1 files changed, 132 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/fallible_impl_from.rs b/src/tools/clippy/clippy_lints/src/fallible_impl_from.rs
new file mode 100644
index 000000000..b88e53aec
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/fallible_impl_from.rs
@@ -0,0 +1,132 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::macros::{is_panic, root_macro_call_first_node};
+use clippy_utils::method_chain_args;
+use clippy_utils::ty::is_type_diagnostic_item;
+use if_chain::if_chain;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{sym, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
+    ///
+    /// ### Why is this bad?
+    /// `TryFrom` should be used if there's a possibility of failure.
+    ///
+    /// ### Example
+    /// ```rust
+    /// struct Foo(i32);
+    ///
+    /// impl From<String> for Foo {
+    ///     fn from(s: String) -> Self {
+    ///         Foo(s.parse().unwrap())
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// struct Foo(i32);
+    ///
+    /// impl TryFrom<String> for Foo {
+    ///     type Error = ();
+    ///     fn try_from(s: String) -> Result<Self, Self::Error> {
+    ///         if let Ok(parsed) = s.parse() {
+    ///             Ok(Foo(parsed))
+    ///         } else {
+    ///             Err(())
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub FALLIBLE_IMPL_FROM,
+    nursery,
+    "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
+}
+
+declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
+
+impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
+        // check for `impl From<???> for ..`
+        if_chain! {
+            if let hir::ItemKind::Impl(impl_) = &item.kind;
+            if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
+            if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
+            then {
+                lint_impl_body(cx, item.span, impl_.items);
+            }
+        }
+    }
+}
+
+fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
+    use rustc_hir::intravisit::{self, Visitor};
+    use rustc_hir::{Expr, ImplItemKind};
+
+    struct FindPanicUnwrap<'a, 'tcx> {
+        lcx: &'a LateContext<'tcx>,
+        typeck_results: &'tcx ty::TypeckResults<'tcx>,
+        result: Vec<Span>,
+    }
+
+    impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
+        fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+            if let Some(macro_call) = root_macro_call_first_node(self.lcx, expr) {
+                if is_panic(self.lcx, macro_call.def_id) {
+                    self.result.push(expr.span);
+                }
+            }
+
+            // check for `unwrap`
+            if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
+                let receiver_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
+                if is_type_diagnostic_item(self.lcx, receiver_ty, sym::Option)
+                    || is_type_diagnostic_item(self.lcx, receiver_ty, sym::Result)
+                {
+                    self.result.push(expr.span);
+                }
+            }
+
+            // and check sub-expressions
+            intravisit::walk_expr(self, expr);
+        }
+    }
+
+    for impl_item in impl_items {
+        if_chain! {
+            if impl_item.ident.name == sym::from;
+            if let ImplItemKind::Fn(_, body_id) =
+                cx.tcx.hir().impl_item(impl_item.id).kind;
+            then {
+                // check the body for `begin_panic` or `unwrap`
+                let body = cx.tcx.hir().body(body_id);
+                let mut fpu = FindPanicUnwrap {
+                    lcx: cx,
+                    typeck_results: cx.tcx.typeck(impl_item.id.def_id),
+                    result: Vec::new(),
+                };
+                fpu.visit_expr(&body.value);
+
+                // if we've found one, lint
+                if !fpu.result.is_empty() {
+                    span_lint_and_then(
+                        cx,
+                        FALLIBLE_IMPL_FROM,
+                        impl_span,
+                        "consider implementing `TryFrom` instead",
+                        move |diag| {
+                            diag.help(
+                                "`From` is intended for infallible conversions only. \
+                                Use `TryFrom` if there's a possibility for the conversion to fail");
+                            diag.span_note(fpu.result, "potential failure(s)");
+                        });
+                }
+            }
+        }
+    }
+}