Server-side syntax highlighting for all code (#12047)

* Server-side syntax hilighting for all code

This PR does a few things:

* Remove all traces of highlight.js
* Use chroma library to provide fast syntax hilighting directly on the server
* Provide syntax hilighting for diffs
* Re-style both unified and split diffs views
* Add custom syntax hilighting styling for both regular and arc-green

Fixes #7729
Fixes #10157
Fixes #11825
Fixes #7728
Fixes #3872
Fixes #3682

And perhaps gets closer to #9553

* fix line marker

* fix repo search

* Fix single line select

* properly load settings

* npm uninstall highlight.js

* review suggestion

* code review

* forgot to call function

* fix test

* Apply suggestions from code review

suggestions from @silverwind thanks

Co-authored-by: silverwind <me@silverwind.io>

* code review

* copy/paste error

* Use const for highlight size limit

* Update web_src/less/_repository.less

Co-authored-by: Lauris BH <lauris@nix.lv>

* update size limit to 1MB and other styling tweaks

* fix highlighting for certain diff sections

* fix test

* add worker back as suggested

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/github.com/alecthomas/chroma/lexers/n/nix.go

@@ -0,0 +1,122 @@
+package n
+
+import (
+	"strings"
+
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// nixb matches right boundary of a nix word. Use it instead of \b.
+const nixb = `(?![a-zA-Z0-9_'-])`
+
+// Nix lexer.
+var Nix = internal.Register(MustNewLexer(
+	&Config{
+		Name:      "Nix",
+		Aliases:   []string{"nixos", "nix"},
+		Filenames: []string{"*.nix"},
+		MimeTypes: []string{"text/x-nix"},
+	},
+	Rules{
+		"root": {
+			Include("keywords"),
+			Include("builtins"),
+			// "./path" and ".float" literals have to be above "." operator
+			Include("literals"),
+			Include("operators"),
+			{`#.*$`, CommentSingle, nil},
+			{`/\*`, CommentMultiline, Push("comment")},
+			{`\(`, Punctuation, Push("paren")},
+			{`\[`, Punctuation, Push("list")},
+			{`"`, StringDouble, Push("qstring")},
+			{`''`, StringSingle, Push("istring")},
+			{`{`, Punctuation, Push("scope")},
+			{`let` + nixb, Keyword, Push("scope")},
+			Include("id"),
+			Include("space"),
+		},
+		"keywords": {
+			{`import` + nixb, KeywordNamespace, nil},
+			{Words(``, nixb, strings.Fields("rec inherit with if then else assert")...), Keyword, nil},
+		},
+		"builtins": {
+			{`throw` + nixb, NameException, nil},
+			{Words(``, nixb, strings.Fields("abort baseNameOf builtins currentTime dependencyClosure derivation dirOf fetchTarball filterSource getAttr getEnv hasAttr isNull map removeAttrs toString toXML")...), NameBuiltin, nil},
+		},
+		"literals": {
+			{Words(``, nixb, strings.Fields("true false null")...), NameConstant, nil},
+			Include("uri"),
+			Include("path"),
+			Include("int"),
+			Include("float"),
+		},
+		"operators": {
+			{` [/-] `, Operator, nil},
+			{`(\.)(\${)`, ByGroups(Operator, StringInterpol), Push("interpol")},
+			{`(\?)(\s*)(\${)`, ByGroups(Operator, Text, StringInterpol), Push("interpol")},
+			{Words(``, ``, strings.Fields("@ . ? ++ + != ! // == && || -> <= < >= > *")...), Operator, nil},
+			{`[;:]`, Punctuation, nil},
+		},
+		"comment": {
+			{`\*/`, CommentMultiline, Pop(1)},
+			{`.|\n`, CommentMultiline, nil},
+		},
+		"paren": {
+			{`\)`, Punctuation, Pop(1)},
+			Include("root"),
+		},
+		"list": {
+			{`\]`, Punctuation, Pop(1)},
+			Include("root"),
+		},
+		"qstring": {
+			{`"`, StringDouble, Pop(1)},
+			{`\${`, StringInterpol, Push("interpol")},
+			{`\\.`, StringEscape, nil},
+			{`.|\n`, StringDouble, nil},
+		},
+		"istring": {
+			{`''\$`, StringEscape, nil},  // "$"
+			{`'''`, StringEscape, nil},   // "''"
+			{`''\\.`, StringEscape, nil}, // "\."
+			{`''`, StringSingle, Pop(1)},
+			{`\${`, StringInterpol, Push("interpol")},
+			// The next rule is important: "$" escapes any symbol except "{"!
+			{`\$.`, StringSingle, nil}, // "$."
+			{`.|\n`, StringSingle, nil},
+		},
+		"scope": {
+			{`}:`, Punctuation, Pop(1)},
+			{`}`, Punctuation, Pop(1)},
+			{`in` + nixb, Keyword, Pop(1)},
+			{`\${`, StringInterpol, Push("interpol")},
+			Include("root"), // "==" has to be above "="
+			{Words(``, ``, strings.Fields("= ? ,")...), Operator, nil},
+		},
+		"interpol": {
+			{`}`, StringInterpol, Pop(1)},
+			Include("root"),
+		},
+		"id": {
+			{`[a-zA-Z_][a-zA-Z0-9_'-]*`, Name, nil},
+		},
+		"uri": {
+			{`[a-zA-Z][a-zA-Z0-9+.-]*:[a-zA-Z0-9%/?:@&=+$,_.!~*'-]+`, StringDoc, nil},
+		},
+		"path": {
+			{`[a-zA-Z0-9._+-]*(/[a-zA-Z0-9._+-]+)+`, StringRegex, nil},
+			{`~(/[a-zA-Z0-9._+-]+)+/?`, StringRegex, nil},
+			{`<[a-zA-Z0-9._+-]+(/[a-zA-Z0-9._+-]+)*>`, StringRegex, nil},
+		},
+		"int": {
+			{`-?[0-9]+` + nixb, NumberInteger, nil},
+		},
+		"float": {
+			{`-?(([1-9][0-9]*\.[0-9]*)|(0?\.[0-9]+))([Ee][+-]?[0-9]+)?` + nixb, NumberFloat, nil},
+		},
+		"space": {
+			{`[ \t\r\n]+`, Text, nil},
+		},
+	},
+))