Bug/652 markdown lint hook fails with unexpected output (#657)

Markdown lint 0.5.0 added a link to the rules after printing the
results. This caused the Mdl hook to fail as it was not expecting
this additional output.

Using the JSON output prevents the link to the rules from being
displayed and provided a more structured output for parsing.

CHANGELOG.md

@@ -7,6 +7,7 @@
 * Relax `childprocess` dependency to allow version 1.x
 * Add `CodeSpellCheck` pre-commit hook
 * Fix deadlock which was more likely to occur when setting `parallelize` on a hook to `false`
+* Fix `Mdl` hook to use JSON output and not fail on unexpected output
 
 ## 0.48.1
 

config/default.yml

@@ -486,6 +486,7 @@ PreCommit:
     enabled: false
     description: 'Analyze markdown files with mdl'
     required_executable: 'mdl'
+    flags: ['--json']
     install_command: 'gem install mdl'
     include: '**/*.md'
 

lib/overcommit/hook/pre_commit/mdl.rb

@@ -5,8 +5,6 @@ module Overcommit::Hook::PreCommit
   #
   # @see https://github.com/mivok/markdownlint
   class Mdl < Base
-    MESSAGE_REGEX = /^(?<file>(?:\w:)?[^:]+):(?<line>\d+):\s(?<msg>.+)/
-
     def run
       result = execute(command, args: applicable_files)
       output = result.stdout.chomp
@@ -15,11 +13,17 @@ def run
       return [:fail, result.stderr] unless result.stderr.empty?
 
       # example message:
-      #   path/to/file.md:1: MD001 Error message
-      extract_messages(
-        output.split("\n"),
-        MESSAGE_REGEX
-      )
+      #   [{"filename":"file1.md","line":1,"rule":"MD013","aliases":["line-length"],
+      #   "description":"Line length"}]
+      json_messages = JSON.parse(output)
+      json_messages.map do |message|
+        Overcommit::Hook::Message.new(
+          :error,
+          message[:filename],
+          message[:line],
+          message[:description]
+        )
+      end
     end
   end
 end

spec/overcommit/hook/pre_commit/mdl_spec.rb

@@ -27,7 +27,10 @@
     let(:success) { false }
 
     context 'and it reports an error' do
-      let(:stdout) { 'file1.md:1: MD013 Line length' }
+      let(:stdout) do
+        '[{"filename":"file1.md","line":1,"rule":"MD013","aliases":["line-length"],'\
+        '"description":"Line length"}]'
+      end
       let(:stderr) { '' }
 
       it { should fail_hook }