clippy_lints/src/fallible_impl_from.rs

   1 use crate::utils::paths::FROM_TRAIT;
   2 use crate::utils::{
   3     is_expn_of, is_type_diagnostic_item, match_def_path, match_panic_def_id, method_chain_args, span_lint_and_then,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_hir as hir;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::hir::map::Map;
   9 use rustc_middle::ty;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::{sym, Span};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  15     ///
  16     /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// struct Foo(i32);
  23     ///
  24     /// // Bad
  25     /// impl From<String> for Foo {
  26     ///     fn from(s: String) -> Self {
  27     ///         Foo(s.parse().unwrap())
  28     ///     }
  29     /// }
  30     /// ```
  31     ///
  32     /// ```rust
  33     /// // Good
  34     /// struct Foo(i32);
  35     ///
  36     /// use std::convert::TryFrom;
  37     /// impl TryFrom<String> for Foo {
  38     ///     type Error = ();
  39     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  40     ///         if let Ok(parsed) = s.parse() {
  41     ///             Ok(Foo(parsed))
  42     ///         } else {
  43     ///             Err(())
  44     ///         }
  45     ///     }
  46     /// }
  47     /// ```
  48     pub FALLIBLE_IMPL_FROM,
  49     nursery,
  50     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  51 }
  52
  53 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  54
  55 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  56     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  57         // check for `impl From<???> for ..`
  58         let impl_def_id = cx.tcx.hir().local_def_id(item.hir_id);
  59         if_chain! {
  60             if let hir::ItemKind::Impl{ items: impl_items, .. } = item.kind;
  61             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  62             if match_def_path(cx, impl_trait_ref.def_id, &FROM_TRAIT);
  63             then {
  64                 lint_impl_body(cx, item.span, impl_items);
  65             }
  66         }
  67     }
  68 }
  69
  70 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef<'_>]) {
  71     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  72     use rustc_hir::{Expr, ExprKind, ImplItemKind, QPath};
  73
  74     struct FindPanicUnwrap<'a, 'tcx> {
  75         lcx: &'a LateContext<'tcx>,
  76         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  77         result: Vec<Span>,
  78     }
  79
  80     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  81         type Map = Map<'tcx>;
  82
  83         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  84             // check for `begin_panic`
  85             if_chain! {
  86                 if let ExprKind::Call(ref func_expr, _) = expr.kind;
  87                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.kind;
  88                 if let Some(path_def_id) = path.res.opt_def_id();
  89                 if match_panic_def_id(self.lcx, path_def_id);
  90                 if is_expn_of(expr.span, "unreachable").is_none();
  91                 then {
  92                     self.result.push(expr.span);
  93                 }
  94             }
  95
  96             // check for `unwrap`
  97             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  98                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  99                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym::option_type)
 100                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym::result_type)
 101                 {
 102                     self.result.push(expr.span);
 103                 }
 104             }
 105
 106             // and check sub-expressions
 107             intravisit::walk_expr(self, expr);
 108         }
 109
 110         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 111             NestedVisitorMap::None
 112         }
 113     }
 114
 115     for impl_item in impl_items {
 116         if_chain! {
 117             if impl_item.ident.name == sym::from;
 118             if let ImplItemKind::Fn(_, body_id) =
 119                 cx.tcx.hir().impl_item(impl_item.id).kind;
 120             then {
 121                 // check the body for `begin_panic` or `unwrap`
 122                 let body = cx.tcx.hir().body(body_id);
 123                 let impl_item_def_id = cx.tcx.hir().local_def_id(impl_item.id.hir_id);
 124                 let mut fpu = FindPanicUnwrap {
 125                     lcx: cx,
 126                     typeck_results: cx.tcx.typeck(impl_item_def_id),
 127                     result: Vec::new(),
 128                 };
 129                 fpu.visit_expr(&body.value);
 130
 131                 // if we've found one, lint
 132                 if !fpu.result.is_empty() {
 133                     span_lint_and_then(
 134                         cx,
 135                         FALLIBLE_IMPL_FROM,
 136                         impl_span,
 137                         "consider implementing `TryFrom` instead",
 138                         move |diag| {
 139                             diag.help(
 140                                 "`From` is intended for infallible conversions only. \
 141                                 Use `TryFrom` if there's a possibility for the conversion to fail.");
 142                             diag.span_note(fpu.result, "potential failure(s)");
 143                         });
 144                 }
 145             }
 146         }
 147     }
 148 }