fix: more reliable dev version tagging

[robbkidd]

Which problem is this PR solving?

• Image builds in Circle were still using the job ID as the version.

Short description of the changes

• Reliably set the version regardless of where the image build is being run.
• Moves the image tagging logic to below the version-determination logic. Now the dev-build tagging can reuse the determined dev version instead of using the CircleCI build ID.
• Sets some defaults for environment variables to appease the nounset shell rule when this script is run outside of CI.

Example Outputs

Dev build in Dev

❯ ./build-docker.sh
++ git describe --tags '--match=v[0-9]*' --always
+ VERSION=2.8.2-58-g264d4af
… 
+ GOFLAGS=-ldflags=-X=main.BuildID=2.8.2-58-g264d4af
… 
+ ./ko publish --tags 2.8.2-55-gcc8c2a2 …
… 
2024/11/12 13:58:26 Adding tag 2.8.2-55-gcc8c2a2
… 

Dev build off branch in CI

#!/bin/bash -eo pipefail
./build-docker.sh
…
+ GOFLAGS=-ldflags=-X=main.BuildID=2.8.2-58-g264d4af-ci13888
…
2024/11/12 18:34:40 Adding tag 2.8.2-58-g264d4af-ci13888
2024/11/12 18:34:40 Adding tag branch-robb.use-new-dev-version-as-tag-for-dev-builds
… 

Dev build off branch in simulated CI

❯ CIRCLE_BUILD_NUM=8675309 CIRCLE_BRANCH=$(git rev-parse --abbrev-ref HEAD) ./build-docker.sh
++ git describe --tags '--match=v[0-9]*' --always
+ VERSION=v2.8.2-55-gcc8c2a2
… 
+ GOFLAGS=-ldflags=-X=main.BuildID=2.8.2-58-g264d4af-ci8675309
… 
+ ./ko publish --tags 2.8.2-55-gcc8c2a2-ci8675309,branch-robb.use-new-dev-version-as-tag-for-dev-builds 
… 
2024/11/12 14:02:32 Adding tag 2.8.2-55-gcc8c2a2-ci8675309
2024/11/12 14:02:32 Adding tag branch-robb.use-new-dev-version-as-tag-for-dev-builds
… 

Dev build off main in simulated CI

❯ CIRCLE_BUILD_NUM=8675309 CIRCLE_BRANCH=main ./build-docker.sh
… 
+ GOFLAGS=-ldflags=-X=main.BuildID=2.8.2-58-g264d4af-ci8675309
… 
2024/11/12 14:13:54 Adding tag 2.8.2-55-gcc8c2a2-ci8675309
2024/11/12 14:13:54 Adding tag branch-main
2024/11/12 14:13:54 Adding tag latest
… 

Tagged release build off main in simulated CI

❯ CIRCLE_BUILD_NUM=8675309 CIRCLE_BRANCH=main CIRCLE_TAG=v999.99.9 ./build-docker.sh
…
+ GOFLAGS=-ldflags=-X=main.BuildID=999.99.9
… 
2024/11/12 14:16:32 Adding tag 999
2024/11/12 14:16:32 Adding tag 999.99
2024/11/12 14:16:32 Adding tag 999.99.9
2024/11/12 14:16:32 Adding tag latest
…

[kentquirk]

Looks plausible, although I haven't run it.

[robbkidd]

@kentquirk I should definitely add some sample run outputs to the PR description!

[robbkidd]

I notice the dev builds (current logic on main and the new logic currently in this PR) have a v prefix for the in-app main.BuildID and the release builds do not. I should probably make that consistent.