[clang] [clang] fix merging of UsingShadowDecl (PR #80245)

[Chuanqi Xu via cfe-commits]

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@@ -0,0 +1,42 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+//
+// RUN: %clang_cc1 -std=c++20 -I %t %t/A.cppm -emit-module-interface -o %t/A.pcm -verify
+// RUN: %clang_cc1 -std=c++20 -I %t %t/B.cpp -fmodule-file=A=%t/A.pcm -fsyntax-only -verify -ast-dump-all -ast-dump-filter baz | FileCheck %s
+
+//--- foo.h
+namespace baz {
+  using foo = char;
+  using baz::foo;
+}
+
+//--- A.cppm
+// expected-no-diagnostics
+module;
+#include "foo.h"
+export module A;
+
+//--- B.cpp
+// expected-no-diagnostics
+#include "foo.h"
+import A;
+// Since modules are loaded lazily, force loading by performing a lookup.
+using xxx = baz::foo;
+
+// CHECK-LABEL: Dumping baz:
+// CHECK-NEXT: NamespaceDecl {{.*}} imported in A.<global> {{.*}} baz
+// CHECK-NEXT: |-original Namespace {{.*}} 'baz'
+// CHECK-NEXT: |-TypeAliasDecl {{.*}} foo 'char'
+// CHECK-NEXT: | `-BuiltinType {{.*}} 'char'
+// CHECK-NEXT: |-UsingDecl {{.*}} baz::foo
+// CHECK-NEXT: | `-NestedNameSpecifier Namespace {{.*}} 'baz'
+// CHECK-NEXT: `-UsingShadowDecl 0x{{[^ ]*}} prev 0x[[SHADOW_ADDR:[^ ]*]] {{.*}} imported in A.<global> {{.*}} 'foo'
+
+// CHECK-LABEL: Dumping baz:
+// CHECK-NEXT: NamespaceDecl {{.*}} baz
+// CHECK-NEXT: |-TypeAliasDecl {{.*}} foo 'char'
+// CHECK-NEXT: | `-BuiltinType {{.*}} 'char'
+// CHECK-NEXT: |-UsingDecl {{.*}} baz::foo
+// CHECK-NEXT: | `-NestedNameSpecifier Namespace {{.*}} 'baz'
+// CHECK-NEXT:  `-UsingShadowDecl 0x[[SHADOW_ADDR]] {{.*}} 'foo'
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ChuanqiXu9 wrote:

While the RFC don't get consensus, I still don't like the test. There is only two `UsingShadowDecl` relevent, but we're checking too many things. I feel better if we can reduce the things we're checking or refactoring this into a unittest.

https://github.com/llvm/llvm-project/pull/80245