From 5383f737ca464c54a2e24fcd330a4bab316cbecf Mon Sep 17 00:00:00 2001
From: Dan Katz <katzdm@gmail.com>
Date: Fri, 16 May 2025 12:00:24 -0400
Subject: [PATCH] Extraction of arrays as pointers.

---
 clang/lib/AST/ExprConstantMeta.cpp            | 25 ++++++++++++++++---
 .../reflection/to-and-from-values.pass.cpp    | 10 ++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/clang/lib/AST/ExprConstantMeta.cpp b/clang/lib/AST/ExprConstantMeta.cpp
index 99bdf01df5e2..db0f7d029897 100644
--- a/clang/lib/AST/ExprConstantMeta.cpp
+++ b/clang/lib/AST/ExprConstantMeta.cpp
@@ -3081,10 +3081,29 @@ bool extract(APValue &Result, ASTContext &C, MetaActions &Meta,
         }
         Synthesized = DeclRefExpr::Create(C, NNSLocBuilder.getTemporary(),
                                           SourceLocation(), Decl, false,
-                                          Range.getBegin(), ResultTy,
-                                          ReturnsLValue ? VK_LValue :
-                                                          VK_PRValue,
+                                          Range.getBegin(), ResultTy, VK_LValue,
                                           Decl, nullptr);
+      } else if (auto *ArrTy = dyn_cast<ArrayType>(Decl->getType())) {
+        QualType PtrTy = C.getPointerType(ArrTy->getElementType());
+
+        ReturnsLValue = true;
+        if (RawResultTy.getCanonicalType().getTypePtr() !=
+            PtrTy.getCanonicalType().getTypePtr())
+          return Diagnoser(Range.getBegin(), diag::metafn_extract_type_mismatch)
+              << 1 << PtrTy << 1 << ResultTy << Range;
+
+        NestedNameSpecifierLocBuilder NNSLocBuilder;
+        if (auto *ParentClsDecl = dyn_cast_or_null<CXXRecordDecl>(
+                Decl->getDeclContext())) {
+          TypeSourceInfo *TSI = C.CreateTypeSourceInfo(
+                  QualType(ParentClsDecl->getTypeForDecl(), 0), 0);
+          NNSLocBuilder.Extend(C, Range.getBegin(), TSI->getTypeLoc(),
+                               Range.getBegin());
+        }
+
+        APValue::LValuePathEntry Path[1] = {APValue::LValuePathEntry::ArrayIndex(0)};
+        return SetAndSucceed(Result,
+                             APValue(Decl, CharUnits::Zero(), Path, false));
       } else {
         // We have a reflection of a (possibly local) non-reference variable.
         // Synthesize an lvalue by reaching up the call stack.
diff --git a/libcxx/test/std/experimental/reflection/to-and-from-values.pass.cpp b/libcxx/test/std/experimental/reflection/to-and-from-values.pass.cpp
index 4801546f7788..e0034a08d2d4 100644
--- a/libcxx/test/std/experimental/reflection/to-and-from-values.pass.cpp
+++ b/libcxx/test/std/experimental/reflection/to-and-from-values.pass.cpp
@@ -205,6 +205,16 @@ namespace extract_ref_semantics {
   }
 }  // namespace extract_ref_semantics
 
+                            // ====================
+                            // extract_array_as_ptr
+                            // ====================
+
+namespace extract_array_as_ptr {
+constexpr int arr[] = {1, 2, 3};
+static_assert(extract<const int *>(^^arr)[2] == 3);
+
+}  // namespace extract_array_as_ptr
+
                                // ==============
                                // value_of_types
                                // ==============