[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[via cfe-commits]

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@@ -2148,6 +2161,35 @@ void CXXRecordDecl::completeDefinition(CXXFinalOverriderMap *FinalOverriders) {
   for (conversion_iterator I = conversion_begin(), E = conversion_end();
        I != E; ++I)
     I.setAccess((*I)->getAccess());
+
+  ASTContext &Context = getASTContext();
+
+  if (isAggregate() && hasUserDeclaredConstructor() &&
+      !Context.getLangOpts().CPlusPlus20) {
+    // Diagnose any aggregate behavior changes in C++20
+    for (field_iterator I = field_begin(), E = field_end(); I != E; ++I) {
+      if (const auto *attr = I->getAttr<ExplicitInitAttr>()) {
+        Context.getDiagnostics().Report(
+            attr->getLocation(),
+            diag::warn_cxx20_compat_requires_explicit_init_non_aggregate)
+            << attr << Context.getRecordType(this);
+      }
+    }
+  }
+
+  if (!isAggregate() && hasUninitializedExplicitInitFields()) {
+    // Diagnose any fields that required explicit initialization in a
+    // non-aggregate type. (Note that the fields may not be directly in this
+    // type, but in a subobject. In such cases we don't emit diagnoses here.)
+    for (field_iterator I = field_begin(), E = field_end(); I != E; ++I) {
+      if (const auto *attr = I->getAttr<ExplicitInitAttr>()) {
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higher-performance wrote:

Done.

https://github.com/llvm/llvm-project/pull/102040