tests: add an autofree regression test before return value ownership changes

vlib/v/tests/valgrind/free_heap_foos.v

@@ -0,0 +1,50 @@
+[has_globals]
+module main
+
+__global frees = []int{cap: 100}
+
+struct Foo {
+	x int
+}
+
+fn create(x int) &Foo {
+	res := &Foo{x}
+	println('> creating Foo $res.x at address: ${voidptr(res)}')
+	return res
+}
+
+fn (f &Foo) free() {
+	println('> freeing Foo $f.x at address: ${voidptr(f)} | frees.len: $frees.len')
+	frees << f.x
+	// TODO: this should NOT be necessary - the compiler should do it automatically in the parent scope
+	unsafe { free(f) }
+}
+
+fn create_some_foos() {
+	starting := frees.len
+	a := create(111)
+	assert frees.len == starting
+	b := create(222)
+	assert frees.len == starting
+	println('  > create_some_foos a: $a.x')
+	println('  > create_some_foos b: $b.x')
+	assert frees.len == starting
+}
+
+fn main() {
+	create_some_foos()
+	if C._VAUTOFREE == 1 {
+		assert frees.len == 2
+		assert frees[0] == 222
+		assert frees[1] == 111
+	}
+	create_some_foos()
+	if C._VAUTOFREE == 1 {
+		assert frees.len == 4
+		assert frees[0] == 222
+		assert frees[1] == 111
+		assert frees[2] == 222
+		assert frees[3] == 111
+	}
+	unsafe { frees.free() }
+}