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

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_opt;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::LateContext;
use rustc_middle::mir::Mutability;
use rustc_middle::ty::{self, Ty, TypeAndMut};

use super::AS_PTR_CAST_MUT;

pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_to: Ty<'_>) {
    if let ty::RawPtr(
        ptrty @ TypeAndMut {
            mutbl: Mutability::Mut, ..
        },
    ) = cast_to.kind()
        && let ty::RawPtr(TypeAndMut {
            mutbl: Mutability::Not, ..
        }) = cx.typeck_results().node_type(cast_expr.hir_id).kind()
        && let ExprKind::MethodCall(method_name, receiver, [], _) = cast_expr.peel_blocks().kind
        && method_name.ident.name == rustc_span::sym::as_ptr
        && let Some(as_ptr_did) = cx
            .typeck_results()
            .type_dependent_def_id(cast_expr.peel_blocks().hir_id)
        && let as_ptr_sig = cx.tcx.fn_sig(as_ptr_did).instantiate_identity()
        && let Some(first_param_ty) = as_ptr_sig.skip_binder().inputs().iter().next()
        && let ty::Ref(_, _, Mutability::Not) = first_param_ty.kind()
        && let Some(recv) = snippet_opt(cx, receiver.span)
    {
        // `as_mut_ptr` might not exist
        let applicability = Applicability::MaybeIncorrect;

        span_lint_and_sugg(
            cx,
            AS_PTR_CAST_MUT,
            expr.span,
            &format!("casting the result of `as_ptr` to *{ptrty}"),
            "replace with",
            format!("{recv}.as_mut_ptr()"),
            applicability,
        );
    }
}