From 315b2deda9aa5e2698b214ac0e5dc5face286a9b Mon Sep 17 00:00:00 2001
From: yuyi <yuyi98@163.com>
Date: Sun, 16 Jan 2022 19:12:27 +0800
Subject: [PATCH] cgen: fix match sumtype var returning sumtype value (#13184)

---
 vlib/v/gen/c/cgen.v                           | 10 +++++--
 .../match_sumtype_var_return_sumtype_test.v   | 30 +++++++++++++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/tests/match_sumtype_var_return_sumtype_test.v

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 73a6f99d4d..61014c2e1f 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -2421,9 +2421,9 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 	got_styp := g.typ(got_type)
 	if expected_type != ast.void_type {
 		unwrapped_expected_type := g.unwrap_generic(expected_type)
-		unwrapped_got_type := g.unwrap_generic(got_type)
 		unwrapped_exp_sym := g.table.sym(unwrapped_expected_type)
-		unwrapped_got_sym := g.table.sym(unwrapped_got_type)
+		mut unwrapped_got_type := g.unwrap_generic(got_type)
+		mut unwrapped_got_sym := g.table.sym(unwrapped_got_type)
 
 		expected_deref_type := if expected_is_ptr {
 			unwrapped_expected_type.deref()
@@ -2445,11 +2445,15 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 					is_already_sum_type = true
 				}
 			}
-			if is_already_sum_type {
+			if is_already_sum_type && !g.inside_return {
 				// Don't create a new sum type wrapper if there is already one
 				g.prevent_sum_type_unwrapping_once = true
 				g.expr(expr)
 			} else {
+				if mut unwrapped_got_sym.info is ast.Aggregate {
+					unwrapped_got_type = unwrapped_got_sym.info.types[g.aggregate_type_idx]
+					unwrapped_got_sym = g.table.sym(unwrapped_got_type)
+				}
 				g.get_sumtype_casting_fn(unwrapped_got_type, unwrapped_expected_type)
 				fname := '${unwrapped_got_sym.cname}_to_sumtype_$unwrapped_exp_sym.cname'
 				g.call_cfn_for_casting_expr(fname, expr, expected_is_ptr, unwrapped_exp_sym.cname,
diff --git a/vlib/v/tests/match_sumtype_var_return_sumtype_test.v b/vlib/v/tests/match_sumtype_var_return_sumtype_test.v
new file mode 100644
index 0000000000..e2fff78c1f
--- /dev/null
+++ b/vlib/v/tests/match_sumtype_var_return_sumtype_test.v
@@ -0,0 +1,30 @@
+module main
+
+type Sum = Struct | int
+
+struct Struct {
+mut:
+	value int
+}
+
+fn sum(mut s Sum) Sum {
+	match mut s {
+		Struct {
+			return s
+		}
+		else {
+			return s
+		}
+	}
+}
+
+fn test_match_sumtype_var_return_sumtype() {
+	mut s := Sum(Struct{
+		value: 42
+	})
+	s = sum(mut s)
+	dump(s)
+	ret := '$s'
+	assert ret.contains('Sum(Struct{')
+	assert ret.contains('value: 42')
+}