Mark impl Trait Functions as reachable. (Fixes rust-lang#50865)

Author: FelixMcFelix

src/Cargo.lock

@@ -2237,6 +2237,7 @@ dependencies = [
 name = "rustc_privacy"
 version = "0.0.0"
 dependencies = [
+ "log 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
  "rustc_data_structures 0.0.0",
  "rustc_typeck 0.0.0",

src/librustc/middle/privacy.rs

@@ -21,6 +21,8 @@ use syntax::ast::NodeId;
 // Accessibility levels, sorted in ascending order
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub enum AccessLevel {
+    // Superset of Reachable used to mark impl Trait items.
+    // ReachableFromImplTrait,
     // Exported items + items participating in various kinds of public interfaces,
     // but not directly nameable. For example, if function `fn f() -> T {...}` is
     // public, then type `T` is reachable. Its values can be obtained by other crates

src/librustc/middle/reachable.rs

@@ -446,6 +446,8 @@ fn reachable_set<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum) ->
     // Step 2: Mark all symbols that the symbols on the worklist touch.
     reachable_context.propagate();
 
+    debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
+
     // Return the set of reachable symbols.
     ReachableSet(Lrc::new(reachable_context.reachable_symbols))
 }

src/librustc_privacy/lib.rs

@@ -159,24 +159,30 @@ impl<'a, 'tcx> Visitor<'tcx> for EmbargoVisitor<'a, 'tcx> {
             hir::ItemKind::ForeignMod(..) => {
                 self.prev_level
             }
+            // Impl trait return types mark their parent function.
+            // It (and its children) are revisited if the change applies.
+            hir::ItemKind::Existential(ref ty_data) => {
+                if let Some(impl_trait_fn) = ty_data.impl_trait_fn {
+                    if let Some(node_id) = self.tcx.hir.as_local_node_id(impl_trait_fn) {
+                        self.update(node_id, Some(AccessLevel::Reachable));
+                    }
+                }
+                if item.vis.node.is_pub() { self.prev_level } else { None }
+            }
             // Other `pub` items inherit levels from parents
             hir::ItemKind::Const(..) | hir::ItemKind::Enum(..) | hir::ItemKind::ExternCrate(..) |
             hir::ItemKind::GlobalAsm(..) | hir::ItemKind::Fn(..) | hir::ItemKind::Mod(..) |
             hir::ItemKind::Static(..) | hir::ItemKind::Struct(..) |
             hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) |
-            hir::ItemKind::Existential(..) |
             hir::ItemKind::Ty(..) | hir::ItemKind::Union(..) | hir::ItemKind::Use(..) => {
-                if let hir::ItemKind::Fn(ref _decl, ref _header, ref _generics, ref _body) = item.node {
-                    debug!("Walked function");
-                }
                 if item.vis.node.is_pub() { self.prev_level } else { None }
             }
         };
 
         // Update level of the item itself
         let item_level = self.update(item.id, inherited_item_level);
 
-        debug!("believed to be: {:?}", item_level);
+        debug!("Its privacy is believed to be: {:?}", item_level);
 
         // Update levels of nested things
         match item.node {