Move runtime.txt handling into base class

This will allow it to be used for Python (and other languages) in future

repo2docker/buildpacks/base.py

@@ -1,3 +1,4 @@
+import datetime
 import hashlib
 import io
 import logging
@@ -750,3 +751,41 @@ class BaseImage(BuildPack):
             # the only path evaluated at container start time rather than build time
             return os.path.join("${REPO_DIR}", start)
         return None
+
+    @property
+    def runtime_info(self):
+        """
+        Return parsed contents of runtime.txt
+
+        Returns (runtime, version, date), tuple components may be None.
+        Returns (None, None, None) if runtime.txt not found.
+        """
+        if hasattr(self, "_runtime"):
+            return self._runtime
+
+        self._runtime = (None, None, None)
+
+        runtime_path = self.binder_path("runtime.txt")
+        try:
+            with open(runtime_path) as f:
+                runtime_txt = f.read().strip()
+        except FileNotFoundError:
+            return self._runtime
+
+        runtime = None
+        version = None
+        date = None
+
+        parts = runtime_txt.split("-", 2)
+        if len(parts) > 0 and parts[0]:
+            runtime = parts[0]
+        if len(parts) > 1 and parts[1]:
+            version = parts[1]
+        if len(parts) > 2 and parts[2]:
+            date = parts[2]
+            if not re.match(r"\d\d\d\d-\d\d-\d\d", date):
+                raise ValueError(f"Invalid date, expected YYYY-MM-DD: {date}")
+            date = datetime.datetime.fromisoformat(date).date()
+
+        self._runtime = (runtime, version, date)
+        return self._runtime

repo2docker/buildpacks/pipfile/__init__.py

@@ -187,12 +187,9 @@ class PipfileBuildPack(CondaBuildPack):
     def detect(self):
         """Check if current repo should be built with the Pipfile buildpack."""
         # first make sure python is not explicitly unwanted
-        runtime_txt = self.binder_path("runtime.txt")
-        if os.path.exists(runtime_txt):
-            with open(runtime_txt) as f:
-                runtime = f.read().strip()
-            if not runtime.startswith("python-"):
-                return False
+        runtime = self.runtime_info[0]
+        if runtime and runtime != "python":
+            return False
 
         pipfile = self.binder_path("Pipfile")
         pipfile_lock = self.binder_path("Pipfile.lock")

repo2docker/buildpacks/python/__init__.py

@@ -15,14 +15,10 @@ class PythonBuildPack(CondaBuildPack):
         if hasattr(self, "_python_version"):
             return self._python_version
 
-        try:
-            with open(self.binder_path("runtime.txt")) as f:
-                runtime = f.read().strip()
-        except FileNotFoundError:
-            runtime = ""
+        runtime, version, _ = self.runtime_info
 
-        if not runtime.startswith("python-"):
-            # not a Python runtime (e.g. R, which subclasses this)
+        if runtime != "python" or not version:
+            # Either not specified, or not a Python runtime (e.g. R, which subclasses this)
             # use the default Python
             self._python_version = self.major_pythons["3"]
             self.log.warning(
@@ -30,7 +26,7 @@ class PythonBuildPack(CondaBuildPack):
             )
             return self._python_version
 
-        py_version_info = runtime.split("-", 1)[1].split(".")
+        py_version_info = version.split(".")
         py_version = ""
         if len(py_version_info) == 1:
             py_version = self.major_pythons[py_version_info[0]]
@@ -138,16 +134,10 @@ class PythonBuildPack(CondaBuildPack):
     def detect(self):
         """Check if current repo should be built with the Python buildpack."""
         requirements_txt = self.binder_path("requirements.txt")
-        runtime_txt = self.binder_path("runtime.txt")
         setup_py = "setup.py"
 
-        if os.path.exists(runtime_txt):
-            with open(runtime_txt) as f:
-                runtime = f.read().strip()
-            if runtime.startswith("python-"):
-                return True
-            else:
-                return False
+        if self.runtime_info[0]:
+            return self.runtime_info[0] == "python"
         if not self.binder_dir and os.path.exists(setup_py):
             return True
         return os.path.exists(requirements_txt)

repo2docker/buildpacks/r.py

@@ -1,6 +1,6 @@
 import datetime
 import os
-import re
+import warnings
 from functools import lru_cache
 
 import requests
@@ -49,7 +49,14 @@ class RBuildPack(PythonBuildPack):
     def runtime(self):
         """
         Return contents of runtime.txt if it exists, '' otherwise
+
+        Deprecated, use `runtime_info` instead.
         """
+        warnings.warn(
+            "`{self.__class__.__name__}.runtime` is deprecated. Use `runtime_info` instead",
+            DeprecationWarning,
+        )
+
         if not hasattr(self, "_runtime"):
             runtime_path = self.binder_path("runtime.txt")
             try:
@@ -90,11 +97,11 @@ class RBuildPack(PythonBuildPack):
         r_version = version_map["4.2"]
 
         if not hasattr(self, "_r_version"):
-            parts = self.runtime.split("-")
+            runtime, version, date = self.runtime_info
             # If runtime.txt is not set, or if it isn't of the form r-<version>-<yyyy>-<mm>-<dd>,
             # we don't use any of it in determining r version and just use the default
-            if len(parts) == 5:
-                r_version = parts[1]
+            if version and date:
+                r_version = version
                 # For versions of form x.y, we want to explicitly provide x.y.z - latest patchlevel
                 # available. Users can however explicitly specify the full version to get something specific
                 if r_version in version_map:
@@ -116,15 +123,11 @@ class RBuildPack(PythonBuildPack):
         Returns '' if no date is specified
         """
         if not hasattr(self, "_checkpoint_date"):
-            match = re.match(r"r-(\d.\d(.\d)?-)?(\d\d\d\d)-(\d\d)-(\d\d)", self.runtime)
-            if not match:
-                self._checkpoint_date = False
+            runtime, version, date = self.runtime_info
+            if runtime == "r" and date:
+                self._checkpoint_date = date
             else:
-                # turn the last three groups of the match into a date
-                self._checkpoint_date = datetime.date(
-                    *[int(s) for s in match.groups()[-3:]]
-                )
-
+                self._checkpoint_date = False
         return self._checkpoint_date
 
     def detect(self):
@@ -142,13 +145,9 @@ class RBuildPack(PythonBuildPack):
 
         description_R = "DESCRIPTION"
         if not self.binder_dir and os.path.exists(description_R):
-            if not self.checkpoint_date:
-                # no R snapshot date set through runtime.txt
-                # Set it to two days ago from today
-                self._checkpoint_date = datetime.date.today() - datetime.timedelta(
-                    days=2
-                )
-                self._runtime = f"r-{str(self._checkpoint_date)}"
+            # no R snapshot date set through runtime.txt
+            # Set it to two days ago from today
+            self._checkpoint_date = datetime.date.today() - datetime.timedelta(days=2)
             return True
 
     @lru_cache

tests/unit/test_buildpack.py

@@ -1,9 +1,14 @@
+from datetime import date
 from os.path import join as pjoin
 from tempfile import TemporaryDirectory
 
 import pytest
 
-from repo2docker.buildpacks import LegacyBinderDockerBuildPack, PythonBuildPack
+from repo2docker.buildpacks import (
+    BaseImage,
+    LegacyBinderDockerBuildPack,
+    PythonBuildPack,
+)
 from repo2docker.utils import chdir
 
 
@@ -46,3 +51,25 @@ def test_unsupported_python(tmpdir, python_version, base_image):
     assert bp.python_version == python_version
     with pytest.raises(ValueError):
         bp.render()
+
+
+@pytest.mark.parametrize(
+    "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))),
+        ("a_b/c-0.0.1-2025-06-22", ("a_b/c", "0.0.1", date(2025, 6, 22))),
+    ],
+)
+def test_runtime_txt(tmpdir, runtime_txt, expected, 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)
+    assert base.runtime_info == expected