src/tools/clippy/clippy_lints/src/types/vec_box.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::last_path_segment;
   3 use clippy_utils::source::snippet;
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{self as hir, def_id::DefId, GenericArg, QPath, TyKind};
   7 use rustc_hir_analysis::hir_ty_to_ty;
   8 use rustc_lint::LateContext;
   9 use rustc_middle::ty::layout::LayoutOf;
  10 use rustc_middle::ty::TypeVisitable;
  11 use rustc_span::symbol::sym;
  12
  13 use super::VEC_BOX;
  14
  15 pub(super) fn check(
  16     cx: &LateContext<'_>,
  17     hir_ty: &hir::Ty<'_>,
  18     qpath: &QPath<'_>,
  19     def_id: DefId,
  20     box_size_threshold: u64,
  21 ) -> bool {
  22     if cx.tcx.is_diagnostic_item(sym::Vec, def_id) {
  23         if_chain! {
  24             // Get the _ part of Vec<_>
  25             if let Some(last) = last_path_segment(qpath).args;
  26             if let Some(ty) = last.args.iter().find_map(|arg| match arg {
  27                 GenericArg::Type(ty) => Some(ty),
  28                 _ => None,
  29             });
  30             // ty is now _ at this point
  31             if let TyKind::Path(ref ty_qpath) = ty.kind;
  32             let res = cx.qpath_res(ty_qpath, ty.hir_id);
  33             if let Some(def_id) = res.opt_def_id();
  34             if Some(def_id) == cx.tcx.lang_items().owned_box();
  35             // At this point, we know ty is Box<T>, now get T
  36             if let Some(last) = last_path_segment(ty_qpath).args;
  37             if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
  38                 GenericArg::Type(ty) => Some(ty),
  39                 _ => None,
  40             });
  41             let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
  42             if !ty_ty.has_escaping_bound_vars();
  43             if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
  44             if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
  45             if ty_ty_size <= box_size_threshold;
  46             then {
  47                 span_lint_and_sugg(
  48                     cx,
  49                     VEC_BOX,
  50                     hir_ty.span,
  51                     "`Vec<T>` is already on the heap, the boxing is unnecessary",
  52                     "try",
  53                     format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
  54                     Applicability::MachineApplicable,
  55                 );
  56                 true
  57             } else {
  58                 false
  59             }
  60         }
  61     } else {
  62         false
  63     }
  64 }