builtin: fix m.clear() having different observable behavior to `m = {…

…}`, after multiple iterations of setting keys and clearing (fix #22145) (#22146)

vlib/builtin/map.v

@@ -314,18 +314,20 @@ pub fn (mut m map) move() map {
 // It does it by setting the map length to `0`
 // 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 = 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))
+		vmemset(m.metas, 0, 2 * (m.even_index + 2 + m.extra_metas))
 	}
+	m.key_values.len = 0
+	m.key_values.deletes = 0
+	m.even_index = init_even_index
+	m.cached_hashbits = max_cached_hashbits
+	m.shift = init_log_capicity
+	m.len = 0
 }
 
 @[inline]

vlib/builtin/map_issue_22145_clear_test.v

@@ -0,0 +1,22 @@
+const t = [30, 38, 36, 31, 39, 37, 24, 32, 25, 33, 18, 26, 11, 18, 12, 4, 10, 17, 16, 11, 3, 9,
+	2, 23, 30, 24, 16, 22, 23, 17, 9, 15, 10, 2, 8, 3, 1, 0, 7, 14, 29, 21]
+
+fn test_multiple_iterations_of_calling_clear_should_be_always_equivalent_to_assigning_a_new_map() {
+	println('array t len: ${t.len}, t: ${t}')
+	mut clr := map[int]int{}
+	for i in 0 .. 0xFFFF {
+		mut new := map[int]int{}
+		clr.clear()
+		for e in t {
+			new[e] = e
+			clr[e] = e
+			assert new.len == clr.len // , 'mismatch found after setting element: $e, on iteration ${i}'
+		}
+		if i & 0x3FFF == 0 {
+			println('index ${i}')
+			println('>> map     new: ${new.len} | ${new.keys().sorted()}')
+			println('>> map cleared: ${clr.len} | ${clr.keys().sorted()}')
+		}
+		assert new == clr // , 'mismatch found for iteration: ${i}'
+	}
+}