fix(docker): office image no longer gets :latest on a release — latest=false

.github/workflows/docker.yml

@@ -84,6 +84,12 @@ jobs:
             type=semver,pattern={{major}}.{{minor}},suffix=${{ matrix.suffix }}
             type=raw,value=${{ matrix.target == 'base' && 'latest' || 'office' }}
             type=sha,format=short,prefix=sha-,suffix=${{ matrix.suffix }}
+          # ``:latest`` comes from the raw entry above, and only from it. By
+          # default (``latest=auto``) the action also adds a ``latest`` tag
+          # to both variants on a release tag, without the ``-office``
+          # suffix, so whichever image finished last would keep ``:latest`` —
+          # usually the office image, the slower build.
+          flavor: latest=false
 
       - name: Build and push Docker image (${{ matrix.target }})
         id: build

CHANGELOG.md

@@ -9,6 +9,37 @@ Versions follow [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
+### Fixed — after a release, `:latest` is the slim image, not the office image
+
+`docker.yml` tags the slim image `:latest` and the office image `:office`, but
+`docker/metadata-action` added a `latest` tag of its own on every release: with
+its default flavor, `latest=auto`, a release tag (`vX.Y.Z` without a
+pre-release part) that matches a `type=semver` entry gets `latest` as well, and
+the office entries' `suffix=-office` does not apply to it. Both images were
+pushed as `:latest`, and the one that finished last kept the tag — usually the
+office image, the slower build. Whoever pulled `:latest` then got LibreOffice
+without choosing the office image, and with the default
+`FILEMORPH_OFFICE_ENGINE=auto` complex DOCX files were converted through it.
+In the v1.1.0 run the office image's build and push finished 12 seconds after
+the slim image's, so on 2026-06-01 `:latest` was most likely the office image
+for about an hour, until the next build of `main`; if you pulled it then and
+not since, pull it again. Builds of `main` were not affected. Found by the security review of
+PR #180.
+
+- **Fix.** The metadata step sets `flavor: latest=false`, so `:latest` comes
+  only from the `type=raw` entry that names it for the slim image. The other
+  tags stay as they were: `:office`, and `X.Y.Z`, `X.Y` and `sha-…`, each with
+  `-office` on the office image. The docs already call `:latest` the slim
+  image; that now holds right after a release too. `docker.yml` pushes images
+  and cannot be tried before merge, so the pinned action (v6.2.0) was run
+  locally on the workflow's inputs: it now tags only the slim image `latest`,
+  on a release tag, a pre-release tag and `main`. The next release is the
+  first real test.
+- **Guard.** `tests/test_supply_chain_hygiene.py` fails if the metadata step's
+  flavor is anything but `latest=false`, if another of its tag entries names
+  `latest`, or if the matrix loses the unsuffixed `base` leg the `type=raw`
+  entry is meant for.
+
 ### Fixed — patch-policy's `cosign verify` names an image tag that exists
 
 `docs/patch-policy.md` told readers to verify the release image

tests/test_supply_chain_hygiene.py

@@ -35,7 +35,10 @@
     digest its build step reports: the SBOM comes from sbom.yml's steps in a
     job that can only read, and the job that signs the attestation checks
     nothing out, installs nothing and runs only GitHub's own actions;
-    docs/release-signing.md verifies it the way it is made.
+    docs/release-signing.md verifies it the way it is made;
+  * only the slim image is tagged ``:latest``: docker.yml switches off
+    metadata-action's automatic ``latest`` tag, which a release would
+    otherwise add to the office image too.
 
 This is a tripwire, not a substitute for the server-side Scorecard run /
 review: the per-job permissions check here is a heuristic (it asserts a
@@ -1095,6 +1098,49 @@ def test_docs_verify_the_sbom_attestation_as_docker_yml_makes_it() -> None:
     )
 
 
+def test_only_the_slim_image_is_tagged_latest() -> None:
+    """docker.yml tags the slim image ``:latest``, and only the slim image.
+
+    metadata-action adds a ``latest`` tag of its own when a ``type=semver``
+    entry matches a release tag (``flavor: latest=auto``, its default), and
+    a tag entry's ``suffix=`` does not reach that tag: on a release both
+    variants pushed ``:latest``, and whichever finished last kept it —
+    usually the office image, the slower build. With ``latest=false`` the
+    ``type=raw`` entry that names ``latest`` for the unsuffixed base leg is
+    the only source of ``:latest``, so that entry and that leg have to stay.
+    The flavor is pinned whole: the action skips only lines that start with
+    ``#`` and unquotes CSV fields, so a looser match could pass a flavor it
+    reads differently.
+    """
+    job = _workflow(_WORKFLOW_DIR / "docker.yml")["jobs"]["build-and-push"]
+    legs = {leg["target"]: leg.get("suffix") for leg in job["strategy"]["matrix"]["include"]}
+    assert legs.get("base") == "", (
+        f"docker.yml: the `latest` entry is meant for the `base` leg, the slim image without "
+        f"a suffix; the matrix has {legs}"
+    )
+    steps = [s for s in _steps(job) if str(s.get("uses", "")).startswith("docker/metadata-action@")]
+    assert steps, "docker.yml no longer uses docker/metadata-action — update this guard"
+    raw_latest = "type=raw,value=${{ matrix.target == 'base' && 'latest' || 'office' }}"
+    for step in steps:
+        inputs = step.get("with") or {}
+        assert str(inputs.get("flavor", "")).strip() == "latest=false", (
+            f"docker.yml step {step.get('name')!r}: `flavor:` must be exactly `latest=false` "
+            f"(this guard pins it whole) — without it, a release tags the office image "
+            f"`:latest` as well"
+        )
+        latest = [
+            line.strip()
+            for line in str(inputs.get("tags", "")).splitlines()
+            # As in the action, only a line starting with "#" is a comment; an
+            # indented "# type=raw,value=latest" is a tag for both images.
+            if "latest" in line and not line.startswith("#")
+        ]
+        assert latest == [raw_latest], (
+            f"docker.yml step {step.get('name')!r}: `:latest` comes from one `type=raw` entry, "
+            f"for the base leg only; found {latest}"
+        )
+
+
 def test_verapdf_image_is_digest_pinned() -> None:
     """The veraPDF gate runs a validator image pinned by digest.