commit bab3d4084ecc24a53ecd33b386625611b9ca18b1
author Joe Tsai <joetsai@digital-static.net> Wed Jul 10 00:15:35 2019 -0700
committer Joe Tsai <joetsai@digital-static.net> Wed Aug 07 22:59:30 2019 +0000
tree 9e2e1c437a9dd1e57bdc6a17401df76c92aef0b8
parent 8d5e6d6927a52dc28f60214a15fb17149b7fd803

runtime/protoimpl, cmd/protoc-gen-go: support release versioning

In order for protoc-gen-go to output the current version,
it needs to know what version it is currently running as.
However, we cannot rely on the git tags since the tags are not
made until *after* the commit has been submitted.
Instead, we manually encode the version into the code and
make sure that git tags match up with the version in the code.

The version.go file in runtime/protoimpl contains instructions
for how to make a release. Essentially:
* Every non-release commit has a version string with "devel" in it.
* Every release commit must not have "devel" in it and must be unique.
* The "release process" involves submitting two CLs.
The first CL creates a version string without "devel",
which is the commit that a git tag will actually reference.
The second CL follows immediately and re-introduces "devel"
into the version string.

The following example shows a possible sequence of VersionStrings
for git commits in time-ascending order:
	v1.19.0-devel      (this CL)
	v1.19.0-devel
	v1.19.0-devel
	v1.19.0-devel
	v1.20.0-rc.1       <- tagged
	v1.20.0-rc.1.devel
	v1.20.0-rc.1.devel
	v1.20.0-rc.1.devel
	v1.20.0-rc.2       <- tagged
	v1.20.0-rc.2.devel
	v1.20.0            <- tagged (future public release)
	v1.20.0-devel
	v1.20.0-devel
	v1.20.0-devel
	v1.20.0-devel
	v1.20.1            <- tagged
	v1.20.1-devel
	v1.20.1-devel
	v1.21.0            <- tagged
	v1.21.0-devel

Note that we start today with v1.19.0-devel, which means that our initial
release will be v1.20.0. This number was intentionally chosen since
1) the number 20 has some correlation to the fact that we keep calling
the new implementation the "v2" implementation, and
2) the set of tagged versions for github.com/golang/protobuf
and google.golang.org/protobuf are unlikely to ever overlap.
This way, the version of protoc-gen-go is never ambiguous which module
it was built from.

Now that we have version information, we add support for generating .pb.go
files with the version information recorded. However, we do not emit
these for .pb.go files in our own repository since they are always guaranteed
to be at the right version (enforced by integration_test.go).

Updates golang/protobuf#524

Change-Id: I25495a45042c2aa39a39cb7e7738ae8e831a9d26
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/186117
Reviewed-by: Damien Neil <dneil@google.com>