clippy_lints/src/fallible_impl_from.rs

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