From 857bfe0c214db2e07334db1a42800dba04f52b5c Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Mon, 25 May 2026 13:41:43 +0300
Subject: [PATCH] ast: count duplicate sumtype fields once (#27253)

---
 vlib/v/ast/table.v                            |  5 +++
 ...mtype_common_fields_duplicate_embed_test.v | 41 +++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 vlib/v/tests/sumtype_common_fields_duplicate_embed_test.v

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 2ed29ba0a..10e3fbbab 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -872,7 +872,12 @@ pub fn (t &Table) resolve_common_sumtype_fields(mut sym TypeSymbol) {
 			}
 		}
 
+		mut counted_field_names := map[string]bool{}
 		for field in fields {
+			if field.name in counted_field_names {
+				continue
+			}
+			counted_field_names[field.name] = true
 			if field.name !in field_map {
 				field_map[field.name] = field
 				field_usages[field.name]++
diff --git a/vlib/v/tests/sumtype_common_fields_duplicate_embed_test.v b/vlib/v/tests/sumtype_common_fields_duplicate_embed_test.v
new file mode 100644
index 000000000..4f553fa62
--- /dev/null
+++ b/vlib/v/tests/sumtype_common_fields_duplicate_embed_test.v
@@ -0,0 +1,41 @@
+struct CommonTrace {
+mut:
+	name   string
+	marker int
+}
+
+struct TraceWithDuplicateMarker {
+	CommonTrace
+mut:
+	marker int
+}
+
+struct TraceWithMarker {
+	CommonTrace
+}
+
+struct TraceWithoutMarker {
+mut:
+	name string
+}
+
+type Trace = TraceWithDuplicateMarker | TraceWithMarker | TraceWithoutMarker
+
+fn test_duplicate_embedded_fields_do_not_create_false_common_sumtype_field() {
+	traces := [
+		Trace(TraceWithDuplicateMarker{
+			name:   'duplicate'
+			marker: 1
+		}),
+		Trace(TraceWithMarker{
+			name: 'marker'
+		}),
+		Trace(TraceWithoutMarker{
+			name: 'plain'
+		}),
+	]
+
+	assert traces[0].name == 'duplicate'
+	assert traces[1].name == 'marker'
+	assert traces[2].name == 'plain'
+}
-- 
2.39.5