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
  39 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
  40     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
  41         // check for `impl From<???> for ..`
  42         let impl_def_id = cx.tcx.hir().local_def_id(item.id);
  43         if_chain! {
  44             if let hir::ItemKind::Impl(.., ref impl_items) = item.node;
  45             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  46             if match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT);
  47             then {
  48                 lint_impl_body(cx, item.span, impl_items);
  49             }
  50         }
  51     }
  52 }
  53
  54 fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &hir::HirVec<hir::ImplItemRef>) {
  55     use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  56     use rustc::hir::*;
  57
  58     struct FindPanicUnwrap<'a, 'tcx: 'a> {
  59         tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
  60         tables: &'tcx ty::TypeckTables<'tcx>,
  61         result: Vec<Span>,
  62     }
  63
  64     impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  65         fn visit_expr(&mut self, expr: &'tcx Expr) {
  66             // check for `begin_panic`
  67             if_chain! {
  68                 if let ExprKind::Call(ref func_expr, _) = expr.node;
  69                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.node;
  70                 if let Some(path_def_id) = opt_def_id(path.def);
  71                 if match_def_path(self.tcx, path_def_id, &BEGIN_PANIC) ||
  72                     match_def_path(self.tcx, path_def_id, &BEGIN_PANIC_FMT);
  73                 if is_expn_of(expr.span, "unreachable").is_none();
  74                 then {
  75                     self.result.push(expr.span);
  76                 }
  77             }
  78
  79             // check for `unwrap`
  80             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  81                 let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
  82                 if match_type(self.tcx, reciever_ty, &OPTION) || match_type(self.tcx, reciever_ty, &RESULT) {
  83                     self.result.push(expr.span);
  84                 }
  85             }
  86
  87             // and check sub-expressions
  88             intravisit::walk_expr(self, expr);
  89         }
  90
  91         fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  92             NestedVisitorMap::None
  93         }
  94     }
  95
  96     for impl_item in impl_items {
  97         if_chain! {
  98             if impl_item.ident.name == "from";
  99             if let ImplItemKind::Method(_, body_id) =
 100                 cx.tcx.hir().impl_item(impl_item.id).node;
 101             then {
 102                 // check the body for `begin_panic` or `unwrap`
 103                 let body = cx.tcx.hir().body(body_id);
 104                 let impl_item_def_id = cx.tcx.hir().local_def_id(impl_item.id.node_id);
 105                 let mut fpu = FindPanicUnwrap {
 106                     tcx: cx.tcx,
 107                     tables: cx.tcx.typeck_tables_of(impl_item_def_id),
 108                     result: Vec::new(),
 109                 };
 110                 fpu.visit_expr(&body.value);
 111
 112                 // if we've found one, lint
 113                 if !fpu.result.is_empty() {
 114                     span_lint_and_then(
 115                         cx,
 116                         FALLIBLE_IMPL_FROM,
 117                         impl_span,
 118                         "consider implementing `TryFrom` instead",
 119                         move |db| {
 120                             db.help(
 121                                 "`From` is intended for infallible conversions only. \
 122                                  Use `TryFrom` if there's a possibility for the conversion to fail.");
 123                             db.span_note(fpu.result, "potential failure(s)");
 124                         });
 125                 }
 126             }
 127         }
 128     }
 129 }
 130
 131 fn match_type(tcx: ty::TyCtxt<'_, '_, '_>, ty: ty::Ty<'_>, path: &[&str]) -> bool {
 132     match ty.sty {
 133         ty::Adt(adt, _) => match_def_path(tcx, adt.did, path),
 134         _ => false,
 135     }
 136 }