builtin: fix incomplete m.clear(), allowing the map to have a duplica…

…ted entry for its first key (fix #22143) (#22144)

vlib/builtin/map.v

@@ -315,12 +315,13 @@ pub fn (mut m map) move() map {
 // Example: a.clear() // `a.len` and `a.key_values.len` is now 0
 pub fn (mut m map) clear() {
 	m.len = 0
-	m.even_index = 0
+	m.even_index = init_even_index
 	m.key_values.len = 0
 	m.key_values.deletes = 0
 	unsafe {
 		if m.key_values.all_deleted != 0 {
 			free(m.key_values.all_deleted)
+			m.key_values.all_deleted = nil
 		}
 		vmemset(m.key_values.keys, 0, m.key_values.key_bytes * m.key_values.cap)
 		vmemset(m.metas, 0, sizeof(u32) * (m.even_index + 2 + m.extra_metas))

vlib/builtin/map_issue_22143_clear_test.v

@@ -0,0 +1,37 @@
+fn add(mut m map[int]int, k int, v int) {
+	m[k] = v
+	dump('${m.len} ${m}')
+	// for x, y in m { println('      > m key: ${x} | value: ${y}') }
+}
+
+fn test_map_clear_there_should_not_be_doble_entries_after_clear() {
+	mut ints := map[int]int{}
+	add(mut ints, 20, 120)
+	add(mut ints, 34, 134)
+	add(mut ints, 20, 150) // no double entry!
+	assert ints.len == 2
+	assert ints[34] == 134
+	assert ints[20] == 150
+	for i in 0 .. 3 {
+		println('>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ints.clear(), i: ${i}')
+		ints.clear()
+		assert ints.len == 0
+		add(mut ints, 20, 2000 + i)
+		assert ints[20] == 2000 + i
+		add(mut ints, 34, 34)
+		assert ints[34] == 34
+		add(mut ints, 50, 50)
+		assert ints[50] == 50
+		assert ints.len == 3
+		add(mut ints, 20, 100) // try setting the first key again
+		assert ints.len == 3
+		assert ints[20] == 100
+		add(mut ints, 34, 55) // try setting the second key again
+		assert ints.len == 3
+		assert ints[34] == 55
+		add(mut ints, 20, 200 + i) // try setting the third key again
+		assert ints.len == 3
+		assert ints[20] == 200 + i
+	}
+	assert ints.len == 3
+}