clippy_lints/src/fallible_impl_from.rs

   1 use crate::utils::{is_expn_of, is_type_diagnostic_item, match_panic_def_id, method_chain_args, span_lint_and_then};
   2 use if_chain::if_chain;
   3 use rustc_hir as hir;
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_middle::hir::map::Map;
   6 use rustc_middle::ty;
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::{sym, Span};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  12     ///
  13     /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     /// ```rust
  19     /// struct Foo(i32);
  20     ///
  21     /// // Bad
  22     /// impl From<String> for Foo {
  23     ///     fn from(s: String) -> Self {
  24     ///         Foo(s.parse().unwrap())
  25     ///     }
  26     /// }
  27     /// ```
  28     ///
  29     /// ```rust
  30     /// // Good
  31     /// struct Foo(i32);
  32     ///
  33     /// use std::convert::TryFrom;
  34     /// impl TryFrom<String> for Foo {
  35     ///     type Error = ();
  36     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  37     ///         if let Ok(parsed) = s.parse() {
  38     ///             Ok(Foo(parsed))
  39     ///         } else {
  40     ///             Err(())
  41     ///         }
  42     ///     }
  43     /// }
  44     /// ```
  45     pub FALLIBLE_IMPL_FROM,
  46     nursery,
  47     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  48 }
  49
  50 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  51
  52 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  53     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  54         // check for `impl From<???> for ..`
  55         let impl_def_id = cx.tcx.hir().local_def_id(item.hir_id);
  56         if_chain! {
  57             if let hir::ItemKind::Impl(impl_) = &item.kind;
  58             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  59             if cx.tcx.is_diagnostic_item(sym::from_trait, impl_trait_ref.def_id);
  60             then {
  61                 lint_impl_body(cx, item.span, impl_.items);
  62             }
  63         }
  64     }
  65 }
  66
  67 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef<'_>]) {
  68     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  69     use rustc_hir::{Expr, ExprKind, ImplItemKind, QPath};
  70
  71     struct FindPanicUnwrap<'a, 'tcx> {
  72         lcx: &'a LateContext<'tcx>,
  73         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  74         result: Vec<Span>,
  75     }
  76
  77     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  78         type Map = Map<'tcx>;
  79
  80         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  81             // check for `begin_panic`
  82             if_chain! {
  83                 if let ExprKind::Call(ref func_expr, _) = expr.kind;
  84                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.kind;
  85                 if let Some(path_def_id) = path.res.opt_def_id();
  86                 if match_panic_def_id(self.lcx, path_def_id);
  87                 if is_expn_of(expr.span, "unreachable").is_none();
  88                 then {
  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     for impl_item in impl_items {
 113         if_chain! {
 114             if impl_item.ident.name == sym::from;
 115             if let ImplItemKind::Fn(_, body_id) =
 116                 cx.tcx.hir().impl_item(impl_item.id).kind;
 117             then {
 118                 // check the body for `begin_panic` or `unwrap`
 119                 let body = cx.tcx.hir().body(body_id);
 120                 let impl_item_def_id = cx.tcx.hir().local_def_id(impl_item.id.hir_id);
 121                 let mut fpu = FindPanicUnwrap {
 122                     lcx: cx,
 123                     typeck_results: cx.tcx.typeck(impl_item_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 }