build: introduce VERSION file (#394)

As a source of entire Envoy version number. Will use this file in envoy
main repo as well.

By this change, document version string will be changed in development
version:

  from: "1.6.0-data-plane-api-${GIT_SHA}"
  to: "1.6.0.dev-data-plane-api-${GIT_SHA}"

And in release version, for example, in v1.6.0 release:

  from: "1.6.0-tag-v1.6.0"
  to: "tag-v1.6.0"

The significant change is dropping the first version number string like
"1.6.0-" in the release version document.

Signed-off-by: Taiki Ono <taiks.4559@gmail.com>

BUILD

@@ -0,0 +1 @@
+exports_files(["VERSION"])

VERSION

@@ -0,0 +1 @@
+1.6.0-dev

docs/build.sh

@@ -73,7 +73,8 @@ done
 rsync -av "${SCRIPT_DIR}"/root/ "${SCRIPT_DIR}"/conf.py "${GENERATED_RST_DIR}"
 
 BUILD_SHA=$(git rev-parse HEAD)
-[[ -z "${ENVOY_DOCS_VERSION_STRING}" ]] && ENVOY_DOCS_VERSION_STRING=data-plane-api-"${BUILD_SHA:0:6}"
+VERSION_NUM=$(cat VERSION)
+[[ -z "${ENVOY_DOCS_VERSION_STRING}" ]] && ENVOY_DOCS_VERSION_STRING="${VERSION_NUM}"-data-plane-api-"${BUILD_SHA:0:6}"
 [[ -z "${ENVOY_DOCS_RELEASE_LEVEL}" ]] && ENVOY_DOCS_RELEASE_LEVEL=pre-release
 
 export ENVOY_DOCS_VERSION_STRING ENVOY_DOCS_RELEASE_LEVEL

docs/conf.py

@@ -67,9 +67,9 @@ if not os.environ.get('ENVOY_DOCS_VERSION_STRING'):
   raise Exception("ENVOY_DOCS_VERSION_STRING env var must be defined")
 
 # The short X.Y version.
-version = u'1.6.0-' + os.environ['ENVOY_DOCS_VERSION_STRING']
+version = os.environ['ENVOY_DOCS_VERSION_STRING']
 # The full version, including alpha/beta/rc tags.
-release = u'1.6.0-' + os.environ['ENVOY_DOCS_VERSION_STRING']
+release = os.environ['ENVOY_DOCS_VERSION_STRING']
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.