Rollup merge of #126568 - bvanjoi:fix-126376, r=petrochenkov

mark undetermined if target binding in current ns is not got

Fixes #126376
Fixes #126389

Add a branch to handle more cases...

r? `@petrochenkov`

Author: matthiaskrgr

compiler/rustc_resolve/src/ident.rs

@@ -966,7 +966,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         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
+                // when we've previously **steal** the `vis` value during an import
                 // process.
                 //
                 // For example:
@@ -998,21 +998,28 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             let Some(module) = single_import.imported_module.get() else {
                 return Err((Undetermined, Weak::No));
             };
-            let ImportKind::Single { source: ident, target, target_bindings, .. } =
-                &single_import.kind
+            let ImportKind::Single { source, target, target_bindings, .. } = &single_import.kind
             else {
                 unreachable!();
             };
-            if (ident != target) && target_bindings.iter().all(|binding| binding.get().is_none()) {
+            if source != target {
                 // This branch allows the binding to be defined or updated later if the target name
-                // can hide the source but these bindings are not obtained.
-                // avoiding module inconsistency between the resolve process and the finalize process.
-                // See more details in #124840
-                return Err((Undetermined, Weak::No));
+                // can hide the source.
+                if target_bindings.iter().all(|binding| binding.get().is_none()) {
+                    // None of the target bindings are available, so we can't determine
+                    // if this binding is correct or not.
+                    // See more details in #124840
+                    return Err((Undetermined, Weak::No));
+                } else if target_bindings[ns].get().is_none() && binding.is_some() {
+                    // `binding.is_some()` avoids the condition where the binding
+                    // truly doesn't exist in this namespace and should return `Err(Determined)`.
+                    return Err((Undetermined, Weak::No));
+                }
             }
+
             match self.resolve_ident_in_module(
                 module,
-                *ident,
+                *source,
                 ns,
                 &single_import.parent_scope,
                 None,

tests/crashes/126376.rs

@@ -0,0 +1,19 @@
+// https://github.com/rust-lang/rust/issues/126389
+
+mod a {
+    pub mod b {
+        pub mod c {}
+    }
+}
+
+use a::*;
+
+use b::c;
+//~^ ERROR: unresolved import `b::c`
+//~| ERROR: cannot determine resolution for the import
+//~| ERROR: cannot determine resolution for the import
+use c as b;
+
+fn c() {}
+
+fn main() { }

tests/crashes/126389.rs

@@ -0,0 +1,23 @@
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution-3.rs:11:5
+   |
+LL | use b::c;
+   |     ^^^^
+
+error: cannot determine resolution for the import
+  --> $DIR/shadow-glob-module-resolution-3.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-3.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/shadow-glob-module-resolution-3.rs

@@ -0,0 +1,20 @@
+// https://github.com/rust-lang/rust/issues/126376
+
+mod a {
+    pub mod b {
+        pub trait C {}
+    }
+}
+
+use a::*;
+
+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() {}
+
+fn main() { }

tests/ui/imports/shadow-glob-module-resolution-3.stderr

@@ -0,0 +1,23 @@
+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
+
+For more information about this error, try `rustc --explain E0432`.