fix(dfns): admit utl-obs under models and make it single-instance

autotest/dfns/__snapshots__/v2.0.0.dev2/utl-obs.json

@@ -2,10 +2,12 @@
   "type": "package",
   "schema_version": "2.0.0.dev2",
   "name": "utl-obs",
-  "parent": "package",
   "ftype": "OBS6",
-  "multi": true,
   "subtype": "utility",
+  "parent": [
+    "model",
+    "package"
+  ],
   "blocks": {
     "options": {
       "fields": {

autotest/dfns/__snapshots__/v2.0.0.dev2/utl-obs.toml

@@ -1,10 +1,12 @@
 type = "package"
 schema_version = "2.0.0.dev2"
 name = "utl-obs"
-parent = "package"
 ftype = "OBS6"
-multi = true
 subtype = "utility"
+parent = [
+    "model",
+    "package",
+]
 
 [blocks.options.fields.digits]
 type = "integer"

autotest/dfns/__snapshots__/v2.0.0.dev2/utl-obs.yaml

@@ -1,10 +1,11 @@
 type: package
 schema_version: 2.0.0.dev2
 name: utl-obs
-parent: package
 ftype: OBS6
-multi: true
 subtype: utility
+parent:
+  - model
+  - package
 blocks:
   options:
     fields:

autotest/dfns/__snapshots__/v2.0.0.dev3/utl-obs.json

@@ -2,10 +2,12 @@
   "type": "package",
   "schema_version": "2.0.0.dev3",
   "name": "utl-obs",
-  "parent": "package",
   "ftype": "OBS6",
-  "multi": true,
   "subtype": "utility",
+  "parent": [
+    "model",
+    "package"
+  ],
   "blocks": {
     "options": {
       "fields": {

autotest/dfns/__snapshots__/v2.0.0.dev3/utl-obs.toml

@@ -1,10 +1,12 @@
 type = "package"
 schema_version = "2.0.0.dev3"
 name = "utl-obs"
-parent = "package"
 ftype = "OBS6"
-multi = true
 subtype = "utility"
+parent = [
+    "model",
+    "package",
+]
 
 [blocks.options.fields.digits]
 type = "integer"

autotest/dfns/__snapshots__/v2.0.0.dev3/utl-obs.yaml

@@ -1,10 +1,11 @@
 type: package
 schema_version: 2.0.0.dev3
 name: utl-obs
-parent: package
 ftype: OBS6
-multi: true
 subtype: utility
+parent:
+  - model
+  - package
 blocks:
   options:
     fields:

autotest/dfns/test_migrate.py

@@ -640,7 +640,9 @@ def test_migrate_link_selectors_resolve(linked_spec):
 def test_migrate_model_packages_exclude_utilities(linked_spec):
     children = linked_spec.children("gwf-nam")
     assert {"gwf-dis", "gwf-gnc", "gwf-mvr"} <= set(children)
-    assert not any(n.startswith("utl-") for n in children)
+    # but a model with observations reads an OBS6 file
+    assert [n for n in children if n.startswith("utl-")] == ["utl-obs"]
+    assert linked_spec.ftype_family("OBS6", "gwf-nam") == ["utl-obs"]
 
 
 def test_migrate_unlinked_files(linked_spec):
@@ -657,7 +659,7 @@ def test_migrate_unlinked_files(linked_spec):
     "name, parent",
     [
         ("utl-ts", "package"),
-        ("utl-obs", "package"),
+        ("utl-obs", ["model", "package"]),
         (
             "utl-ncf",
             [f"{m}-{d}" for m in ("gwe", "gwf", "gwt", "prt") for d in ("dis", "disv")],
@@ -682,6 +684,17 @@ def test_migrate_derives_parents_from_links(linked_spec, name, parent):
     assert linked_spec.components[name].parent == parent
 
 
+@pytest.mark.parametrize("name, multi", [("utl-obs", False), ("utl-ts", True)])
+def test_migrate_multi_overrides(linked_spec, name, multi):
+    # flopy3 marks both multi-package, but MF6 reads one OBS6 per parent
+    assert linked_spec.components[name].multi is multi
+
+
+def test_migrate_obs_keeps_any_model_dims(linked_spec):
+    # utl-obs's parent gains `model`; it still sees any model's dims
+    assert {"nodes", "nlay"} <= linked_spec.inherited_dims("utl-obs")
+
+
 def test_migrate_subpackage_keeps_model_dims(linked_spec):
     # tvk's parent is now gwf-npf, not `package`; it must still see grid dims
     assert {"nodes", "nlay"} <= linked_spec.inherited_dims("utl-tvk")

autotest/dfns/test_schema_relations.py

@@ -409,6 +409,10 @@ def test_covering_selector():
     assert covering_selector([wel, spc], all_) == "package"
     # no single term covers a model and an exchange: concrete names
     assert covering_selector([nam, exg], all_) == ["exg-gwfgwf", "gwf-nam"]
+    # models and packages: their types
+    gwt = Model(name="gwt-nam")
+    all_[gwt.name] = gwt
+    assert covering_selector([wel, npf, nam, gwt], all_) == ["model", "package"]
 
 
 def test_children_list_parent():

modflow_devtools/dfns/migrate_to_v2_0_0_dev2.py

@@ -7,6 +7,7 @@
 
 from modflow_devtools.dfn import schema as v1
 from modflow_devtools.dfns import schema as v2
+from modflow_devtools.dfns.observations import OBSERVATIONS
 from modflow_devtools.misc import try_literal_eval
 
 _IDENT_RE = re.compile(r"^[A-Za-z_]\w*$")
@@ -114,6 +115,11 @@ def try_parse_bool(v: Any, default: bool = False) -> bool:
 # to the base type when matching name-file ftypes (InputLoadType.f90).
 _FTYPE_VARIANTS = frozenset({"evta", "rcha", "spca", "rivg", "chdg", "welg", "drng", "ghbg"})
 
+# Components flopy3 marks `multi-package` that MF6 reads at most once per
+# parent. utl-obs: one OBS6 per package (BoundaryPackage.f90 errors on a
+# second) and per model (the last row wins). The DFN header stays for flopy3.
+_SINGLE_INSTANCE = frozenset({"utl-obs"})
+
 _MODEL_TYPES = frozenset({*_DEPENDENT_VARS, "prt"})
 
 
@@ -2158,7 +2164,8 @@ def _lookup(rname: str) -> dict | None:
         )
         is_stress_pkg = is_stress_package(name, meta)
         subtype = "advanced" if is_advanced else "stress" if is_stress_pkg else None
-    return v2.Package(**d, subtype=subtype, multi=is_multi_package(meta))
+    multi = is_multi_package(meta) and name not in _SINGLE_INSTANCE
+    return v2.Package(**d, subtype=subtype, multi=multi)
 
 
 def subpackage_keys(metas: Mapping[str, list[str]]) -> dict[str, str]:
@@ -2206,8 +2213,13 @@ def link_components(
     The links themselves are made per file, by `to_v2_0_0_dev2`. Only
     concrete links count: a name file's type selectors (``model``,
     ``package``, ...) pick among components whose parents are already known.
+    The exception is OBS: a model with observation types reads one OBS6 file
+    from its packages block, so it links ``utl-obs`` like a package does.
     """
     links = {name: _links(c) for name, c in components.items()}
+    for name in OBSERVATIONS:
+        if name.endswith("-nam") and name in components:
+            links[name] = [*links[name], "utl-obs"]
 
     for name, meta in metas.items():
         if name not in components: