Scopes: Add 'file' scope

[szuend]

This is straw-man PR to discuss whether we want to distinguish "global" and "file" ("script" or "module") scope.

An example of this may be the following:

// a.js
var foo = 'a';
const bar=  'b';

Both Firefox DevTools and Chrome DevTools would show different scopes for a and b. Specifically a would be in the "global" scope as it gets hoisted to globalThis/window. Whereas b would be only in the "script" scope.

This could simplify handling of the "global" scope across multiple authored files. To expand on the initial example let's add another file:

// b.js
var fooB = 'foo';
const barB = 'bar';

debugger;

And the combined bundle:

// bundle.js
var foo = 'a';
const bar=  'b';
var fooB = 'foo';
const barB = 'bar';

debugger;

If we pause on the debugger statement then the expected scope chain is:

• script
  • barB: 'bar'
• global
  • foo: 'a'
  • fooB: 'foo'

Since the global scope is combined. Generators can achieve this by generating the following "generated ranges" for the bundle:

// bundle.js
var foo = 'a';      | (1)  | (2)  | (3)  
const bar=  'b';    |      |      |
var fooB = 'foo';   |      |             | (4)
const barB = 'bar'; |      |             |
                    |      |             |
debugger;           |      |             |  

(1) and (2) are the respective "global" scopes. (3) is the file scope of a.js and (4) is the file scope of b.js.

[hbenl]

whether we want to distinguish "global" and "script" scope

Yes, I think we should do so. The proposed solution makes sense to me.

[jkup]

Change looks good. @nicolo-ribaudo mentioned in the monthly meeting we should consider if we need both script and module or can get away with just global and file

[szuend]

As discussed in the meeting, consolidated the script / module scope into a single file scope.

[jkup]

Closing in favor of replacing ScopeKind with an index into the names array. That way JS can store "module", "function" and other languages can make their own.