fix(stage): fall back to the installed library version for Code.version

src/exaspim_swc_processing/stage.py

@@ -19,6 +19,7 @@
 import sys
 from collections.abc import Mapping, Sequence
 from datetime import datetime, timezone
+from importlib import metadata
 from pathlib import Path
 
 from aind_data_schema.components.identifiers import Code
@@ -54,11 +55,37 @@ def _resources() -> ResourceUsage:
     )
 
 
+def installed_version(distribution: str) -> str | None:
+    """Return the installed version of a distribution, if it is installed.
+
+    Used as the fallback for ``Code.version``. Code Ocean generates ``main.nf`` and
+    exports only ``CO_CAPSULE_ID``, ``CO_CPUS`` and ``CO_MEMORY``, so the pinned capsule
+    commit is not available to the running code. The version of the library the capsule
+    installed is available, is what actually determines behaviour for these thin
+    capsules, and is a value AIND accepts in place of a commit hash.
+
+    Parameters
+    ----------
+    distribution : str
+        Distribution name, e.g. ``"exaspim-swc-processing"``.
+
+    Returns
+    -------
+    str | None
+        The installed version, or ``None`` if the distribution is not installed.
+    """
+    try:
+        return metadata.version(distribution)
+    except metadata.PackageNotFoundError:
+        return None
+
+
 def resolve_code(
     name: str,
     url: str | None = None,
     version: str | None = None,
     run_script: str = "code/run",
+    distribution: str = "exaspim-swc-processing",
 ) -> Code:
     """Describe the code a stage ran, from the environment.
 
@@ -70,9 +97,12 @@ def resolve_code(
         Repository URL. AIND prefers a GitHub URL; when omitted the Code Ocean capsule
         URL is built from ``CO_CAPSULE_ID``.
     version : str | None, optional
-        Version or commit of the code that ran. Read from ``CODE_VERSION`` when omitted.
+        Version of the code that ran. When omitted, ``CODE_VERSION`` is read, then the
+        installed version of ``distribution``. See :func:`installed_version`.
     run_script : str, optional
         Entry point, relative to the repository root, by default ``"code/run"``.
+    distribution : str, optional
+        Installed package to fall back to for the version, by default this library.
 
     Returns
     -------
@@ -85,7 +115,7 @@ def resolve_code(
     return Code(
         url=resolved_url,
         name=name,
-        version=version or os.environ.get("CODE_VERSION") or None,
+        version=version or os.environ.get("CODE_VERSION") or installed_version(distribution),
         run_script=Path(run_script),
         language="Python",
         language_version=(

tests/test_stage.py

@@ -10,6 +10,7 @@
 from exaspim_swc_processing.stage import (
     DATA_PROCESS_FILENAME,
     build_stage_process,
+    installed_version,
     resolve_code,
     write_stage_process,
 )
@@ -41,13 +42,31 @@ def test_a_github_url_is_preferred_when_given(monkeypatch: pytest.MonkeyPatch) -
     assert code.url == "https://github.com/peter-grotz/exaspim-swc-processing"
 
 
-def test_version_is_none_rather_than_empty_when_unknown(
+def test_version_falls_back_to_the_installed_library(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Code Ocean generates main.nf and does not export the pinned capsule commit.
+
+    The installed library version is what actually determines a thin capsule's
+    behaviour, and AIND accepts a version in place of a commit hash.
+    """
+    monkeypatch.setenv("CO_CAPSULE_ID", CAPSULE_ID)
+    monkeypatch.delenv("CODE_VERSION", raising=False)
+    assert resolve_code("x").version == installed_version("exaspim-swc-processing")
+
+
+def test_version_is_none_when_nothing_identifies_the_code(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
     """An absent version is null, not an empty string that looks recorded."""
     monkeypatch.setenv("CO_CAPSULE_ID", CAPSULE_ID)
     monkeypatch.delenv("CODE_VERSION", raising=False)
-    assert resolve_code("x").version is None
+    assert resolve_code("x", distribution="not-installed-anywhere").version is None
+
+
+def test_installed_version_returns_none_for_an_absent_distribution() -> None:
+    """A capsule that did not install the library still produces a valid record."""
+    assert installed_version("definitely-not-installed") is None
 
 
 def test_url_is_empty_outside_code_ocean(monkeypatch: pytest.MonkeyPatch) -> None: