Don't give APITs names with macro expansion placeholder fragments in it

compiler/rustc_expand/src/base.rs

@@ -1116,6 +1116,10 @@ pub trait ResolverExpand {
         trait_def_id: DefId,
         impl_def_id: LocalDefId,
     ) -> Result<Vec<(Ident, Option<Ident>)>, Indeterminate>;
+
+    /// Record the name of an opaque `Ty::ImplTrait` pre-expansion so that it can be used
+    /// to generate an item name later that does not reference placeholder macros.
+    fn insert_impl_trait_name(&mut self, id: NodeId, name: Symbol);
 }
 
 pub trait LintStoreExpand {

compiler/rustc_expand/src/expand.rs

@@ -26,7 +26,7 @@ use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
 use rustc_session::parse::feature_err;
 use rustc_session::{Limit, Session};
 use rustc_span::hygiene::SyntaxContext;
-use rustc_span::{ErrorGuaranteed, FileName, Ident, LocalExpnId, Span, sym};
+use rustc_span::{ErrorGuaranteed, FileName, Ident, LocalExpnId, Span, Symbol, sym};
 use smallvec::SmallVec;
 
 use crate::base::*;
@@ -2315,7 +2315,17 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
     }
 
     fn visit_ty(&mut self, node: &mut P<ast::Ty>) {
-        self.visit_node(node)
+        // Save the pre-expanded name of this `ImplTrait`, so that later when defining
+        // an APIT we use a name that doesn't have any placeholder fragments in it.
+        if let ast::TyKind::ImplTrait(id, _) = &mut node.kind {
+            // HACK: Assign an ID to this node out-of-order.
+            self.visit_id(id);
+            let id = *id;
+            let name = Symbol::intern(&pprust::ty_to_string(node).replace('\n', " "));
+            self.cx.resolver.insert_impl_trait_name(id, name);
+        }
+
+        self.visit_node(node);
     }
 
     fn visit_pat(&mut self, node: &mut P<ast::Pat>) {

compiler/rustc_resolve/src/def_collector.rs

@@ -2,12 +2,12 @@ use std::mem;
 
 use rustc_ast::visit::FnKind;
 use rustc_ast::*;
-use rustc_ast_pretty::pprust;
 use rustc_attr_parsing::{AttributeParser, OmitDoc};
 use rustc_expand::expand::AstFragment;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind};
 use rustc_hir::def_id::LocalDefId;
+use rustc_middle::span_bug;
 use rustc_span::hygiene::LocalExpnId;
 use rustc_span::{Span, Symbol, sym};
 use tracing::debug;
@@ -381,7 +381,11 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
                 // gets too long. We don't want these to show up in compiler
                 // output or built artifacts, so replace them here...
                 // Perhaps we should instead format APITs more robustly.
-                let name = Symbol::intern(&pprust::ty_to_string(ty).replace('\n', " "));
+                let name = *self
+                    .resolver
+                    .impl_trait_names
+                    .get(id)
+                    .unwrap_or_else(|| span_bug!(ty.span, "expected this opaque to be named"));
                 let kind = match self.invocation_parent.impl_trait_context {
                     ImplTraitContext::Universal => DefKind::TyParam,
                     ImplTraitContext::Existential => DefKind::OpaqueTy,

compiler/rustc_resolve/src/lib.rs

@@ -1224,6 +1224,11 @@ pub struct Resolver<'ra, 'tcx> {
     current_crate_outer_attr_insert_span: Span,
 
     mods_with_parse_errors: FxHashSet<DefId>,
+
+    // Stores pre-expansion and pre-placeholder-fragment-insertion names for `impl Trait` types
+    // that were encountered during resolution. These names are used to generate item names
+    // for APITs, so we don't want to leak details of resolution into these names.
+    impl_trait_names: FxHashMap<NodeId, Symbol>,
 }
 
 /// This provides memory for the rest of the crate. The `'ra` lifetime that is
@@ -1579,6 +1584,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             impl_binding_keys: Default::default(),
             current_crate_outer_attr_insert_span,
             mods_with_parse_errors: Default::default(),
+            impl_trait_names: Default::default(),
         };
 
         let root_parent_scope = ParentScope::module(graph_root, &resolver);

compiler/rustc_resolve/src/macros.rs

@@ -511,6 +511,10 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         });
         Ok(idents)
     }
+
+    fn insert_impl_trait_name(&mut self, id: NodeId, name: Symbol) {
+        self.impl_trait_names.insert(id, name);
+    }
 }
 
 impl<'ra, 'tcx> Resolver<'ra, 'tcx> {

tests/ui/impl-trait/name-mentioning-macro.rs

@@ -0,0 +1,12 @@
+trait Foo<T> {}
+
+macro_rules! bar {
+    () => { () }
+}
+
+fn foo(x: impl Foo<bar!()>) {
+    let () = x;
+    //~^ ERROR mismatched types
+}
+
+fn main() {}

tests/ui/impl-trait/name-mentioning-macro.stderr

@@ -0,0 +1,16 @@
+error[E0308]: mismatched types
+  --> $DIR/name-mentioning-macro.rs:8:9
+   |
+LL | fn foo(x: impl Foo<bar!()>) {
+   |           ---------------- expected this type parameter
+LL |     let () = x;
+   |         ^^   - this expression has type `impl Foo<bar!()>`
+   |         |
+   |         expected type parameter `impl Foo<bar!()>`, found `()`
+   |
+   = note: expected type parameter `impl Foo<bar!()>`
+                   found unit type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/impl-trait/struct-field-fragment-in-name.rs

@@ -0,0 +1,16 @@
+//@ check-pass
+
+trait Trait<T> {}
+
+fn a(_: impl Trait<
+    [(); {
+        struct D {
+            #[rustfmt::skip]
+            bar: (),
+        }
+        0
+    }],
+>) {
+}
+
+fn main() {}