Merge branch 'docker_build_strip_timestamp' into HEAD

.github/workflows/docker.yml

@@ -244,9 +244,16 @@ jobs:
         # The arcane "find" command is a replacement for "pkill make",
         # which we use because pkill is not installed in the "minimal" package
         # configuration on many platforms.
+        #
+        # The "sed" command strips away timestamps from "docker build" (buildkit)
+        # such as "#25 1211.0" at the beginning of each line. The timestamps are
+        # redundant because GH Actions provides timestamps for each line already.
+        # Stripping the timestamps from the beginnings of lines also allows
+        # GitHub Actions to recognize workflow commands such as ::error etc.
+        #
         run: |
           (sleep ${{ inputs.timeout }}; for id in $(docker ps -q); do docker exec $id find /proc -maxdepth 2 -name cmdline -exec bash -c "grep -l [m][a][k][e] {} | cut -d/ -f3 | xargs --no-run-if-empty kill" \;; done) &
-          set -o pipefail; EXTRA_DOCKER_BUILD_ARGS="--build-arg NUMPROC=9 --build-arg USE_MAKEFLAGS=\"-k V=0 SAGE_NUM_THREADS=5\"" tox -e $TOX_ENV -- $TARGETS 2>&1 | sed "/^configure: notice:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: warning:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: error:/s|^|::error file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;"
+          set -o pipefail; EXTRA_DOCKER_BUILD_ARGS="--build-arg NUMPROC=9 --build-arg USE_MAKEFLAGS=\"-k V=0 SAGE_NUM_THREADS=5\"" tox -e $TOX_ENV -- $TARGETS 2>&1 | sed -E --unbuffered "s/^#[0-9]+ [0-9]+[.][0-9]+ //;/^configure: notice:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: warning:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: error:/s|^|::error file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;"
       - name: Copy logs from the Docker image or build container
         run: |
           mkdir -p "artifacts/$LOGS_ARTIFACT_NAME"