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

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::{path_def_id, qpath_generic_tys};
   3 use rustc_hir::{self as hir, def_id::DefId, QPath};
   4 use rustc_lint::LateContext;
   5 use rustc_span::{sym, Symbol};
   6
   7 use super::BOX_COLLECTION;
   8
   9 pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_>, def_id: DefId) -> bool {
  10     if_chain! {
  11         if Some(def_id) == cx.tcx.lang_items().owned_box();
  12         if let Some(item_type) = get_std_collection(cx, qpath);
  13         then {
  14             let generic = match item_type {
  15                 sym::String => "",
  16                 _ => "<..>",
  17             };
  18
  19             let box_content = format!("{item_type}{generic}");
  20             span_lint_and_help(
  21                 cx,
  22                 BOX_COLLECTION,
  23                 hir_ty.span,
  24                 &format!(
  25                     "you seem to be trying to use `Box<{box_content}>`. Consider using just `{box_content}`"),
  26                 None,
  27                 &format!(
  28                     "`{box_content}` is already on the heap, `Box<{box_content}>` makes an extra allocation")
  29             );
  30             true
  31         } else {
  32             false
  33         }
  34     }
  35 }
  36
  37 fn get_std_collection(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Symbol> {
  38     let param = qpath_generic_tys(qpath).next()?;
  39     let id = path_def_id(cx, param)?;
  40     cx.tcx.get_diagnostic_name(id).filter(|&name| {
  41         matches!(
  42             name,
  43             sym::HashMap
  44                 | sym::String
  45                 | sym::Vec
  46                 | sym::HashSet
  47                 | sym::VecDeque
  48                 | sym::LinkedList
  49                 | sym::BTreeMap
  50                 | sym::BTreeSet
  51                 | sym::BinaryHeap
  52         )
  53     })
  54 }