Trac #28457: Build binder compatible docker images from Trac

By tagging all our images with the commit SHA in GitLab registry.

You cannot sanely create a binder that points to a moving target such as
a branch. Therefore, all images need to have unique tags.

With the changes merged, links like this should work for all branches on
trac:

https://gitlab-hooks-flau3jeaza-
ew.a.run.app/status/trac/branch/u%2Fsaraedum%2F28457

URL: https://trac.sagemath.org/28457
Reported by: saraedum
Ticket author(s): Julian Rüth
Reviewer(s): David Roe

.ci/build-docker.sh

@@ -47,6 +47,9 @@ rsync html_/ html/ -a --copy-links
 
 # Build the release image without build artifacts.
 docker_build --target sagemath --tag "$DOCKER_IMAGE_CLI" .
+# Tag the sagemath:$DOCKER_TAG image that CI has just built as
+# sagemath:$COMMIT_HASH so we can refer to it uniquely later.
+docker tag "$DOCKER_IMAGE_CLI" "$DOCKER_IMAGE_BINDER"
 # Display the layers of this image
 docker history "$DOCKER_IMAGE_CLI"
 # Build the developer image with the build artifacts intact.

.ci/update-env.sh

@@ -45,6 +45,8 @@ fi
 export DOCKER_IMAGE_CLI=${DOCKER_NAMESPACE:-sagemath}/sagemath:$DOCKER_TAG
 export DOCKER_IMAGE_DEV=${DOCKER_NAMESPACE:-sagemath}/sagemath-dev:$DOCKER_TAG
 
+export DOCKER_IMAGE_BINDER="${DOCKER_NAMESPACE:-sagemath}/sagemath:${CI_COMMIT_SHA}"
+
 # Seed the build cache with this image (set to source-clean to build from
 # scratch.)
 export ARTIFACT_BASE=${ARTIFACT_BASE:-$DEFAULT_ARTIFACT_BASE}

.gitlab-ci.yml

@@ -100,6 +100,7 @@ build-from-latest:
  - .ci/build-docker.sh | tee gitlab-build-docker.log | .ci/head-tail.sh 1048576
  - .ci/push-gitlab.sh sagemath-dev
  - .ci/push-gitlab.sh sagemath
+ - DOCKER_TAG=$CI_COMMIT_SHA .ci/push-gitlab.sh sagemath
  except:
  - master
  - develop