clippy_lints/src/fallible_impl_from.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use clippy_utils::{is_expn_of, match_panic_def_id, method_chain_args};
   4 use if_chain::if_chain;
   5 use rustc_hir as hir;
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_middle::hir::map::Map;
   8 use rustc_middle::ty;
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::{sym, Span};
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  15     ///
  16     /// ### Why is this bad?
  17     /// `TryFrom` should be used if there's a possibility of failure.
  18     ///
  19     /// ### Example
  20     /// ```rust
  21     /// struct Foo(i32);
  22     ///
  23     /// // Bad
  24     /// impl From<String> for Foo {
  25     ///     fn from(s: String) -> Self {
  26     ///         Foo(s.parse().unwrap())
  27     ///     }
  28     /// }
  29     /// ```
  30     ///
  31     /// ```rust
  32     /// // Good
  33     /// struct Foo(i32);
  34     ///
  35     /// use std::convert::TryFrom;
  36     /// impl TryFrom<String> for Foo {
  37     ///     type Error = ();
  38     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  39     ///         if let Ok(parsed) = s.parse() {
  40     ///             Ok(Foo(parsed))
  41     ///         } else {
  42     ///             Err(())
  43     ///         }
  44     ///     }
  45     /// }
  46     /// ```
  47     pub FALLIBLE_IMPL_FROM,
  48     nursery,
  49     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  50 }
  51
  52 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  53
  54 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  55     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  56         // check for `impl From<???> for ..`
  57         if_chain! {
  58             if let hir::ItemKind::Impl(impl_) = &item.kind;
  59             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  60             if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
  61             then {
  62                 lint_impl_body(cx, item.span, impl_.items);
  63             }
  64         }
  65     }
  66 }
  67
  68 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
  69     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  70     use rustc_hir::{Expr, ExprKind, ImplItemKind, QPath};
  71
  72     struct FindPanicUnwrap<'a, 'tcx> {
  73         lcx: &'a LateContext<'tcx>,
  74         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  75         result: Vec<Span>,
  76     }
  77
  78     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  79         type Map = Map<'tcx>;
  80
  81         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  82             // check for `begin_panic`
  83             if_chain! {
  84                 if let ExprKind::Call(func_expr, _) = expr.kind;
  85                 if let ExprKind::Path(QPath::Resolved(_, path)) = func_expr.kind;
  86                 if let Some(path_def_id) = path.res.opt_def_id();
  87                 if match_panic_def_id(self.lcx, path_def_id);
  88                 if is_expn_of(expr.span, "unreachable").is_none();
  89                 then {
  90                     self.result.push(expr.span);
  91                 }
  92             }
  93
  94             // check for `unwrap`
  95             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  96                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  97                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym::Option)
  98                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym::Result)
  99                 {
 100                     self.result.push(expr.span);
 101                 }
 102             }
 103
 104             // and check sub-expressions
 105             intravisit::walk_expr(self, expr);
 106         }
 107
 108         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 109             NestedVisitorMap::None
 110         }
 111     }
 112
 113     for impl_item in impl_items {
 114         if_chain! {
 115             if impl_item.ident.name == sym::from;
 116             if let ImplItemKind::Fn(_, body_id) =
 117                 cx.tcx.hir().impl_item(impl_item.id).kind;
 118             then {
 119                 // check the body for `begin_panic` or `unwrap`
 120                 let body = cx.tcx.hir().body(body_id);
 121                 let mut fpu = FindPanicUnwrap {
 122                     lcx: cx,
 123                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 124                     result: Vec::new(),
 125                 };
 126                 fpu.visit_expr(&body.value);
 127
 128                 // if we've found one, lint
 129                 if !fpu.result.is_empty() {
 130                     span_lint_and_then(
 131                         cx,
 132                         FALLIBLE_IMPL_FROM,
 133                         impl_span,
 134                         "consider implementing `TryFrom` instead",
 135                         move |diag| {
 136                             diag.help(
 137                                 "`From` is intended for infallible conversions only. \
 138                                 Use `TryFrom` if there's a possibility for the conversion to fail");
 139                             diag.span_note(fpu.result, "potential failure(s)");
 140                         });
 141                 }
 142             }
 143         }
 144     }
 145 }