From ca410ed8abf588a48b75d9b75a495a6b6a7d1fd9 Mon Sep 17 00:00:00 2001
From: Devajith Valaparambil Sreeramaswamy
 <devajith.valaparambil.sreeramaswamy@cern.ch>
Date: Wed, 8 May 2024 18:00:19 +0200
Subject: [PATCH] [cling] Make cling::utils::Lookup::Named look into using
 directives

---
 interpreter/cling/lib/Utils/AST.cpp   | 10 +++++++++-
 interpreter/cling/test/.clang-format  |  1 +
 interpreter/cling/test/Lookup/named.C | 24 ++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 interpreter/cling/test/.clang-format

diff --git a/interpreter/cling/lib/Utils/AST.cpp b/interpreter/cling/lib/Utils/AST.cpp
index 29505895b22c7..54dad90487318 100644
--- a/interpreter/cling/lib/Utils/AST.cpp
+++ b/interpreter/cling/lib/Utils/AST.cpp
@@ -1501,7 +1501,15 @@ namespace utils {
         // No definition, no lookup result.
         return;
       }
-      S->LookupQualifiedName(R, const_cast<DeclContext*>(primaryWithin));
+      bool res =
+          S->LookupQualifiedName(R, const_cast<DeclContext*>(primaryWithin));
+
+      // If the lookup fails and the context is a namespace, try to lookup in
+      // the namespaces by setting NotForRedeclaration.
+      if (!res && primaryWithin->isNamespace()) {
+        R.setRedeclarationKind(Sema::NotForRedeclaration);
+        S->LookupQualifiedName(R, const_cast<DeclContext*>(primaryWithin));
+      }
     }
   }
 
diff --git a/interpreter/cling/test/.clang-format b/interpreter/cling/test/.clang-format
new file mode 100644
index 0000000000000..e3845288a2aec
--- /dev/null
+++ b/interpreter/cling/test/.clang-format
@@ -0,0 +1 @@
+DisableFormat: true
diff --git a/interpreter/cling/test/Lookup/named.C b/interpreter/cling/test/Lookup/named.C
index 2462d30bbcb56..cc18419fe282c 100644
--- a/interpreter/cling/test/Lookup/named.C
+++ b/interpreter/cling/test/Lookup/named.C
@@ -37,6 +37,13 @@ namespace AnotherNext {
 class Inside_AnotherNext {};
 }
 
+namespace A {
+  class C;
+}
+namespace B {
+  using namespace A;
+}
+
 .rawInput 0
 
 // ROOT-6095: names introduced in a scopeless enum should be available in the
@@ -106,3 +113,20 @@ decl
 decl = utils::Lookup::Named(&S, "EvenLess", context);
 decl
 //CHECK: (const clang::NamedDecl *) {{0x0*$|nullptr}}
+
+// Lookup the declaration for namespace B.
+decl = utils::Lookup::Named(&S, "B", nullptr);
+decl
+// CHECK: (const clang::NamedDecl *) 0x{{[1-9a-f][0-9a-f]*$}}
+
+const clang::DeclContext* contextB = llvm::dyn_cast<clang::DeclContext>(decl);
+contextB
+// CHECK: (const clang::DeclContext *) 0x{{[1-9a-f][0-9a-f]*$}}
+
+// Lookup 'C' from namespace B.
+decl = utils::Lookup::Named(&S, "C", contextB);
+decl
+// CHECK: (const clang::NamedDecl *) 0x{{[1-9a-f][0-9a-f]*$}}
+
+decl->getQualifiedNameAsString()
+// CHECK: (std::string) "A::C"