Revert "Remove nested $fork handling from union detection"

This reverts commit 10a4056.

Author: akashlevy

kernel/fstdata.cc

@@ -175,6 +175,26 @@ void FstData::extractVarNames()
 
 	while ((h = fstReaderIterateHier(ctx))) {
 		switch (h->htyp) {
+			case FST_HT_SCOPE: {
+				// Handle tracking for potential union structs with $fork.
+				if (!detect_union && h->u.scope.typ == FST_ST_VCD_FORK) {
+					detect_union = true;
+					fork_parent_scope = fst_scope_name;
+					fork_name = h->u.scope.name;
+					fork_vars.clear();
+				} else if (detect_union && h->u.scope.typ == FST_ST_VCD_STRUCT) {
+					// Signal that a nested $fork can not be a candidate for union struct detection.
+					log_warning("Nested $fork '%s' inside $fork '%s'; "
+						"abandoning union detection for this scope...\n",
+						h->u.scope.name, fork_name.c_str());
+					for (auto &v : fork_vars) registerVar(v);
+					detect_union = false;
+					fork_vars.clear();
+				}
+				// Push the scope onto the stack to 'descend' into the hierarchy.
+				fst_scope_name = fstReaderPushScope(ctx, h->u.scope.name, NULL);
+				break;
+			}
 			case FST_HT_SCOPE: {
 				// Handle tracking for potential union structs with $fork.
 				if (!detect_union && h->u.scope.typ == FST_ST_VCD_FORK) {