clippy_lints/src/types/box_collection.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::is_ty_param_diagnostic_item;
   3 use rustc_hir::{self as hir, def_id::DefId, QPath};
   4 use rustc_lint::LateContext;
   5 use rustc_span::symbol::sym;
   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 = if item_type == "String" {
  15                 ""
  16             } else {
  17                 "<..>"
  18             };
  19             span_lint_and_help(
  20                 cx,
  21                 BOX_COLLECTION,
  22                 hir_ty.span,
  23                 &format!(
  24                     "you seem to be trying to use `Box<{outer}{generic}>`. Consider using just `{outer}{generic}`",
  25                     outer=item_type,
  26                     generic = generic),
  27                 None,
  28                 &format!(
  29                     "`{outer}{generic}` is already on the heap, `Box<{outer}{generic}>` makes an extra allocation",
  30                     outer=item_type,
  31                     generic = generic)
  32             );
  33             true
  34         } else {
  35             false
  36         }
  37     }
  38 }
  39
  40 fn get_std_collection(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<&'static str> {
  41     if is_ty_param_diagnostic_item(cx, qpath, sym::Vec).is_some() {
  42         Some("Vec")
  43     } else if is_ty_param_diagnostic_item(cx, qpath, sym::String).is_some() {
  44         Some("String")
  45     } else if is_ty_param_diagnostic_item(cx, qpath, sym::HashMap).is_some() {
  46         Some("HashMap")
  47     } else {
  48         None
  49     }
  50 }