fix(gatsby-plugin-google-analytics): Don't create tracking code without an ID.

[laradevitt]

Hello, this is my first code-related PR.

Fixes #19479

There is no fancy string validation here; this fix just stops the tracking code from being created if (option) "trackingId" is empty or false. It also outputs a warning.

I'm not sure about my changes to tests. With this fix the existing tests now rely on "trackingId" being set, so I've made this the default while adding a new test that tests the opposite condition ("trackingId" is unset).

Edit: Fixed linked to related issue.

[wardpeet]

This looks great! 😍 Thanks a bunch for adding this @laradevitt. This PR is 💯

[muescha]

Should there also a warning if there is the default YOUR_GOOGLE_ANALYTICS_TRACKING_ID ?

(If I search over Gatsby Repo issues I see some gatsby-configs with this and if I search over GitHub also many starters with it)

[laradevitt]

@muescha - I looked around and I couldn't find any issues where the example ID given in the README is a problem. Or am I misunderstanding?

You have me thinking about this, though. Since people copy-and-paste the example I'm not crazy about having anything other than the actual sensible defaults there. And do we really need to scream YOUR_GOOGLE_ANALYTICS_TRACKING_ID for people to understand what goes there? I don't think so.

(This goes for all of the option properties that need an ID.)

[muescha]

i see many people leave exactly this text in the code (see issues #4693 #8099 #1449) or in code base like this search shows many places: Github Code Search for 'YOUR_GOOGLE_ANALYTICS_TRACKING_ID'

ok - leave it as it is - so people don't think the plugin is not working.

[laradevitt]

I agree that this is potentially problematic but unfortunately if we implemented that check here we would have to do it for all of the plugins that do the same thing. I think a better solution might be to be more careful in how we document examples, since people do tend to just copy-and-paste into the config file, but that's a whole issue in itself. 🤷‍♀

[muescha]

🤷‍♀ yes you are right.

only soulution would be to use a process.env.YOUR_GOOGLE_ANALYTICS_TRACKING_ID then the value would be null, the user is pointed a little bit into the direction that he need to secure his settings. but this makes the examples also more complicated.