[clang] [Clang][Sema] Fix regression due to missing ambiguity check before attempting access check. (PR #80730)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik updated https://github.com/llvm/llvm-project/pull/80730

>From 80f7b2004a9ae980f8d652e870080a8ff53e3664 Mon Sep 17 00:00:00 2001
From: Shafik Yaghmour <shafik.yaghmour at intel.com>
Date: Mon, 5 Feb 2024 11:08:25 -0800
Subject: [PATCH] [Clang][Sema] Fix regression due to missing ambiguity check
 before attempting access check.

Previously when fixing ambiguous lookup diagnostics in cc1b6668c57170cd440d321037ced89d6a61a9cb
The change refactored `LookupResult` to split out diagnosing access and ambiguous
lookups. The call to `getSema().CheckLookupAccess(...)` should have guarded by a
check for isAmbiguous(). This change adds that guard.

Fixes: https://github.com/llvm/llvm-project/issues/80435
---
 clang/include/clang/Sema/Lookup.h             |  3 ++-
 .../class.derived/class.member.lookup/p11.cpp | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/Sema/Lookup.h b/clang/include/clang/Sema/Lookup.h
index 9c93bf1e6fb42..2f2f2607a937f 100644
--- a/clang/include/clang/Sema/Lookup.h
+++ b/clang/include/clang/Sema/Lookup.h
@@ -754,7 +754,8 @@ class LookupResult {
 
 private:
   void diagnoseAccess() {
-    if (isClassLookup() && getSema().getLangOpts().AccessControl)
+    if (!isAmbiguous() && isClassLookup() &&
+        getSema().getLangOpts().AccessControl)
       getSema().CheckLookupAccess(*this);
   }
 
diff --git a/clang/test/CXX/class.derived/class.member.lookup/p11.cpp b/clang/test/CXX/class.derived/class.member.lookup/p11.cpp
index e0899b227e69b..a42febaca3f04 100644
--- a/clang/test/CXX/class.derived/class.member.lookup/p11.cpp
+++ b/clang/test/CXX/class.derived/class.member.lookup/p11.cpp
@@ -23,3 +23,25 @@ struct D: I1, I2, B2 {
     int D::* mpD = &D::i; // expected-error {{non-static member 'i' found in multiple base-class subobjects of type 'B1'}}
   }
 };
+
+namespace GH80435 {
+struct A {
+  void *data; // expected-note {{member found by ambiguous name lookup}}
+};
+
+class B {
+  void *data; // expected-note {{member found by ambiguous name lookup}}
+};
+
+struct C : A, B {};
+
+decltype(C().data) x; // expected-error {{member 'data' found in multiple base classes of different types}}
+
+struct D { // expected-note {{candidate constructor (the implicit copy constructor) not viable: no known conversion from 'C' to 'const D' for 1st argument}}
+           // expected-note at -1{{candidate constructor (the implicit move constructor) not viable: no known conversion from 'C' to 'D' for 1st argument}}
+  template <typename Container, decltype(Container().data) = 0 >
+  D(Container); // expected-note {{candidate template ignored: substitution failure [with Container = C]: member 'data' found in multiple base classes of different types}}
+};
+
+D y(C{}); // expected-error {{no matching constructor for initialization of 'D'}}
+}