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

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
(cherry picked from commit a7bc9cb6ffa91ff0ebabc45c0c7263c7c2c3a4de)

2 files changed, 24 insertions, 1 deletions

diff --git a/clang/include/clang/Sema/Lookup.h b/clang/include/clang/Sema/Lookup.h
index 9c93bf1..2f2f2607 100644
--- a/clang/include/clang/Sema/Lookup.h
+++ b/clang/include/clang/Sema/Lookup.h
@@ -754,7 +754,8 @@ public:
 
 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 e0899b2..a42feba 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@-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'}}
+}