Merge commit '27afd6ade4bb1123a8bf82001629b69d23d62aff' into clippyup

clippy_lints/src/derivable_impls.rs

@@ -0,0 +1,108 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::{in_macro, is_automatically_derived, is_default_equivalent, remove_blocks};
+use rustc_hir::{
+    def::{DefKind, Res},
+    Body, Expr, ExprKind, Impl, ImplItemKind, Item, ItemKind, Node, QPath,
+};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::TypeFoldable;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Detects manual `std::default::Default` implementations that are identical to a derived implementation.
+    ///
+    /// ### Why is this bad?
+    /// It is less concise.
+    ///
+    /// ### Example
+    /// ```rust
+    /// struct Foo {
+    ///     bar: bool
+    /// }
+    ///
+    /// impl std::default::Default for Foo {
+    ///     fn default() -> Self {
+    ///         Self {
+    ///             bar: false
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Could be written as:
+    ///
+    /// ```rust
+    /// #[derive(Default)]
+    /// struct Foo {
+    ///     bar: bool
+    /// }
+    /// ```
+    ///
+    /// ### Known problems
+    /// Derive macros [sometimes use incorrect bounds](https://github.com/rust-lang/rust/issues/26925)
+    /// in generic types and the user defined `impl` maybe is more generalized or
+    /// specialized than what derive will produce. This lint can't detect the manual `impl`
+    /// has exactly equal bounds, and therefore this lint is disabled for types with
+    /// generic parameters.
+    ///
+    pub DERIVABLE_IMPLS,
+    complexity,
+    "manual implementation of the `Default` trait which is equal to a derive"
+}
+
+declare_lint_pass!(DerivableImpls => [DERIVABLE_IMPLS]);
+
+fn is_path_self(e: &Expr<'_>) -> bool {
+    if let ExprKind::Path(QPath::Resolved(_, p)) = e.kind {
+        matches!(p.res, Res::SelfCtor(..) | Res::Def(DefKind::Ctor(..), _))
+    } else {
+        false
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for DerivableImpls {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
+        if_chain! {
+            if let ItemKind::Impl(Impl {
+                of_trait: Some(ref trait_ref),
+                items: [child],
+                ..
+            }) = item.kind;
+            if let attrs = cx.tcx.hir().attrs(item.hir_id());
+            if !is_automatically_derived(attrs);
+            if !in_macro(item.span);
+            if let Some(def_id) = trait_ref.trait_def_id();
+            if cx.tcx.is_diagnostic_item(sym::Default, def_id);
+            if let impl_item_hir = child.id.hir_id();
+            if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
+            if let ImplItemKind::Fn(_, b) = &impl_item.kind;
+            if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
+            if let Some(adt_def) = cx.tcx.type_of(item.def_id).ty_adt_def();
+            then {
+                if cx.tcx.type_of(item.def_id).definitely_has_param_types_or_consts(cx.tcx) {
+                    return;
+                }
+                let should_emit = match remove_blocks(func_expr).kind {
+                    ExprKind::Tup(fields) => fields.iter().all(|e| is_default_equivalent(cx, e)),
+                    ExprKind::Call(callee, args)
+                        if is_path_self(callee) => args.iter().all(|e| is_default_equivalent(cx, e)),
+                    ExprKind::Struct(_, fields, _) => fields.iter().all(|ef| is_default_equivalent(cx, ef.expr)),
+                    _ => false,
+                };
+                if should_emit {
+                    let path_string = cx.tcx.def_path_str(adt_def.did);
+                    span_lint_and_help(
+                        cx,
+                        DERIVABLE_IMPLS,
+                        item.span,
+                        "this `impl` can be derived",
+                        None,
+                        &format!("try annotating `{}` with `#[derive(Default)]`", path_string),
+                    );
+                }
+            }
+        }
+    }
+}