clippy_lints/src/panic_in_result_fn.rs

   1 use crate::utils::{find_macro_calls, return_ty, span_lint_and_then};
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use rustc_hir as hir;
   4 use rustc_hir::intravisit::FnKind;
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::{sym, Span};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for usage of `panic!`, `unimplemented!`, `todo!`, `unreachable!` or assertions in a function of type result.
  11     ///
  12     /// **Why is this bad?** For some codebases, it is desirable for functions of type result to return an error instead of crashing. Hence panicking macros should be avoided.
  13     ///
  14     /// **Known problems:** Functions called from a function returning a `Result` may invoke a panicking macro. This is not checked.
  15     ///
  16     /// **Example:**
  17     ///
  18     /// ```rust
  19     /// fn result_with_panic() -> Result<bool, String>
  20     /// {
  21     ///     panic!("error");
  22     /// }
  23     /// ```
  24     /// Use instead:
  25     /// ```rust
  26     /// fn result_without_panic() -> Result<bool, String> {
  27     ///     Err(String::from("error"))
  28     /// }
  29     /// ```
  30     pub PANIC_IN_RESULT_FN,
  31     restriction,
  32     "functions of type `Result<..>` that contain `panic!()`, `todo!()`, `unreachable()`, `unimplemented()` or assertion"
  33 }
  34
  35 declare_lint_pass!(PanicInResultFn  => [PANIC_IN_RESULT_FN]);
  36
  37 impl<'tcx> LateLintPass<'tcx> for PanicInResultFn {
  38     fn check_fn(
  39         &mut self,
  40         cx: &LateContext<'tcx>,
  41         fn_kind: FnKind<'tcx>,
  42         _: &'tcx hir::FnDecl<'tcx>,
  43         body: &'tcx hir::Body<'tcx>,
  44         span: Span,
  45         hir_id: hir::HirId,
  46     ) {
  47         if !matches!(fn_kind, FnKind::Closure) && is_type_diagnostic_item(cx, return_ty(cx, hir_id), sym::result_type) {
  48             lint_impl_body(cx, span, body);
  49         }
  50     }
  51 }
  52
  53 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, body: &'tcx hir::Body<'tcx>) {
  54     let panics = find_macro_calls(
  55         &[
  56             "unimplemented",
  57             "unreachable",
  58             "panic",
  59             "todo",
  60             "assert",
  61             "assert_eq",
  62             "assert_ne",
  63             "debug_assert",
  64             "debug_assert_eq",
  65             "debug_assert_ne",
  66         ],
  67         body,
  68     );
  69     if !panics.is_empty() {
  70         span_lint_and_then(
  71             cx,
  72             PANIC_IN_RESULT_FN,
  73             impl_span,
  74             "used `unimplemented!()`, `unreachable!()`, `todo!()`, `panic!()` or assertion in a function that returns `Result`",
  75             move |diag| {
  76                 diag.help(
  77                     "`unimplemented!()`, `unreachable!()`, `todo!()`, `panic!()` or assertions should not be used in a function that returns `Result` as `Result` is expected to return an error instead of crashing",
  78                 );
  79                 diag.span_note(panics, "return Err() instead of panicking");
  80             },
  81         );
  82     }
  83 }