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             span_lint_and_help(
  19                 cx,
  20                 BOX_COLLECTION,
  21                 hir_ty.span,
  22                 &format!(
  23                     "you seem to be trying to use `Box<{outer}{generic}>`. Consider using just `{outer}{generic}`",
  24                     outer=item_type,
  25                     generic = generic),
  26                 None,
  27                 &format!(
  28                     "`{outer}{generic}` is already on the heap, `Box<{outer}{generic}>` makes an extra allocation",
  29                     outer=item_type,
  30                     generic = generic)
  31             );
  32             true
  33         } else {
  34             false
  35         }
  36     }
  37 }
  38
  39 fn get_std_collection(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Symbol> {
  40     let param = qpath_generic_tys(qpath).next()?;
  41     let id = path_def_id(cx, param)?;
  42     cx.tcx
  43         .get_diagnostic_name(id)
  44         .filter(|&name| matches!(name, sym::HashMap | sym::String | sym::Vec))
  45 }