clippy_lints/src/casts/fn_to_numeric_cast.rs

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use rustc_errors::Applicability;
use rustc_hir::Expr;
use rustc_lint::LateContext;
use rustc_middle::ty::Ty;

use super::{FN_TO_NUMERIC_CAST, utils};

pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
    // We only want to check casts to `ty::Uint` or `ty::Int`
    let Some(to_nbits) = utils::int_ty_to_nbits(cx.tcx, cast_to) else {
        return;
    };

    if cast_from.is_fn() {
        let mut applicability = Applicability::MaybeIncorrect;

        if to_nbits >= cx.tcx.data_layout.pointer_size().bits() && !cast_to.is_usize() {
            let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
            span_lint_and_sugg(
                cx,
                FN_TO_NUMERIC_CAST,
                expr.span,
                format!("casting function pointer `{from_snippet}` to `{cast_to}`"),
                "try",
                format!("{from_snippet} as usize"),
                applicability,
            );
        }
    }
}