src: don't overwrite non-writable vm globals

[fhinkel]

Another try for #10223.

This is @bnoordhuis reverted commit, without removing is_contextual_store.

Now defineProperty(this, ..., {value: }) is intercepted and copied by the SetterCallback and global assignment succeeds the first time. The callback does not overwrite read-only values.

The first assert in the test is different from the reverted commit, because defineProperty(..., {value: }) is intercepted and copied by the SetterCallback.

https://github.com/nodejs/node/blob/master/test/known_issues/test-vm-data-property-writable.js is still a known issue, because the property descriptor is taken from the sandbox not the vm context. The test is not testing that read-only properties are not overwritten, but that defineProperty works.

[thefourtheye]

Nit: These tests can be logically grouped. Can you group them in blocks?

[fhinkel]

Which groups did you have in mind?

[thefourtheye]

Maybe something like this?

{
  // https://github.com/nodejs/node/issues/10223
  const ctx = vm.createContext();

  {
    vm.runInContext('Object.defineProperty(this, "x", { value: 42 })', ctx);
    assert.strictEqual(ctx.x, 42);
    assert.strictEqual(vm.runInContext('x', ctx), 42);
  }

  {
    vm.runInContext('x = 0', ctx);                      // Does not throw but x...
    assert.strictEqual(vm.runInContext('x', ctx), 42);  // ...should be unaltered.
  }

  {
    assert.throws(() => vm.runInContext('"use strict"; x = 0', ctx),
                  /Cannot assign to read only property 'x'/);
    assert.strictEqual(vm.runInContext('x', ctx), 42);
  }

}

[fhinkel]

Blocks in JS Code look weird to me. I added some extra blank lines. OK like this?

[thefourtheye]

Cool :-) This looks clean to my eyes now.

[thefourtheye]

Cool :-) This looks clean to my eyes now.

[fhinkel]

Thanks for the reviews. Landed in e116cbe.

[jasnell]

This would need a backport PR in order to land on v4 or v6 (if it should land on those at all)