src/tools/clippy/clippy_lints/src/fallible_impl_from.rs

   1 use crate::utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT};
   2 use crate::utils::{is_expn_of, is_type_diagnostic_item, match_def_path, method_chain_args, span_lint_and_then};
   3 use if_chain::if_chain;
   4 use rustc_hir as hir;
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_middle::hir::map::Map;
   7 use rustc_middle::ty;
   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     ///
  22     /// // Bad
  23     /// impl From<String> for Foo {
  24     ///     fn from(s: String) -> Self {
  25     ///         Foo(s.parse().unwrap())
  26     ///     }
  27     /// }
  28     /// ```
  29     ///
  30     /// ```rust
  31     /// // Good
  32     /// struct Foo(i32);
  33     ///
  34     /// use std::convert::TryFrom;
  35     /// impl TryFrom<String> for Foo {
  36     ///     type Error = ();
  37     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  38     ///         if let Ok(parsed) = s.parse() {
  39     ///             Ok(Foo(parsed))
  40     ///         } else {
  41     ///             Err(())
  42     ///         }
  43     ///     }
  44     /// }
  45     /// ```
  46     pub FALLIBLE_IMPL_FROM,
  47     nursery,
  48     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  49 }
  50
  51 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  52
  53 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  54     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  55         // check for `impl From<???> for ..`
  56         let impl_def_id = cx.tcx.hir().local_def_id(item.hir_id);
  57         if_chain! {
  58             if let hir::ItemKind::Impl{ items: impl_items, .. } = item.kind;
  59             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  60             if match_def_path(cx, impl_trait_ref.def_id, &FROM_TRAIT);
  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(ref func_expr, _) = expr.kind;
  85                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.kind;
  86                 if let Some(path_def_id) = path.res.opt_def_id();
  87                 if match_def_path(self.lcx, path_def_id, &BEGIN_PANIC) ||
  88                     match_def_path(self.lcx, path_def_id, &BEGIN_PANIC_FMT);
  89                 if is_expn_of(expr.span, "unreachable").is_none();
  90                 then {
  91                     self.result.push(expr.span);
  92                 }
  93             }
  94
  95             // check for `unwrap`
  96             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  97                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  98                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym!(option_type))
  99                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym!(result_type))
 100                 {
 101                     self.result.push(expr.span);
 102                 }
 103             }
 104
 105             // and check sub-expressions
 106             intravisit::walk_expr(self, expr);
 107         }
 108
 109         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 110             NestedVisitorMap::None
 111         }
 112     }
 113
 114     for impl_item in impl_items {
 115         if_chain! {
 116             if impl_item.ident.name == sym!(from);
 117             if let ImplItemKind::Fn(_, body_id) =
 118                 cx.tcx.hir().impl_item(impl_item.id).kind;
 119             then {
 120                 // check the body for `begin_panic` or `unwrap`
 121                 let body = cx.tcx.hir().body(body_id);
 122                 let impl_item_def_id = cx.tcx.hir().local_def_id(impl_item.id.hir_id);
 123                 let mut fpu = FindPanicUnwrap {
 124                     lcx: cx,
 125                     typeck_results: cx.tcx.typeck(impl_item_def_id),
 126                     result: Vec::new(),
 127                 };
 128                 fpu.visit_expr(&body.value);
 129
 130                 // if we've found one, lint
 131                 if !fpu.result.is_empty() {
 132                     span_lint_and_then(
 133                         cx,
 134                         FALLIBLE_IMPL_FROM,
 135                         impl_span,
 136                         "consider implementing `TryFrom` instead",
 137                         move |diag| {
 138                             diag.help(
 139                                 "`From` is intended for infallible conversions only. \
 140                                 Use `TryFrom` if there's a possibility for the conversion to fail.");
 141                             diag.span_note(fpu.result, "potential failure(s)");
 142                         });
 143                 }
 144             }
 145         }
 146     }
 147 }