From 9ad14757cb6dd20e98c22a89c566467498947a95 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:22 +0300
Subject: [PATCH] checker: fix enum values set with constants from $if/$else
 (fixes #23348)

---
 vlib/v/checker/checker.v                          | 15 +++++++++++++++
 .../tests/enum_field_value_duplicate_f.out        |  7 +++++++
 .../checker/tests/enum_field_value_duplicate_f.vv |  7 +++++++
 3 files changed, 29 insertions(+)
 create mode 100644 vlib/v/checker/tests/enum_field_value_duplicate_f.out
 create mode 100644 vlib/v/checker/tests/enum_field_value_duplicate_f.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 697b25191..31ba71932 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3116,6 +3116,20 @@ fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 						if field.expr.kind == .constant && field.expr.obj.typ.is_int() {
 							// accepts int constants as enum value
 							if mut field.expr.obj is ast.ConstField {
+								if comptime_value := c.eval_comptime_const_expr(field.expr,
+									0)
+								{
+									if comptime_lit := c.comptime_value_to_integer_literal(comptime_value,
+										field.expr.pos)
+									{
+										c.check_enum_field_integer_literal(comptime_lit,
+											signed, node.is_multi_allowed, senum_type,
+											field.expr.pos, mut useen, enum_umin, enum_umax, mut
+											iseen, enum_imin, enum_imax)
+										field.expr = comptime_lit
+										continue
+									}
+								}
 								folded_expr := c.checker_transformer.expr(mut field.expr.obj.expr)
 
 								if folded_expr is ast.IntegerLiteral {
@@ -3123,6 +3137,7 @@ fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 										node.is_multi_allowed, senum_type, field.expr.pos, mut
 										useen, enum_umin, enum_umax, mut iseen, enum_imin,
 										enum_imax)
+									field.expr = folded_expr
 								}
 							}
 							continue
diff --git a/vlib/v/checker/tests/enum_field_value_duplicate_f.out b/vlib/v/checker/tests/enum_field_value_duplicate_f.out
new file mode 100644
index 000000000..9bac86838
--- /dev/null
+++ b/vlib/v/checker/tests/enum_field_value_duplicate_f.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/enum_field_value_duplicate_f.vv:6:8: error: enum value `2` already exists
+    4 | enum Foo {
+    5 |     foo = x
+    6 |     bar = y
+      |           ^
+    7 | }
+Details: use `@[_allow_multiple_values]` attribute to allow multiple enum values. Use only when it is needed
diff --git a/vlib/v/checker/tests/enum_field_value_duplicate_f.vv b/vlib/v/checker/tests/enum_field_value_duplicate_f.vv
new file mode 100644
index 000000000..64e9dcd8a
--- /dev/null
+++ b/vlib/v/checker/tests/enum_field_value_duplicate_f.vv
@@ -0,0 +1,7 @@
+const x = $if duplicate_enum_value_check ? { 1 } $else { 2 }
+const y = $if duplicate_enum_value_check ? { 3 } $else { 2 }
+
+enum Foo {
+	foo = x
+	bar = y
+}
-- 
2.39.5