[Transforms] Import external helpers module

[rbuckton]

This change adds support for referencing emit helpers from an external module.

Compiler Options

• --importHelpers - Import emit helpers from "tslib".

Emit

When importHelpers is specified, a synthetic ImportDeclaration is added to the top of each external module that needs an emit helper, such as __extends. As a result, no emit helpers will be added to these files during emit. In addition, any place where the emit helper would be referenced, it would instead reference a member of the imported module.

For example:

// @module: commonjs
// @importHelpers: true
export class A { }
export class B extends A { }

Outputs:

var tslib_1 = require("tslib");
var A = (function () {
  function A() {
  }
  return A;
})();
exports.A = A;
var B = (function (_super) {
  tslib_1.__extends(B, _super);
  function B() {
  }
  return B;
})(A);
exports.B = B;

Script files

If a file is detected as a non-external-module (e.g. script file), the existing behavior for emit helpers is used. As long as the --noEmitHelpers option is not set, emit helpers will be added to the top of the file as usual.

Fixes #3364

[rbuckton]

CC: @mhegazy, @vladima, @ahejlsberg

[mhegazy]

side note, we should get rid of this flag, specially that it is not used except in one place, and is at bit 30, which will cause a conversion on node-32 bit.

[rbuckton]

Actually, this is a bug in printer. This flag needs to be used and isn't.

[rbuckton]

Also, we need to consolidate the node flag values now that I've extracted the modifiers out of NodeFlags, that should help us avoid the SMI overflow on 32-bit node.

[mhegazy]

__asing seems to be emitted still.

other than that, can you add a test for something that explicitly includes an import to tslib.

[mhegazy]

We previously talked about adding a check in the program creating to make sure that tslib can be resolved as a module. and possibly, that it does have an exported function __extends, etc..

[mhegazy]

consider returning after the first error, to avoid reporting the same error for every file.

[rbuckton]

I need to traverse each file to determine which helpers I need to verify. I can possibly add some additional short-circuiting logic, but nothing as simple as "bail on first error".

[mhegazy]

Baselines need to be updated for error spans i would expect.

[mhegazy]

👍

[develar]

Will be useful to allow specify own module name. In my project https://github.com/electron-userland/electron-builder/blob/master/src/codeSign.ts I need only awaiter and since bluebird is forbidden, I disable emit helpers and add custom awaiter impl to each file. And new option is not solution because I cannot specify helper module name.

[gilboa23]

Will the new --importHelpers flag also apply to the __export helper? Currently, the --noEmitHelpers controls all the other helpers (e.g., __extends, __decorate, etc.), except for __export. See issue #10905.

[rbuckton]

@gilboa23, no it doesn't yet apply to __export as that helper is currently a closure over the local exports symbol defined in the module body. We are considering a change to make this possible, but it would be a breaking change for anyone using --noEmitHelpers.

[gilboa23]

Yes, but I was not referring to the existing --noEmitHelpers flag. What I meant was to apply this change just over the new --importHelpers flag by passing the local exports symbol in the invocations of the imported tslib.__export() function. This should not be a breaking change since this is a new flag that no one is using yet. Something like:

// @module: amd
// @importHelpers: true
export * from "A";
export * from "B";

Output:

define(["require", "exports", "A", "B"], function (require, exports, A_1, B_1) {
    "use strict";
   var tslib_1 = require("tslib");
    tslib_1.__export(A_1, exports);
    tslib_1.__export(B_1, exports);
});

[mhegazy]

@gilboa23 if issue #10905 is fixed, it will work for both.

[wyntau]

[email protected] is missing __generator function. But the source code has.

should tslib on npm be updated and release a new version?

[itaysabato]

So, if I would like to use --importHelpers with tslib and replace only a specific helper (say, __awaiter) with my own implementation, how would I go about that?

[mhegazy]

So, if I would like to use --importHelpers with tslib and replace only a specific helper (say, __awaiter) with my own implementation, how would I go about that?

1. Use [email protected] or later
2. Install tslib
3. Set --importHelpers on the command line or in your tsconfig.json