chore(lerna): add lerna-changelog (open-telemetry#432)

* chore(lerna): add lerna-changelog

closes open-telemetry#372
add docs related to lerna-changelog

Signed-off-by: Olivier Albertini <olivier.albertini@montreal.ca>

* fix: add draffensperger recommendations

Signed-off-by: Olivier Albertini <olivier.albertini@montreal.ca>

.gitignore

@@ -68,3 +68,6 @@ packages/**/package-lock.json
 docs
 
 .nyc_output
+
+#lerna
+.changelog

CONTRIBUTING.md

@@ -63,3 +63,4 @@ The `opentelemetry-js` project is written in TypeScript.
 - `yarn test` or `npm test` tests code the same way that our CI will test it.
 - `yarn fix` or `npm run fix` lint (and maybe fix) any changes.
 - `yarn docs` or `npm run docs` to generate API documentation.
+- `yarn changelog` or `npm run changelog` to generate CHANGELOG documentation in your terminal (see [RELEASING.md](RELEASING.md) for more details).

RELEASING.md

@@ -0,0 +1,43 @@
+# Releasing OpenTelemetry Packages (for Maintainers Only)
+
+This document explains how to publish all OT modules at version x.y.z. Ensure that you’re following semver when choosing a version number.
+
+## Use the Changelog to create a GitHub Release
+
+### Generate the changelog with lerna
+
+Since we use `lerna`, we can use [lerna-changelog](https://github.com/lerna/lerna-changelog#lerna-changelog)
+
+#### How to use
+Pass your [github token](https://help.github.com/en/articles/creating-a-personal-access-token-for-the-command-line) to generate the changelog automatically. 
+For security reasons, when you create a Github token, select the permissions: under **repo**, select **Access public repositories**, **commit status**.
+
+In your terminal, execute the following command:
+```bash
+GITHUB_AUTH=<your token> lerna-changelog
+```
+It will print something like:
+
+```md
+## Unreleased (2018-05-24)
+
+#### :bug: Bug Fix
+* [#198](https://github.com/my-org/my-repo/pull/198) Avoid an infinite loop ([@helpful-hacker](https://github.com/helpful-hacker))
+
+#### :house: Internal
+* [#183](https://github.com/my-org/my-repo/pull/183) Standardize error messages ([@careful-coder](https://github.com/careful-coder))
+
+#### Commiters: 2
+- Helpful Hacker ([@helpful-hacker](https://github.com/helpful-hacker))
+- [@careful-coder](https://github.com/careful-coder)
+```
+By default lerna-changelog will show all pull requests that have been merged since the latest tagged commit in the repository. That is however only true for pull requests **with certain labels applied** (see [lerna.json](lerna.json) for authorized labels).
+
+You can also use the `--from` and `--to` options to view a different range of pull requests:
+```
+GITHUB_AUTH=xxxxx lerna-changelog --from=v1.0.0 --to=v2.0.0
+```
+
+#### Update Changelog file
+
+From what `lerna-changelog` has generated, starts new Unreleased label. Follow the example set by recent Released label.

lerna.json

@@ -5,5 +5,17 @@
     "packages/*",
     "examples/*"
   ],
-  "version": "0.1.0"
+  "version": "0.1.0",
+  "changelog": {
+    "repo": "open-telemetry/opentelemetry-js",
+    "labels": {
+      "breaking": ":boom: Breaking Change",
+      "enhancement": ":rocket: (Enhancement)",
+      "bug": ":bug: (Bug Fix)",
+      "core": ":wrench: Core",
+      "document": ":books: (Refine Doc)",
+      "feature-request": ":sparkles: (Feature)"
+    },
+    "cacheDir": ".changelog"
+  }
 }

package.json

@@ -15,6 +15,7 @@
     "bump": "lerna publish",
     "codecov": "lerna run codecov",
     "codecov:browser": "lerna run codecov:browser",
+    "changelog": "lerna-changelog",
     "check": "lerna run check",
     "predocs-test": "yarn docs",
     "docs-test": "lerna run docs-test",
@@ -31,12 +32,13 @@
   "author": "OpenTelemetry Authors",
   "license": "Apache-2.0",
   "devDependencies": {
-    "@commitlint/cli": "^8.1.0",
-    "@commitlint/config-conventional": "^8.1.0",
-    "husky": "^3.0.1",
+    "@commitlint/cli": "^8.2.0",
+    "@commitlint/config-conventional": "^8.2.0",
+    "husky": "^3.0.9",
     "gts": "^1.0.0",
-    "lerna": "^3.13.4",
-    "typescript": "^3.6.3"
+    "lerna": "^3.17.0",
+    "lerna-changelog": "^0.8.2",
+    "typescript": "^3.6.4"
   },
   "husky": {
     "hooks": {