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https://issues.apache.org/jira/browse/TAP5-2753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17709942#comment-17709942
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Ben Weidig commented on TAP5-2753:
----------------------------------

Hi [~lrein],

the CssCompressor is based on the YUI Compressor 
[https://github.com/yui/yuicompressor], which is a dead project for quite some 
time now.

There are a lot of minor issues, especially regarding newer CSS features.
It's been on my to-do list for a long time to think about a solution to keep it 
functioning and make it more maintainable without introducing another 
dependency.

I haven't tested it yet, but I believe the code block can't be removed in 
general, as spaces are required between operators, see 
https://developer.mozilla.org/fr/docs/Web/CSS/calc and 
https://github.com/yui/yuicompressor/issues/238

However, maybe the regex could be changed for "-" to ignore variables.

If you need an immediate fix, you could override the CSS ResourceMinimizer, 
which we did for our projects due to an other issues with CssCompressor:

{code:java}
 @Contribute(ResourceMinimizer.class)
 @Primary
 public static void setupDefaultResourceMinimizers(MappedConfiguration<String, 
ResourceMinimizer> conf) {
    conf.overrideInstance("text/css", CustomCssCompressor.class);
}
{code}

The CssCompressor isn't a ResourceMinimizer, but we made the 
CustomCssCompressor one by moving the code from 
org.apache.tapestry5.internal.webresources.CSSMinimizer directly into it.

Long term, I think it makes sense to move the test CSS files from the YUI 
project over to Tapestry, so the CssCompressor can be changed without breaking 
other features.



> CssCompressor for CSS files produces wrong minification if calc contains 
> variables.
> -----------------------------------------------------------------------------------
>
>                 Key: TAP5-2753
>                 URL: https://issues.apache.org/jira/browse/TAP5-2753
>             Project: Tapestry 5
>          Issue Type: Bug
>          Components: tapestry-webresources
>    Affects Versions: 5.8.2
>            Reporter: LRein
>            Priority: Minor
>
> CssCompressor for CSS files produces wrong minification if calc contains 
> variables.
> {code:css}
> .some-class
> {
> padding-top: calc(10px + var(--default-page-header-height));
> }
> {code}
> produces spaces between dashes within the variable:
> {code:css}
> .some-class
> {
> padding-top: calc(10px + var( - - default - page - header - height));
> }
> {code}
> Just removing this code block at the end helps:
> {code:java}
> // Add spaces back in between operators for css calc function
> // https://developer.mozilla.org/en-US/docs/Web/CSS/calc
> // Added by Eric Arnol-Martin (earnolmar...@gmail.com)
> sb = new StringBuffer();
> p = Pattern.compile("calc\\([^\\)]*\\)");
> m = p.matcher(css);
> while (m.find()) {
>     String s = m.group();
>     
>     s = s.replaceAll("(?<=[-|%|px|em|rem|vw|\\d]+)\\+", " + ");
>     s = s.replaceAll("(?<=[-|%|px|em|rem|vw|\\d]+)\\-", " - ");
>     s = s.replaceAll("(?<=[-|%|px|em|rem|vw|\\d]+)\\*", " * ");
>     s = s.replaceAll("(?<=[-|%|px|em|rem|vw|\\d]+)\\/", " / ");
>     
>     m.appendReplacement(sb, s);
> }
> m.appendTail(sb);
> css = sb.toString(); 
> {code}



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