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

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::{snippet, snippet_with_applicability};
   3 use clippy_utils::{path_def_id, qpath_generic_tys};
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{self as hir, def_id::DefId, QPath, TyKind};
   6 use rustc_lint::LateContext;
   7 use rustc_span::symbol::sym;
   8
   9 use super::{utils, REDUNDANT_ALLOCATION};
  10
  11 pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_>, def_id: DefId) -> bool {
  12     let outer_sym = if Some(def_id) == cx.tcx.lang_items().owned_box() {
  13         "Box"
  14     } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
  15         "Rc"
  16     } else if cx.tcx.is_diagnostic_item(sym::Arc, def_id) {
  17         "Arc"
  18     } else {
  19         return false;
  20     };
  21
  22     if let Some(span) = utils::match_borrows_parameter(cx, qpath) {
  23         let mut applicability = Applicability::MaybeIncorrect;
  24         let generic_snippet = snippet_with_applicability(cx, span, "..", &mut applicability);
  25         span_lint_and_then(
  26             cx,
  27             REDUNDANT_ALLOCATION,
  28             hir_ty.span,
  29             &format!("usage of `{}<{}>`", outer_sym, generic_snippet),
  30             |diag| {
  31                 diag.span_suggestion(hir_ty.span, "try", format!("{}", generic_snippet), applicability);
  32                 diag.note(&format!(
  33                     "`{generic}` is already a pointer, `{outer}<{generic}>` allocates a pointer on the heap",
  34                     outer = outer_sym,
  35                     generic = generic_snippet
  36                 ));
  37             },
  38         );
  39         return true;
  40     }
  41
  42     let Some(ty) = qpath_generic_tys(qpath).next() else { return false };
  43     let Some(id) = path_def_id(cx, ty) else { return false };
  44     let (inner_sym, ty) = match cx.tcx.get_diagnostic_name(id) {
  45         Some(sym::Arc) => ("Arc", ty),
  46         Some(sym::Rc) => ("Rc", ty),
  47         _ if Some(id) == cx.tcx.lang_items().owned_box() => ("Box", ty),
  48         _ => return false,
  49     };
  50
  51     let inner_qpath = match &ty.kind {
  52         TyKind::Path(inner_qpath) => inner_qpath,
  53         _ => return false,
  54     };
  55     let inner_span = match qpath_generic_tys(inner_qpath).next() {
  56         Some(ty) => {
  57             // Box<Box<dyn T>> is smaller than Box<dyn T> because of wide pointers
  58             if matches!(ty.kind, TyKind::TraitObject(..)) {
  59                 return false;
  60             }
  61             ty.span
  62         },
  63         None => return false,
  64     };
  65     if inner_sym == outer_sym {
  66         let mut applicability = Applicability::MaybeIncorrect;
  67         let generic_snippet = snippet_with_applicability(cx, inner_span, "..", &mut applicability);
  68         span_lint_and_then(
  69             cx,
  70             REDUNDANT_ALLOCATION,
  71             hir_ty.span,
  72             &format!("usage of `{}<{}<{}>>`", outer_sym, inner_sym, generic_snippet),
  73             |diag| {
  74                 diag.span_suggestion(
  75                     hir_ty.span,
  76                     "try",
  77                     format!("{}<{}>", outer_sym, generic_snippet),
  78                     applicability,
  79                 );
  80                 diag.note(&format!(
  81                     "`{inner}<{generic}>` is already on the heap, `{outer}<{inner}<{generic}>>` makes an extra allocation",
  82                     outer = outer_sym,
  83                     inner = inner_sym,
  84                     generic = generic_snippet
  85                 ));
  86             },
  87         );
  88     } else {
  89         let generic_snippet = snippet(cx, inner_span, "..");
  90         span_lint_and_then(
  91             cx,
  92             REDUNDANT_ALLOCATION,
  93             hir_ty.span,
  94             &format!("usage of `{}<{}<{}>>`", outer_sym, inner_sym, generic_snippet),
  95             |diag| {
  96                 diag.note(&format!(
  97                     "`{inner}<{generic}>` is already on the heap, `{outer}<{inner}<{generic}>>` makes an extra allocation",
  98                     outer = outer_sym,
  99                     inner = inner_sym,
 100                     generic = generic_snippet
 101                 ));
 102                 diag.help(&format!(
 103                     "consider using just `{outer}<{generic}>` or `{inner}<{generic}>`",
 104                     outer = outer_sym,
 105                     inner = inner_sym,
 106                     generic = generic_snippet
 107                 ));
 108             },
 109         );
 110     }
 111     true
 112 }