Add support for HTML & XML source

[gucong3000]

• Infer HTML and XML by source for unknown file extension
• return css for other unknown file extension

stylelint/stylelint#3328 (comment)

[codecov]

Codecov Report

Merging #26 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #26   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          11     13    +2     
  Lines         250    258    +8     
=====================================
+ Hits          250    258    +8

Impacted Files	Coverage Δ
index.js	100% <100%> (ø)	⬆️
parse.js	100% <100%> (ø)	⬆️
is-html.js	100% <100%> (ø)
languages.js	100% <100%> (ø)
parser.js	100% <100%> (ø)	⬆️

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[gucong3000]

@shinnn
I used a new scheme to determine whether the file is XML.
I use regular expressions to determine if the source of the file is XML.
However, it is not valid for empty files.
I suggest that before applying the XML file to stylelint, determine if it contains <xsl:stylesheet>

[shinnn]

What do you mean by "empty files"?

At least the following code doesn't throw any errors.

const postcss = require('postcss');

const result = postcss().process('', {
  syntax: require('postcss-syntax'),
  from: '/path/to/example.xml'
});

[gucong3000]

What do you mean by "empty files"?

Empty string source.

*.xml is the only exception because this is the case in the regular, but the XML format supported by vscode has many other extensions, just like: *.svg, *.atom *.mxml, *.xhvml, *xvml, *xvm, I can't write all of them into this regular, because there are so many.

const postcss = require('postcss');

const result = postcss().process('', {
  syntax: require('postcss-syntax'),
  // empty source `*.svg` file will berak postcss-syntax
  from: '/path/to/example.svg'
});

[gucong3000]

[shinnn]

Post #26 (comment) first. #26 (comment) was extremely confusing to me.

I can't write all of them into this regular, because there are so many.

Could you at least support all the XML-related extensions you know currently?

[gucong3000]

In addition to XSL, other XML is actually not supported by us because they are not style files.
I'm very puzzled, why should we apply a style-independent file to a tool that handles styles?

I found that there are about 100+ extensions for XML format, but in fact we only support one (XSL).

[shinnn]

Fair enough.

[shinnn]

@gucong3000 What is blocking this from being merged?

[gucong3000]

What is blocking this from being merged?

Some integration test runs failed:

packages	version	build
postcss-syntax
postcss-html
postcss-markdown
postcss-jsx
postcss-styled

[gucong3000]

Replace with #28