Note: new PR description written by @timneutkens
## What?
Improves the detection of Google Tag Manager vs Google Analytics.
As indicated by the author of this PR it was confusing that when you
have Google Tag Manager set up it gives you an error message saying
you're adding Google Analytics even though it's Tag Manager.
I've updated the PR to have a separate message for Google Tag Manager
and expanded the error message docs too.
It also mentioned `next/script` in a bunch of places even though the
error doc recommends `@next/third-parties`. I've updated all cases to
refer to `@next/third-parties` instead.
<details>
<summary>Previous PR description</summary>
Google has multiple products with similar names: the "Google Tag" and
"Google Tag Manager". Google Tag Manager uses `gtm.js` whereas the
"Google Tag" uses `gtag`. Google Analytics previously used
`analytics.js` (<2017) and is now delivered via the "Google Tag".
Google Tag: `www.googletagmanager.com/gtag/js`
Google Tag Manager: `www.googletagmanager.com/gtm.js`
The `next-script-for-ga.ts` rule's matching list
(`SUPPORTED_HTML_CONTENT_URLS`) includes `gtm.js` which means when a
developer adds Google Tag Manager to their NextJS website, they'll
receive the warning and be encouraged to swap from `gtm.js` to `gtag`. A
developer asleep at the wheel (...me) may think...
> I'm using Google Analytics via Google Tag Manager, and NextJS is
suggesting I swap `gtm.js` for `gtag` because it will improve
performance. `gtag` sounds like it is part of "Google Tag Manager" so I
am going to follow the instructions so that my website is faster.
However, `gtag` is **not** compatible with `gtm.js` (they're different
products with similar names and similar purposes) and so making this
change will cause very confusing Google Tag Manager behaviour. I am
suggesting that `gtm.js` is removed completely from the rule, because
anyone using `gtm.js` should not be following these instructions. A
separate rule could be added specifically for Google Tag Manager, that
does not refer to `gtag`.
</details>
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Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
sam