Question: What is the point of the `typescript` option?

[brandon-leapyear]

This says that if the option isn't set, the plugin will automatically set it to require('typescript').

rollup-plugin-typescript2/src/index.ts

Lines 72 to 74 in 5ce7676

	if (!pluginOptions.typescript) {
	pluginOptions.typescript = require("typescript");
	}

I'm wondering why you would ever want to manually set the typescript option to require('typescript') then. Wouldn't calling require('typescript') in rollup.config.js always give the same answer as require('typescript') in the plugin?

[ezolenko]

You might want to use multiple versions of typescript for example, or have it in a non-standard place.

[brandon-leapyear]

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---

I see. But the docs say

When typescript version installed by the plugin (latest 2.x) is unacceptable, you can import your own typescript module and pass it in as typescript: require("typescript"). Must be 2.0+, things might break if transpiler interfaces changed enough from what the plugin was built against.

You would never literally do typescript: require("typescript"), you'd do typescript: require("path/to/other/typescript"), right? I'm mostly asking about a docs change, here

[ezolenko]

Yeah, typescript: require("typescript") is redundant -- the plugin will do that on its own if you don't provide typescript option. I'll change the doc.

[agilgur5]

Worth noting, require('typescript') from within rpt2 (vs. from within your rollup.config.js) actually could resolve to something different depending on how your node_modules ends up being laid out.

For example, if it somehow ended up like this:

my-project
│   README.md
│   rollup.config.js
└───node_modules
│   └───typescript
│   └───rollup-plugin-typescript2
|       └───node_modules
|           └───typescript

You'd have two different TS versions depending on where require('typescript') was called.

Realistically, that shouldn't really happen unless node_modules is an erroneous state (e.g. need to run npm dedupe etc) since rpt2 sets TS as a peerDep, but it is something to be aware of in the Node ecosystem.

EDIT: actually that seems to have been the original purpose of the tsconfig option, as implemented in #27.
I believe NPM placed things differently in node_modules back then, so this scenario was more common then. Also this package had TS listed as both a peerDep and a dep back then instead of as a peer and devDep.

[agilgur5]

You can also use this for alternative TS implementations, such as ttypescript, for instance for the purpose of #201 or something else.