Use a generic markup class to display externally rendered files and diffs

[6543]

This pull is based on #12261

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This PR will be a follow-on from #8299 and #7614.

It builds on the work done in #8300 and the patch #8357

The idea is to have a generic class .markup that has some default rendering, that is near identical to the current .markdown

More details

The current .markdown is defined at

https://github.com/go-gitea/gitea/blob/master/web_src/less/_markdown.less

and overwritten at:

gitea/web_src/less/themes/theme-arc-green.less

Lines 851 to 885 in 84a419d

	.markdown:not(code) .highlight pre,
	.markdown:not(code) pre {
	background-color: #2a2e3a;
	border: 1px solid #404552;
	}
	.markdown:not(code) table tr:nth-child(2n) {
	background-color: #2a2e39;
	}
	.markdown:not(code) table tr:nth-child(2n-1) {
	background-color: #383b44;
	}
	.markdown:not(code) table thead tr:nth-child(2n-1) {
	background-color: #464c5d !important;
	}
	.markdown:not(code) table td,
	.markdown:not(code) table th {
	border-color: #4c505c !important;
	}
	.repository.file.editor.edit,
	.repository.wiki.new .CodeMirror {
	.editor-preview,
	.editor-preview-side,
	& + .editor-preview-side {
	background: #353945;
	.markdown:not(code).ui.segment {
	border-width: 0;
	}
	}
	}

and

gitea/web_src/less/themes/theme-arc-green.less

Lines 1856 to 1867 in 84a419d

	.markdown:not(code) h1 {
	border-bottom-color: #888;
	}
	.markdown:not(code) blockquote {
	border-left-color: #888;
	}
	.markdown:not(code) code,
	.markdown:not(code) tt {
	background-color: #2a2e3a;
	}

⚠️ BREAKING ⚠️

Administrators with css/less customization targeting the .markdown class should update these to use .markup.

[codecov-commenter]

Codecov Report

Merging #15735 (ead5a0b) into main (eed88dc) will increase coverage by 0.12%.
The diff coverage is n/a.

❗ Current head ead5a0b differs from pull request most recent head a122a98. Consider uploading reports for the commit a122a98 to get more accurate results

@@            Coverage Diff             @@
##             main   #15735      +/-   ##
==========================================
+ Coverage   43.83%   43.95%   +0.12%     
==========================================
  Files         678      678              
  Lines       81882    81882              
==========================================
+ Hits        35893    35995     +102     
+ Misses      40133    40017     -116     
- Partials     5856     5870      +14     

Impacted Files	Coverage Δ
modules/git/repo_base_nogogit.go	63.63% <0.00%> (-9.10%)	⬇️
modules/git/utils.go	77.77% <0.00%> (-2.78%)	⬇️
models/gpg_key.go	53.51% <0.00%> (-0.57%)	⬇️
models/error.go	39.84% <0.00%> (+0.31%)	⬆️
services/pull/pull.go	43.83% <0.00%> (+0.45%)	⬆️
routers/repo/view.go	41.24% <0.00%> (+0.58%)	⬆️
modules/templates/helper.go	50.76% <0.00%> (+0.68%)	⬆️
models/notification.go	66.07% <0.00%> (+0.88%)	⬆️
modules/log/file.go	75.39% <0.00%> (+1.58%)	⬆️
services/pull/patch.go	55.93% <0.00%> (+1.69%)	⬆️
... and 9 more

---

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[silverwind]

More changes pushed:

• Rename markdown to markup everywhere where feasible
• Simplify docs by not suggesting to load Less code in the browser, that's just horrible advice.

[6543]

LGTM from my side ... :)

[lunny]

For wiki and issue/comment, maybe we should still keep in markdown? Or both markup markdown because we currently only support markdown syntax in these places.

[silverwind]

For wiki and issue/comment, maybe we should still keep in markdown? Or both markup markdown because we currently only support markdown syntax in these places.

It would have to be both but there's probably not much of a benefit doing so. We use double classes for the cases where the user can define the format, which I think is only for repo (and lfs) content.

[silverwind]

Marking this as breaking because users might have existing customization targeting the previous .markdown class which is not present anymore except for custom renderers and markdown files in the repo content, they should update these to use .markup.