fix(resolve): prevent infinite loop when glob-import self

Author: bvanjoi

compiler/rustc_resolve/src/ident.rs

@@ -1032,6 +1032,12 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 Some(_) => continue,
                 None => return Err((Undetermined, Weak::Yes)),
             };
+
+            if ptr::eq(module, glob_import.parent_scope.module) {
+                // do not glob-import a module into itself
+                continue;
+            }
+
             let tmp_parent_scope;
             let (mut adjusted_parent_scope, mut ident) =
                 (parent_scope, ident.normalize_to_macros_2_0());

tests/ui/underscore-imports/issue-110164.rs

@@ -0,0 +1,19 @@
+use self::*;
+//~^ ERROR unresolved import `self::*`
+use crate::*;
+//~^ ERROR unresolved import `crate::*`
+use _::a;
+//~^ ERROR expected identifier, found reserved identifier `_`
+//~| ERROR unresolved import `_`
+use _::*;
+//~^ ERROR expected identifier, found reserved identifier `_`
+//~| ERROR unresolved import `_`
+
+fn main() {
+    use _::a;
+    //~^ ERROR expected identifier, found reserved identifier `_`
+    //~| ERROR unresolved import `_`
+    use _::*;
+    //~^ ERROR expected identifier, found reserved identifier `_`
+    //~| ERROR unresolved import `_`
+}

tests/ui/underscore-imports/issue-110164.stderr

@@ -0,0 +1,71 @@
+error: expected identifier, found reserved identifier `_`
+  --> $DIR/issue-110164.rs:5:5
+   |
+LL | use _::a;
+   |     ^ expected identifier, found reserved identifier
+
+error: expected identifier, found reserved identifier `_`
+  --> $DIR/issue-110164.rs:8:5
+   |
+LL | use _::*;
+   |     ^ expected identifier, found reserved identifier
+
+error: expected identifier, found reserved identifier `_`
+  --> $DIR/issue-110164.rs:13:9
+   |
+LL |     use _::a;
+   |         ^ expected identifier, found reserved identifier
+
+error: expected identifier, found reserved identifier `_`
+  --> $DIR/issue-110164.rs:16:9
+   |
+LL |     use _::*;
+   |         ^ expected identifier, found reserved identifier
+
+error[E0432]: unresolved import `self::*`
+  --> $DIR/issue-110164.rs:1:5
+   |
+LL | use self::*;
+   |     ^^^^^^^ cannot glob-import a module into itself
+
+error[E0432]: unresolved import `crate::*`
+  --> $DIR/issue-110164.rs:3:5
+   |
+LL | use crate::*;
+   |     ^^^^^^^^ cannot glob-import a module into itself
+
+error[E0432]: unresolved import `_`
+  --> $DIR/issue-110164.rs:8:5
+   |
+LL | use _::*;
+   |     ^ maybe a missing crate `_`?
+   |
+   = help: consider adding `extern crate _` to use the `_` crate
+
+error[E0432]: unresolved import `_`
+  --> $DIR/issue-110164.rs:5:5
+   |
+LL | use _::a;
+   |     ^ maybe a missing crate `_`?
+   |
+   = help: consider adding `extern crate _` to use the `_` crate
+
+error[E0432]: unresolved import `_`
+  --> $DIR/issue-110164.rs:13:9
+   |
+LL |     use _::a;
+   |         ^ maybe a missing crate `_`?
+   |
+   = help: consider adding `extern crate _` to use the `_` crate
+
+error[E0432]: unresolved import `_`
+  --> $DIR/issue-110164.rs:16:9
+   |
+LL |     use _::*;
+   |         ^ maybe a missing crate `_`?
+   |
+   = help: consider adding `extern crate _` to use the `_` crate
+
+error: aborting due to 10 previous errors
+
+For more information about this error, try `rustc --explain E0432`.