[BuilderTransform] Inject buildOptional to top-level if else conditions

Author: xedin

lib/Sema/BuilderTransform.cpp

@@ -1237,10 +1237,26 @@ class ResultBuilderTransform
         auto *builderCall =
             buildWrappedChainPayload(branchVarRef, i, numPayloads, isOptional);
 
+        auto isTopLevel = [&](Stmt *anchor) {
+          if (ifStmt->getThenStmt() == anchor)
+            return true;
+
+          // The situation is this:
+          //
+          // if <cond> {
+          //   ...
+          // } else if <other-cond> {
+          //   ...
+          // }
+          if (auto *innerIf = getAsStmt<IfStmt>(ifStmt->getElseStmt()))
+            return innerIf->getThenStmt() == anchor;
+
+          return ifStmt->getElseStmt() == anchor;
+        };
+
         // The operand should have optional type if we had optional results,
         // so we just need to call `buildIf` now, since we're at the top level.
-        if (isOptional && (ifStmt->getThenStmt() == anchor ||
-                           ifStmt->getElseStmt() == anchor)) {
+        if (isOptional && isTopLevel(anchor)) {
           builderCall = buildCallIfWanted(ifStmt->getEndLoc(),
                                           builder.getBuildOptionalId(),
                                           builderCall, /*argLabels=*/{});