Adding automatic release notes from changelog file. (microsoft#16)

* Adding automatic release notes from changelog file.

* PR fixes

CHANGELOG.md

@@ -0,0 +1,9 @@
+
+[//]: # (This file contains all the changes that should be displayed in our releases.)
+[//]: # (In order to use it, add new lines below this comment session, above existing ones.)
+[//]: # (The build and release systems will only add the new lines to the release, so NEVER edit an existing line,)
+[//]: # (since it would make it appear again in the release.)
+[//]: # (Add meaningful description of your changes, and if relevant how to make use of a new feature you're adding,)
+[//]: # (as well as pointers to relevant documentation in our docs folder.)
+
+- Officially releasing on GitHub.

build/release.txt

@@ -0,0 +1,8 @@
+
+[//]: # (This file contains all the changes that should be displayed in our releases.)
+[//]: # (In order to use it, add new lines below this comment session, leaving the remaining lines in the file.)
+[//]: # (The build and release systems will only add the new lines to the release, so NEVER edit an existing line,)
+[//]: # (since it would make it appear again in the release.)
+[//]: # (Add meaningful description of your changes, and if relevant how to make use of a new feature you're adding,)
+[//]: # (as well as pointers to relevant documentation in our docs folder.)
+

vsts/pipelines/_buildTemplate.yml

@@ -178,6 +178,12 @@ steps:
     scriptPath: ./vsts/scripts/dockerCleanup.sh
   condition: or(eq(variables['TestBuildImages'], 'true'), eq(variables['TestRuntimeImages'], 'true'), eq(variables['TestIntegration'], 'true'))
 
+- task: ShellScript@2
+  displayName: 'Generate release notes'
+  inputs:
+    scriptPath: ./vsts/scripts/generate-release-notes.sh
+  condition: and(succeeded(), eq(variables['PushBuildImages'], 'true'), eq(variables['BuildBuildImages'], 'true'))
+
 - task: ArchiveFiles@2
   displayName: 'Archive docker files and scripts for Oryx build and runtime images'
   inputs:

vsts/scripts/generate-release-notes.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+# --------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT license.
+# --------------------------------------------------------------------------------------------
+
+# This script reads `./CHANGELOG.md` file and produces a file that is added as a build artifact which
+# contains the changes only to a partcular build.
+# To achieve this, we use the tags that the release adds to the git repo, and do a `git diff` between the
+# changelog file in that tag and HEAD. The output of this diff is later parsed to only output the new lines.
+# In order for this script to work, the agent running it should have the full git repo available.
+
+set -e
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+CHANGELOG_FILE="$DIR/../CHANGELOG.md"
+
+OUTPUT_FILE=$1
+if [ -z "$OUTPUT_FILE" ]; then
+    # Create a default file using DevOps' pipeline artifacts directory
+    OUTPUT_FILE=$BUILD_ARTIFACTSTAGINGDIRECTORY/Release-notes.md
+fi
+
+echo "Release notes will be placed in $OUTPUT_FILE"
+
+# First, we look for the latest tag that was pushed. Since our builds numbers are lexicographically ordered,
+# YYYYMMDD.P, we just take the latest value that starts with a `2` to avoid other tags that might be in the repo.
+# Optimistic note: yes, this script will break in year 3000, but we can fix it then.
+LAST_TAG=$(git tag --sort=committerdate | tail -n 1)
+
+if [ -z "$LAST_TAG" ]; then
+    echo "Couldn't find a base tag, will output the entire file"
+    # Ignore the lines starting with [//] which we're using as comments.
+    cat $CHANGELOG_FILE | grep -v -e '^\[//\]' > $OUTPUT_FILE
+else
+    echo "Getting the diff from latest tag, $LAST_TAG"
+    # Get the diff for the changelog file
+    # The regex ^+[^+] is used to capture only the added lines, and the [^+], which means "exclude '+', removes the
+    # lines that git adds to the diff output containing the file name. Finally, we remove the '+' from the beginning
+    # of the selected lines.    
+    git diff $LAST_TAG HEAD | grep -e ^+[^+] | sed 's/^+//' > $OUTPUT_FILE
+fi