Not removing calls with @nosideeffect functions

[sean.l]

When I compile codes which contains some `Object.defineProperty` calls whose return value are not used, closure compiler does not remove the call entirely, although `Object.defineProperty` is annotated with `@nosideeffect` in `es3.js`. 

Here is a repro:

closure-compiler-debugger

```

let a = Object.getOwnPropertyDescriptor;

let b = Object.getOwnPropertyDescriptor(Object.prototype, 'hasOwnProperty');

let c = a(Object.prototype,'__proto__').get;

```

output:

```

'use strict'; var a = Object.getOwnPropertyDescriptor; Object.getOwnPropertyDescriptor(Object.prototype, "hasOwnProperty"); a(Object.prototype, "__proto__");

```

Is this an expected result? Is there something that I can tweak to let Closure Compiler to remove those calls?

[sean.l]

Correction: `Object.getOwnPropertyDescriptor` is in `es5.js`, not `es3.js`

[Nick Reid]

Hey Sean, thanks for the report.

This looks like a bug caused by PureFunctionIdentifier being too cautious with respect to function aliases. If you remove the `let a =` alias everything works as expected. Hopefully that's an acceptable workaround for now.

Can you file a GitHub issue for this? It should be a simple fix.

Nick

[sean.l]

Done here, thanks!

[sean.l]

Hi, the issue seems to be fixed in the Closure Compiler debugger, but it's not fixed with npm google-closure-compiler 20210601 version.

When I fed the same file

```

// a.js

let a = Object.getOwnPropertyDescriptor;

let b = Object.getOwnPropertyDescriptor(Object.prototype, 'hasOwnProperty');

let c = a(Object.prototype,'__proto__').get;

```

and CLI flags

```

--compilation_level=ADVANCED

--js a.js

--js_output_file=out.js

--language_in=ECMASCRIPT_2017

--language_out=ECMASCRIPT_2017

```

the output still retains `Object.getOwnPropertyDescriptor` calls. Is this an intended behavior, or the npm version hasn't kept up with the fix in March yet?