text/template: allow newlines within actions and pipelines

[bep]

This issue resurfaced in gohugoio/hugo#5604 -- but has been mentioned enough times to have proven its value.

In Hugo we have many variadic template functions. One relevant example would be the dict func that accepts a list of key/value pairs.

A current example would look like this:

{{ dict "country" "Norway" "population" "5 millions" "language" "Norwegian" "languageCode" "nb" "weather" "freezing cold" "capitol" "Oslo" "largest_city" "Oslo" "currency"  "Norwegian krone" "dialing_code" "+47" }}

The above would obviously be easier to read if it could be written something like this:

{{ dict 
	"country" "Norway" 
	"population" "5 millions"
	"language" "Norwegian"
	"language_code" "nb"
	"weather" "freezing cold"
	"capitol" "Oslo"
	"largest_city" "Oslo"
	"currency"  "Norwegian krone"
	"dialing_code" "+47" 
}}

The above creates a parser error, and is a common problem when you try to use one of the "HTML beautifiers" out there on Go templates.

As a person who have spent some thousand hours inside Go templates I would say that this issue is really, really worth it. And if you don't come from that background, I think it helps to be reminded that many Go applications needs a user interface, and Go templates is a natural choice. No one questions the value of gofmt and pretty Go code, not sure why the UI code should be treated differently. I know @natefinch tinkered with a "Go template formatter" some time ago. A solution to this partucular issue would make that task more enjoyable, me thinks.

/cc @regisphilibert

[mvdan]

This seems reasonable to me. I'm a bit confused by the wording of the title, however. I assume what you want is for newlines to be allowed whithin pipelines - I'm not sure I understand how delimiters play a part here.

I also wonder if there's any disadvantage in allowing newlines in those cases. I can't think of any right now, but then again I haven't written complex pipelines in Go templates.

[mvdan]

Here's a quote from the package godoc:

Except for raw strings, actions may not span newlines, although comments can.

@bep have you given any thought to whether all actions would be allowed to span many newlines? Or would this be restricted to just pipelines, or just commands?

/cc @robpike

[bep]

I'm a bit confused by the wording of the title, however. I assume what you want is for newlines to be allowed whithin pipelines - I'm not sure I understand how delimiters play a part here.

I'm not sure how "what I want" translates to "Go template terms", and I don't remember the difference between commands and pipe. But currently the items between {{ and }} are separated by spaces. If you also allow newline as a separator, it would make many people happy.

[mvdan]

Thanks, I understand what you meant now. So I think what you're suggesting is to allow newlines within all actions, which includes pipelines as well as if, range, and everything else that can go between {{ and }}.

[natefinch]

strong +1 for this. I can't think of any reason this would cause problems, and I've often wanted to have a template node span more than one line.

As for the template formatter..... I tried and eventually gave up. The stdlib template parser is extremely lossy, so in order to use it for formatting, I was having to dive deep into modifying the parser to be lossless, and that turned into too heavy a lift for the time I had.

[bep]

@mvdan yes, that is correct. So, my primary "pain case" would be the example below. But I suspect that the changes in the template lexer/parser, and its documentation, will not be simpler if you try to somehow narrow the scope.

{{ $mymap := someTemplateFunc 
	"country" "Norway" 
	"population" "5 millions"
	"language" "Norwegian"
	"language_code" "nb"
	"weather" "freezing cold"
	"capitol" "Oslo"
	"largest_city" "Oslo"
	"currency"  "Norwegian krone"
	"dialing_code" "+47" 
}}

[regisphilibert]

Mind you, if this simplifies things, this could be limited to certain user defined actions: in the line of {{-, a character attached to the opening curlies could indicate the content of this action accepts newlines:

{{> $mymap := someTemplateFunc 
	"country" "Norway" 
	"population" "5 millions"
	"language" "Norwegian"
}}