fix(upload-coverage): an artifact that was never created is not a coverage bug

.github/workflows/CI.yml

@@ -121,6 +121,27 @@ jobs:
           codecov-token: ${{ secrets.CODECOV_TOKEN }}
           dry-run: true
 
+  # The state this action exists to survive, and the one its own CI never reaches on its own: the
+  # merged report is NOT there. Every consumer is in it right now — an Actions storage quota is
+  # enforced at `CreateArtifact` before any bytes are sent, so nothing gets created — and this
+  # repository is public, so its storage is free and it can never reproduce that by accident.
+  #
+  # Naming an artifact that cannot exist reproduces it exactly. What is under test is not the
+  # message: it is that `continue-on-error` on a step of a COMPOSITE action is honoured at all, and
+  # that `steps.<id>.outcome` is readable from a later step of the same composite. If either is not
+  # true the action dies at the download exactly as before, and this job is the only thing that
+  # would say so.
+  action-absent-artifact:
+    name: The upload action survives a missing report
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: ./actions/upload-coverage
+        with:
+          codecov-token: ${{ secrets.CODECOV_TOKEN }}
+          artifact: testshards-lcov-deliberately-absent
+          dry-run: true
+
   # The sharded path runs on one Julia version. Compatibility across the supported range is a
   # different question, so it is asked separately and unsharded — a version matrix times a
   # shard matrix would be 8N jobs to answer a question that does not need the split.

Project.toml

@@ -1,6 +1,6 @@
 name = "TestShards"
 uuid = "acceef1d-f5e0-4fe4-a546-818dc56ce7b2"
-version = "0.3.37"
+version = "0.3.38"
 authors = ["sota shimozono <shimozono-sota631@g.ecc.u-tokyo.ac.jp>"]
 
 [deps]

actions/upload-coverage/action.yml

@@ -116,18 +116,54 @@ runs:
       with:
         submodules: ${{ inputs.submodules }}
 
-    - uses: actions/download-artifact@v8
+    # ABSENT and EMPTY are different states and get different treatment. This download is by
+    # `name:`, which HARD-FAILS when the artifact does not exist — unlike the workflow's own
+    # `pattern:` download, which succeeds with zero results. So an account that cannot create
+    # artifacts at all turned this job red at the download, before anything about coverage was
+    # even attempted:
+    #
+    #   Unable to download artifact(s): Artifact not found for name: testshards-lcov
+    #
+    # An artifact that was never created is an infrastructure state — the run's own storage quota
+    # is enforced at `CreateArtifact`, before any bytes are sent, so no producer error is
+    # involved and there is nothing here to fix by failing. Losing the coverage REPORT is the
+    # correct degradation; losing the TEST RESULT to it is not.
+    - id: fetch
+      continue-on-error: true
+      uses: actions/download-artifact@v8
       with:
         name: ${{ inputs.artifact }}
 
+    # THE TRADE THIS MAKES, SAID OUT LOUD. `outcome != 'success'` is every reason the download can
+    # fail, not only absence — a network fault and a genuinely lost `-lcov` land here too. So a
+    # real regression in the producer degrades to a warning where it used to be red. That is
+    # accepted because the alternative is worse (a storage condition taking down every consumer's
+    # test result) and because the step summary carries it where a warning alone would be missed.
+    # What is NOT accepted is claiming a cause this step has not established: it says the download
+    # failed and lists what usually does that, rather than asserting the artifact does not exist.
     - shell: bash
       run: |
         set -euo pipefail
-        [ -s lcov.info ] || { echo "::error::${{ inputs.artifact }} contained no lcov.info — did the sharded run finish with coverage on?"; exit 1; }
+        if [ "${{ steps.fetch.outcome }}" != "success" ]; then
+          echo "::warning::could not download ${{ inputs.artifact }}, so there is no merged report to send. Coverage is not reported for this run; the tests themselves are unaffected. The usual cause is that the run could not create artifacts at all — an Actions storage quota is enforced at CreateArtifact, before any bytes are sent, so it stops a 0-byte artifact exactly as it stops a large one. A lost upload or a transient fault reach this branch too, so check whether the run produced any artifacts at all before assuming the quota."
+          # `${GITHUB_STEP_SUMMARY:-}` because this runs under `set -u`, and an unbound variable
+          # here would kill the step in the middle of degrading gracefully — turning the fallback
+          # into a second, more confusing failure.
+          if [ -n "${GITHUB_STEP_SUMMARY:-}" ]; then
+            {
+              echo "### Coverage"
+              echo "Not reported: \`${{ inputs.artifact }}\` could not be downloaded."
+            } >> "$GITHUB_STEP_SUMMARY"
+          fi
+          exit 0
+        fi
+        # PRESENT BUT EMPTY is a different thing entirely: something produced the artifact and put
+        # no report in it. That is a producer bug and stays fatal.
+        [ -s lcov.info ] || { echo "::error::${{ inputs.artifact }} exists but contained no lcov.info — did the sharded run finish with coverage on?"; exit 1; }
         echo "Merged report: $(grep -c '^SF:' lcov.info) source files."
 
     - uses: codecov/codecov-action@v7
-      if: ${{ steps.token.outputs.have == 'true' }}
+      if: ${{ steps.token.outputs.have == 'true' && steps.fetch.outcome == 'success' }}
       continue-on-error: ${{ inputs.fail-on-error != 'true' }}
       with:
         files: lcov.info