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