From a3613866bfc18ec44c707554c667f90b064dd6a7 Mon Sep 17 00:00:00 2001
From: Akash Levy <akashlevy@gmail.com>
Date: Wed, 27 May 2026 02:41:40 -0700
Subject: [PATCH] Update kernel/fstdata.cc

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>
---
 kernel/fstdata.cc | 37 +++++++++++++++----------------------
 1 file changed, 15 insertions(+), 22 deletions(-)

diff --git a/kernel/fstdata.cc b/kernel/fstdata.cc
index f1d85f1eb..b98b8d1a0 100644
--- a/kernel/fstdata.cc
+++ b/kernel/fstdata.cc
@@ -195,33 +195,26 @@ void FstData::extractVarNames()
 				fst_scope_name = fstReaderPushScope(ctx, h->u.scope.name, NULL);
 				break;
 			}
-			case FST_HT_UPSCOPE: {
-				if (detect_union) {
-					// A union is detected if there are at least 2 variables in the fork scope and they all have the same fstHandle.
-					bool is_union = fork_vars.size() >= 2 &&
-							std::all_of(fork_vars.begin() + 1, fork_vars.end(),
-									[&](const FstVar &v) { return v.id == fork_vars[0].id; });
-					if (is_union) {
-							// If a union, register the fork name as the variable at the parent scope.
-							FstVar u = fork_vars[0];
-							u.name = fork_name;
-							u.scope = fork_parent_scope;
-							normalize_brackets(u.scope);
-							u.is_alias = false;
-							registerVar(u);
-					} else {
-							// If not a union, register all variables in the fork scope as normal.
-							for (auto &v : fork_vars) {
-								registerVar(v);
-							}
-					}
+			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_FORK) {
+					// Nested $fork: abandon union detection. Warning is emitted
+					// at upscope time, only if the outer fork would have been a union.
+					for (auto &v : fork_vars) registerVar(v);
 					detect_union = false;
 					fork_vars.clear();
+					fork_vars_had_nested_fork = true;
 				}
-				// Pop the scope off the stack.
-				fst_scope_name = fstReaderPopScope(ctx);
+				// 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_VAR: {
 				FstVar var;
 				var.id = h->u.var.handle;