From 0e4eea80ca3b2928a6e1a1ed5d40ac2bc5d44ccd Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Thu, 22 Jun 2023 22:39:05 +0300
Subject: [PATCH] cgen: fix code generation for generic unions (#18513)

---
 vlib/v/gen/c/struct.v                   |  6 +++++-
 vlib/v/tests/generics_union_dump_test.v | 28 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/generics_union_dump_test.v

diff --git a/vlib/v/gen/c/struct.v b/vlib/v/gen/c/struct.v
index 8cd01034f2..f037958ba1 100644
--- a/vlib/v/gen/c/struct.v
+++ b/vlib/v/gen/c/struct.v
@@ -393,7 +393,11 @@ fn (mut g Gen) struct_decl(s ast.Struct, name string, is_anon bool) {
 		return
 	}
 	if name.contains('_T_') {
-		g.typedefs.writeln('typedef struct ${name} ${name};')
+		if s.is_union {
+			g.typedefs.writeln('typedef union ${name} ${name};')
+		} else {
+			g.typedefs.writeln('typedef struct ${name} ${name};')
+		}
 	}
 	// TODO avoid buffer manip
 	start_pos := g.type_definitions.len
diff --git a/vlib/v/tests/generics_union_dump_test.v b/vlib/v/tests/generics_union_dump_test.v
new file mode 100644
index 0000000000..31c6471390
--- /dev/null
+++ b/vlib/v/tests/generics_union_dump_test.v
@@ -0,0 +1,28 @@
+union Convertor[T] {
+	value T
+	bytes [8]u8
+}
+
+fn test_conversion_works() {
+	a := Convertor[i64]{
+		value: 21474837714
+	}
+	$if little_endian {
+		assert unsafe { a.bytes } == [u8(210), 4, 0, 0, 5, 0, 0, 0]!
+	}
+}
+
+fn test_dumping_of_a_generic_union_value() {
+	dump(Convertor[u8]{
+		bytes: [u8(210), 4, 0, 0, 5, 0, 0, 0]!
+	})
+	dump(Convertor[i16]{
+		bytes: [u8(210), 4, 0, 0, 5, 0, 0, 0]!
+	})
+	dump(Convertor[int]{
+		bytes: [u8(210), 4, 0, 0, 5, 0, 0, 0]!
+	})
+	dump(Convertor[i64]{
+		bytes: [u8(210), 4, 0, 0, 5, 0, 0, 0]!
+	})
+}