            default: Some(Box::new(constant.clone())),
            name: Identifier::new("x", TextRange::default()),
        });
        assert!(
            any_over_type_param(&param_spec_with_default, &mut |expr| {
                assert_eq!(
                    *expr, constant,
                    "the received expression should be the unwrapped default"
                );
                true
            }),
            "if true is returned from `func` it should be respected"
        );
    }
}