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
  16     /// Checks for functions of type Result that contain `expect()` or `unwrap()`
  17     ///
  18     /// ### Why is this bad?
  19     /// These functions promote recoverable errors to non-recoverable errors which may be undesirable in code bases which wish to avoid panics.
  20     ///
  21     /// ### Known problems
  22     /// This can cause false positives in functions that handle both recoverable and non recoverable errors.
  23     ///
  24     /// ### Example
  25     /// Before:
  26     /// ```rust
  27     /// fn divisible_by_3(i_str: String) -> Result<(), String> {
  28     ///     let i = i_str
  29     ///         .parse::<i32>()
  30     ///         .expect("cannot divide the input by three");
  31     ///
  32     ///     if i % 3 != 0 {
  33     ///         Err("Number is not divisible by 3")?
  34     ///     }
  35     ///
  36     ///     Ok(())
  37     /// }
  38     /// ```
  39     ///
  40     /// After:
  41     /// ```rust
  42     /// fn divisible_by_3(i_str: String) -> Result<(), String> {
  43     ///     let i = i_str
  44     ///         .parse::<i32>()
  45     ///         .map_err(|e| format!("cannot divide the input by three: {}", e))?;
  46     ///
  47     ///     if i % 3 != 0 {
  48     ///         Err("Number is not divisible by 3")?
  49     ///     }
  50     ///
  51     ///     Ok(())
  52     /// }
  53     /// ```
  54     pub UNWRAP_IN_RESULT,
  55     restriction,
  56     "functions of type `Result<..>` or `Option`<...> that contain `expect()` or `unwrap()`"
  57 }
  58
  59 declare_lint_pass!(UnwrapInResult=> [UNWRAP_IN_RESULT]);
  60
  61 impl<'tcx> LateLintPass<'tcx> for UnwrapInResult {
  62     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
  63         if_chain! {
  64             // first check if it's a method or function
  65             if let hir::ImplItemKind::Fn(ref _signature, _) = impl_item.kind;
  66             // checking if its return type is `result` or `option`
  67             if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::result_type)
  68                 || is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::option_type);
  69             then {
  70                 lint_impl_body(cx, impl_item.span, impl_item);
  71             }
  72         }
  73     }
  74 }
  75
  76 struct FindExpectUnwrap<'a, 'tcx> {
  77     lcx: &'a LateContext<'tcx>,
  78     typeck_results: &'tcx ty::TypeckResults<'tcx>,
  79     result: Vec<Span>,
  80 }
  81
  82 impl<'a, 'tcx> Visitor<'tcx> for FindExpectUnwrap<'a, 'tcx> {
  83     type Map = Map<'tcx>;
  84
  85     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  86         // check for `expect`
  87         if let Some(arglists) = method_chain_args(expr, &["expect"]) {
  88             let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  89             if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
  90                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
  91             {
  92                 self.result.push(expr.span);
  93             }
  94         }
  95
  96         // check for `unwrap`
  97         if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  98             let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  99             if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
 100                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
 101             {
 102                 self.result.push(expr.span);
 103             }
 104         }
 105
 106         // and check sub-expressions
 107         intravisit::walk_expr(self, expr);
 108     }
 109
 110     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 111         NestedVisitorMap::None
 112     }
 113 }
 114
 115 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_item: &'tcx hir::ImplItem<'_>) {
 116     if let ImplItemKind::Fn(_, body_id) = impl_item.kind {
 117         let body = cx.tcx.hir().body(body_id);
 118         let mut fpu = FindExpectUnwrap {
 119             lcx: cx,
 120             typeck_results: cx.tcx.typeck(impl_item.def_id),
 121             result: Vec::new(),
 122         };
 123         fpu.visit_expr(&body.value);
 124
 125         // if we've found one, lint
 126         if !fpu.result.is_empty() {
 127             span_lint_and_then(
 128                 cx,
 129                 UNWRAP_IN_RESULT,
 130                 impl_span,
 131                 "used unwrap or expect in a function that returns result or option",
 132                 move |diag| {
 133                     diag.help("unwrap and expect should not be used in a function that returns result or option");
 134                     diag.span_note(fpu.result, "potential non-recoverable error(s)");
 135                 },
 136             );
 137         }
 138     }
 139 }