Output content format is strange

[sillykelvin]

Hi,

When I am using mustache.el to render templates, I find something strange, let's take the code snippets below as example:

(mustache-render
 "<{{a}} />
  {{#b}}
  <{{b}} />
  {{/b}}
  {{#c}}
  <{{c}} />
  {{/c}}"
 (ht ("a" "AA")
     ("b" "BB")
     ("c" "CC")))

the output is:

<AA />
    <BB />
      <CC /> (Note: two more spaces are added than original format)
  (Note: there are two spaces at the beginning of this line)

what I expect is that the output should be consistent with the original format:

<AA />
  <BB />
  <CC />

no more extra spaces before <CC /> and the last line.

I don't know if this is an issue, or there is something, maybe a switch, can change the behavior.

Thanks,
Kelvin

[sillykelvin]

And another issue:

(mustache-render
 "{{a}}
  {{b}}"
 (ht ("a" "AA")
     ("b" "BB")))

will produce:

AA  BB

but NOT:

AA
  BB

As you see, the newline character is missing, I think it should keep the original format.

[sillykelvin]

I read your source code, and find the root cause for the second problem, it is because a cond branch in function mst--render-section:

...
(t
 (s-chop-prefix
  "\n"
  (second parsed-lexeme)))

the prefix newline character is dropped, I don't quite understand your design intention about this, could you please do some explanation?

Thanks,
Kelvin

[Wilfred]

The mustache standard has a lot to say on handling newlines: https://github.com/mustache/spec/blob/v1.0.2/specs/sections.yml#L135

So, a fully compliant mustache implementation will change whitespace in some circumstances. Also, mustache.el isn't perfectly compliant with the specification yet. However, removing the s-chop-prefix call makes the following unit test fail:

(ert-deftest mustache-test-standalone-lines ()
  (should
   (equal "| This Is
|
| A Line
"
    (mustache-render "| This Is
{{#boolean}}
|
{{/boolean}}
| A Line
" (ht ("boolean" t))))))

This example is from the specification: https://github.com/mustache/spec/blob/v1.0.2/specs/sections.yml#L155

That being said, mustache.el is clearly doing the wrong thing here. I tested python-mustache (a fully compliant implementation), and it renders your second example to "AA\n BB" as expected.

I'll try to fix this when I can. I need to read the specification again to understand how we should treat whitespace.

[sillykelvin]

Thanks for your reply, waiting for your great solution solving this~~ :-D

[Wilfred]

OK, this should now all work according to the spec. Your examples now give the output expected. Let me know if you find any other issues.

[sillykelvin]

Yeah, thanks for your great work, it works well now, except a little defect, let's take the following example:

(mustache-render
 "{{a}}
{{#b}}
{{b}}
{{/b}}
{{#c}}
{{c}}
    {{/c}}    "  ;; Note: there are four spaces both at the beginning and the end
 (ht ("a" "AA")
     ("b" "BB")
     ("c" "CC")))

the output is:

AA
BB
CC
        (Note: the extra 8 spaces are included)

As you see, the last line only contains a condition validation close tag, according to this spec(https://github.com/mustache/spec/blob/v1.0.2/specs/sections.yml#L155), this line should be removed also.

However, this does not affect much, but I am a perfactionist, so if this issue is smooth to fix, please help fix it, thanks very much~~ :-D