clippy_lints/src/fallible_impl_from.rs

   1 use crate::utils::{is_expn_of, match_panic_def_id, method_chain_args, span_lint_and_then};
   2 use clippy_utils::ty::is_type_diagnostic_item;
   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::{sym, 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         if_chain! {
  57             if let hir::ItemKind::Impl(impl_) = &item.kind;
  58             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.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 mut fpu = FindPanicUnwrap {
 121                     lcx: cx,
 122                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 123                     result: Vec::new(),
 124                 };
 125                 fpu.visit_expr(&body.value);
 126
 127                 // if we've found one, lint
 128                 if !fpu.result.is_empty() {
 129                     span_lint_and_then(
 130                         cx,
 131                         FALLIBLE_IMPL_FROM,
 132                         impl_span,
 133                         "consider implementing `TryFrom` instead",
 134                         move |diag| {
 135                             diag.help(
 136                                 "`From` is intended for infallible conversions only. \
 137                                 Use `TryFrom` if there's a possibility for the conversion to fail");
 138                             diag.span_note(fpu.result, "potential failure(s)");
 139                         });
 140                 }
 141             }
 142         }
 143     }
 144 }