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