[clang] [Clang] Require base element type of `__has_unique_object_representations` to be complete (PR #95432)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok updated https://github.com/llvm/llvm-project/pull/95432

>From 3874b20e44c67e8ac0d2eb2665fb0ea9f09c6f5d Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Thu, 13 Jun 2024 17:26:50 +0100
Subject: [PATCH 1/2] [Clang] Require base element type of
 __has_unique_object_representations to be complete

---
 clang/docs/ReleaseNotes.rst        |  3 +++
 clang/lib/AST/ASTContext.cpp       |  6 ++++++
 clang/lib/Sema/SemaExprCXX.cpp     |  5 ++++-
 clang/test/SemaCXX/type-traits.cpp | 11 +++++++++++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8c2f737836a9d..4359213286fa0 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -660,6 +660,9 @@ Bug Fixes in This Version
 - Correctly reject declarations where a statement is required in C.
   Fixes #GH92775
 
+- ``__has_unique_object_representations`` correctly handles arrays of unknown bounds of
+  types by ensuring they are complete and instantiating them if needed. Fixes (#GH95311).
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index aa22825602a40..f3b698b3f0c59 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -2791,6 +2791,12 @@ bool ASTContext::hasUniqueObjectRepresentations(
     return hasUniqueObjectRepresentations(getBaseElementType(Ty),
                                           CheckIfTriviallyCopyable);
 
+  if (Ty->isVoidType())
+    return false;
+
+  assert(!Ty->isIncompleteType() && "hasUniqueObjectRepresentations should not "
+                                    "be called with an incomplete type");
+
   // (9.1) - T is trivially copyable...
   if (CheckIfTriviallyCopyable && !Ty.isTriviallyCopyableType(*this))
     return false;
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index f3af8dee6b090..127621a31470d 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -5149,6 +5149,10 @@ static bool CheckUnaryTypeTraitTypeCompleteness(Sema &S, TypeTrait UTT,
   case UTT_HasTrivialCopy:
   case UTT_HasTrivialDestructor:
   case UTT_HasVirtualDestructor:
+  // has_unique_object_representations<T> when T is an array is defined in terms
+  // of has_unique_object_representations<remove_all_extents_t<T>>, so the base
+  // type needs to be complete even if the type is an incomplete array type.
+  case UTT_HasUniqueObjectRepresentations:
     ArgTy = QualType(ArgTy->getBaseElementTypeUnsafe(), 0);
     [[fallthrough]];
 
@@ -5157,7 +5161,6 @@ static bool CheckUnaryTypeTraitTypeCompleteness(Sema &S, TypeTrait UTT,
   case UTT_IsDestructible:
   case UTT_IsNothrowDestructible:
   case UTT_IsTriviallyDestructible:
-  case UTT_HasUniqueObjectRepresentations:
     if (ArgTy->isIncompleteArrayType() || ArgTy->isVoidType())
       return true;
 
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index d40605f56f1ed..b5cefb18fa13e 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -3505,6 +3505,17 @@ static_assert(__has_unique_object_representations(_BitInt(8)), "BitInt:");
 static_assert(!__has_unique_object_representations(_BitInt(127)), "BitInt:");
 static_assert(__has_unique_object_representations(_BitInt(128)), "BitInt:");
 
+namespace GH95311 {
+
+template <int>
+class Foo {
+  int x;
+};
+static_assert(__has_unique_object_representations(Foo<0>[]));
+class Bar; // expected-note {{forward declaration of 'GH95311::Bar'}}
+static_assert(__has_unique_object_representations(Bar[])); // expected-error {{incomplete type}}
+
+}
 
 namespace PR46209 {
   // Foo has both a trivial assignment operator and a non-trivial one.

>From 60a66efac75e872cf257b00058a53286a374a8ec Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Thu, 13 Jun 2024 19:46:55 +0100
Subject: [PATCH 2/2] Address feedback on assertion

---
 clang/lib/AST/ASTContext.cpp | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index f3b698b3f0c59..d82936e991173 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -2791,11 +2791,9 @@ bool ASTContext::hasUniqueObjectRepresentations(
     return hasUniqueObjectRepresentations(getBaseElementType(Ty),
                                           CheckIfTriviallyCopyable);
 
-  if (Ty->isVoidType())
-    return false;
-
-  assert(!Ty->isIncompleteType() && "hasUniqueObjectRepresentations should not "
-                                    "be called with an incomplete type");
+  assert((Ty->isVoidType() || !Ty->isIncompleteType()) &&
+         "hasUniqueObjectRepresentations should not be called with an "
+         "incomplete type");
 
   // (9.1) - T is trivially copyable...
   if (CheckIfTriviallyCopyable && !Ty.isTriviallyCopyableType(*this))