clippy_lints/src/functions/result_unit_err.rs

   1 use rustc_hir as hir;
   2 use rustc_lint::{LateContext, LintContext};
   3 use rustc_middle::lint::in_external_macro;
   4 use rustc_middle::ty;
   5 use rustc_span::{sym, Span};
   6 use rustc_typeck::hir_ty_to_ty;
   7
   8 use if_chain::if_chain;
   9
  10 use clippy_utils::diagnostics::span_lint_and_help;
  11 use clippy_utils::trait_ref_of_method;
  12 use clippy_utils::ty::is_type_diagnostic_item;
  13
  14 use super::RESULT_UNIT_ERR;
  15
  16 pub(super) fn check_item(cx: &LateContext<'_>, item: &hir::Item<'_>) {
  17     if let hir::ItemKind::Fn(ref sig, ref _generics, _) = item.kind {
  18         let is_public = cx.access_levels.is_exported(item.def_id);
  19         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
  20         if is_public {
  21             check_result_unit_err(cx, sig.decl, item.span, fn_header_span);
  22         }
  23     }
  24 }
  25
  26 pub(super) fn check_impl_item(cx: &LateContext<'_>, item: &hir::ImplItem<'_>) {
  27     if let hir::ImplItemKind::Fn(ref sig, _) = item.kind {
  28         let is_public = cx.access_levels.is_exported(item.def_id);
  29         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
  30         if is_public && trait_ref_of_method(cx, item.hir_id()).is_none() {
  31             check_result_unit_err(cx, sig.decl, item.span, fn_header_span);
  32         }
  33     }
  34 }
  35
  36 pub(super) fn check_trait_item(cx: &LateContext<'_>, item: &hir::TraitItem<'_>) {
  37     if let hir::TraitItemKind::Fn(ref sig, _) = item.kind {
  38         let is_public = cx.access_levels.is_exported(item.def_id);
  39         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
  40         if is_public {
  41             check_result_unit_err(cx, sig.decl, item.span, fn_header_span);
  42         }
  43     }
  44 }
  45
  46 fn check_result_unit_err(cx: &LateContext<'_>, decl: &hir::FnDecl<'_>, item_span: Span, fn_header_span: Span) {
  47     if_chain! {
  48         if !in_external_macro(cx.sess(), item_span);
  49         if let hir::FnRetTy::Return(ty) = decl.output;
  50         let ty = hir_ty_to_ty(cx.tcx, ty);
  51         if is_type_diagnostic_item(cx, ty, sym::Result);
  52         if let ty::Adt(_, substs) = ty.kind();
  53         let err_ty = substs.type_at(1);
  54         if err_ty.is_unit();
  55         then {
  56             span_lint_and_help(
  57                 cx,
  58                 RESULT_UNIT_ERR,
  59                 fn_header_span,
  60                 "this returns a `Result<_, ()>`",
  61                 None,
  62                 "use a custom `Error` type instead",
  63             );
  64         }
  65     }
  66 }