clippy_lints/src/assertions_on_result_states.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::macros::{find_assert_args, root_macro_call_first_node, PanicExpn};
   3 use clippy_utils::path_res;
   4 use clippy_utils::source::snippet_with_context;
   5 use clippy_utils::ty::{implements_trait, is_copy, is_type_diagnostic_item};
   6 use clippy_utils::usage::local_used_after_expr;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::def::Res;
   9 use rustc_hir::{Expr, ExprKind};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::ty::{self, Ty};
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::sym;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for `assert!(r.is_ok())` or `assert!(r.is_err())` calls.
  18     ///
  19     /// ### Why is this bad?
  20     /// An assertion failure cannot output an useful message of the error.
  21     ///
  22     /// ### Example
  23     /// ```rust,ignore
  24     /// # let r = Ok::<_, ()>(());
  25     /// assert!(r.is_ok());
  26     /// # let r = Err::<_, ()>(());
  27     /// assert!(r.is_err());
  28     /// ```
  29     #[clippy::version = "1.64.0"]
  30     pub ASSERTIONS_ON_RESULT_STATES,
  31     style,
  32     "`assert!(r.is_ok())`/`assert!(r.is_err())` gives worse error message than directly calling `r.unwrap()`/`r.unwrap_err()`"
  33 }
  34
  35 declare_lint_pass!(AssertionsOnResultStates => [ASSERTIONS_ON_RESULT_STATES]);
  36
  37 impl<'tcx> LateLintPass<'tcx> for AssertionsOnResultStates {
  38     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  39         if let Some(macro_call) = root_macro_call_first_node(cx, e)
  40             && matches!(cx.tcx.get_diagnostic_name(macro_call.def_id), Some(sym::assert_macro))
  41             && let Some((condition, panic_expn)) = find_assert_args(cx, e, macro_call.expn)
  42             && matches!(panic_expn, PanicExpn::Empty)
  43             && let ExprKind::MethodCall(method_segment, [recv], _) = condition.kind
  44             && let result_type_with_refs = cx.typeck_results().expr_ty(recv)
  45             && let result_type = result_type_with_refs.peel_refs()
  46             && is_type_diagnostic_item(cx, result_type, sym::Result)
  47             && let ty::Adt(_, substs) = result_type.kind()
  48         {
  49             if !is_copy(cx, result_type) {
  50                 if result_type_with_refs != result_type {
  51                     return;
  52                 } else if let Res::Local(binding_id) = path_res(cx, recv)
  53                     && local_used_after_expr(cx, binding_id, recv) {
  54                     return;
  55                 }
  56             }
  57             let mut app = Applicability::MachineApplicable;
  58             match method_segment.ident.as_str() {
  59                 "is_ok" if has_debug_impl(cx, substs.type_at(1)) => {
  60                     span_lint_and_sugg(
  61                         cx,
  62                         ASSERTIONS_ON_RESULT_STATES,
  63                         macro_call.span,
  64                         "called `assert!` with `Result::is_ok`",
  65                         "replace with",
  66                         format!(
  67                             "{}.unwrap()",
  68                             snippet_with_context(cx, recv.span, condition.span.ctxt(), "..", &mut app).0
  69                         ),
  70                         app,
  71                     );
  72                 }
  73                 "is_err" if has_debug_impl(cx, substs.type_at(0)) => {
  74                     span_lint_and_sugg(
  75                         cx,
  76                         ASSERTIONS_ON_RESULT_STATES,
  77                         macro_call.span,
  78                         "called `assert!` with `Result::is_err`",
  79                         "replace with",
  80                         format!(
  81                             "{}.unwrap_err()",
  82                             snippet_with_context(cx, recv.span, condition.span.ctxt(), "..", &mut app).0
  83                         ),
  84                         app,
  85                     );
  86                 }
  87                 _ => (),
  88             };
  89         }
  90     }
  91 }
  92
  93 /// This checks whether a given type is known to implement Debug.
  94 fn has_debug_impl<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
  95     cx.tcx
  96         .get_diagnostic_item(sym::Debug)
  97         .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
  98 }