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

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::macros::{is_panic, root_macro_call_first_node};
   3 use clippy_utils::method_chain_args;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_hir as hir;
   7 use rustc_lint::{LateContext, LateLintPass};
   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     /// impl From<String> for Foo {
  24     ///     fn from(s: String) -> Self {
  25     ///         Foo(s.parse().unwrap())
  26     ///     }
  27     /// }
  28     /// ```
  29     ///
  30     /// Use instead:
  31     /// ```rust
  32     /// struct Foo(i32);
  33     ///
  34     /// impl TryFrom<String> for Foo {
  35     ///     type Error = ();
  36     ///     fn try_from(s: String) -> Result<Self, Self::Error> {
  37     ///         if let Ok(parsed) = s.parse() {
  38     ///             Ok(Foo(parsed))
  39     ///         } else {
  40     ///             Err(())
  41     ///         }
  42     ///     }
  43     /// }
  44     /// ```
  45     #[clippy::version = "pre 1.29.0"]
  46     pub FALLIBLE_IMPL_FROM,
  47     nursery,
  48     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  49 }
  50
  51 declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
  52
  53 impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
  54     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  55         // check for `impl From<???> for ..`
  56         if_chain! {
  57             if let hir::ItemKind::Impl(impl_) = &item.kind;
  58             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  59             if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
  60             then {
  61                 lint_impl_body(cx, item.span, impl_.items);
  62             }
  63         }
  64     }
  65 }
  66
  67 fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
  68     use rustc_hir::intravisit::{self, Visitor};
  69     use rustc_hir::{Expr, ImplItemKind};
  70
  71     struct FindPanicUnwrap<'a, 'tcx> {
  72         lcx: &'a LateContext<'tcx>,
  73         typeck_results: &'tcx ty::TypeckResults<'tcx>,
  74         result: Vec<Span>,
  75     }
  76
  77     impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  78         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  79             if let Some(macro_call) = root_macro_call_first_node(self.lcx, expr) {
  80                 if is_panic(self.lcx, macro_call.def_id) {
  81                     self.result.push(expr.span);
  82                 }
  83             }
  84
  85             // check for `unwrap`
  86             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  87                 let receiver_ty = self.typeck_results.expr_ty(arglists[0].0).peel_refs();
  88                 if is_type_diagnostic_item(self.lcx, receiver_ty, sym::Option)
  89                     || is_type_diagnostic_item(self.lcx, receiver_ty, sym::Result)
  90                 {
  91                     self.result.push(expr.span);
  92                 }
  93             }
  94
  95             // and check sub-expressions
  96             intravisit::walk_expr(self, expr);
  97         }
  98     }
  99
 100     for impl_item in impl_items {
 101         if_chain! {
 102             if impl_item.ident.name == sym::from;
 103             if let ImplItemKind::Fn(_, body_id) =
 104                 cx.tcx.hir().impl_item(impl_item.id).kind;
 105             then {
 106                 // check the body for `begin_panic` or `unwrap`
 107                 let body = cx.tcx.hir().body(body_id);
 108                 let mut fpu = FindPanicUnwrap {
 109                     lcx: cx,
 110                     typeck_results: cx.tcx.typeck(impl_item.id.def_id),
 111                     result: Vec::new(),
 112                 };
 113                 fpu.visit_expr(body.value);
 114
 115                 // if we've found one, lint
 116                 if !fpu.result.is_empty() {
 117                     span_lint_and_then(
 118                         cx,
 119                         FALLIBLE_IMPL_FROM,
 120                         impl_span,
 121                         "consider implementing `TryFrom` instead",
 122                         move |diag| {
 123                             diag.help(
 124                                 "`From` is intended for infallible conversions only. \
 125                                 Use `TryFrom` if there's a possibility for the conversion to fail");
 126                             diag.span_note(fpu.result, "potential failure(s)");
 127                         });
 128                 }
 129             }
 130         }
 131     }
 132 }