pre-commit: Add markdownlint support

[Holzhaus]

This prevents introducing broken markdown.

[uklotzde]

Please update the comments in .pre-commit-config.yam. You now also have to install Ruby in addition to Python for running the pre-commit hooks.

[Holzhaus]

You now also have to install Ruby in addition to Python for running the pre-commit hooks.

Are you sure? According to https://pre-commit.com/#ruby, ruby hooks work without any system level dependencies. It should download a suitable ruby installation automatically.

[uklotzde]

You now also have to install Ruby in addition to Python for running the pre-commit hooks.

Are you sure? According to https://pre-commit.com/#ruby, ruby hooks work without any system level dependencies. It should download a suitable ruby installation automatically.

The pre-commit hook failed until I manually installed rubygem.

[uklotzde]

[INFO] Installing environment for https://github.com/markdownlint/markdownlint.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: command: ('gem', 'build', 'mdl.gemspec')
return code: 1
expected return code: 0
stdout:
    Executable `gem` not found
stderr: (none)

[Holzhaus]

[INFO] Installing environment for https://github.com/markdownlint/markdownlint.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: command: ('gem', 'build', 'mdl.gemspec')
return code: 1
expected return code: 0
stdout:
    Executable `gem` not found
stderr: (none)

This looks like you have an incomplete ruby version installed. According to the code, it should only use the system ruby if you have both ruby and gem installed. Let me double check, maybe a bug in pre-commit.

[Holzhaus]

@uklotzde please retest, it should now always install ruby regardless of the system.

[uklotzde]

None of the Ruby stuff was installed (ruby/gem/rake).

The first check took ages and failed again:

[INFO] Installing environment for https://github.com/markdownlint/markdownlint.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: command: ('/usr/bin/bash', '/home/uk/.cache/pre-commit/repor6re3vs4/rbenv-2.6.6/bin/rbenv', 'install', '2.6.6')
return code: 1
expected return code: 0
stdout: (none)
stderr:
    Downloading ruby-2.6.6.tar.bz2...
    -> https://cache.ruby-lang.org/pub/ruby/2.6/ruby-2.6.6.tar.bz2
    Installing ruby-2.6.6...
    
    BUILD FAILED (Fedora 34 using ruby-build 20210510)
    
    Inspect or clean up the working tree at /tmp/ruby-build.20210818170924.121021.2GsUAL
    Results logged to /tmp/ruby-build.20210818170924.121021.log
    
    Last 10 log lines:
    installing capi-docs:               /home/uk/.cache/pre-commit/repor6re3vs4/rbenv-2.6.6/versions/2.6.6/share/doc/ruby
    The Ruby readline extension was not compiled.
    ERROR: Ruby install aborted due to missing extensions
    Try running `yum install -y readline-devel` to fetch missing dependencies.
    
    Configure options used:
      --prefix=/home/uk/.cache/pre-commit/repor6re3vs4/rbenv-2.6.6/versions/2.6.6
      --enable-shared
      LDFLAGS=-L/home/uk/.cache/pre-commit/repor6re3vs4/rbenv-2.6.6/versions/2.6.6/lib 
      CPPFLAGS=-I/home/uk/.cache/pre-commit/repor6re3vs4/rbenv-2.6.6/versions/2.6.6/include 
    
Check the log at /home/uk/.cache/pre-commit/pre-commit.log

[uklotzde]

ruby-build.20210818170924.121021.log

[Holzhaus]

I opened a bug report upstream: pre-commit/pre-commit#2016

@uklotzde For now I switched to a nodejs-based markdown linter. Please retest.

[uklotzde]

Nice side-effect: If you already use his markdownlint VS Code plugin then the configuration is recognized and warnings are also shown there.

[uklotzde]

I still get warnings in CONTRIBUTING.md:

SKIP=end-of-file-fixer,trailing-whitespace,clang-format,eslint,no-commit-to-branch \
pre-commit run --all-files

[Holzhaus]

I still get warnings in CONTRIBUTING.md:

SKIP=end-of-file-fixer,trailing-whitespace,clang-format,eslint,no-commit-to-branch \
pre-commit run --all-files

Weird. I don't get any warnings. Maybe it also uses some global config from vscode?

[Holzhaus]

I still get warnings in CONTRIBUTING.md:

SKIP=end-of-file-fixer,trailing-whitespace,clang-format,eslint,no-commit-to-branch \
pre-commit run --all-files

Weird. I don't get any warnings. Maybe it also uses some global config from vscode?

No, CONTRIBUTING.md does not exist in my tree, because this PR targets the 2.3 branch.

[uklotzde]

I still get warnings in CONTRIBUTING.md:

SKIP=end-of-file-fixer,trailing-whitespace,clang-format,eslint,no-commit-to-branch \
pre-commit run --all-files

Weird. I don't get any warnings. Maybe it also uses some global config from vscode?

No, CONTRIBUTING.md does not exist in my tree, because this PR targets the 2.3 branch.

My bad, tested on main.

[uklotzde]

Thank you! LGTM