Filter changes

[Keats]

Here is the issue to mention:

• missing filters from v1
• wanted changes of behaviour
• new filters wanted (no deps only)

Known missing:

• sort: do people use it? It's a lot of code

Current changes:

• trim filters have been merged in trim/trim_start/trim_end with an optional pat argument for start/end rather than separate filters
• int and float filter do not have a default anymore
• round filter does not take a common method anymore, it's the default and should not be filled if needed
• indent filter now takes a width param rather than prefix
• map, group_by and filter filter will error if the attribute ends up being undefined on one of the value
• as_str has been renamed to str
• truncate length does not have a default anymore

[uncenter]

I could be wrong but it looks like you also changed as_str to str?

[uncenter]

new filters wanted (no deps only)

• pad (see Add pad filter tera#921)
• repeat(n) - repeat a string n times, result could either be an array or a joined string, though an array would probably be better for broader usecases

wanted changes of behaviour

1. I know you have some opinions on Please add regex-aware replace filter. tera#421 though I think it should be revisited, at least concerning basic regex - no need for complicated capture groups and such.

2. It would be nice to be able to use positional args, though this isn't filters-specific as it also applies to macros. Maybe through some prefix before the argument name in the declaration, e.g. {% macro say_hello(*name) %} where the asterisk changes it from a kwarg to a positional arg?

3. Would it ever be possible to use https://keats.github.io/tera/docs/#map to apply a macro/filter to all elements of an array? This could be implemented without breaking existing behavior since a new kwarg could be used, e.g. | map(func=self::say_hello).

[Keats]

For repeat I would follow what Python does, eg:

>>> " " * 10
'          '
>>> [0] * 10
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
>>> 

so the output depends on the input.

For pad, I think a format filter would be better so it can be used for padding but also for displaying floats with 2 decimals for example.

---

1. I'm not going to work on anything requiring dependencies yet but that could be added later in a tera-contrib crate
2. I want to keep kwargs only. It's slightly less nice when there's a single required argument but otherwise it's much more readable imo.
3. If you look at the code, there is a TODO to do exactly that. The main issue from my pov is how to pass arguments to that filter. I didn't consider macro but that could be nice as well.

[uncenter]

For repeat I would follow what Python does, eg:

>>> " " * 10
'          '
>>> [0] * 10
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
>>> 

so the output depends on the input.

Makes sense to me... are you saying you are okay adding a filter like this?

For pad, I think a format filter would be better so it can be used for padding but also for displaying floats with 2 decimals for example.

Hmm how would displaying a float with 2 decimals work? I'm thinking of pad being used like {{ "def" | pad(len=6, fill="_", before=true) }} -> "___def".

2. I want to keep kwargs only. It's slightly less nice when there's a single required argument but otherwise it's much more readable imo.

I agree but even that case where there is only a single required argument is pretty common I'd think. Besides, most programming languages default to positional arguments and the only language I can think of off the top of my head that does kwargs is Python, which also supports positional args.

[Keats]

are you saying you are okay adding a filter like this?

Yes. Either that or overload * to do that automatically in the template without the repeat filter, one or the other.

For format, I'm thinking to basically use the Rust format: https://saghm.github.io/five-rust-things/#padding-format-operator

[azemlya]

The sort filter is very necessary. Very much so. I want to use multi-sorting, but at least like in tera v1.

[asimpletune]

Glad there's a dedicated issue for filters. I will take a closer look soon. In the meanwhile, I did notice that truncate is missing in v2. Was that intentional?

Also, slice on strings would be convenient. Even if it can be accomplished with split | slice | join I think that's all the more reason to consider having an alias for that on strings.

[Keats]

Looks like I forgot to add truncate.

Slicing on strings is available

[Keats]

I've added the truncate filter

[asimpletune]

Any plans to bring concat back? I see it as essential when working with list.

[Keats]

I was thinking something like [array] + [array] is nicer than using a filter so probably do that instead?

[asimpletune]

I was thinking something like [array] + [array] is nicer than using a filter so probably do that instead?

O yeah, that would be nice too.

I noticed that indent now is different. Instead of taking a prefix arg it takes just a width. I think in this case the new filter isn't as good and I prefer just being able to prefix " " if I want x number of spaces. I need it because a lot of times I'm templating emails and quoting replies and so I need to prepend > to every line.

Speaking of which, a clamp filter would also be nice. Again with email I often want to simulate exact line widths followed by line breaks.

I'm happy to make the changes to filter if you agree or add that functionality in a clamp filter if that also sounds like something the project would like.

[Keats]

I don't really want to change the current indent filter. Filters are now easier to write and I don't want to cover every single thing in tera-contrib, just the common things.

[Keats]

I've added all the filters afaik except concat while I'm thinking about how to make it work better. I've removed a few filters (addslashes, escape_xml, get_env, and slice) intentionally.
I've also added a way to use a filter in map, eg:

map(filter): {{ ["hello", "world"] | map(filter="upper") | safe }}
map(filter+args): {{ ["hello world", "foo bar"] | map(filter="truncate", args={"length": 5}) | safe }}
map(attr+filter): {{ reviews | map(attribute="title", filter="upper") | safe }}
map(attr+filter+args): {{ reviews | map(attribute="title", filter="truncate", args={"length": 5}) | safe }}

I've also added a format filter based on https://crates.io/crates/formatx which handles padding, precisions etc