Allow to configure the HttpCache trace level using an environment variable

[Toflar]

While debugging #1033 I noticed that we cannot configure the trace level of HttpCache. It absolutely makes no sense to bind that to $this->isDebug because in our case, this is always the case when we are in dev mode which again disables the HttpCache completely.

So here we go, by setting TRACE_LEVEL=full the Contao-Cache header gives you a lot more insight into the fragment requests.

[aschempp]

This means I can trace the cache in production, right?

Is there any other option then full or short? If not I would prefer a boolean trigger.

Also, I wonder if an ENV is necessary, or just something you adjust in the entry point? Would you ever enable this long-term?

[Toflar]

This means I can trace the cache in production, right?

Yes, which is the only place where you need to trace that. That's why the current implementation makes no sense.

Is there any other option then full or short? If not I would prefer a boolean trigger.

Not today, but maybe tomorrow. That's why I want to keep that a string.

Would you ever enable this long-term?

No, that's why it has to be an env var, there's no alternative.

[richardhj]

I would prefix the variable name with CACHE_

[Toflar]

I would prefix the variable name with CACHE_

I thought about that but we also did not prefix the COOKIE_WHITELIST and I don't think we're going to introduce another hundred env variables. I can't think of any other atm so I guess this is fine :)

[leofeyer]

Thank you @Toflar.