Add hint of progress to the output of docker build

[yongtang]

- What I did

This fix tries to address the issue raised in #24912 where docker build only consists of the current step without overall total steps.

- How I did it

This fix adds the overall total steps so that end user could follow
the progress of the docker build.

- How to verify it

An additonal test has been added to cover the changes.

- Description for the changelog

Add hint of progress (e.g., Step 1/5) to the output of docker build so that the total steps is known during the build progress.

- A picture of a cute animal (not mandatory but encouraged)

This fix fixes #24912.

Signed-off-by: Yong Tang yong.tang.github@outlook.com

[AkihiroSuda]

This change breaks compatibility for those who greps the stream with a regexp like Step ([0-9]+) :.

So I think "Step 1 : FOOBAR (1/5)" is better for compatibility.

[thaJeztah]

ping @duglin wdyt?

[duglin]

At first I thought we'd have to turn the Dockerfile processing into a 2-pass parsing thing, so I'm glad that I forgot that we read it all into memory and can know the number of steps easily. I'll try to find some time over the next day or so to review it. But, overall, I don't have an issue with the idea of doing this, I just personally don't see much value in it, but if others do it might help to have them explain why this would help aside from "just to know".

[thaJeztah]

I just personally don't see much value in it

Yeah, it won't give any clue as to how long the remaining steps will take, so it's not adding a lot, other than you know how many steps it takes until completion

[tianon]

Perhaps instead just print out the "Total Steps" right at the start?

ie:

$ docker build .
Sending build context to Docker daemon 8.192 kB
Total Steps: 9
Step 1 : FROM alpine:3.4
...
Step 9 : CMD sh
 ---> Running in 2c2a1c7f3aa1
 ---> fdbc4e5a9e55
Removing intermediate container 2c2a1c7f3aa1
Successfully built fdbc4e5a9e55

[duglin]

I have a slight preference for the Step x/y form, just so I don't have to scroll up to see the total.

[thaJeztah]

I agree with @duglin

[thaJeztah]

moving this to code review

[tianon]

LGTM

[duglin]

LGTM