runtime.txt: allow name-yyyy-mm-dd (no version)

repo2docker/buildpacks/base.py

@@ -759,6 +759,11 @@ class BaseImage(BuildPack):
 
         Returns (runtime, version, date), tuple components may be None.
         Returns (None, None, None) if runtime.txt not found.
+
+        Supported formats:
+          name-version
+          name-version-yyyy-mm-dd
+          name-yyyy-mm-dd
         """
         if hasattr(self, "_runtime"):
             return self._runtime
@@ -776,15 +781,19 @@ class BaseImage(BuildPack):
         version = None
         date = None
 
-        parts = runtime_txt.split("-", 2)
-        if len(parts) > 0 and parts[0]:
-            name = parts[0]
-        if len(parts) > 1 and parts[1]:
+        parts = runtime_txt.split("-")
+        if len(parts) not in (2, 4, 5) or any(not (p) for p in parts):
+            raise ValueError(f"Invalid runtime.txt: {runtime_txt}")
+
+        name = parts[0]
+
+        if len(parts) in (2, 5):
             version = parts[1]
-        if len(parts) > 2 and parts[2]:
-            date = parts[2]
+
+        if len(parts) in (4, 5):
+            date = "-".join(parts[-3:])
             if not re.match(r"\d\d\d\d-\d\d-\d\d", date):
-                raise ValueError(f"Invalid date, expected YYYY-MM-DD: {date}")
+                raise ValueError(f"Invalid runtime.txt date: {date}")
             date = datetime.datetime.fromisoformat(date).date()
 
         self._runtime = (name, version, date)

tests/unit/test_buildpack.py

@@ -57,10 +57,9 @@ def test_unsupported_python(tmpdir, python_version, base_image):
     "runtime_txt, expected",
     [
         (None, (None, None, None)),
-        ("", (None, None, None)),
-        ("abc", ("abc", None, None)),
         ("abc-001", ("abc", "001", None)),
         ("abc-001-2025-06-22", ("abc", "001", date(2025, 6, 22))),
+        ("abc-2025-06-22", ("abc", None, date(2025, 6, 22))),
         ("a_b/c-0.0.1-2025-06-22", ("a_b/c", "0.0.1", date(2025, 6, 22))),
     ],
 )
@@ -73,3 +72,24 @@ def test_runtime(tmpdir, runtime_txt, expected, base_image):
 
     base = BaseImage(base_image)
     assert base.runtime == expected
+
+
+@pytest.mark.parametrize(
+    "runtime_txt",
+    [
+        "",
+        "abc",
+        "abc-001-25-06-22",
+    ],
+)
+def test_invalid_runtime(tmpdir, runtime_txt, base_image):
+    tmpdir.chdir()
+
+    if runtime_txt is not None:
+        with open("runtime.txt", "w") as f:
+            f.write(runtime_txt)
+
+    base = BaseImage(base_image)
+
+    with pytest.raises(ValueError, match=r"^Invalid runtime.txt.*"):
+        base.runtime