Add MarkdownLint CLI checker

Adds support for the MarkdownLint Command Line Interface based on the
Node.js markdownlint package.

 - https://github.com/igorshubovych/markdownlint-cli

Vagrantfile

@@ -162,6 +162,7 @@ Vagrant.configure("2") do |config|
                                                   jshint \
                                                   eslint \
                                                   jscs \
+                                                  markdownlint-cli \
                                                   standard \
                                                   semistandard \
                                                   jsonlint \

doc/languages.rst

@@ -719,6 +719,14 @@ to view the docstring of the syntax checker.  Likewise, you may use
 
 .. supported-language:: Markdown
 
+   .. syntax-checker:: markdown-markdownlint-cli
+
+      Check Markdown with `markdownlint <https://github.com/igorshubovych/markdownlint-cli>`_.
+
+      .. defcustom:: flycheck-markdown-markdownlint-cli-config
+
+         Path to configuration file.
+
    .. syntax-checker:: markdown-mdl
 
       Check Markdown with `markdownlint <https://github.com/mivok/markdownlint/>`_.

flycheck.el

@@ -226,6 +226,7 @@ attention to case differences."
     r-lintr
     racket
     rpm-rpmlint
+    markdown-markdownlint-cli
     markdown-mdl
     nix
     rst-sphinx
@@ -8949,6 +8950,28 @@ See URL `https://sourceforge.net/projects/rpmlint/'."
                             ;; In `sh-mode', we need the proper shell
                             (eq sh-shell 'rpm))))
 
+(flycheck-def-config-file-var flycheck-markdown-markdownlint-cli-config
+    markdown-markdownlint-cli nil
+  :safe #'stringp
+  :package-version '(flycheck . "31"))
+
+(flycheck-define-checker markdown-markdownlint-cli
+  "Markdown checker using markdownlint-cli.
+
+See URL `https://github.com/igorshubovych/markdownlint-cli'."
+  :command ("markdownlint"
+            (config-file "--config" flycheck-markdown-markdownlint-cli-config)
+            source)
+  :error-patterns
+  ((error line-start
+          (file-name) ": " line ": " (id (one-or-more (not (any space))))
+          " " (message) line-end))
+  :error-filter
+  (lambda (errors)
+    (flycheck-sanitize-errors
+     (flycheck-remove-error-file-names "(string)" errors)))
+  :modes (markdown-mode gfm-mode))
+
 (flycheck-def-option-var flycheck-markdown-mdl-rules nil markdown-mdl
   "Rules to enable for mdl.
 

test/flycheck-test.el

@@ -3833,6 +3833,14 @@ Why not:
        :checker rpm-rpmlint)
    '(22 nil warning "macro-in-%changelog %{_bindir}" :checker rpm-rpmlint)))
 
+(flycheck-ert-def-checker-test markdown-markdownlint-cli markdown nil
+  (flycheck-ert-should-syntax-check
+   "language/markdown.md" 'markdown-mode
+   '(1 nil error "First header should be a top level header [Expected: h1; Actual: h2]"
+       :id "MD002/first-header-h1" :checker markdown-markdownlint-cli)
+   '(1 nil error "First line in file should be a top level header [Context: "## Second Header First"]"
+       :id "MD041/first-line-h1" :checker markdown-markdownlint-cli)))
+
 (flycheck-ert-def-checker-test markdown-mdl markdown nil
   (flycheck-ert-should-syntax-check
    "language/markdown.md" 'markdown-mode