resolve: Remove a special case for dummy imports

It is no longer needed to pass import validation, and the removal avoids some secondary errors.

Also add a couple of asserts

Author: petrochenkov

compiler/rustc_resolve/src/imports.rs

@@ -456,13 +456,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             warn_ambiguity,
             |this, resolution| {
                 assert!(!decl.warn_ambiguity.get());
-                if res == Res::Err
-                    && let Some(old_decl) = resolution.best_decl()
-                    && old_decl.res() != Res::Err
-                {
-                    // Do not override real declarations with `Res::Err`s from error recovery.
-                    return Ok(());
-                }
                 if decl.is_glob_import() {
                     resolution.glob_decl = Some(match resolution.glob_decl {
                         Some(old_decl) => this.select_glob_decl(
@@ -533,13 +526,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             };
             if self.is_accessible_from(binding.vis(), scope) {
                 let import_decl = self.new_import_decl(binding, *import);
-                let _ = self.try_plant_decl_into_local_module(
+                self.try_plant_decl_into_local_module(
                     ident,
                     orig_ident_span,
                     key.ns,
                     import_decl,
                     warn_ambiguity,
-                );
+                )
+                .expect("planting a glob cannot fail");
             }
         }
 
@@ -558,6 +552,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             self.per_ns(|this, ns| {
                 let module = import.parent_scope.module;
                 let ident = IdentKey::new(target);
+                // This can fail, dummies are inserted only in non-occupied slots.
                 let _ = this.try_plant_decl_into_local_module(
                     ident,
                     target.span,
@@ -1613,13 +1608,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     .resolution(import.parent_scope.module, key)
                     .and_then(|r| r.determined_decl())
                     .is_some_and(|binding| binding.warn_ambiguity_recursive());
-                let _ = self.try_plant_decl_into_local_module(
+                self.try_plant_decl_into_local_module(
                     key.ident,
                     orig_ident_span,
                     key.ns,
                     import_decl,
                     warn_ambiguity,
-                );
+                )
+                .expect("planting a glob cannot fail");
             }
         }
 

tests/ui/imports/issue-56125.rs

@@ -15,7 +15,7 @@ mod m2 {
 mod m3 {
     mod empty {}
     use empty::issue_56125; //~ ERROR unresolved import `empty::issue_56125`
-    use issue_56125::*; //~ ERROR `issue_56125` is ambiguous
+    use issue_56125::*;
 }
 
 fn main() {}

tests/ui/imports/issue-56125.stderr

@@ -54,24 +54,7 @@ LL |     use issue_56125::non_last_segment::non_last_segment::*;
    = help: consider adding an explicit import of `issue_56125` to disambiguate
    = help: or use `self::issue_56125` to refer to this module unambiguously
 
-error[E0659]: `issue_56125` is ambiguous
-  --> $DIR/issue-56125.rs:18:9
-   |
-LL |     use issue_56125::*;
-   |         ^^^^^^^^^^^ ambiguous name
-   |
-   = note: ambiguous because of a conflict between a name from a glob import and an outer scope during import or macro resolution
-   = note: `issue_56125` could refer to a crate passed with `--extern`
-   = help: use `::issue_56125` to refer to this crate unambiguously
-note: `issue_56125` could also refer to the module imported here
-  --> $DIR/issue-56125.rs:18:9
-   |
-LL |     use issue_56125::*;
-   |         ^^^^^^^^^^^^^^
-   = help: consider adding an explicit import of `issue_56125` to disambiguate
-   = help: or use `self::issue_56125` to refer to this module unambiguously
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0432, E0659.
 For more information about an error, try `rustc --explain E0432`.

tests/ui/imports/shadow-glob-module-resolution-2.rs

@@ -14,7 +14,5 @@ use a::*;
 use e as b;
 //~^ ERROR: unresolved import `e`
 use b::c::D as e;
-//~^ ERROR: cannot determine resolution for the import
-//~| ERROR: cannot determine resolution for the import
 
 fn main() { }

tests/ui/imports/shadow-glob-module-resolution-2.stderr

@@ -1,17 +1,3 @@
-error: cannot determine resolution for the import
-  --> $DIR/shadow-glob-module-resolution-2.rs:16:5
-   |
-LL | use b::c::D as e;
-   |     ^^^^^^^^^^^^
-
-error: cannot determine resolution for the import
-  --> $DIR/shadow-glob-module-resolution-2.rs:16:5
-   |
-LL | use b::c::D as e;
-   |     ^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error[E0432]: unresolved import `e`
   --> $DIR/shadow-glob-module-resolution-2.rs:14:5
    |
@@ -24,6 +10,6 @@ LL - use e as b;
 LL + use a as b;
    |
 
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0432`.

tests/ui/imports/shadow-glob-module-resolution-4.rs

@@ -12,8 +12,6 @@ use e as b;
 
 use b::C as e;
 //~^ ERROR: unresolved import `b::C`
-//~| ERROR: cannot determine resolution for the import
-//~| ERROR: cannot determine resolution for the import
 
 fn e() {}
 

tests/ui/imports/shadow-glob-module-resolution-4.stderr

@@ -1,23 +1,9 @@
-error: cannot determine resolution for the import
-  --> $DIR/shadow-glob-module-resolution-4.rs:13:5
-   |
-LL | use b::C as e;
-   |     ^^^^^^^^^
-
-error: cannot determine resolution for the import
-  --> $DIR/shadow-glob-module-resolution-4.rs:13:5
-   |
-LL | use b::C as e;
-   |     ^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error[E0432]: unresolved import `b::C`
   --> $DIR/shadow-glob-module-resolution-4.rs:13:5
    |
 LL | use b::C as e;
    |     ^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0432`.