GitHub syntax highlighting for Spack specs

[adamjstewart]

It would be awesome if we could add GitHub syntax highlighting support for Spack specs.

Rationale

Right now, if I share a Spack spec on GitHub, it looks like:

python@3.8.8%apple-clang@12.0.0+bz2+ctypes+dbm~debug+libxml2+lzma~nis~optimizations+pic+pyexpat+pythoncmd+readline+shared+sqlite3+ssl~tix~tkinter~ucs4+uuid+zlib patches=0d98e93189bc278fbc37a50ed7f183bd8aaf249a8e1670a465f0db6bb4f8cf87 arch=darwin-catalina-x86_64
    ^apple-libuuid@1353.100.2%apple-clang@12.0.0 arch=darwin-catalina-x86_64
    ^bzip2@1.0.8%apple-clang@12.0.0+shared arch=darwin-catalina-x86_64
        ^diffutils@3.7%apple-clang@12.0.0 arch=darwin-catalina-x86_64
            ^libiconv@1.16%apple-clang@12.0.0 arch=darwin-catalina-x86_64
    ^expat@2.2.10%apple-clang@12.0.0~libbsd arch=darwin-catalina-x86_64
    ^gdbm@1.19%apple-clang@12.0.0 arch=darwin-catalina-x86_64
        ^readline@8.0%apple-clang@12.0.0 arch=darwin-catalina-x86_64
            ^ncurses@6.2%apple-clang@12.0.0~symlinks+termlib arch=darwin-catalina-x86_64
                ^pkgconf@1.7.3%apple-clang@12.0.0 arch=darwin-catalina-x86_64
    ^gettext@0.21%apple-clang@12.0.0+bzip2+curses+git~libunistring+libxml2+tar+xz arch=darwin-catalina-x86_64
        ^libxml2@2.9.10%apple-clang@12.0.0~python arch=darwin-catalina-x86_64
            ^xz@5.2.5%apple-clang@12.0.0~pic arch=darwin-catalina-x86_64
            ^zlib@1.2.11%apple-clang@12.0.0+optimize+pic+shared arch=darwin-catalina-x86_64
        ^tar@1.32%apple-clang@12.0.0 arch=darwin-catalina-x86_64
    ^libffi@3.3%apple-clang@12.0.0 patches=26f26c6f29a7ce9bf370ad3ab2610f99365b4bdd7b82e7c31df41a3370d685c0 arch=darwin-catalina-x86_64
    ^openssl@1.1.1k%apple-clang@12.0.0~docs+systemcerts arch=darwin-catalina-x86_64
        ^perl@5.32.1%apple-clang@12.0.0+cpanm+shared+threads arch=darwin-catalina-x86_64
            ^berkeley-db@18.1.40%apple-clang@12.0.0~docs patches=b231fcc4d5cff05e5c3a4814f6a5af0e9a966428dc2176540d2c05aff41de522 arch=darwin-catalina-x86_64
    ^sqlite@3.34.0%apple-clang@12.0.0+column_metadata+fts~functions~rtree arch=darwin-catalina-x86_64

It would be much easier to read if it looked like:

Description

Ideally, users would be able to do something like:

```spack
...
```

Additional information

It looks like being able to specify a custom repo-specific language is a common feature request:

• Custom Markdown syntax highlighting within locally specified code fences github-linguist/linguist#2598
• [Feature Request] Repository-local language highlighting github-linguist/linguist#2627

So far, GitHub doesn't seem interested in supporting this. One possible solution would be to submit a PR to https://github.com/github/linguist to add support for Spack spec syntax highlighting. I'm not sure if they'll allow this, since Spack's specs aren't exactly a "programming language", but it's worth a shot.

Here are the instructions for adding support for a new language: https://github.com/github/linguist/blob/master/CONTRIBUTING.md#adding-a-language

It looks like they require a "language" to be popular on GitHub (at least 200 repos use it). Not sure if we can count repos with spack.yaml files since that's really just a YAML file, not a Spack spec syntax, but we have plenty of those: https://github.com/search?q=filename%3Aspack.yaml&type=Code

Pinging some main contributors to linguist to see if they have any thoughts on this: @josh @arfon @pchaigno @tnm @Alhadis. If you instead want me to open an issue on https://github.com/github/linguist for discussion let me know.

[haampie]

See https://github.com/haampie/spack-spec-highlight-vscode for highlighting in vscode, maybe that can be reused. I'm not familiar with linguist

[adamjstewart]

Apparently Easybuild has support: https://github.com/github/linguist/blob/v7.24.1/lib/linguist/languages.yml#L1650