[core] Fix AssetCheckKey.from_user_string for asset keys containing colons

AssetCheckKey.to_user_string() renders a check key as
"<asset_key>:<check_name>", but from_user_string() split on every colon and
unpacked into exactly two values. Asset keys can legitimately contain colons
(for example the dagster-looker integration emits keys such as
["my_model::my_explore"]), so such a key raised
"ValueError: too many values to unpack (expected 2)" when parsed back.

This surfaces in the freshness-check sensor, which stores a check key via
to_user_string() as its cursor and reads it back with from_user_string() on
the next tick; a colon-containing asset key makes every subsequent tick fail.

Split off only the trailing ":<name>" segment with rsplit(":", 1). The check
name is a plain identifier, so the last segment is unambiguous, and colon-free
keys are parsed exactly as before.

Author: zelinewang

python_modules/dagster/dagster/_core/definitions/asset_key.py

@@ -230,7 +230,11 @@ def to_user_string(self) -> str:
 
     @staticmethod
     def from_user_string(user_string: str) -> "AssetCheckKey":
-        asset_key_str, name = user_string.split(":")
+        # to_user_string() appends ":<name>" to the asset key's user string, and asset keys
+        # can themselves contain colons (e.g. dagster-looker emits keys like
+        # ["my_model::my_explore"]). Split off only the final segment so the asset key portion
+        # is preserved.
+        asset_key_str, name = user_string.rsplit(":", 1)
         return AssetCheckKey(AssetKey.from_user_string(asset_key_str), name)
 
     @staticmethod

python_modules/dagster/dagster_tests/definitions_tests/test_entity_key.py

@@ -50,6 +50,22 @@ def test_asset_job_key_user_string_roundtrip() -> None:
     assert AssetJobKey.from_user_string("my_job") == key
 
 
+@pytest.mark.parametrize(
+    "check_key",
+    [
+        dg.AssetCheckKey(dg.AssetKey("a"), "b"),
+        dg.AssetCheckKey(dg.AssetKey(["prefix", "asset1"]), "freshness_check"),
+        # Asset keys can contain colons. For example the dagster-looker integration emits
+        # keys such as AssetKey(["my_model::my_explore"]). The check name is a plain
+        # identifier, so the trailing ":<name>" segment is unambiguous.
+        dg.AssetCheckKey(dg.AssetKey(["my_model::my_explore"]), "freshness_check"),
+        dg.AssetCheckKey(dg.AssetKey(["snowflake", "db:schema:table"]), "row_count"),
+    ],
+)
+def test_asset_check_key_user_string_roundtrip(check_key: AssetCheckKey) -> None:
+    assert AssetCheckKey.from_user_string(check_key.to_user_string()) == check_key
+
+
 def test_asset_job_key_from_db_string_returns_none_for_non_matching() -> None:
     assert AssetJobKey.from_db_string('["a"]') is None
     assert AssetJobKey.from_db_string('{"asset_key": "[\\"a\\"]", "check_name": "b"}') is None