src/tools/clippy/clippy_lints/src/casts/ptr_as_ptr.rs

use clippy_config::msrvs::{self, Msrv};
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::sugg::Sugg;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, Mutability, TyKind};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, TypeAndMut};

use super::PTR_AS_PTR;

pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, msrv: &Msrv) {
    if !msrv.meets(msrvs::POINTER_CAST) {
        return;
    }

    if let ExprKind::Cast(cast_expr, cast_to_hir_ty) = expr.kind
        && let (cast_from, cast_to) = (cx.typeck_results().expr_ty(cast_expr), cx.typeck_results().expr_ty(expr))
        && let ty::RawPtr(TypeAndMut { mutbl: from_mutbl, .. }) = cast_from.kind()
        && let ty::RawPtr(TypeAndMut { ty: to_pointee_ty, mutbl: to_mutbl }) = cast_to.kind()
        && matches!((from_mutbl, to_mutbl),
            (Mutability::Not, Mutability::Not) | (Mutability::Mut, Mutability::Mut))
        // The `U` in `pointer::cast` have to be `Sized`
        // as explained here: https://github.com/rust-lang/rust/issues/60602.
        && to_pointee_ty.is_sized(cx.tcx, cx.param_env)
    {
        let mut app = Applicability::MachineApplicable;
        let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut app);
        let turbofish = match &cast_to_hir_ty.kind {
            TyKind::Infer => String::new(),
            TyKind::Ptr(mut_ty) => {
                if matches!(mut_ty.ty.kind, TyKind::Infer) {
                    String::new()
                } else {
                    format!(
                        "::<{}>",
                        snippet_with_applicability(cx, mut_ty.ty.span, "/* type */", &mut app)
                    )
                }
            },
            _ => return,
        };

        span_lint_and_sugg(
            cx,
            PTR_AS_PTR,
            expr.span,
            "`as` casting between raw pointers without changing its mutability",
            "try `pointer::cast`, a safer alternative",
            format!("{}.cast{turbofish}()", cast_expr_sugg.maybe_par()),
            app,
        );
    }
}