This enables `AND` (`intersect`) and `OR` (`union`) filters when combined with `where`.
Example:
```go
{{ $pages := where .Site.RegularPages "Type" "not in" (slice "page" "about") }}
{{ $pages := $pages | union (where .Site.RegularPages "Params.pinned" true) }}
{{ $pages := $pages | intersect (where .Site.RegularPages "Params.images" "!=" nil) }}
```
The above fetches regular pages not of `page` or `about` type unless they are pinned. And finally, we exclude all pages with no `images` set in Page params.
Fixes#3174
Unsupported types are currently silently ignored by IsSet. An earlier
attempt was made to solve the issue by returning an error. That attempt
was reverted since it broke some existing themes.
So instead, we'll log an error. Hopefully, people will stop using IsSet
in this way, and we can eventually return an error outright.
Updates #3092
This commit moves almost all of the template functions into separate
packages under tpl/ and adds a namespace framework. All changes should
be backward compatible for end users, as all existing function names in
the template funcMap are left intact.
Seq and DoArithmatic have been moved out of the helpers package and into
template namespaces.
Most of the tests involved have been refactored, and many new tests have
been written. There's still work to do, but this is a big improvement.
I got a little overzealous and added some new functions along the way:
- strings.Contains
- strings.ContainsAny
- strings.HasSuffix
- strings.TrimPrefix
- strings.TrimSuffix
Documentation is forthcoming.
Fixes#3042
