resolve: mark it undetermined if single import is not has any bindings

Author: bvanjoi

compiler/rustc_resolve/src/ident.rs

@@ -965,6 +965,21 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // if it can then our result is not determined and can be invalidated.
         for single_import in &resolution.single_imports {
             let Some(import_vis) = single_import.vis.get() else {
+                // This branch handles a cycle in single imports, which occurs
+                // when we've previously captured the `vis` value during an import
+                // process.
+                //
+                // For example:
+                // ```
+                // use a::b;
+                // use b as a;
+                // ```
+                // 1. Steal the `vis` in `use a::b` and attempt to locate `a` in the
+                //    current module.
+                // 2. Encounter the import `use b as a`, which is a `single_import` for `a`,
+                //    and try to find `b` in the current module.
+                // 3. Re-encounter the `use a::b` import since it's a `single_import` of `b`.
+                //    This leads to entering this branch.
                 continue;
             };
             if !self.is_accessible_from(import_vis, parent_scope.module) {
@@ -979,15 +994,25 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 // named imports.
                 continue;
             }
+
             let Some(module) = single_import.imported_module.get() else {
                 return Err((Undetermined, Weak::No));
             };
-            let ImportKind::Single { source: ident, .. } = single_import.kind else {
+            let ImportKind::Single { source: ident, source_bindings, .. } = &single_import.kind
+            else {
                 unreachable!();
             };
+            if binding.map_or(false, |binding| binding.module().is_some())
+                && source_bindings.iter().all(|binding| matches!(binding.get(), Err(Undetermined)))
+            {
+                // This branch allows the binding to be defined or updated later,
+                // avoiding module inconsistency between the resolve process and the finalize process.
+                // See more details in #124840
+                return Err((Undetermined, Weak::No));
+            }
             match self.resolve_ident_in_module(
                 module,
-                ident,
+                *ident,
                 ns,
                 &single_import.parent_scope,
                 None,

compiler/rustc_resolve/src/imports.rs

@@ -352,9 +352,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     (old_glob @ true, false) | (old_glob @ false, true) => {
                         let (glob_binding, nonglob_binding) =
                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
-                        if glob_binding.res() != nonglob_binding.res()
-                            && key.ns == MacroNS
+                        if key.ns == MacroNS
                             && nonglob_binding.expansion != LocalExpnId::ROOT
+                            && glob_binding.res() != nonglob_binding.res()
                         {
                             resolution.binding = Some(this.ambiguity(
                                 AmbiguityKind::GlobVsExpanded,

tests/crashes/124490.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+// https://github.com/rust-lang/rust/pull/124840#issuecomment-2098148587
+
+mod a {
+    pub(crate) use crate::S;
+}
+mod b {
+    pub struct S;
+}
+use self::a::S;
+use self::b::*;
+
+fn main() {}

tests/crashes/125013-1.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+// similar `cycle-import-in-diff-module-0.rs`
+
+mod a {
+    pub(crate) use crate::s;
+}
+mod b {
+    pub mod s {}
+}
+use self::b::*;
+use self::a::s;
+
+fn main() {}

tests/crashes/125013-2.rs

@@ -0,0 +1,17 @@
+// https://github.com/rust-lang/rust/issues/124490
+
+mod a {
+    pub mod b {
+        pub mod c {}
+    }
+}
+
+use a::*;
+
+use b::c;
+//~^ ERROR: cannot determine resolution for the import
+//~| ERROR: cannot determine resolution for the import
+//~| ERROR: unresolved import `b::c`
+use c as b;
+
+fn main() {}

tests/ui/imports/cycle-import-in-diff-module-0.rs

@@ -0,0 +1,23 @@
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution-1.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution-1.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error[E0432]: unresolved import `b::c`
+  --> $DIR/shadow-glob-module-resolution-1.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0432`.

tests/ui/imports/cycle-import-in-diff-module-1.rs

@@ -0,0 +1,19 @@
+// https://github.com/rust-lang/rust/issues/125013
+
+mod a {
+  pub mod b {
+    pub mod c {
+      pub trait D {}
+    }
+  }
+}
+
+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() { }