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::sym;
   3 use crate::utils::{is_expn_of, match_def_path, method_chain_args, span_lint_and_then, walk_ptrs_ty};
   4 use if_chain::if_chain;
   5 use rustc::hir;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc::ty::{self, Ty};
   8 use rustc::{declare_lint_pass, declare_tool_lint};
   9 use syntax::symbol::Symbol;
  10 use syntax_pos::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_from_hir_id(item.hir_id);
  39         if_chain! {
  40             if let hir::ItemKind::Impl(.., ref impl_items) = item.node;
  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::HirVec<hir::ImplItemRef>) {
  51     use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  52     use rustc::hir::*;
  53
  54     struct FindPanicUnwrap<'a, 'tcx: 'a> {
  55         lcx: &'a LateContext<'a, 'tcx>,
  56         tables: &'tcx ty::TypeckTables<'tcx>,
  57         result: Vec<Span>,
  58     }
  59
  60     impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  61         fn visit_expr(&mut self, expr: &'tcx Expr) {
  62             // check for `begin_panic`
  63             if_chain! {
  64                 if let ExprKind::Call(ref func_expr, _) = expr.node;
  65                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.node;
  66                 if let Some(path_def_id) = path.res.opt_def_id();
  67                 if match_def_path(self.lcx, path_def_id, &*BEGIN_PANIC) ||
  68                     match_def_path(self.lcx, path_def_id, &*BEGIN_PANIC_FMT);
  69                 if is_expn_of(expr.span, *sym::unreachable).is_none();
  70                 then {
  71                     self.result.push(expr.span);
  72                 }
  73             }
  74
  75             // check for `unwrap`
  76             if let Some(arglists) = method_chain_args(expr, &[*sym::unwrap]) {
  77                 let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
  78                 if match_type(self.lcx, reciever_ty, &*OPTION) || match_type(self.lcx, reciever_ty, &*RESULT) {
  79                     self.result.push(expr.span);
  80                 }
  81             }
  82
  83             // and check sub-expressions
  84             intravisit::walk_expr(self, expr);
  85         }
  86
  87         fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  88             NestedVisitorMap::None
  89         }
  90     }
  91
  92     for impl_item in impl_items {
  93         if_chain! {
  94             if impl_item.ident.name == *sym::from;
  95             if let ImplItemKind::Method(_, body_id) =
  96                 cx.tcx.hir().impl_item(impl_item.id).node;
  97             then {
  98                 // check the body for `begin_panic` or `unwrap`
  99                 let body = cx.tcx.hir().body(body_id);
 100                 let impl_item_def_id = cx.tcx.hir().local_def_id_from_hir_id(impl_item.id.hir_id);
 101                 let mut fpu = FindPanicUnwrap {
 102                     lcx: cx,
 103                     tables: cx.tcx.typeck_tables_of(impl_item_def_id),
 104                     result: Vec::new(),
 105                 };
 106                 fpu.visit_expr(&body.value);
 107
 108                 // if we've found one, lint
 109                 if !fpu.result.is_empty() {
 110                     span_lint_and_then(
 111                         cx,
 112                         FALLIBLE_IMPL_FROM,
 113                         impl_span,
 114                         "consider implementing `TryFrom` instead",
 115                         move |db| {
 116                             db.help(
 117                                 "`From` is intended for infallible conversions only. \
 118                                  Use `TryFrom` if there's a possibility for the conversion to fail.");
 119                             db.span_note(fpu.result, "potential failure(s)");
 120                         });
 121                 }
 122             }
 123         }
 124     }
 125 }
 126
 127 fn match_type(cx: &LateContext<'_, '_>, ty: Ty<'_>, path: &[Symbol]) -> bool {
 128     match ty.sty {
 129         ty::Adt(adt, _) => match_def_path(cx, adt.did, path),
 130         _ => false,
 131     }
 132 }