feat: lint commit messages

Will lint between remotes/origin/master and HEAD.

To lint between different commits use:

```sh
$ aegir lint-commits  --from $COMMITISH --to $COMMITISH
```

This should be set up as a pre-push or post-commit hook as regular
linting runs pre-commit so the messages we want to examine won't
be in the history yet..

cmds/lint-commits.js

@@ -0,0 +1,23 @@
+'use strict'
+
+module.exports = {
+  command: 'lint-commits',
+  desc: 'Lint commit messages',
+  builder: {
+    from: {
+      alias: 'f',
+      describe: 'The commit-ish to lint from',
+      default: 'remotes/origin/master'
+    },
+    to: {
+      alias: 't',
+      describe: 'The commit-ish to lint to',
+      default: 'HEAD'
+    }
+  },
+  handler (argv) {
+    const lintCommits = require('../src/lint-commits')
+    const onError = require('../src/error-handler')
+    lintCommits(argv).catch(onError)
+  }
+}

package.json

@@ -29,6 +29,10 @@
   ],
   "license": "MIT",
   "dependencies": {
+    "@commitlint/config-conventional": "^7.0.1",
+    "@commitlint/lint": "^7.0.0",
+    "@commitlint/load": "^7.0.0",
+    "@commitlint/read": "^7.0.0",
     "async": "^2.6.0",
     "browserify-zlib": "~0.2.0",
     "chalk": "^2.3.0",

src/lint-commits.js

@@ -0,0 +1,64 @@
+'use strict'
+
+const loadCommitLintConfig = require('@commitlint/load')
+const readCommits = require('@commitlint/read')
+const lintCommitMessage = require('@commitlint/lint')
+const conventionalCommits = require('@commitlint/config-conventional')
+
+function lintCommitMessages (opts = {}) {
+  const from = opts.from || 'remotes/origin/master'
+  const to = opts.to || 'HEAD'
+
+  return Promise.all([
+    loadCommitLintConfig({
+      rules: conventionalCommits.rules
+    }),
+    readCommits({
+      from,
+      to
+    })
+  ])
+    .then(([ { rules, parserPreset }, commits ]) => {
+      return Promise.all(
+        commits.map(commit => {
+          return lintCommitMessage(commit, rules, parserPreset ? { parserOpts: parserPreset.parserOpts } : {})
+        })
+      )
+    })
+    .then(results => {
+      let valid = true
+
+      results.forEach(report => {
+        if (valid === true) {
+          valid = report.valid
+        }
+
+        const firstLine = `${report.input.trim().split('\n')[0]}`.trim()
+
+        if (!report.valid) {
+          console.log(`Commit message '${firstLine}' failed validation:`)
+          console.log('')
+
+          report.errors.forEach(error => {
+            console.log('  [ERROR]', `${error.name}:`, error.message)
+          })
+
+          report.warnings.forEach(warning => {
+            console.log('  [WARNING]', `${warning.name}:`, warning.message)
+          })
+
+          console.log('')
+        }
+      })
+
+      if (!valid) {
+        throw new Error(`Linting commits ${from}..${to} failed`)
+      }
+    })
+}
+
+function lintCommits (opts) {
+  return lintCommitMessages(opts)
+}
+
+module.exports = lintCommits

test/lint-commits.spec.js

@@ -0,0 +1,83 @@
+/* eslint-env mocha */
+'use strict'
+
+const lintCommits = require('../src/lint-commits')
+const expect = require('chai').expect
+const path = require('path')
+const os = require('os')
+const fs = require('fs')
+const series = require('async/series')
+const child = require('child_process')
+
+function commitFile (directory, name, contents, message, callback) {
+  series([
+    (cb) => fs.writeFile(path.join(directory, name), contents, cb),
+    (cb) => child.exec('git add -A', {
+      cwd: directory
+    }, cb),
+    (cb) => child.exec(`git commit -m "${message}"`, {
+      cwd: directory
+    }, cb)
+  ], callback)
+}
+
+// Sets up two directories, an origin to represent a remote git repository
+// and another to be the current project.
+const setupProject = (commitMessage = 'chore: initial commit') => {
+  const tmpDir = path.join(os.tmpdir(), `test-${Math.random()}`)
+
+  return new Promise((resolve, reject) => {
+    series([
+      (cb) => fs.mkdir(tmpDir, cb),
+      (cb) => child.exec('git init', {
+        cwd: tmpDir
+      }, cb),
+      (cb) => commitFile(tmpDir, 'hello.txt', 'Amazing', 'chore: initial import', cb),
+      (cb) => commitFile(tmpDir, 'goodbye.txt', 'Amazing', commitMessage, cb)
+    ], (error) => {
+      if (error) {
+        return reject(error)
+      }
+
+      process.chdir(tmpDir)
+
+      resolve()
+    })
+  })
+}
+
+const commitMessageShouldPassLinting = (commitMessage) => {
+  return setupProject(commitMessage)
+    .then(() => lintCommits({
+      from: 'HEAD~1'
+    }))
+}
+
+const commitMessageShouldFailLinting = (commitMessage) => {
+  return setupProject(commitMessage)
+    .then(() => lintCommits({
+      from: 'HEAD~1'
+    }))
+    .then(() => {
+      throw new Error('Should have failed!')
+    })
+    .catch(error => {
+      expect(error.message).to.contain('Linting commits HEAD~1..HEAD failed')
+    })
+}
+
+describe('lint commit messages', () => {
+  const cwd = process.cwd()
+
+  after(() => {
+    process.chdir(cwd)
+  })
+
+  it('passes with good commit messages', function () {
+    return commitMessageShouldPassLinting('chore: such a chore')
+  })
+
+  it('fails with bad commit messages', function () {
+    return commitMessageShouldFailLinting('Ahahallolol!!!11shift+1')
+  })
+})