Replace markdownlint with mdformat

Markdownlint does not offer an automatic way to apply its formatting
rules, so we have decided to replace it with a tool that does allow us
to do so.

Mdformat's formatting rules are listed at
https://mdformat.readthedocs.io/en/stable/users/style.html

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

.mdformat.toml

@@ -0,0 +1,4 @@
+wrap = 80
+# Defaults from https://mdformat.readthedocs.io/en/stable/users/configuration_file.html
+number = false
+end_of_line = "lf"

.mdlrc

@@ -17,9 +17,18 @@ def test_markdown_style():
     # Assert if somehow no markdown files were found.
     assert len(md_files) != 0
 
+    needs_format = False
+
     # Run commands
-    cmd = "mdl -c ../.mdlrc "
-    for fname in md_files:
-        cmd += fname + " "
-    _, output, _ = utils.run_cmd(cmd)
-    assert output == ""
+    for md_file in md_files:
+        rc, output, _ = utils.run_cmd(
+            f"bash -c 'diff -u --color {md_file} <(mdformat - < {md_file})'",
+            ignore_return_code=True,
+        )
+        if rc != 0:
+            print(output)
+            needs_format = True
+
+    assert (
+        not needs_format
+    ), "Some markdown files need formatting. Either run `mdformat .` in the repository root, or apply the above diffs manually."

tests/host_tools/mdl_style.rb

@@ -79,8 +79,6 @@ RUN apt-get update \
         screen tmux \
         tzdata \
         tini \
-        # for mdl
-        ruby \
         # for cpu-template-helper
         # TODO: Remove `dmidecode` after the end of kernel 4.14 support.
         # https://github.com/firecracker-microvm/firecracker/issues/3677
@@ -94,8 +92,7 @@ RUN apt-get update \
         # for debugging
         gdb strace \
     && rm -rf /var/lib/apt/lists/* \
-    && pip3 install --upgrade pip poetry \
-    && gem install mdl
+    && pip3 install --upgrade pip poetry
 
 
 COPY tools/devctr /tmp/poetry

tests/integration_tests/style/test_markdown.py

@@ -12,6 +12,10 @@ click = "8.1.3"
 gitlint = "^0.19.1"
 ipython = "^8.15.0"
 isort = "^5.12.0"
+mdformat = "^0.7.17"
+mdformat-gfm = "^0.3.5"
+mdformat-footnote = "^0.1.1"
+mdformat-frontmatter = "^2.0.8"
 # numpy >1.25.0,<=1.25.2 trigger an illegal instruction on AL2 4.14 on c7g.metal instances, due to these instances
 # not advertising SVE support. See https://github.com/numpy/numpy/issues/24028
 numpy = "1.24.3"