workflows: add and configure a Markdown linter

Signed-off-by: Luca Zeuch <[email protected]>

Author: l-zeuch

.github/workflows/lint.yml

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+name: Lint
+
+on:
+  pull_request:
+    paths:
+      - 'content/**/*.md'
+
+jobs:
+  lint-markdown:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Lint markdown files
+        uses: actionshub/markdownlint@main
+        with:
+          filesToIgnoreRegex: 'all-commands.md|scripts/.*|.github/.*'

.mdlrc

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+git_recurse true
+ignore_front_matter true
+style 'config/markdownlint.rb'

config/markdownlint.rb

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+# Enable all rules; we'll configure some of them below.
+all
+
+# MD001: Header levels should only increment by one level at a time.
+# Normally, this is a fair rule, but it does not quite work for our cases,
+# especially in our humongous functions list. So disable it.
+exclude_rule 'MD001'
+
+# MD002: First header should be a top level header.
+# Some files do not have a top-level header, because it doesn't make sense for
+# them, or just looks incredibly stupid on the rendered page. So disable this
+# entire rule.
+exclude_rule 'MD002'
+
+# MD004: Unordered list style.
+# Use dashes for unordered lists. All lists. Even sublists.
+rule 'MD004', :style => :dash
+
+# MD013: Line length.
+# Allow lines to be up to 120 characters long, see the .editorconfig file.
+# We also ignore code blocks, because they are often long and should not be
+# wrapped at all. Same goes for tables.
+rule 'MD013', :line_length => 120, :ignore_code_blocks => true, :tables => false
+
+# MD024: Multiple headers with the same content.
+# Allow multiple headers with the same content so long they are under different
+# parent headers.
+rule 'MD024', :allow_different_nesting => true
+
+# MD026: Trailling punctuation in header.
+# Allow question marks (FAQ-style).
+rule 'MD026', :punctuation => '.,;:!'
+
+# MD029: Ordered list item prefix.
+# Should increase in numerical order.
+rule 'MD029', :style => :ordered
+
+# MD033: Inline HTML.
+# Allow certain HTML elements, because we use them for nicer page layout.
+rule 'MD033', :allowed_elements => 'center, div, sup, br, kbd'
+
+# MD037: Spaces inside emphasis markers.
+# This rule is broken. See https://github.com/markdownlint/markdownlint/issues/84
+exclude_rule 'MD037'
+
+# MD041: First line in file should be a top-level header.
+# See comment to MD002. It makes no sense to set this to H2 for similar reasons,
+# we have TOML frontmatter with an automatic h1 in the rendered page.
+exclude_rule 'MD041'