From 2dd65872dc9f38443b1f139c5cca04e68797fac6 Mon Sep 17 00:00:00 2001
From: Hector Peeters <hector.peeters@gmail.com>
Date: Tue, 5 Nov 2024 11:35:22 +0100
Subject: [PATCH] v: fix redundant emission of left expression in in infix
 expressions (#22763)

---
 vlib/v/gen/c/infix.v                         | 3 ++-
 vlib/v/gen/c/testdata/for_in_side_effect.out | 1 +
 vlib/v/gen/c/testdata/for_in_side_effect.vv  | 8 ++++++++
 3 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/gen/c/testdata/for_in_side_effect.out
 create mode 100644 vlib/v/gen/c/testdata/for_in_side_effect.vv

diff --git a/vlib/v/gen/c/infix.v b/vlib/v/gen/c/infix.v
index 13334cc67..5160d7584 100644
--- a/vlib/v/gen/c/infix.v
+++ b/vlib/v/gen/c/infix.v
@@ -517,7 +517,8 @@ fn (mut g Gen) infix_expr_in_op(node ast.InfixExpr) {
 		if node.right is ast.ArrayInit {
 			elem_type := node.right.elem_type
 			elem_sym := g.table.sym(elem_type)
-			if node.right.exprs.len > 0 {
+			// TODO: replace ast.Ident check with proper side effect analysis
+			if node.right.exprs.len > 0 && node.left is ast.Ident {
 				// `a in [1,2,3]` optimization => `a == 1 || a == 2 || a == 3`
 				// avoids an allocation
 				g.write('(')
diff --git a/vlib/v/gen/c/testdata/for_in_side_effect.out b/vlib/v/gen/c/testdata/for_in_side_effect.out
new file mode 100644
index 000000000..e2d8a3257
--- /dev/null
+++ b/vlib/v/gen/c/testdata/for_in_side_effect.out
@@ -0,0 +1 @@
+side effect
diff --git a/vlib/v/gen/c/testdata/for_in_side_effect.vv b/vlib/v/gen/c/testdata/for_in_side_effect.vv
new file mode 100644
index 000000000..40eb22370
--- /dev/null
+++ b/vlib/v/gen/c/testdata/for_in_side_effect.vv
@@ -0,0 +1,8 @@
+fn test() bool {
+	println('side effect')
+	return true
+}
+
+fn main() {
+	assert (test() in [false, true]) == true
+}
-- 
2.39.5