From 16d14c660bd5bb79b6de3c2d202081aa83e90cf1 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 16:02:13 +0300
Subject: [PATCH] checker: fix assert expression with -(-2) or +2 sub
 expression (fixes #26815)

---
 vlib/v/checker/checker.v        |  4 ++--
 vlib/v/parser/expr.v            | 11 ++++++++---
 vlib/v/tests/prefix_expr_test.v | 17 +++++++++++++++++
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 731b8295e..057f30616 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -7625,8 +7625,8 @@ fn (mut c Checker) prefix_expr(mut node ast.PrefixExpr) ast.Type {
 	// FIXME
 	// there are currently other issues to investigate if right_type
 	// is unwrapped directly as initialization, so do it here
-	if node.op == .minus && !right_sym.is_number() {
-		c.type_error_for_operator('-', 'numeric', right_sym.name, node.pos)
+	if node.op in [.plus, .minus] && !right_sym.is_number() {
+		c.type_error_for_operator(node.op.str(), 'numeric', right_sym.name, node.pos)
 	}
 	if node.op == .arrow {
 		raw_right_sym := c.table.final_sym(right_type)
diff --git a/vlib/v/parser/expr.v b/vlib/v/parser/expr.v
index cfe8a0182..ce1af9df4 100644
--- a/vlib/v/parser/expr.v
+++ b/vlib/v/parser/expr.v
@@ -177,6 +177,10 @@ fn (mut p Parser) check_expr(precedence int) !ast.Expr {
 		.power {
 			node = p.power_prefix_expr()
 		}
+		.plus {
+			// +1, +a
+			node = p.prefix_expr()
+		}
 		.minus {
 			// -1, -a
 			if p.peek_tok.kind == .number && !(p.peek_token(2).kind == .power
@@ -1057,11 +1061,12 @@ fn (mut p Parser) infix_expr(left ast.Expr) ast.Expr {
 		right = p.expr(if op == .power { precedence - 1 } else { precedence })
 	}
 	p.inside_assign_rhs = old_assign_rhs
-	if op in [.plus, .minus, .mul, .power, .div, .mod, .lt, .eq] && mut right is ast.PrefixExpr {
+	// Keep rejecting doubled operator forms like `5 - - -5`, but allow valid
+	// infix rhs expressions such as `a == -(-2)` and `a == +2`.
+	if op in [.plus, .minus, .mul] && mut right is ast.PrefixExpr {
 		mut right_expr := right.right
 		right_expr = right_expr.remove_par()
-		if right.op in [.plus, .minus, .mul, .power, .div, .mod, .lt, .eq]
-			&& right_expr.is_pure_literal() {
+		if right.op == op && right_expr.is_pure_literal() {
 			p.error_with_pos('invalid expression: unexpected token `${op}`', right_op_pos)
 		}
 	}
diff --git a/vlib/v/tests/prefix_expr_test.v b/vlib/v/tests/prefix_expr_test.v
index 2e3aae3d8..72c777f49 100644
--- a/vlib/v/tests/prefix_expr_test.v
+++ b/vlib/v/tests/prefix_expr_test.v
@@ -1,3 +1,5 @@
+import strconv
+
 fn value(n int) int {
 	return n
 }
@@ -27,3 +29,18 @@ fn test_negative() {
 	assert -arr[0] == -1
 	assert -arr[1] == -2
 }
+
+fn test_positive() {
+	two := 2
+	assert +two == 2
+	assert +(two - 1) == 1
+}
+
+fn test_prefix_expr_in_assert_comparison() ! {
+	i := 2
+	assert strconv.atoi('1')! == 1
+	assert strconv.atoi('-2')! == -2
+	assert strconv.atoi('+2')! == i - 1 + 1
+	assert strconv.atoi('+2')! == -(-2)
+	assert strconv.atoi('+2')! == +2
+}
-- 
2.39.5