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::declare_lint_pass;
   5 use rustc::hir;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc::ty::{self, Ty};
   8 use rustc_session::declare_tool_lint;
   9 use syntax_pos::Span;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  13     ///
  14     /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust
  20     /// struct Foo(i32);
  21     /// impl From<String> for Foo {
  22     ///     fn from(s: String) -> Self {
  23     ///         Foo(s.parse().unwrap())
  24     ///     }
  25     /// }
  26     /// ```
  27     pub FALLIBLE_IMPL_FROM,
  28     nursery,
  29     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  30 }
  31
  32 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  33
  34 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
  35     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'_>) {
  36         // check for `impl From<???> for ..`
  37         let impl_def_id = cx.tcx.hir().local_def_id(item.hir_id);
  38         if_chain! {
  39             if let hir::ItemKind::Impl(.., impl_items) = item.kind;
  40             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  41             if match_def_path(cx, impl_trait_ref.def_id, &FROM_TRAIT);
  42             then {
  43                 lint_impl_body(cx, item.span, impl_items);
  44             }
  45         }
  46     }
  47 }
  48
  49 fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
  50     use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  51     use rustc::hir::*;
  52
  53     struct FindPanicUnwrap<'a, 'tcx> {
  54         lcx: &'a LateContext<'a, 'tcx>,
  55         tables: &'tcx ty::TypeckTables<'tcx>,
  56         result: Vec<Span>,
  57     }
  58
  59     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  60         fn visit_expr(&mut self, expr: &'tcx Expr) {
  61             // check for `begin_panic`
  62             if_chain! {
  63                 if let ExprKind::Call(ref func_expr, _) = expr.kind;
  64                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.kind;
  65                 if let Some(path_def_id) = path.res.opt_def_id();
  66                 if match_def_path(self.lcx, path_def_id, &BEGIN_PANIC) ||
  67                     match_def_path(self.lcx, path_def_id, &BEGIN_PANIC_FMT);
  68                 if is_expn_of(expr.span, "unreachable").is_none();
  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.lcx, reciever_ty, &OPTION) || match_type(self.lcx, 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.ident.name == sym!(from);
  94             if let ImplItemKind::Method(_, body_id) =
  95                 cx.tcx.hir().impl_item(impl_item.id).kind;
  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.hir_id);
 100                 let mut fpu = FindPanicUnwrap {
 101                     lcx: cx,
 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(cx: &LateContext<'_, '_>, ty: Ty<'_>, path: &[&str]) -> bool {
 127     match ty.kind {
 128         ty::Adt(adt, _) => match_def_path(cx, adt.did, path),
 129         _ => false,
 130     }
 131 }