Introduce a top-level Version() and SemVersion() function (#225)

* Introduce a top-level `Version()` and `SemVersion()` function.

These are intended to be used by submodules within the repo that need
to specify an "instrumentation version" when creating a tracer or meter.

* Included PR number in CHANGELOG

* Update contrib.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* use predeclared constant regex

* Add comment about how/when Version() string is updated

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- Top-level `Version()` and `SemVersion()` functions defining the current version of the contrib package. (#225)
+
 ## [0.10.1] - 2020-08-13
 
 ### Added

contrib.go

@@ -0,0 +1,28 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package contrib contains common values used across all
+// instrumentation, exporter, and detector contributions.
+package contrib // import "go.opentelemetry.io/contrib"
+
+// Version is the current release version of OpenTelemetry Contrib in use.
+func Version() string {
+	return "0.10.1"
+	// This string is updated by the pre_release.sh script during release
+}
+
+// SemVersion is the semantic version to be supplied to tracer/meter creation.
+func SemVersion() string {
+	return "semver:" + Version()
+}

pre_release.sh

@@ -88,6 +88,11 @@ else
     CONTRIB_TAG=${OTEL_TAG}  # if contrib_tag not specified, but OTEL_TAG is, then set it to OTEL_TAG
 fi
 
+# Get version for contrib.go
+OTEL_CONTRIB_VERSION=$(echo "${CONTRIB_TAG}" | egrep -o "${SEMVER_REGEX}")
+# Strip leading v
+OTEL_CONTRIB_VERSION="${OTEL_CONTRIB_VERSION#v}"
+
 cd "$(dirname "$0")"
 
 if ! git diff --quiet; then \
@@ -97,6 +102,10 @@ if ! git diff --quiet; then \
     exit 1
 fi
 
+# Update contrib.go version definition
+sed -i .bak "s/\(return \"\)[0-9]*\.[0-9]*\.[0-9]*\"/\1${OTEL_CONTRIB_VERSION}\"/" ./contrib.go
+rm -f ./contrib.go.bak
+
 declare -r BRANCH_NAME=pre_release_${CONTRIB_TAG}
 
 patch_gomods() {