clippy_lints/src/fallible_impl_from.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::macros::{is_panic, root_macro_call_first_node};
   3 use clippy_utils::method_chain_args;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_hir as hir;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::hir::map::Map;
   9 use rustc_middle::ty;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::{sym, Span};
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  16     ///
  17     /// ### Why is this bad?
  18     /// `TryFrom` should be used if there's a possibility of failure.
  19     ///
  20     /// ### Example
  21     /// ```rust
  22     /// struct Foo(i32);
  23     ///
  24     /// // Bad
  25     /// impl From<String> for Foo {
  26     ///     fn from(s: String) -> Self {
  27     ///         Foo(s.parse().unwrap())
  28     ///     }
  29     /// }
  30     /// ```
  31     ///
  32     /// ```rust
  33     /// // Good
  34     /// struct Foo(i32);
  35     ///
  36     /// use std::convert::TryFrom;
  37     /// impl TryFrom<String> for Foo {
  38     ///     type Error = ();
  39     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  40     ///         if let Ok(parsed) = s.parse() {
  41     ///             Ok(Foo(parsed))
  42     ///         } else {
  43     ///             Err(())
  44     ///         }
  45     ///     }
  46     /// }
  47     /// ```
  48     #[clippy::version = "pre 1.29.0"]
  49     pub FALLIBLE_IMPL_FROM,
  50     nursery,
  51     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  52 }
  53
  54 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  55
  56 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  57     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  58         // check for `impl From<???> for ..`
  59         if_chain! {
  60             if let hir::ItemKind::Impl(impl_) = &item.kind;
  61             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  62             if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
  63             then {
  64                 lint_impl_body(cx, item.span, impl_.items);
  65             }
  66         }
  67     }
  68 }
  69
  70 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
  71     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  72     use rustc_hir::{Expr, ImplItemKind};
  73
  74     struct FindPanicUnwrap<'a, 'tcx> {
  75         lcx: &'a LateContext<'tcx>,
  76         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  77         result: Vec<Span>,
  78     }
  79
  80     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  81         type Map = Map<'tcx>;
  82
  83         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  84             if let Some(macro_call) = root_macro_call_first_node(self.lcx, expr) {
  85                 if is_panic(self.lcx, macro_call.def_id) {
  86                     self.result.push(expr.span);
  87                 }
  88             }
  89
  90             // check for `unwrap`
  91             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  92                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  93                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym::Option)
  94                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym::Result)
  95                 {
  96                     self.result.push(expr.span);
  97                 }
  98             }
  99
 100             // and check sub-expressions
 101             intravisit::walk_expr(self, expr);
 102         }
 103
 104         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 105             NestedVisitorMap::None
 106         }
 107     }
 108
 109     for impl_item in impl_items {
 110         if_chain! {
 111             if impl_item.ident.name == sym::from;
 112             if let ImplItemKind::Fn(_, body_id) =
 113                 cx.tcx.hir().impl_item(impl_item.id).kind;
 114             then {
 115                 // check the body for `begin_panic` or `unwrap`
 116                 let body = cx.tcx.hir().body(body_id);
 117                 let mut fpu = FindPanicUnwrap {
 118                     lcx: cx,
 119                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 120                     result: Vec::new(),
 121                 };
 122                 fpu.visit_expr(&body.value);
 123
 124                 // if we've found one, lint
 125                 if !fpu.result.is_empty() {
 126                     span_lint_and_then(
 127                         cx,
 128                         FALLIBLE_IMPL_FROM,
 129                         impl_span,
 130                         "consider implementing `TryFrom` instead",
 131                         move |diag| {
 132                             diag.help(
 133                                 "`From` is intended for infallible conversions only. \
 134                                 Use `TryFrom` if there's a possibility for the conversion to fail");
 135                             diag.span_note(fpu.result, "potential failure(s)");
 136                         });
 137                 }
 138             }
 139         }
 140     }
 141 }