clippy_lints/src/fallible_impl_from.rs

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