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>

1 files changed, 37 insertions, 0 deletions

diff --git a/vendor/github.com/alecthomas/chroma/lexers/README.md b/vendor/github.com/alecthomas/chroma/lexers/README.md
new file mode 100644
index 0000000000..2421710ef5
--- /dev/null
+++ b/vendor/github.com/alecthomas/chroma/lexers/README.md
@@ -0,0 +1,37 @@
+# Lexer tests
+
+The tests in this directory feed a known input `testdata/<name>.actual` into the parser for `<name>` and check
+that its output matches `<name>.exported`.
+
+## Running the tests
+
+Run the tests as normal:
+```go
+go test ./lexers
+```
+
+## Update existing tests
+When you add a new test data file (`*.actual`), you need to regenerate all tests. That's how Chroma creates the `*.expected` test file based on the corresponding lexer.
+
+To regenerate all tests, type in your terminal:
+
+```go
+RECORD=true go test ./lexers
+```
+
+This first sets the `RECORD` environment variable to `true`. Then it runs `go test` on the `./lexers` directory of the Chroma project.
+
+(That environment variable tells Chroma it needs to output test data. After running `go test ./lexers` you can remove or reset that variable.)
+
+### Windows users
+Windows users will find that the `RECORD=true go test ./lexers` command fails in both the standard command prompt terminal and in PowerShell.
+
+Instead we have to perform both steps separately:
+
+- Set the `RECORD` environment variable to `true`.
+	+ In the regular command prompt window, the `set` command sets an environment variable for the current session: `set RECORD=true`. See [this page](https://superuser.com/questions/212150/how-to-set-env-variable-in-windows-cmd-line) for more.
+	+ In PowerShell, you can use the `$env:RECORD = 'true'` command for that. See [this article](https://mcpmag.com/articles/2019/03/28/environment-variables-in-powershell.aspx) for more.
+	+ You can also make a persistent environment variable by hand in the Windows computer settings. See [this article](https://www.computerhope.com/issues/ch000549.htm) for how.
+- When the environment variable is set, run `go tests ./lexers`.
+
+Chroma will now regenerate the test files and print its results to the console window.