Auto merge of #67298 - Mark-Simulacrum:beta-backports, r=Mark-Simulacrum

[beta] Beta backports

Backporting the following pull requests:

 * resolve: Always resolve visibilities on impl items #67236
 * resolve: Resolve visibilities on fields with non-builtin attributes #67106
 * E0023: handle expected != tuple pattern type #67044
 * Fix `unused_parens` triggers on macro by example code #66983
 * Fix some issues with attributes on unnamed fields #66669
 * Ensure that we get a hard error on generic ZST constants if their bodies #67134 (via #67297)

Some of these conflicted on merge, I resolved where possible, sometimes by cherry-picking a commit or two more from the relevant PRs. Since those changes are necessary though for backport to proceed (otherwise not even std/core compile), seems fine -- they're fairly minor cleanups anyway.

src/librustc/hir/map/def_collector.rs

@@ -75,15 +75,16 @@ impl<'a> DefCollector<'a> {
     }
 
     fn collect_field(&mut self, field: &'a StructField, index: Option<usize>) {
+        let index = |this: &Self| index.unwrap_or_else(|| {
+            let node_id = NodeId::placeholder_from_expn_id(this.expansion);
+            this.definitions.placeholder_field_index(node_id)
+        });
+
         if field.is_placeholder {
+            self.definitions.set_placeholder_field_index(field.id, index(self));
             self.visit_macro_invoc(field.id);
         } else {
-            let name = field.ident.map(|ident| ident.name)
-                .or_else(|| index.map(sym::integer))
-                .unwrap_or_else(|| {
-                    let node_id = NodeId::placeholder_from_expn_id(self.expansion);
-                    sym::integer(self.definitions.placeholder_field_indices[&node_id])
-                });
+            let name = field.ident.map_or_else(|| sym::integer(index(self)), |ident| ident.name);
             let def = self.create_def(field.id, DefPathData::ValueNs(name), field.span);
             self.with_parent(def, |this| visit::walk_struct_field(this, field));
         }
@@ -190,9 +191,6 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
         // and every such attribute expands into a single field after it's resolved.
         for (index, field) in data.fields().iter().enumerate() {
             self.collect_field(field, Some(index));
-            if field.is_placeholder && field.ident.is_none() {
-                self.definitions.placeholder_field_indices.insert(field.id, index);
-            }
         }
     }
 

src/librustc/hir/map/definitions.rs

@@ -105,7 +105,7 @@ pub struct Definitions {
     /// we know what parent node that fragment should be attached to thanks to this table.
     invocation_parents: FxHashMap<ExpnId, DefIndex>,
     /// Indices of unnamed struct or variant fields with unresolved attributes.
-    pub(super) placeholder_field_indices: NodeMap<usize>,
+    pub placeholder_field_indices: NodeMap<usize>,
 }
 
 /// A unique identifier that we can use to lookup a definition
@@ -544,6 +544,15 @@ impl Definitions {
         let old_parent = self.invocation_parents.insert(invoc_id, parent);
         assert!(old_parent.is_none(), "parent `DefIndex` is reset for an invocation");
     }
+
+    pub fn placeholder_field_index(&self, node_id: ast::NodeId) -> usize {
+        self.placeholder_field_indices[&node_id]
+    }
+
+    pub fn set_placeholder_field_index(&mut self, node_id: ast::NodeId, index: usize) {
+        let old_index = self.placeholder_field_indices.insert(node_id, index);
+        assert!(old_index.is_none(), "placeholder field index is reset for a node ID");
+    }
 }
 
 impl DefPathData {

src/librustc_codegen_ssa/mir/constant.rs

@@ -23,7 +23,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     instance,
                     promoted: None,
                 };
-                self.cx.tcx().const_eval(ty::ParamEnv::reveal_all().and(cid))
+                self.cx.tcx().const_eval(ty::ParamEnv::reveal_all().and(cid)).map_err(|err| {
+                    self.cx.tcx().sess.span_err(constant.span, "erroneous constant encountered");
+                    err
+                })
             },
             _ => Ok(self.monomorphize(&constant.literal)),
         }

src/librustc_lint/unused.rs

@@ -374,7 +374,9 @@ impl UnusedParens {
         match value.kind {
             ast::ExprKind::Paren(ref inner) => {
                 if !Self::is_expr_parens_necessary(inner, followed_by_block) &&
-                    value.attrs.is_empty() {
+                    value.attrs.is_empty() &&
+                    !value.span.from_expansion()
+                {
                     let expr_text = if let Ok(snippet) = cx.sess().source_map()
                         .span_to_snippet(value.span) {
                             snippet

src/librustc_mir/transform/simplify.rs

@@ -363,9 +363,14 @@ impl<'a, 'tcx> Visitor<'tcx> for DeclMarker<'a, 'tcx> {
             let stmt =
                 &self.body.basic_blocks()[location.block].statements[location.statement_index];
             if let StatementKind::Assign(box (p, Rvalue::Use(Operand::Constant(c)))) = &stmt.kind {
-                if p.as_local().is_some() {
-                    trace!("skipping store of const value {:?} to {:?}", c, local);
-                    return;
+                match c.literal.val {
+                    // Keep assignments from unevaluated constants around, since the evaluation
+                    // may report errors, even if the use of the constant is dead code.
+                    interpret::ConstValue::Unevaluated(..) => {}
+                    _ => if p.as_local().is_some() {
+                        trace!("skipping store of const value {:?} to {:?}", c, p);
+                        return;
+                    },
                 }
             }
         }