src/tools/clippy/clippy_lints/src/fallible_impl_from.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use clippy_utils::{is_expn_of, match_panic_def_id, method_chain_args};
   4 use if_chain::if_chain;
   5 use rustc_hir as hir;
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_middle::hir::map::Map;
   8 use rustc_middle::ty;
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::{sym, Span};
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  15     ///
  16     /// ### Why is this bad?
  17     /// `TryFrom` should be used if there's a possibility of failure.
  18     ///
  19     /// ### Example
  20     /// ```rust
  21     /// struct Foo(i32);
  22     ///
  23     /// // Bad
  24     /// impl From<String> for Foo {
  25     ///     fn from(s: String) -> Self {
  26     ///         Foo(s.parse().unwrap())
  27     ///     }
  28     /// }
  29     /// ```
  30     ///
  31     /// ```rust
  32     /// // Good
  33     /// struct Foo(i32);
  34     ///
  35     /// use std::convert::TryFrom;
  36     /// impl TryFrom<String> for Foo {
  37     ///     type Error = ();
  38     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  39     ///         if let Ok(parsed) = s.parse() {
  40     ///             Ok(Foo(parsed))
  41     ///         } else {
  42     ///             Err(())
  43     ///         }
  44     ///     }
  45     /// }
  46     /// ```
  47     #[clippy::version = "pre 1.29.0"]
  48     pub FALLIBLE_IMPL_FROM,
  49     nursery,
  50     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  51 }
  52
  53 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  54
  55 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  56     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  57         // check for `impl From<???> for ..`
  58         if_chain! {
  59             if let hir::ItemKind::Impl(impl_) = &item.kind;
  60             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  61             if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
  62             then {
  63                 lint_impl_body(cx, item.span, impl_.items);
  64             }
  65         }
  66     }
  67 }
  68
  69 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
  70     use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  71     use rustc_hir::{Expr, ExprKind, ImplItemKind, QPath};
  72
  73     struct FindPanicUnwrap<'a, 'tcx> {
  74         lcx: &'a LateContext<'tcx>,
  75         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  76         result: Vec<Span>,
  77     }
  78
  79     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  80         type Map = Map<'tcx>;
  81
  82         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  83             // check for `begin_panic`
  84             if_chain! {
  85                 if let ExprKind::Call(func_expr, _) = expr.kind;
  86                 if let ExprKind::Path(QPath::Resolved(_, path)) = func_expr.kind;
  87                 if let Some(path_def_id) = path.res.opt_def_id();
  88                 if match_panic_def_id(self.lcx, path_def_id);
  89                 if is_expn_of(expr.span, "unreachable").is_none();
  90                 then {
  91                     self.result.push(expr.span);
  92                 }
  93             }
  94
  95             // check for `unwrap`
  96             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  97                 let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
  98                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym::Option)
  99                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym::Result)
 100                 {
 101                     self.result.push(expr.span);
 102                 }
 103             }
 104
 105             // and check sub-expressions
 106             intravisit::walk_expr(self, expr);
 107         }
 108
 109         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 110             NestedVisitorMap::None
 111         }
 112     }
 113
 114     for impl_item in impl_items {
 115         if_chain! {
 116             if impl_item.ident.name == sym::from;
 117             if let ImplItemKind::Fn(_, body_id) =
 118                 cx.tcx.hir().impl_item(impl_item.id).kind;
 119             then {
 120                 // check the body for `begin_panic` or `unwrap`
 121                 let body = cx.tcx.hir().body(body_id);
 122                 let mut fpu = FindPanicUnwrap {
 123                     lcx: cx,
 124                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 125                     result: Vec::new(),
 126                 };
 127                 fpu.visit_expr(&body.value);
 128
 129                 // if we've found one, lint
 130                 if !fpu.result.is_empty() {
 131                     span_lint_and_then(
 132                         cx,
 133                         FALLIBLE_IMPL_FROM,
 134                         impl_span,
 135                         "consider implementing `TryFrom` instead",
 136                         move |diag| {
 137                             diag.help(
 138                                 "`From` is intended for infallible conversions only. \
 139                                 Use `TryFrom` if there's a possibility for the conversion to fail");
 140                             diag.span_note(fpu.result, "potential failure(s)");
 141                         });
 142                 }
 143             }
 144         }
 145     }
 146 }