Remove DummyAstNode.

It was added in #91519 to allow `visit_clobber` to be used in one extra
place, but is seemingly no longer needed.

Author: nnethercote

compiler/rustc_ast/src/mut_visit.rs

@@ -310,21 +310,19 @@ pub trait MutVisitor: Sized {
 
 /// Use a map-style function (`FnOnce(T) -> T`) to overwrite a `&mut T`. Useful
 /// when using a `flat_map_*` or `filter_map_*` method within a `visit_`
-/// method.
+/// method. Abort the program if the closure panics. (We used to overwrite `t`
+/// with a dummy value and then resume unwinding, but having to provide a dummy
+/// value for all the relevant AST nodes was a pain. If you need that back,
+/// revert the relevant change from #121827.)
 //
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
-pub fn visit_clobber<T: DummyAstNode>(t: &mut T, f: impl FnOnce(T) -> T) {
+pub fn visit_clobber<T>(t: &mut T, f: impl FnOnce(T) -> T) {
     unsafe {
         // Safe because `t` is used in a read-only fashion by `read()` before
         // being overwritten by `write()`.
         let old_t = ptr::read(t);
-        let new_t =
-            panic::catch_unwind(panic::AssertUnwindSafe(|| f(old_t))).unwrap_or_else(|err| {
-                // Set `t` to some valid but possible meaningless value,
-                // and pass the fatal error further.
-                ptr::write(t, T::dummy());
-                panic::resume_unwind(err);
-            });
+        let new_t = panic::catch_unwind(panic::AssertUnwindSafe(|| f(old_t)))
+            .unwrap_or_else(|_| std::process::abort());
         ptr::write(t, new_t);
     }
 }
@@ -1602,111 +1600,3 @@ pub fn noop_visit_capture_by<T: MutVisitor>(capture_by: &mut CaptureBy, vis: &mu
         }
     }
 }
-
-/// Some value for the AST node that is valid but possibly meaningless. The
-/// value will never be used meaningfully, it exists just to support unwinding
-/// in `visit_clobber` in the case where its closure panics. 
-pub trait DummyAstNode {
-    fn dummy() -> Self;
-}
-
-impl<T> DummyAstNode for Option<T> {
-    fn dummy() -> Self {
-        Default::default()
-    }
-}
-
-impl<T: DummyAstNode + 'static> DummyAstNode for P<T> {
-    fn dummy() -> Self {
-        P(DummyAstNode::dummy())
-    }
-}
-
-impl DummyAstNode for Item {
-    fn dummy() -> Self {
-        Item {
-            attrs: Default::default(),
-            id: DUMMY_NODE_ID,
-            span: Default::default(),
-            vis: Visibility {
-                kind: VisibilityKind::Public,
-                span: Default::default(),
-                tokens: Default::default(),
-            },
-            ident: Ident::empty(),
-            kind: ItemKind::ExternCrate(None),
-            tokens: Default::default(),
-        }
-    }
-}
-
-impl DummyAstNode for Expr {
-    fn dummy() -> Self {
-        Expr {
-            id: DUMMY_NODE_ID,
-            kind: ExprKind::Dummy,
-            span: Default::default(),
-            attrs: Default::default(),
-            tokens: Default::default(),
-        }
-    }
-}
-
-impl DummyAstNode for Ty {
-    fn dummy() -> Self {
-        Ty {
-            id: DUMMY_NODE_ID,
-            kind: TyKind::Dummy,
-            span: Default::default(),
-            tokens: Default::default(),
-        }
-    }
-}
-
-impl DummyAstNode for Pat {
-    fn dummy() -> Self {
-        Pat {
-            id: DUMMY_NODE_ID,
-            kind: PatKind::Wild,
-            span: Default::default(),
-            tokens: Default::default(),
-        }
-    }
-}
-
-impl DummyAstNode for Stmt {
-    fn dummy() -> Self {
-        Stmt { id: DUMMY_NODE_ID, kind: StmtKind::Empty, span: Default::default() }
-    }
-}
-
-impl DummyAstNode for Block {
-    fn dummy() -> Self {
-        Block {
-            stmts: Default::default(),
-            id: DUMMY_NODE_ID,
-            rules: BlockCheckMode::Default,
-            span: Default::default(),
-            tokens: Default::default(),
-            could_be_bare_literal: Default::default(),
-        }
-    }
-}
-
-impl DummyAstNode for Crate {
-    fn dummy() -> Self {
-        Crate {
-            attrs: Default::default(),
-            items: Default::default(),
-            spans: Default::default(),
-            id: DUMMY_NODE_ID,
-            is_placeholder: Default::default(),
-        }
-    }
-}
-
-impl<N: DummyAstNode, T: DummyAstNode> DummyAstNode for crate::ast_traits::AstNodeWrapper<N, T> {
-    fn dummy() -> Self {
-        crate::ast_traits::AstNodeWrapper::new(N::dummy(), T::dummy())
-    }
-}

compiler/rustc_expand/src/expand.rs

@@ -1556,11 +1556,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
 /// This struct is a hack to workaround unstable of `stmt_expr_attributes`.
 /// It can be removed once that feature is stabilized.
 struct MethodReceiverTag;
-impl DummyAstNode for MethodReceiverTag {
-    fn dummy() -> MethodReceiverTag {
-        MethodReceiverTag
-    }
-}
+
 impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, MethodReceiverTag> {
     type OutputTy = Self;
     type AttrsTy = ast::AttrVec;
@@ -1822,10 +1818,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         }
     }
 
-    fn visit_node<Node: InvocationCollectorNode<OutputTy = Node> + DummyAstNode>(
-        &mut self,
-        node: &mut Node,
-    ) {
+    fn visit_node<Node: InvocationCollectorNode<OutputTy = Node>>(&mut self, node: &mut Node) {
         loop {
             return match self.take_first_attr(node) {
                 Some((attr, pos, derives)) => match attr.name_or_empty() {