v8/test/mjsunit/regress/regress-1493017.js

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// Test collection of abandoned maps.  Tests that deleted map
// transitions do not show up as properties in for in.

// Flags: --expose-gc

function C() {}


// Create an instance of C.  Add a property to the instance and then
// remove all references to instances of C.
var o = new C();
o.x = 42;
o = null;

// Force a global GC. This will collect the maps starting from C and
// delete map transitions.
gc();

// Create a new instance of C.
o = new C();

// Test that the deleted map transitions do not show up in for in.
for (var p in o) {
  assertTrue(false);
}