Match the old logic closer

Author: petrochenkov

compiler/rustc_resolve/src/ident.rs

@@ -491,6 +491,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             // Found another solution, if the first one was "weak", report an error.
                             if this.get_mut().maybe_push_ambiguity(
                                 orig_ident,
+                                ns,
+                                scope_set,
                                 parent_scope,
                                 binding,
                                 innermost_binding,
@@ -798,6 +800,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     fn maybe_push_ambiguity(
         &mut self,
         orig_ident: Ident,
+        ns: Namespace,
+        scope_set: ScopeSet<'ra>,
         parent_scope: &ParentScope<'ra>,
         binding: NameBinding<'ra>,
         innermost_binding: NameBinding<'ra>,
@@ -811,6 +815,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             return false;
         }
 
+        let module_only = matches!(scope_set, ScopeSet::Module(..));
         let is_builtin = |res| matches!(res, Res::NonMacroAttr(NonMacroAttrKind::Builtin(..)));
         let derive_helper = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
         let derive_helper_compat = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
@@ -839,9 +844,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             )
         } else if innermost_binding.is_glob_import() {
             Some(AmbiguityKind::GlobVsOuter)
-        } else if innermost_binding.may_appear_after(parent_scope.expansion, binding) {
+        } else if !module_only
+            && innermost_binding.may_appear_after(parent_scope.expansion, binding)
+        {
             Some(AmbiguityKind::MoreExpandedVsOuter)
         } else if innermost_binding.expansion != LocalExpnId::ROOT
+            && (!module_only || ns == MacroNS)
             && binding.is_glob_import()
             && !innermost_binding.is_glob_import()
             && self.binding_parent_modules.get(&innermost_binding)

tests/ui/underscore-imports/shadow.rs

@@ -14,7 +14,6 @@ mod b {
 
 mod c {
     use crate::b::Shadow as _; // Only imports the struct
-    //~^ ERROR `Shadow` is ambiguous
 
     fn f(x: &()) {
         x.deref(); //~ ERROR no method named `deref` found

tests/ui/underscore-imports/shadow.stderr

@@ -1,29 +1,5 @@
-error[E0659]: `Shadow` is ambiguous
-  --> $DIR/shadow.rs:16:19
-   |
-LL |     use crate::b::Shadow as _; // Only imports the struct
-   |                   ^^^^^^ ambiguous name
-   |
-   = note: ambiguous because of a conflict between a macro-expanded name and a less macro-expanded name from outer scope during import or macro resolution
-note: `Shadow` could refer to the struct defined here
-  --> $DIR/shadow.rs:10:25
-   |
-LL |         ($i:ident) => { pub struct $i; }
-   |                         ^^^^^^^^^^^^^^
-LL |     }
-LL |     m!(Shadow);
-   |     ---------- in this macro invocation
-   = help: use `self::Shadow` to refer to this struct unambiguously
-note: `Shadow` could also refer to the trait imported here
-  --> $DIR/shadow.rs:8:13
-   |
-LL |     pub use crate::a::*;
-   |             ^^^^^^^^^^^
-   = help: use `self::Shadow` to refer to this trait unambiguously
-   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0599]: no method named `deref` found for reference `&()` in the current scope
-  --> $DIR/shadow.rs:20:11
+  --> $DIR/shadow.rs:19:11
    |
 LL |         x.deref();
    |           ^^^^^ method not found in `&()`
@@ -34,7 +10,6 @@ help: trait `Deref` which provides `deref` is implemented but not in scope; perh
 LL +     use std::ops::Deref;
    |
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0599, E0659.
-For more information about an error, try `rustc --explain E0599`.
+For more information about this error, try `rustc --explain E0599`.