Auto merge of #13055 - Jarcho:auto_derive, r=Alexendoo

Only check for `automatically_derived` on impl blocks

This brings us in line with how rustc checks for the attribute. Also note that `unused_attributes` will trigger if it's placed anywhere else.

See:
https://github.com/rust-lang/rust/blob/9a21ac8e7efe9ea26a8065d0959a976ca32039bb/compiler/rustc_passes/src/dead.rs#L400-L403
https://github.com/rust-lang/rust/blob/9a21ac8e7efe9ea26a8065d0959a976ca32039bb/compiler/rustc_passes/src/liveness.rs#L143-L148

changelog: none

Author: bors

clippy_lints/src/default.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::{span_lint_and_note, span_lint_and_sugg};
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::ty::{has_drop, is_copy};
-use clippy_utils::{any_parent_is_automatically_derived, contains_name, get_parent_expr, is_from_proc_macro};
+use clippy_utils::{contains_name, get_parent_expr, in_automatically_derived, is_from_proc_macro};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
@@ -84,7 +84,7 @@ impl<'tcx> LateLintPass<'tcx> for Default {
             // Avoid cases already linted by `field_reassign_with_default`
             && !self.reassigned_linted.contains(&expr.span)
             && let ExprKind::Call(path, ..) = expr.kind
-            && !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
+            && !in_automatically_derived(cx.tcx, expr.hir_id)
             && let ExprKind::Path(ref qpath) = path.kind
             && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
             && cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
@@ -113,9 +113,9 @@ impl<'tcx> LateLintPass<'tcx> for Default {
         // start from the `let mut _ = _::default();` and look at all the following
         // statements, see if they re-assign the fields of the binding
         let stmts_head = match block.stmts {
+            [] | [_] => return,
             // Skip the last statement since there cannot possibly be any following statements that re-assign fields.
-            [head @ .., _] if !head.is_empty() => head,
-            _ => return,
+            [head @ .., _] => head,
         };
         for (stmt_idx, stmt) in stmts_head.iter().enumerate() {
             // find all binding statements like `let mut _ = T::default()` where `T::default()` is the
@@ -124,7 +124,7 @@ impl<'tcx> LateLintPass<'tcx> for Default {
             let (local, variant, binding_name, binding_type, span) = if let StmtKind::Let(local) = stmt.kind
                 // only take `let ...` statements
                 && let Some(expr) = local.init
-                && !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
+                && !in_automatically_derived(cx.tcx, expr.hir_id)
                 && !expr.span.from_expansion()
                 // only take bindings to identifiers
                 && let PatKind::Binding(_, binding_id, ident, _) = local.pat.kind

clippy_lints/src/misc.rs

@@ -2,8 +2,8 @@ use clippy_utils::diagnostics::{span_lint, span_lint_and_then, span_lint_hir_and
 use clippy_utils::source::{snippet, snippet_with_context};
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
-    any_parent_is_automatically_derived, fulfill_or_allowed, get_parent_expr, is_lint_allowed, iter_input_pats,
-    last_path_segment, SpanlessEq,
+    fulfill_or_allowed, get_parent_expr, in_automatically_derived, is_lint_allowed, iter_input_pats, last_path_segment,
+    SpanlessEq,
 };
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
@@ -206,7 +206,7 @@ impl<'tcx> LateLintPass<'tcx> for LintPass {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if in_external_macro(cx.sess(), expr.span)
             || expr.span.desugaring_kind().is_some()
-            || any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
+            || in_automatically_derived(cx.tcx, expr.hir_id)
         {
             return;
         }

clippy_lints/src/no_effect.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then};
 use clippy_utils::source::snippet_opt;
 use clippy_utils::ty::has_drop;
 use clippy_utils::{
-    any_parent_is_automatically_derived, is_inside_always_const_context, is_lint_allowed, path_to_local, peel_blocks,
+    in_automatically_derived, is_inside_always_const_context, is_lint_allowed, path_to_local, peel_blocks,
 };
 use rustc_errors::Applicability;
 use rustc_hir::def::{DefKind, Res};
@@ -187,7 +187,7 @@ impl NoEffect {
                 && has_no_effect(cx, init)
                 && let PatKind::Binding(_, hir_id, ident, _) = local.pat.kind
                 && ident.name.to_ident_string().starts_with('_')
-                && !any_parent_is_automatically_derived(cx.tcx, local.hir_id)
+                && !in_automatically_derived(cx.tcx, local.hir_id)
             {
                 if let Some(l) = self.local_bindings.last_mut() {
                     l.push(hir_id);

clippy_utils/src/lib.rs

@@ -103,8 +103,9 @@ use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
 use rustc_hir::{
     self as hir, def, Arm, ArrayLen, BindingMode, Block, BlockCheckMode, Body, ByRef, Closure, ConstContext,
     Destination, Expr, ExprField, ExprKind, FnDecl, FnRetTy, GenericArgs, HirId, Impl, ImplItem, ImplItemKind,
-    ImplItemRef, Item, ItemKind, LangItem, LetStmt, MatchSource, Mutability, Node, OwnerId, Param, Pat, PatKind, Path,
-    PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitItemRef, TraitRef, TyKind, UnOp,
+    ImplItemRef, Item, ItemKind, LangItem, LetStmt, MatchSource, Mutability, Node, OwnerId, OwnerNode, Param, Pat,
+    PatKind, Path, PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitItemRef, TraitRef,
+    TyKind, UnOp,
 };
 use rustc_lexer::{tokenize, TokenKind};
 use rustc_lint::{LateContext, Level, Lint, LintContext};
@@ -1924,8 +1925,18 @@ pub fn any_parent_has_attr(tcx: TyCtxt<'_>, node: HirId, symbol: Symbol) -> bool
     false
 }
 
-pub fn any_parent_is_automatically_derived(tcx: TyCtxt<'_>, node: HirId) -> bool {
-    any_parent_has_attr(tcx, node, sym::automatically_derived)
+/// Checks if the given HIR node is inside an `impl` block with the `automatically_derived`
+/// attribute.
+pub fn in_automatically_derived(tcx: TyCtxt<'_>, id: HirId) -> bool {
+    tcx.hir()
+        .parent_owner_iter(id)
+        .filter(|(_, node)| matches!(node, OwnerNode::Item(item) if matches!(item.kind, ItemKind::Impl(_))))
+        .any(|(id, _)| {
+            has_attr(
+                tcx.hir().attrs(tcx.local_def_id_to_hir_id(id.def_id)),
+                sym::automatically_derived,
+            )
+        })
 }
 
 /// Matches a function call with the given path and returns the arguments.