Auto merge of rust-lang#78784 - Mark-Simulacrum:revert-77421, r=petrochenkov

Revert "Revert "resolve: Avoid "self-confirming" import resolutions in one more case""

Specifically, this reverts commit b20bce8 from rust-lang#77421 to fix rust-lang#77586.

The lang team has decided that for the time being we want to avoid the breakage here (perhaps for a future edition; though almost certainly not the upcoming one), though a future PR may want to add a lint around this case (and perhaps others) which are unlikely to be readable code.

r? `@petrochenkov` to confirm this is the right way to fix rust-lang#77586.

Author: bors

compiler/rustc_resolve/src/imports.rs

@@ -872,6 +872,12 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
     /// consolidate multiple unresolved import errors into a single diagnostic.
     fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
         let orig_vis = import.vis.replace(ty::Visibility::Invisible);
+        let orig_unusable_binding = match &import.kind {
+            ImportKind::Single { target_bindings, .. } => {
+                Some(mem::replace(&mut self.r.unusable_binding, target_bindings[TypeNS].get()))
+            }
+            _ => None,
+        };
         let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
         let path_res = self.r.resolve_path(
             &import.module_path,
@@ -882,6 +888,9 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
             import.crate_lint(),
         );
         let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
+        if let Some(orig_unusable_binding) = orig_unusable_binding {
+            self.r.unusable_binding = orig_unusable_binding;
+        }
         import.vis.set(orig_vis);
         if let PathResult::Failed { .. } | PathResult::NonModule(..) = path_res {
             // Consider erroneous imports used to avoid duplicate diagnostics.
@@ -892,8 +901,7 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
                 // Consistency checks, analogous to `finalize_macro_resolutions`.
                 if let Some(initial_module) = import.imported_module.get() {
                     if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
-                        let msg = "inconsistent resolution for an import";
-                        self.r.session.span_err(import.span, msg);
+                        span_bug!(import.span, "inconsistent resolution for an import");
                     }
                 } else if self.r.privacy_errors.is_empty() {
                     let msg = "cannot determine resolution for the import";
@@ -913,6 +921,7 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
             }
             PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
                 if no_ambiguity {
+                    assert!(import.imported_module.get().is_none());
                     let err = match self.make_path_suggestion(
                         span,
                         import.module_path.clone(),

src/test/ui/imports/issue-62767.rs

@@ -1,3 +1,5 @@
+// check-pass
+
 // Minimized case from #62767.
 mod m {
     pub enum Same {
@@ -9,7 +11,7 @@ use m::*;
 
 // The variant `Same` introduced by this import is also considered when resolving the prefix
 // `Same::` during import validation to avoid effects similar to time travel (#74556).
-use Same::Same; //~ ERROR unresolved import `Same`
+use Same::Same;
 
 // Case from #74556.
 mod foo {
@@ -21,8 +23,8 @@ mod foo {
 }
 
 use foo::*;
-use bar::bar; //~ ERROR unresolved import `bar::bar`
-              //~| ERROR inconsistent resolution for an import
+use bar::bar;
+
 use bar::foobar;
 
 fn main() {}