rust/clippy_lints/src/bool_to_int_with_if.rs

use rustc_ast::{ExprPrecedence, LitKind};
use rustc_hir::{Block, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};

use clippy_utils::{diagnostics::span_lint_and_then, is_else_clause, source::snippet_block_with_applicability};
use rustc_errors::Applicability;

declare_clippy_lint! {
    /// ### What it does
    /// Instead of using an if statement to convert a bool to an int,
    /// this lint suggests using a `from()` function or an `as` coercion.
    ///
    /// ### Why is this bad?
    /// Coercion or `from()` is idiomatic way to convert bool to a number.
    /// Both methods are guaranteed to return 1 for true, and 0 for false.
    ///
    /// See https://doc.rust-lang.org/std/primitive.bool.html#impl-From%3Cbool%3E
    ///
    /// ### Example
    /// ```rust
    /// # let condition = false;
    /// if condition {
    ///     1_i64
    /// } else {
    ///     0
    /// };
    /// ```
    /// Use instead:
    /// ```rust
    /// # let condition = false;
    /// i64::from(condition);
    /// ```
    /// or
    /// ```rust
    /// # let condition = false;
    /// condition as i64;
    /// ```
    #[clippy::version = "1.65.0"]
    pub BOOL_TO_INT_WITH_IF,
    style,
    "using if to convert bool to int"
}
declare_lint_pass!(BoolToIntWithIf => [BOOL_TO_INT_WITH_IF]);

impl<'tcx> LateLintPass<'tcx> for BoolToIntWithIf {
    fn check_expr(&mut self, ctx: &LateContext<'tcx>, expr: &'tcx rustc_hir::Expr<'tcx>) {
        if !expr.span.from_expansion() {
            check_if_else(ctx, expr);
        }
    }
}

fn check_if_else<'tcx>(ctx: &LateContext<'tcx>, expr: &'tcx rustc_hir::Expr<'tcx>) {
    if let ExprKind::If(check, then, Some(else_)) = expr.kind
        && let Some(then_lit) = int_literal(then)
        && let Some(else_lit) = int_literal(else_)
        && check_int_literal_equals_val(then_lit, 1)
        && check_int_literal_equals_val(else_lit, 0)
    {
        let mut applicability = Applicability::MachineApplicable;
        let snippet = snippet_block_with_applicability(ctx, check.span, "..", None, &mut applicability);
        let snippet_with_braces = {
            let need_parens = should_have_parentheses(check);
            let (left_paren, right_paren) = if need_parens {("(", ")")} else {("", "")};
            format!("{left_paren}{snippet}{right_paren}")
        };

        let ty = ctx.typeck_results().expr_ty(then_lit); // then and else must be of same type

        let suggestion = {
            let wrap_in_curly = is_else_clause(ctx.tcx, expr);
            let (left_curly, right_curly) = if wrap_in_curly {("{", "}")} else {("", "")};
            format!(
                "{left_curly}{ty}::from({snippet}){right_curly}"
            )
        }; // when used in else clause if statement should be wrapped in curly braces

        span_lint_and_then(ctx,
            BOOL_TO_INT_WITH_IF,
            expr.span,
            "boolean to int conversion using if",
            |diag| {
            diag.span_suggestion(
                expr.span,
                "replace with from",
                suggestion,
                applicability,
            );
            diag.note(format!("`{snippet_with_braces} as {ty}` or `{snippet_with_braces}.into()` can also be valid options"));
        });
    };
}

// If block contains only a int literal expression, return literal expression
fn int_literal<'tcx>(expr: &'tcx rustc_hir::Expr<'tcx>) -> Option<&'tcx rustc_hir::Expr<'tcx>> {
    if let ExprKind::Block(block, _) = expr.kind
        && let Block {
            stmts: [],       // Shouldn't lint if statements with side effects
            expr: Some(expr),
            ..
        } = block
        && let ExprKind::Lit(lit) = &expr.kind
        && let LitKind::Int(_, _) = lit.node
    {
        Some(expr)
    } else {
        None
    }
}

fn check_int_literal_equals_val<'tcx>(expr: &'tcx rustc_hir::Expr<'tcx>, expected_value: u128) -> bool {
    if let ExprKind::Lit(lit) = &expr.kind
        && let LitKind::Int(val, _) = lit.node
        && val == expected_value
    {
        true
    } else {
        false
    }
}

fn should_have_parentheses<'tcx>(check: &'tcx rustc_hir::Expr<'tcx>) -> bool {
    check.precedence().order() < ExprPrecedence::Cast.order()
}