[esinstall] enable native esm for node v12+

[FredKSchott]

/cc @ChristopherBiscardi

Changes

• Resolves esinstall doesn't export esm for use in node v14 #1076
• Supercedes enable native mjs for node v14 #1092
• Adds ESM support for Node v12+
• Removes @pika/pack (doesn't support export maps, see rationale here)

Testing

• Covered by tests

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[FredKSchott]

I went one step further and removed @pika/pack from Snowpack as well. I love @pika/pack as much as the next person, but in this exact usecase it was causing more harm than good. See the contributing docs for all the weirdness that this removes.

Also, we now have a build:watch command: make changes and see the reflected instantly. Way overdue, imo!

[gr2m]

😍 😍 😍

[gr2m]

I have tested the pull request locally with the example documented in https://github.com/pikapkg/snowpack/tree/0fe3dccb4b957d301718cfac82abbb035e740d17/esinstall#esinstall and worked as expected 👍🏼

[drwpow]

I’m seeing some weird behavior in the tests, I think from this PR?

Before, all of our test repos symlinked node_modules/.bin/snowpack to the snowpack bin in pkg/. That means we were testing locally.

Now, it seems all of our build tests download snowpack from npm, which means we’re no longer testing the local version (so any test success or failure in a PR can’t be trusted).

To confirm this, in snowpack/package.json I see version 2.12.0-pre.1. But inside test/**/node_modules/snowpack/package.json, I see a separate copy with 2.11.1 (latest on npm). Are we sure our tests are still using the local build?

[FredKSchott]

Hmm, I do see "snowpack" being installed locally, but the bin is still from the symlinked. Something is definitely going on here though, let me update the yarn.lock file and see if that helps.

[FredKSchott]

Okay, think that fixed it. I think it was the 2.12.0-pre.1 release, which yarn seemed to not like when it came time to resolve workspace deps

[drwpow]

Ah good to know! Sorry—my mistake. 🤔 What if in the test deps we just did "snowpack": "file:../../…"? Would that be a little less “magic”?

[FredKSchott]

+1 if that means also moving the tests out of lerna/yarn workspaces entirely :) (at that point we’d only be using them to manage the test deps, which we’ve been bitten by “did this snapshot change because of a test dep or a Snowpack dep” when doing a fresh “yarn install”)

[drwpow]

As long as tests surface regressions in a PR before merging that’s all that matters to me! I don’t care if they’re a part of the Lerna/Yarn workspace or not. As long as CI runs quickly and setup for contributors is easy, that’s mostly what matters.