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         if_chain! {
  56             if let hir::ItemKind::Impl(impl_) = &item.kind;
  57             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  58             if cx.tcx.is_diagnostic_item(sym::from_trait, impl_trait_ref.def_id);
  59             then {
  60                 lint_impl_body(cx, item.span, impl_.items);
  61             }
  62         }
  63     }
  64 }
  65
  66 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef<'_>]) {
  67     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  68     use rustc_hir::{Expr, ExprKind, ImplItemKind, QPath};
  69
  70     struct FindPanicUnwrap<'a, 'tcx> {
  71         lcx: &'a LateContext<'tcx>,
  72         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  73         result: Vec<Span>,
  74     }
  75
  76     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  77         type Map = Map<'tcx>;
  78
  79         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  80             // check for `begin_panic`
  81             if_chain! {
  82                 if let ExprKind::Call(ref func_expr, _) = expr.kind;
  83                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.kind;
  84                 if let Some(path_def_id) = path.res.opt_def_id();
  85                 if match_panic_def_id(self.lcx, path_def_id);
  86                 if is_expn_of(expr.span, "unreachable").is_none();
  87                 then {
  88                     self.result.push(expr.span);
  89                 }
  90             }
  91
  92             // check for `unwrap`
  93             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  94                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  95                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
  96                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
  97                 {
  98                     self.result.push(expr.span);
  99                 }
 100             }
 101
 102             // and check sub-expressions
 103             intravisit::walk_expr(self, expr);
 104         }
 105
 106         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 107             NestedVisitorMap::None
 108         }
 109     }
 110
 111     for impl_item in impl_items {
 112         if_chain! {
 113             if impl_item.ident.name == sym::from;
 114             if let ImplItemKind::Fn(_, body_id) =
 115                 cx.tcx.hir().impl_item(impl_item.id).kind;
 116             then {
 117                 // check the body for `begin_panic` or `unwrap`
 118                 let body = cx.tcx.hir().body(body_id);
 119                 let mut fpu = FindPanicUnwrap {
 120                     lcx: cx,
 121                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 122                     result: Vec::new(),
 123                 };
 124                 fpu.visit_expr(&body.value);
 125
 126                 // if we've found one, lint
 127                 if !fpu.result.is_empty() {
 128                     span_lint_and_then(
 129                         cx,
 130                         FALLIBLE_IMPL_FROM,
 131                         impl_span,
 132                         "consider implementing `TryFrom` instead",
 133                         move |diag| {
 134                             diag.help(
 135                                 "`From` is intended for infallible conversions only. \
 136                                 Use `TryFrom` if there's a possibility for the conversion to fail.");
 137                             diag.span_note(fpu.result, "potential failure(s)");
 138                         });
 139                 }
 140             }
 141         }
 142     }
 143 }