rust/src/mem_forget.rs

use rustc::lint::*;
use rustc::hir::{Expr, ExprCall, ExprPath};
use utils::{get_trait_def_id, implements_trait, match_def_path, paths, span_lint};

/// **What it does:** This lint checks for usage of `std::mem::forget(t)` where `t` is `Drop`.
///
/// **Why is this bad?** `std::mem::forget(t)` prevents `t` from running its destructor, possibly causing leaks
///
/// **Known problems:** None.
///
/// **Example:** `mem::forget(Rc::new(55)))`
declare_lint! {
    pub MEM_FORGET,
    Allow,
    "`mem::forget` usage on `Drop` types is likely to cause memory leaks"
}

pub struct MemForget;

impl LintPass for MemForget {
    fn get_lints(&self) -> LintArray {
        lint_array![MEM_FORGET]
    }
}

impl LateLintPass for MemForget {
    fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
        if let ExprCall(ref path_expr, ref args) = e.node {
            if let ExprPath(None, _) = path_expr.node {
                let def_id = cx.tcx.def_map.borrow()[&path_expr.id].def_id();
                if match_def_path(cx, def_id, &paths::MEM_FORGET) {
                    if let Some(drop_trait_id) = get_trait_def_id(cx, &paths::DROP) {
                        let forgot_ty = cx.tcx.expr_ty(&args[0]);

                        if implements_trait(cx, forgot_ty, drop_trait_id, Vec::new()) {
                            span_lint(cx, MEM_FORGET, e.span, "usage of mem::forget on Drop type");
                        }
                    }
                }
            }
        }
    }
}