fix: anonymous volumes crash the emitter

architecture/supported-subset.md

@@ -47,6 +47,13 @@ warns (ignored, behavior-neutral inside a single pod) or raises
 Short bind-mount syntax only (`source:target`). The source must be a host path
 (starts with `.` or `/`); named volumes and the long mapping form raise.
 
+A single absolute container path with no `source:target` (e.g.
+`- /var/cache/models`) is accepted as an **anonymous volume** and emitted
+verbatim as `-v <path>` — podman creates an anonymous volume at that path (the
+common way to shadow a subdirectory of a bind mount). No host-path translation
+is applied, since the entry names a container path, not a host source. A
+colon-less entry that is not absolute (e.g. `./cache`) is malformed and raises.
+
 ## depends_on
 
 All three conditions are honored: `service_started`, `service_healthy`,

compose2pod/emit.py

@@ -57,6 +57,10 @@ def run_flags(name: str, svc: dict[str, Any], pod: str, hosts: list[str], projec
     for env_file in env_files:
         flags += ["--env-file", str(Path(project_dir, env_file))]
     for volume in svc.get("volumes") or []:
+        if ":" not in volume:
+            # Anonymous volume: a bare container path, no host source to translate.
+            flags += ["-v", volume]
+            continue
         source, destination = volume.split(":", 1)
         if not source.startswith("/"):
             source = str(Path(project_dir, source))

compose2pod/parsing.py

@@ -41,6 +41,12 @@ def _validate_service_volumes(name: str, svc: dict[str, Any]) -> None:
         if not isinstance(volume, str):
             msg = f"service {name!r}: only short volume syntax is supported"
             raise UnsupportedComposeError(msg)
+        if ":" not in volume:
+            # Anonymous volume: must be an absolute container path.
+            if not volume.startswith("/"):
+                msg = f"service {name!r}: anonymous volume '{volume}' must be an absolute path"
+                raise UnsupportedComposeError(msg)
+            continue
         source = volume.split(":", 1)[0]
         if not source.startswith((".", "/")):
             msg = f"service {name!r}: named volume '{source}' is not supported (bind mounts only)"

planning/changes/2026-07-08.02-anonymous-volumes.md

@@ -0,0 +1,58 @@
+---
+summary: Emit absolute anonymous volumes as `-v <path>` instead of crashing; reject non-absolute colon-less entries loudly.
+---
+
+# Change: Support anonymous volumes
+
+**Lane:** lightweight — one source file (`emit.py`), a resolved design choice,
+two tests, plus the capability-doc promotion.
+
+## Goal
+
+A Compose short-form volume can be a single container path with no
+`source:target` (an *anonymous volume*, e.g. `- /var/cache/models`). Such an
+entry passes `validate()` (its path starts with `/`) but crashes
+`emit.run_flags` at `volume.split(":", 1)` with
+`ValueError: not enough values to unpack (expected 2, got 1)`. This shipped in
+0.1.2 and breaks real compose files that use anonymous volumes to shadow
+subdirectories of a bind mount. Fix: emit an anonymous volume as `-v <path>`.
+
+## Approach
+
+In `run_flags` (`compose2pod/emit.py`), branch on whether the volume string
+contains a `:`. No colon → anonymous volume: append `["-v", volume]` verbatim
+(no `project_dir` translation — an anonymous volume names a container path, not
+a host source) and continue. With a colon → the existing bind-mount path
+(source translated against `project_dir` when relative).
+
+Design choice (resolved): **support**, not reject. Anonymous volumes are valid
+Compose; podman's `-v <path>` creates an anonymous volume at that path, which is
+exactly the compose semantics. Rejecting in `validate()` would fix the crash but
+break compose files that rely on them.
+
+`_validate_service_volumes` also gains a guard: a colon-less entry that is *not*
+absolute (e.g. `./cache`) is malformed Compose and now raises
+`UnsupportedComposeError` rather than slipping through to emit a broken
+`-v ./cache`. This keeps the project's "refuse loudly, never emit a silently
+broken script" contract. Absolute anonymous volumes (`/var/cache/models`)
+continue to be accepted.
+
+Promote into `architecture/supported-subset.md`: the Volumes section currently
+says "Short bind-mount syntax only (`source:target`)" — extend it to note that a
+single absolute container path is accepted as an anonymous volume and emitted as
+`-v <path>`.
+
+## Files
+
+- `compose2pod/emit.py` — `run_flags`: handle the no-colon (anonymous) volume case.
+- `tests/test_emit.py` — anonymous volume emits `-v <path>`; regression for the crash.
+- `tests/test_parsing.py` — anonymous volume passes `validate()` (pins the accept).
+- `architecture/supported-subset.md` — Volumes section promotion.
+
+## Verification
+
+- [ ] Failing test first: `run_flags` with `volumes: ["/var/cache/models"]` — expected RED `ValueError: not enough values to unpack`.
+- [ ] Apply the `emit.py` branch.
+- [ ] Test passes: the emitted flags contain `["-v", "/var/cache/models"]`.
+- [ ] `just test-ci` — full suite green at 100% line coverage.
+- [ ] `just lint-ci` — clean (ruff ALL, ruff format, ty, eof-fixer, planning check).

planning/releases/0.1.3.md

@@ -0,0 +1,32 @@
+# compose2pod 0.1.3 — anonymous volumes no longer crash
+
+A patch release fixing a crash on Compose files that use anonymous volumes. A
+short-form volume that is a single container path with no `source:target` (e.g.
+`- /var/cache/models`) passed validation but then crashed the emitter with
+`ValueError: not enough values to unpack`. Such files now convert.
+
+## Fix
+
+- **Anonymous volumes are emitted as `-v <path>`.** A colon-less volume entry
+  is a Compose anonymous volume; it is now rendered verbatim as `podman run -v
+  <path>` (podman creates an anonymous volume at that container path) instead of
+  crashing `run_flags`. No host-path translation is applied — the entry names a
+  container path, not a host source.
+- **Malformed colon-less volumes are rejected loudly.** A colon-less entry that
+  is not absolute (e.g. `./cache`) is invalid Compose and now raises a clear
+  `unsupported`-style error instead of silently emitting a broken `-v ./cache`,
+  keeping compose2pod's "refuse loudly, never emit a silently broken script"
+  contract.
+
+## Downstream
+
+No action needed — additive and backward compatible. Compose files that
+previously crashed with `ValueError: not enough values to unpack` on an
+anonymous volume now emit a pod script; nothing that converted before changes.
+
+## Internals
+
+- `architecture/supported-subset.md` documents anonymous volumes in the Volumes
+  matrix (absolute accepted and emitted as `-v <path>`; non-absolute raises).
+- 89 tests at 100% line coverage (enforced); `ruff select=ALL`, `ty`, and
+  `eof-fixer` clean.

tests/test_emit.py

@@ -49,6 +49,10 @@ def test_absolute_volume_source_is_kept_as_is(self) -> None:
         flags = run_flags("app", {"image": "x", "volumes": ["/data/app:/srv/www/"]}, "p", [], "/builds/x")
         assert flags[4:6] == ["-v", "/data/app:/srv/www/"]
 
+    def test_anonymous_volume_emitted_as_single_path(self) -> None:
+        flags = run_flags("app", {"image": "x", "volumes": ["/var/cache/models"]}, "p", [], "/builds/x")
+        assert flags[4:6] == ["-v", "/var/cache/models"]
+
     def test_healthcheck_without_timeout_omits_health_timeout_flag(self) -> None:
         flags = run_flags("app", {"image": "x", "healthcheck": {"test": "true"}}, "p", [], "/builds/x")
         assert flags[4:6] == ["--health-cmd", "true"]

tests/test_parsing.py

@@ -35,6 +35,13 @@ def test_long_volume_syntax_raises(self) -> None:
         with pytest.raises(UnsupportedComposeError, match="short volume syntax"):
             validate(compose)
 
+    def test_anonymous_volume_is_accepted(self) -> None:
+        assert validate({"services": {"app": {"image": "x", "volumes": ["/var/cache/models"]}}}) == []
+
+    def test_relative_anonymous_volume_raises(self) -> None:
+        with pytest.raises(UnsupportedComposeError, match="absolute"):
+            validate({"services": {"app": {"image": "x", "volumes": ["./cache"]}}})
+
     def test_no_services_raises(self) -> None:
         with pytest.raises(UnsupportedComposeError, match="no services"):
             validate({"services": {}})