feat(semantic-release): implement an automated changelog

* .travis.yml: enable the “release” stage.

* pre-commit_semantic-release.sh: mangle “FORMULA” and convert
  markdown files to RST.

* release-rules.js: configure the commit type / release type
  associations.

* release.config.js: configure the semantic-release process.

.travis.yml

@@ -4,8 +4,8 @@
 stages:
   - test
   - commitlint
-  # - name: release
-  #   if: branch = master AND type != pull_request
+  - name: release
+    if: branch = master AND type != pull_request
 
 sudo: required
 cache: bundler
@@ -66,23 +66,23 @@ jobs:
         - npm install @commitlint/travis-cli -D
         - commitlint-travis
     # Define the release stage that runs semantic-release
-    # - stage: release
-    #   language: node_js
-    #   node_js: lts/*
-    #   before_install: skip
-    #   script:
-    #     # Update `AUTHORS.md`
-    #     - export MAINTAINER_TOKEN=${GH_TOKEN}
-    #     - go get github.com/myii/maintainer
-    #     - maintainer contributor
+    - stage: release
+      language: node_js
+      node_js: lts/*
+      before_install: skip
+      script:
+        # Update `AUTHORS.md`
+        - export MAINTAINER_TOKEN=${GH_TOKEN}
+        - go get github.com/myii/maintainer
+        - maintainer contributor
 
-    #     # Install all dependencies required for `semantic-release`
-    #     - npm install @semantic-release/changelog@3 -D
-    #     - npm install @semantic-release/exec@3 -D
-    #     - npm install @semantic-release/git@7 -D
-    #   deploy:
-    #     provider: script
-    #     skip_cleanup: true
-    #     script:
-    #       # Run `semantic-release`
-    #       - npx semantic-release@15
+        # Install all dependencies required for `semantic-release`
+        - npm install @semantic-release/changelog@3 -D
+        - npm install @semantic-release/exec@3 -D
+        - npm install @semantic-release/git@7 -D
+      deploy:
+        provider: script
+        skip_cleanup: true
+        script:
+          # Run `semantic-release`
+          - npx semantic-release@15

pre-commit_semantic-release.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+###############################################################################
+# (A) Update `FORMULA` with `${nextRelease.version}`
+###############################################################################
+sed -i -e "s_^\(version:\).*_\1 ${1}_" FORMULA
+
+
+###############################################################################
+# (B) Use `m2r` to convert automatically produced `.md` docs to `.rst`
+###############################################################################
+
+# Install `m2r`
+sudo -H pip install m2r
+
+# Copy and then convert the `.md` docs
+cp *.md docs/
+cd docs/
+m2r --overwrite *.md
+
+# Change excess `H1` headings to `H2` in converted `CHANGELOG.rst`
+sed -i -e '/^=.*$/s/=/-/g' CHANGELOG.rst
+sed -i -e '1,4s/-/=/g' CHANGELOG.rst
+
+# Use for debugging output, when required
+# cat AUTHORS.rst
+# cat CHANGELOG.rst
+
+# Return back to the main directory
+cd ..

release-rules.js

@@ -0,0 +1,18 @@
+// No release is triggered for the types commented out below.
+// Commits using these types will be incorporated into the next release.
+//
+// NOTE: Any changes here must be reflected in `CONTRIBUTING.md`.
+module.exports = [
+  {breaking: true, release: 'major'},
+  // {type: 'build', release: 'patch'},
+  // {type: 'chore', release: 'patch'},
+  // {type: 'ci', release: 'patch'},
+  {type: 'docs', release: 'patch'},
+  {type: 'feat', release: 'minor'},
+  {type: 'fix', release: 'patch'},
+  {type: 'perf', release: 'patch'},
+  {type: 'refactor', release: 'patch'},
+  {type: 'revert', release: 'patch'},
+  {type: 'style', release: 'patch'},
+  {type: 'test', release: 'patch'},
+];

release.config.js

@@ -0,0 +1,106 @@
+module.exports = {
+  branch: 'master',
+  plugins: [
+      ['@semantic-release/commit-analyzer', {
+        preset: 'angular',
+        releaseRules: './release-rules.js',
+      }],
+      '@semantic-release/release-notes-generator',
+      ['@semantic-release/changelog', {
+        changelogFile: 'CHANGELOG.md',
+        changelogTitle: '# Changelog',
+      }],
+      ['@semantic-release/exec', {
+        prepareCmd: 'sh ./pre-commit_semantic-release.sh ${nextRelease.version}',
+      }],
+      ['@semantic-release/git', {
+        assets: ['*.md', 'docs/*.rst', 'FORMULA'],
+      }],
+      '@semantic-release/github',
+  ],
+  generateNotes: {
+    preset: 'angular',
+    writerOpts: {
+      // Required due to upstream bug preventing all types being displayed.
+      // Bug: https://github.com/conventional-changelog/conventional-changelog/issues/317
+      // Fix: https://github.com/conventional-changelog/conventional-changelog/pull/410
+      transform: (commit, context) => {
+          const issues = []
+
+          commit.notes.forEach(note => {
+              note.title = `BREAKING CHANGES`
+          })
+
+          // NOTE: Any changes here must be reflected in `CONTRIBUTING.md`.
+          if (commit.type === `feat`) {
+              commit.type = `Features`
+          } else if (commit.type === `fix`) {
+              commit.type = `Bug Fixes`
+          } else if (commit.type === `perf`) {
+              commit.type = `Performance Improvements`
+          } else if (commit.type === `revert`) {
+              commit.type = `Reverts`
+          } else if (commit.type === `docs`) {
+              commit.type = `Documentation`
+          } else if (commit.type === `style`) {
+              commit.type = `Styles`
+          } else if (commit.type === `refactor`) {
+              commit.type = `Code Refactoring`
+          } else if (commit.type === `test`) {
+              commit.type = `Tests`
+          } else if (commit.type === `build`) {
+              commit.type = `Build System`
+          // } else if (commit.type === `chore`) {
+          //     commit.type = `Maintenance`
+          } else if (commit.type === `ci`) {
+              commit.type = `Continuous Integration`
+          } else {
+              return
+          }
+
+          if (commit.scope === `*`) {
+              commit.scope = ``
+          }
+
+          if (typeof commit.hash === `string`) {
+              commit.hash = commit.hash.substring(0, 7)
+          }
+
+          if (typeof commit.subject === `string`) {
+              let url = context.repository
+                  ? `${context.host}/${context.owner}/${context.repository}`
+                  : context.repoUrl
+              if (url) {
+                  url = `${url}/issues/`
+                  // Issue URLs.
+                  commit.subject = commit.subject.replace(/#([0-9]+)/g, (_, issue) => {
+                      issues.push(issue)
+                      return `[#${issue}](${url}${issue})`
+                  })
+              }
+              if (context.host) {
+                  // User URLs.
+                  commit.subject = commit.subject.replace(/\B@([a-z0-9](?:-?[a-z0-9/]){0,38})/g, (_, username) => {
+                  if (username.includes('/')) {
+                      return `@${username}`
+                  }
+
+                  return `[@${username}](${context.host}/${username})`
+                  })
+              }
+          }
+
+          // remove references that already appear in the subject
+          commit.references = commit.references.filter(reference => {
+              if (issues.indexOf(reference.issue) === -1) {
+                  return true
+              }
+
+              return false
+          })
+
+          return commit
+      },
+    },
+  },
+};