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, opt_def_id, 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;
   7 use rustc::{declare_tool_lint, lint_array};
   8 use syntax_pos::Span;
   9
  10 /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  11 ///
  12 /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
  13 ///
  14 /// **Known problems:** None.
  15 ///
  16 /// **Example:**
  17 /// ```rust
  18 /// struct Foo(i32);
  19 /// impl From<String> for Foo {
  20 ///     fn from(s: String) -> Self {
  21 ///         Foo(s.parse().unwrap())
  22 ///     }
  23 /// }
  24 /// ```
  25 declare_clippy_lint! {
  26     pub FALLIBLE_IMPL_FROM,
  27     nursery,
  28     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  29 }
  30
  31 pub struct FallibleImplFrom;
  32
  33 impl LintPass for FallibleImplFrom {
  34     fn get_lints(&self) -> LintArray {
  35         lint_array!(FALLIBLE_IMPL_FROM)
  36     }
  37
  38     fn name(&self) -> &'static str {
  39         "FallibleImpleFrom"
  40     }
  41 }
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
  44     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
  45         // check for `impl From<???> for ..`
  46         let impl_def_id = cx.tcx.hir().local_def_id(item.id);
  47         if_chain! {
  48             if let hir::ItemKind::Impl(.., ref impl_items) = item.node;
  49             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  50             if match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT);
  51             then {
  52                 lint_impl_body(cx, item.span, impl_items);
  53             }
  54         }
  55     }
  56 }
  57
  58 fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &hir::HirVec<hir::ImplItemRef>) {
  59     use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  60     use rustc::hir::*;
  61
  62     struct FindPanicUnwrap<'a, 'tcx: 'a> {
  63         tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
  64         tables: &'tcx ty::TypeckTables<'tcx>,
  65         result: Vec<Span>,
  66     }
  67
  68     impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  69         fn visit_expr(&mut self, expr: &'tcx Expr) {
  70             // check for `begin_panic`
  71             if_chain! {
  72                 if let ExprKind::Call(ref func_expr, _) = expr.node;
  73                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.node;
  74                 if let Some(path_def_id) = opt_def_id(path.def);
  75                 if match_def_path(self.tcx, path_def_id, &BEGIN_PANIC) ||
  76                     match_def_path(self.tcx, path_def_id, &BEGIN_PANIC_FMT);
  77                 if is_expn_of(expr.span, "unreachable").is_none();
  78                 then {
  79                     self.result.push(expr.span);
  80                 }
  81             }
  82
  83             // check for `unwrap`
  84             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  85                 let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
  86                 if match_type(self.tcx, reciever_ty, &OPTION) || match_type(self.tcx, reciever_ty, &RESULT) {
  87                     self.result.push(expr.span);
  88                 }
  89             }
  90
  91             // and check sub-expressions
  92             intravisit::walk_expr(self, expr);
  93         }
  94
  95         fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  96             NestedVisitorMap::None
  97         }
  98     }
  99
 100     for impl_item in impl_items {
 101         if_chain! {
 102             if impl_item.ident.name == "from";
 103             if let ImplItemKind::Method(_, body_id) =
 104                 cx.tcx.hir().impl_item(impl_item.id).node;
 105             then {
 106                 // check the body for `begin_panic` or `unwrap`
 107                 let body = cx.tcx.hir().body(body_id);
 108                 let impl_item_def_id = cx.tcx.hir().local_def_id(impl_item.id.node_id);
 109                 let mut fpu = FindPanicUnwrap {
 110                     tcx: cx.tcx,
 111                     tables: cx.tcx.typeck_tables_of(impl_item_def_id),
 112                     result: Vec::new(),
 113                 };
 114                 fpu.visit_expr(&body.value);
 115
 116                 // if we've found one, lint
 117                 if !fpu.result.is_empty() {
 118                     span_lint_and_then(
 119                         cx,
 120                         FALLIBLE_IMPL_FROM,
 121                         impl_span,
 122                         "consider implementing `TryFrom` instead",
 123                         move |db| {
 124                             db.help(
 125                                 "`From` is intended for infallible conversions only. \
 126                                  Use `TryFrom` if there's a possibility for the conversion to fail.");
 127                             db.span_note(fpu.result, "potential failure(s)");
 128                         });
 129                 }
 130             }
 131         }
 132     }
 133 }
 134
 135 fn match_type(tcx: ty::TyCtxt<'_, '_, '_>, ty: ty::Ty<'_>, path: &[&str]) -> bool {
 136     match ty.sty {
 137         ty::Adt(adt, _) => match_def_path(tcx, adt.did, path),
 138         _ => false,
 139     }
 140 }