compiler/rustc_lint/src/pass_by_value.rs

   1 use crate::{LateContext, LateLintPass, LintContext};
   2 use rustc_errors::{fluent, Applicability};
   3 use rustc_hir as hir;
   4 use rustc_hir::def::Res;
   5 use rustc_hir::{GenericArg, PathSegment, QPath, TyKind};
   6 use rustc_middle::ty;
   7 use rustc_span::symbol::sym;
   8
   9 declare_tool_lint! {
  10     /// The `rustc_pass_by_value` lint marks a type with `#[rustc_pass_by_value]` requiring it to
  11     /// always be passed by value. This is usually used for types that are thin wrappers around
  12     /// references, so there is no benefit to an extra layer of indirection. (Example: `Ty` which
  13     /// is a reference to an `Interned<TyS>`)
  14     pub rustc::PASS_BY_VALUE,
  15     Warn,
  16     "pass by reference of a type flagged as `#[rustc_pass_by_value]`",
  17     report_in_external_macro: true
  18 }
  19
  20 declare_lint_pass!(PassByValue => [PASS_BY_VALUE]);
  21
  22 impl<'tcx> LateLintPass<'tcx> for PassByValue {
  23     fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx>) {
  24         match &ty.kind {
  25             TyKind::Rptr(_, hir::MutTy { ty: inner_ty, mutbl: hir::Mutability::Not }) => {
  26                 if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
  27                     if cx.tcx.impl_trait_ref(impl_did).is_some() {
  28                         return;
  29                     }
  30                 }
  31                 if let Some(t) = path_for_pass_by_value(cx, &inner_ty) {
  32                     cx.struct_span_lint(
  33                         PASS_BY_VALUE,
  34                         ty.span,
  35                         fluent::lint_pass_by_value,
  36                         |lint| {
  37                             lint.set_arg("ty", t.clone()).span_suggestion(
  38                                 ty.span,
  39                                 fluent::suggestion,
  40                                 t,
  41                                 // Changing type of function argument
  42                                 Applicability::MaybeIncorrect,
  43                             )
  44                         },
  45                     )
  46                 }
  47             }
  48             _ => {}
  49         }
  50     }
  51 }
  52
  53 fn path_for_pass_by_value(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> Option<String> {
  54     if let TyKind::Path(QPath::Resolved(_, path)) = &ty.kind {
  55         match path.res {
  56             Res::Def(_, def_id) if cx.tcx.has_attr(def_id, sym::rustc_pass_by_value) => {
  57                 let name = cx.tcx.item_name(def_id).to_ident_string();
  58                 let path_segment = path.segments.last().unwrap();
  59                 return Some(format!("{}{}", name, gen_args(cx, path_segment)));
  60             }
  61             Res::SelfTyAlias { alias_to: did, is_trait_impl: false, .. } => {
  62                 if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
  63                     if cx.tcx.has_attr(adt.did(), sym::rustc_pass_by_value) {
  64                         return Some(cx.tcx.def_path_str_with_substs(adt.did(), substs));
  65                     }
  66                 }
  67             }
  68             _ => (),
  69         }
  70     }
  71
  72     None
  73 }
  74
  75 fn gen_args(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> String {
  76     if let Some(args) = &segment.args {
  77         let params = args
  78             .args
  79             .iter()
  80             .map(|arg| match arg {
  81                 GenericArg::Lifetime(lt) => lt.name.ident().to_string(),
  82                 GenericArg::Type(ty) => {
  83                     cx.tcx.sess.source_map().span_to_snippet(ty.span).unwrap_or_else(|_| "_".into())
  84                 }
  85                 GenericArg::Const(c) => {
  86                     cx.tcx.sess.source_map().span_to_snippet(c.span).unwrap_or_else(|_| "_".into())
  87                 }
  88                 GenericArg::Infer(_) => String::from("_"),
  89             })
  90             .collect::<Vec<_>>();
  91
  92         if !params.is_empty() {
  93             return format!("<{}>", params.join(", "));
  94         }
  95     }
  96
  97     String::new()
  98 }