P1008R1 Classes with user-declared constructors are never aggregates in

C++20.

llvm-svn: 343131

2 files changed, 40 insertions, 6 deletions

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 5c708694913..00ae7c9cda1 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -731,9 +731,14 @@ void CXXRecordDecl::addedMember(Decl *D) {
     }
 
     // C++11 [dcl.init.aggr]p1: DR1518
-    //   An aggregate is an array or a class with no user-provided, explicit, or
-    //   inherited constructors
-    if (Constructor->isUserProvided() || Constructor->isExplicit())
+    //   An aggregate is an array or a class with no user-provided [or]
+    //   explicit [...] constructors
+    // C++20 [dcl.init.aggr]p1:
+    //   An aggregate is an array or a class with no user-declared [...]
+    //   constructors
+    if (getASTContext().getLangOpts().CPlusPlus2a
+            ? !Constructor->isImplicit()
+            : (Constructor->isUserProvided() || Constructor->isExplicit()))
       data().Aggregate = false;
   }
 
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index a25818f0fd3..a678a31a5ac 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -964,6 +964,14 @@ void InitListChecker::CheckImplicitInitList(const InitializedEntity &Entity,
                      StructuredSubobjectInitList->getEndLoc()),
                  "}");
     }
+
+    // Warn if this type won't be an aggregate in future versions of C++.
+    auto *CXXRD = T->getAsCXXRecordDecl();
+    if (CXXRD && CXXRD->hasUserDeclaredConstructor()) {
+      SemaRef.Diag(StructuredSubobjectInitList->getBeginLoc(),
+                   diag::warn_cxx2a_compat_aggregate_init_with_ctors)
+          << StructuredSubobjectInitList->getSourceRange() << T;
+    }
   }
 }
 
@@ -1106,9 +1114,30 @@ void InitListChecker::CheckExplicitInitList(const InitializedEntity &Entity,
     }
   }
 
-  if (!VerifyOnly && T->isScalarType() &&
-      IList->getNumInits() == 1 && !isa<InitListExpr>(IList->getInit(0)))
-    warnBracedScalarInit(SemaRef, Entity, IList->getSourceRange());
+  if (!VerifyOnly) {
+    if (T->isScalarType() && IList->getNumInits() == 1 &&
+        !isa<InitListExpr>(IList->getInit(0)))
+      warnBracedScalarInit(SemaRef, Entity, IList->getSourceRange());
+
+    // Warn if this is a class type that won't be an aggregate in future
+    // versions of C++.
+    auto *CXXRD = T->getAsCXXRecordDecl();
+    if (CXXRD && CXXRD->hasUserDeclaredConstructor()) {
+      // Don't warn if there's an equivalent default constructor that would be
+      // used instead.
+      bool HasEquivCtor = false;
+      if (IList->getNumInits() == 0) {
+        auto *CD = SemaRef.LookupDefaultConstructor(CXXRD);
+        HasEquivCtor = CD && !CD->isDeleted();
+      }
+
+      if (!HasEquivCtor) {
+        SemaRef.Diag(IList->getBeginLoc(),
+                     diag::warn_cxx2a_compat_aggregate_init_with_ctors)
+            << IList->getSourceRange() << T;
+      }
+    }
+  }
 }
 
 void InitListChecker::CheckListElementTypes(const InitializedEntity &Entity,