src/tools/clippy/clippy_lints/src/panic_in_result_fn.rs

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