src/tools/clippy/clippy_lints/src/unwrap_in_result.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use clippy_utils::{method_chain_args, return_ty};
   4 use if_chain::if_chain;
   5 use rustc_hir as hir;
   6 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
   7 use rustc_hir::{Expr, ImplItemKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::hir::map::Map;
  10 use rustc_middle::ty;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::{sym, Span};
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for functions of type Result that contain `expect()` or `unwrap()`
  16     ///
  17     /// **Why is this bad?** These functions promote recoverable errors to non-recoverable errors which may be undesirable in code bases which wish to avoid panics.
  18     ///
  19     /// **Known problems:** This can cause false positives in functions that handle both recoverable and non recoverable errors.
  20     ///
  21     /// **Example:**
  22     /// Before:
  23     /// ```rust
  24     /// fn divisible_by_3(i_str: String) -> Result<(), String> {
  25     ///     let i = i_str
  26     ///         .parse::<i32>()
  27     ///         .expect("cannot divide the input by three");
  28     ///
  29     ///     if i % 3 != 0 {
  30     ///         Err("Number is not divisible by 3")?
  31     ///     }
  32     ///
  33     ///     Ok(())
  34     /// }
  35     /// ```
  36     ///
  37     /// After:
  38     /// ```rust
  39     /// fn divisible_by_3(i_str: String) -> Result<(), String> {
  40     ///     let i = i_str
  41     ///         .parse::<i32>()
  42     ///         .map_err(|e| format!("cannot divide the input by three: {}", e))?;
  43     ///
  44     ///     if i % 3 != 0 {
  45     ///         Err("Number is not divisible by 3")?
  46     ///     }
  47     ///
  48     ///     Ok(())
  49     /// }
  50     /// ```
  51     pub UNWRAP_IN_RESULT,
  52     restriction,
  53     "functions of type `Result<..>` or `Option`<...> that contain `expect()` or `unwrap()`"
  54 }
  55
  56 declare_lint_pass!(UnwrapInResult=> [UNWRAP_IN_RESULT]);
  57
  58 impl<'tcx> LateLintPass<'tcx> for UnwrapInResult {
  59     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
  60         if_chain! {
  61             // first check if it's a method or function
  62             if let hir::ImplItemKind::Fn(ref _signature, _) = impl_item.kind;
  63             // checking if its return type is `result` or `option`
  64             if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::result_type)
  65                 || is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::option_type);
  66             then {
  67                 lint_impl_body(cx, impl_item.span, impl_item);
  68             }
  69         }
  70     }
  71 }
  72
  73 struct FindExpectUnwrap<'a, 'tcx> {
  74     lcx: &'a LateContext<'tcx>,
  75     typeck_results: &'tcx ty::TypeckResults<'tcx>,
  76     result: Vec<Span>,
  77 }
  78
  79 impl<'a, 'tcx> Visitor<'tcx> for FindExpectUnwrap<'a, 'tcx> {
  80     type Map = Map<'tcx>;
  81
  82     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  83         // check for `expect`
  84         if let Some(arglists) = method_chain_args(expr, &["expect"]) {
  85             let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  86             if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
  87                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
  88             {
  89                 self.result.push(expr.span);
  90             }
  91         }
  92
  93         // check for `unwrap`
  94         if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  95             let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  96             if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
  97                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
  98             {
  99                 self.result.push(expr.span);
 100             }
 101         }
 102
 103         // and check sub-expressions
 104         intravisit::walk_expr(self, expr);
 105     }
 106
 107     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 108         NestedVisitorMap::None
 109     }
 110 }
 111
 112 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_item: &'tcx hir::ImplItem<'_>) {
 113     if let ImplItemKind::Fn(_, body_id) = impl_item.kind {
 114         let body = cx.tcx.hir().body(body_id);
 115         let mut fpu = FindExpectUnwrap {
 116             lcx: cx,
 117             typeck_results: cx.tcx.typeck(impl_item.def_id),
 118             result: Vec::new(),
 119         };
 120         fpu.visit_expr(&body.value);
 121
 122         // if we've found one, lint
 123         if !fpu.result.is_empty() {
 124             span_lint_and_then(
 125                 cx,
 126                 UNWRAP_IN_RESULT,
 127                 impl_span,
 128                 "used unwrap or expect in a function that returns result or option",
 129                 move |diag| {
 130                     diag.help("unwrap and expect should not be used in a function that returns result or option");
 131                     diag.span_note(fpu.result, "potential non-recoverable error(s)");
 132                 },
 133             );
 134         }
 135     }
 136 }