LogQL: Improve template format

[cyriltovena]

This add errors in case of problem when executing template for line/label_format.

It also add functions that are easier to use with pipelines.

Docs & tests are updated.

[oddlittlebird]

Some doc edits, mostly minor. I suggest having someone else review the code.

[sandeepsukhani]

LGTM! Just a minor nit.

[owen-d]

Good catch on the function param positions. We can probably deprecate the old ones officially in the future.

All the string indexing math should use []rune instead of string indices, because the latter doesn't play well with all code points. I've left a couple ideas about implementation, curious what you think.

[achatterjee-grafana]

Added a bunch of minor copy-edit suggestions.

[achatterjee-grafana]

Suggested change

	All labels are added as variables in the template engine. They can be referenced using they label name prefixed by a `.`(e.g `.label_name`) for example the following template will output the value of the path label:
	Labels are added as variables in the template engine. They can be referenced using the label name prefixed by a `.`(e.g. `.label_name`). The following template will output the value of the path label:

[achatterjee-grafana]

Suggested change

	> **Note:** In Loki 2.1 you can also use respectively [`lower`](#lower) and [`upper`](#upper) shortcut, e.g `{{.request_method | lower }}`
	> **Note:** In Loki 2.1 you can also respectively use [`lower`](#lower) and [`upper`](#upper) shortcut, e.g `{{.request_method | lower }}`

[owen-d]

Cool bits around negative truncation. Code LGTM (thanks for fixing rune support).

[cyriltovena]

@oddlittlebird @achatterjee-grafana I think after 5 suggestions it would better to just add a commit to my PR on your own.

The result is the same, but for me it's less time wasted it's not easy to accept all those suggestions with github UI, but also remembering what I've solved or not.

WDYT ?

[cyriltovena]

I wasn't able to accept all of them because I think some are overlapping on the same lines and they became outdated.

[oddlittlebird]

@oddlittlebird @achatterjee-grafana I think after 5 suggestions it would better to just add a commit to my PR on your own.

The result is the same, but for me it's less time wasted it's not easy to accept all those suggestions with github UI, but also remembering what I've solved or not.

WDYT ?

No one has shown us how to do that, so theoretically maybe?

Would that still allow you (or users in general) to accept some suggestions and reject others?

[cyriltovena]

@oddlittlebird @achatterjee-grafana I think after 5 suggestions it would better to just add a commit to my PR on your own.
The result is the same, but for me it's less time wasted it's not easy to accept all those suggestions with github UI, but also remembering what I've solved or not.
WDYT ?

No one has shown us how to do that, so theoretically maybe?

Would that still allow you (or users in general) to accept some suggestions and reject others?

I could technically revert a commit if really I wasn't happy about the changes, but honestly, you're the code owner of this, I fully trust you, specially for documentation.

I think when there's so many suggestions/mistakes/edits, it's fine to do that. (At least for me, I allow you to do so, I'll still learn from seeing the changes, but I won't waste time trying to get everything right, I was able to batch but it's only by 8.)

Now how to do it, might not be all simple if you're not familiar to git, I'll admit that.

However you might be able to do it directly in github using this edit button which should get you into an editor.

Or using git locally

1. get github cli https://github.com/cli/cli
2. gh auth login (first time to auth)
3. gh pr checkout number (to get my changes locally)
4. edit files
5. git add .
6. git commit -m "documentation changes"
7. git push

I think this was a rare case of many changes required, so I don't think this is required for every PR.

[oddlittlebird]

Thanks for the lesson! I'll try the commit the next time I have a lot of changes to make.