Remove build time in binary

[ulyssessouza]

- What I did
Replace build time in binary with commit time

- How I did it
By changing the date by the git commiter date in the Makefile

- How to verify it

$ docker app --version

- Description for the changelog
Replace build time in binary with commit time

- A picture of a cute animal (not mandatory)

[silvin-lubecki]

LGTM

[thaJeztah]

Do we need/want the date to be in UTC?

(I recall having to go through date to get that, but it's been a while, and it's dirty. Perhaps there's an easier way docker/docker-ce-packaging#125)

[ulyssessouza]

Actually this is just an input format. According to https://github.com/docker/app/blob/master/internal/version.go#L24 this will just be used as input to the function that will return in the final format in https://github.com/docker/app/blob/master/internal/version.go#L32.

Here I had a look at the FIXME comment on line 31, but since the file does not exist in the cli, I didn't do the suggested change.

[ndeloof]

Why do we need such date?
Commit Sha is enough to track code matching binary. IMHO binary from commit should be fully reproducible.

[ulyssessouza]

@ndeloof I see this more as a user feature to know from when is the commit of the current binary and not a dev/debug information. Maybe we need to confirm with @chris-crone before merging.

[codecov]

Codecov Report

Merging #787 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #787   +/-   ##
======================================
  Coverage    70.4%   70.4%           
======================================
  Files          67      67           
  Lines        3740    3740           
======================================
  Hits         2633    2633           
  Misses        760     760           
  Partials      347     347

---

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[chris-crone]

The only real use of the build time is when you're testing your local build between commits and want to make sure you're using the latest version. We can:

1. Remove the build time completely
2. Only store the build time when building with uncommitted changes (i.e.: git describe --always shows <sha>-dirty)

I'm happy with either of the above solutions.

[thaJeztah]

Was having a chat with @chris-crone (not related to this PR) Just recalled there's a "standard" env-var to use for commit-time; SOURCE_DATE_EPOCH (see https://reproducible-builds.org/specs/source-date-epoch/). Same variable was added in the "engine" in moby/moby#34176

[ulyssessouza]

I've chosen approach 1, removing build time.

[silvin-lubecki]

LGTM

[thaJeztah]

SGTM

[thaJeztah]

Windows CI is failing (not clear what on though)

[ulyssessouza]

@thaJeztah I just rerun the tests in the CI. Windows machines are a bit unstable

[thaJeztah]

All green now; @chris-crone PTAL