Capture and expose build-time meta data

Summary:
The `go build` tool can accept linker options that dynamically set
variable values at build time. Let's make use of that in our `Makefile`
and `debian/rules` to know and expose meta data such as version and Git
commit at runtime.

Test Plan:
Run `make bin/blubber && bin/blubber --version` and verify that it outputs
"0.0.1-[git head commit]". Build and install the debian package and verify
the same using the installed binary.

Reviewers: thcipriani, hashar, Joe, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D816

1 files changed, 13 insertions, 0 deletions

diff --git a/meta/meta.go b/meta/meta.go
new file mode 100644
index 0000000..a5ee581
--- /dev/null
+++ b/meta/meta.go
@@ -0,0 +1,13 @@
+package meta
+
+// Meta variables set dynamically by the linker at build time
+var (
+	Version   string
+	GitCommit string
+)
+
+// FullVersion returns the version string in the form of
+// ([major].[minor].[patch]+[commit])
+func FullVersion() string {
+	return Version + "+" + GitCommit
+}