From d08a0b5a7ca2077197ad8ea2d02870610f10a42d Mon Sep 17 00:00:00 2001
From: zakuro <z@kuro.red>
Date: Tue, 16 Feb 2021 00:41:04 +0900
Subject: [PATCH] parser: check not used expression for all exprs in multi-expr
 (#8733)

---
 vlib/v/parser/parser.v                          | 17 ++++++++++-------
 .../tests/expr_evaluated_but_not_used_d.out     |  9 ++++-----
 .../tests/expr_evaluated_but_not_used_d.vv      |  5 ++---
 .../tests/expr_evaluated_but_not_used_e.out     |  7 +++++++
 .../tests/expr_evaluated_but_not_used_e.vv      |  5 +++++
 5 files changed, 28 insertions(+), 15 deletions(-)
 create mode 100644 vlib/v/parser/tests/expr_evaluated_but_not_used_e.out
 create mode 100644 vlib/v/parser/tests/expr_evaluated_but_not_used_e.vv

diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index b0e5b96c18..853731d965 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1020,13 +1020,16 @@ fn (mut p Parser) parse_multi_expr(is_top_level bool) ast.Stmt {
 	if p.tok.kind in [.assign, .decl_assign] || p.tok.kind.is_assign() {
 		return p.partial_assign_stmt(left, left_comments)
 	} else if !p.pref.translated
-		&& tok.kind !in [.key_if, .key_match, .key_lock, .key_rlock, .key_select]
-		&& left0 !is ast.CallExpr && (is_top_level || p.tok.kind != .rcbr)
-		&& left0 !is ast.PostfixExpr && !(left0 is ast.InfixExpr
-		&& (left0 as ast.InfixExpr).op in [.left_shift, .arrow]) && left0 !is ast.ComptimeCall
-		&& left0 !is ast.SelectorExpr {
-		p.error_with_pos('expression evaluated but not used', left0.position())
-		return ast.Stmt{}
+		&& tok.kind !in [.key_if, .key_match, .key_lock, .key_rlock, .key_select] {
+		for node in left {
+			if node !is ast.CallExpr && (is_top_level || p.tok.kind != .rcbr)
+				&& node !is ast.PostfixExpr && !(node is ast.InfixExpr
+				&& (node as ast.InfixExpr).op in [.left_shift, .arrow]) && node !is ast.ComptimeCall
+				&& node !is ast.SelectorExpr {
+				p.error_with_pos('expression evaluated but not used', node.position())
+				return ast.Stmt{}
+			}
+		}
 	}
 	pos.update_last_line(p.prev_tok.line_nr)
 	if left.len == 1 {
diff --git a/vlib/v/parser/tests/expr_evaluated_but_not_used_d.out b/vlib/v/parser/tests/expr_evaluated_but_not_used_d.out
index 663a7c9e4b..03639ea803 100644
--- a/vlib/v/parser/tests/expr_evaluated_but_not_used_d.out
+++ b/vlib/v/parser/tests/expr_evaluated_but_not_used_d.out
@@ -1,7 +1,6 @@
-vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv:4:5: error: expression evaluated but not used
+vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv:4:19: error: expression evaluated but not used
     2 |     a := 1
     3 |     b := 2
-    4 |     a+b
-      |     ~~~
-    5 |     println(a*b)
-    6 | }
+    4 |     println(a*b), a+b
+      |                   ~~~
+    5 | }
diff --git a/vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv b/vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv
index d4cb9e1545..6dbacb764e 100644
--- a/vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv
+++ b/vlib/v/parser/tests/expr_evaluated_but_not_used_d.vv
@@ -1,6 +1,5 @@
 fn main() {
     a := 1
     b := 2
-    a+b
-    println(a*b)
-}
\ No newline at end of file
+    println(a*b), a+b
+}
diff --git a/vlib/v/parser/tests/expr_evaluated_but_not_used_e.out b/vlib/v/parser/tests/expr_evaluated_but_not_used_e.out
new file mode 100644
index 0000000000..c31212467c
--- /dev/null
+++ b/vlib/v/parser/tests/expr_evaluated_but_not_used_e.out
@@ -0,0 +1,7 @@
+vlib/v/parser/tests/expr_evaluated_but_not_used_e.vv:3:14: error: expression evaluated but not used
+    1 | fn main() {
+    2 |     mut array := [1, 2, 3]
+    3 |     array << 4, 5
+      |                 ^
+    4 |     println(array)
+    5 | }
diff --git a/vlib/v/parser/tests/expr_evaluated_but_not_used_e.vv b/vlib/v/parser/tests/expr_evaluated_but_not_used_e.vv
new file mode 100644
index 0000000000..763624acf3
--- /dev/null
+++ b/vlib/v/parser/tests/expr_evaluated_but_not_used_e.vv
@@ -0,0 +1,5 @@
+fn main() {
+	mut array := [1, 2, 3]
+	array << 4, 5
+	println(array)
+}