ENH: Support restart cases with no iteration folder

src/fmu/dataio/providers/_fmu.py

@@ -53,6 +53,7 @@
 # case metadata relative to casepath
 ERT_RELATIVE_CASE_METADATA_FILE: Final = "share/metadata/fmu_case.yml"
 RESTART_PATH_ENVNAME: Final = "RESTART_FROM_PATH"
+DEFAULT_ITER_NAME: Final = "iter-0"
 
 logger: Final = null_logger(__name__)
 
@@ -145,7 +146,7 @@ def __post_init__(self) -> None:
                     self._real_name = self._runpath.parent.name
                 else:
                     logger.debug("No iteration folder found, using default name iter-0")
-                    self._iter_name = "iter-0"
+                    self._iter_name = DEFAULT_ITER_NAME
                     self._real_name = self._runpath.name
 
                 logger.debug("Found iter name from runpath: %s", self._iter_name)
@@ -256,6 +257,12 @@ def _get_restart_data_uuid(self) -> UUID | None:
             restart_case_metafile = (
                 restart_path.parent.parent / ERT_RELATIVE_CASE_METADATA_FILE
             )
+            restart_iter_name = restart_path.name
+        elif _casepath_has_metadata(restart_path.parent):
+            restart_case_metafile = (
+                restart_path.parent / ERT_RELATIVE_CASE_METADATA_FILE
+            )
+            restart_iter_name = DEFAULT_ITER_NAME
         else:
             warn(
                 f"Environment variable {RESTART_PATH_ENVNAME} resolves to the path "
@@ -270,7 +277,7 @@ def _get_restart_data_uuid(self) -> UUID | None:
                 ut.yaml_load(restart_case_metafile)
             )
             return _utils.uuid_from_string(
-                f"{restart_metadata.fmu.case.uuid}{restart_path.name}"
+                f"{restart_metadata.fmu.case.uuid}{restart_iter_name}"
             )
         except pydantic.ValidationError as err:
             warn(

tests/test_units/test_fmuprovider_class.py

@@ -11,7 +11,12 @@
 # from conftest import pretend_ert_env_run1
 from fmu.dataio._model.enums import FMUContext
 from fmu.dataio.exceptions import InvalidMetadataError
-from fmu.dataio.providers._fmu import RESTART_PATH_ENVNAME, FmuEnv, FmuProvider
+from fmu.dataio.providers._fmu import (
+    DEFAULT_ITER_NAME,
+    RESTART_PATH_ENVNAME,
+    FmuEnv,
+    FmuProvider,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -293,6 +298,26 @@ def test_fmuprovider_valid_relative_restart_env(
     assert meta_restart.iteration.restart_from == meta_restart_from.iteration.uuid
 
 
+def test_fmuprovider_restart_env_no_iter_folder(
+    monkeypatch, fmurun_no_iter_folder, fmurun_pred
+):
+    """
+    Test giving a valid RESTART_FROM_PATH environment variable
+    for a fmu run without iteration folders
+    """
+    monkeypatch.chdir(fmurun_no_iter_folder)
+    meta_restart_from = FmuProvider(fmu_context=FMUContext.realization).get_metadata()
+    assert meta_restart_from.iteration.name == DEFAULT_ITER_NAME
+
+    # using a relative path as input
+    monkeypatch.setenv(RESTART_PATH_ENVNAME, str(fmurun_no_iter_folder))
+
+    monkeypatch.chdir(fmurun_pred)
+    meta_restart = FmuProvider(fmu_context=FMUContext.realization).get_metadata()
+    assert meta_restart.iteration.restart_from is not None
+    assert meta_restart.iteration.restart_from == meta_restart_from.iteration.uuid
+
+
 def test_fmuprovider_invalid_restart_env(
     monkeypatch, fmurun_w_casemetadata, fmurun_pred
 ):