hg-evolve required for Mercurial support (simpler)

.github/workflows/test.yml

@@ -106,7 +106,9 @@ jobs:
           python setup.py bdist_wheel
           pip install dist/*.whl
           pip freeze
-          pip install mercurial hg-evolve
+          # hg-evolve pinned to 9.2 because hg-evolve dropped support for
+          # hg 4.5, installed with apt in Ubuntu 18.04
+          $(hg debuginstall --template "{pythonexe}") -m pip install hg-evolve==9.2 --user
 
       - name: "Run tests"
         run: |

docs/source/contributing/tasks.md

@@ -24,8 +24,8 @@ py.test -s tests/<path-to-test>
 ```
 
 To skip the tests related to Mercurial repositories (to avoid to install
-Mercurial or hg-evolve), one can use the environment variables
-``REPO2DOCKER_SKIP_HG_TESTS`` or ``REPO2DOCKER_SKIP_HG_EVOLVE_TESTS``.
+Mercurial and hg-evolve), one can use the environment variable
+``REPO2DOCKER_SKIP_HG_TESTS``.
 
 ### Troubleshooting Tests
 

docs/source/install.rst

@@ -25,13 +25,19 @@ for more details.
 Optional: Mercurial
 -------------------
 
-For `Mercurial <https://www.mercurial-scm.org>`_ repositories, `Mercurial needs
-to be installed <https://www.mercurial-scm.org/download>`_. For support of
-`Mercurial topics
-<https://www.mercurial-scm.org/doc/evolution/tutorials/topic-tutorial.html>`_,
-also install `hg-evolve <https://www.mercurial-scm.org/doc/evolution/>`_ which
-provides the topic extension (however, no need to explicitly enable it in a
-Mercurial configuration file).
+For `Mercurial <https://www.mercurial-scm.org>`_ repositories, Mercurial and
+`hg-evolve <https://www.mercurial-scm.org/doc/evolution/>`_ need to be
+installed. For example, on Debian based distributions, one can do::
+
+  sudo apt install mercurial
+  $(hg debuginstall --template "{pythonexe}") -m pip install hg-evolve --user
+
+To install Mercurial on other systems, see `here
+<https://www.mercurial-scm.org/download>`_.
+
+Note that for old Mercurial versions, you may need to specify a version for
+hg-evolve. For example, ``hg-evolve==9.2`` for hg 4.5 (which is installed with
+`apt` on Ubuntu 18.4).
 
 Installing with ``pip``
 -----------------------

tests/unit/contentproviders/test_mercurial.py

@@ -10,34 +10,24 @@ from repo2docker.contentproviders import Mercurial
 from repo2docker.contentproviders.mercurial import args_enabling_topic
 
 SKIP_HG = strtobool(os.environ.get("REPO2DOCKER_SKIP_HG_TESTS", "False"))
-SKIP_HG_EVOLVE = SKIP_HG or strtobool(
-    os.environ.get("REPO2DOCKER_SKIP_HG_EVOLVE_TESTS", "False")
-)
 
 skip_if_no_hg_tests = pytest.mark.skipif(
     SKIP_HG,
     reason="REPO2DOCKER_SKIP_HG_TESTS",
 )
-skip_if_no_evolve_tests = pytest.mark.skipif(
-    SKIP_HG_EVOLVE,
-    reason="REPO2DOCKER_SKIP_HG_EVOLVE_TESTS",
-)
-
-if SKIP_HG_EVOLVE:
-    args_enabling_topic = []
 
 
 @skip_if_no_hg_tests
 def test_if_mercurial_is_available():
     """
     To skip the tests related to Mercurial repositories (to avoid to install
-    Mercurial), one can use the environment variable
+    Mercurial and hg-evolve), one can use the environment variable
     REPO2DOCKER_SKIP_HG_TESTS.
     """
     subprocess.check_output(["hg", "version"])
 
 
-@skip_if_no_evolve_tests
+@skip_if_no_hg_tests
 def test_if_topic_is_available():
     """Check that the topic extension can be enabled"""
     output = subprocess.getoutput("hg version -v --config extensions.topic=")
@@ -50,17 +40,14 @@ def _add_content_to_hg(repo_dir):
     with open(Path(repo_dir) / "test", "a") as f:
         f.write("Hello")
 
-    subprocess.check_call(["hg", "add", "test"], cwd=repo_dir)
-    subprocess.check_call(["hg", "commit", "-m", "Test commit"], cwd=repo_dir)
+    def check_call(command):
+        subprocess.check_call(command + args_enabling_topic, cwd=repo_dir)
 
-    if not SKIP_HG_EVOLVE:
-
-        def check_call(command):
-            subprocess.check_call(command + args_enabling_topic, cwd=repo_dir)
-
-        check_call(["hg", "topic", "test-topic"])
-        check_call(["hg", "commit", "-m", "Test commit in topic test-topic"])
-        check_call(["hg", "up", "default"])
+    check_call(["hg", "add", "test"])
+    check_call(["hg", "commit", "-m", "Test commit"])
+    check_call(["hg", "topic", "test-topic"])
+    check_call(["hg", "commit", "-m", "Test commit in topic test-topic"])
+    check_call(["hg", "up", "default"])
 
 
 def _get_node_id(repo_dir):
@@ -135,13 +122,13 @@ def test_bad_ref(hg_repo_with_content):
                 pass
 
 
-@skip_if_no_evolve_tests
+@skip_if_no_hg_tests
 def test_ref_topic(hg_repo_with_content):
     """
     Test trying to update to a topic
 
-    To skip this test (to avoid to install hg-evolve), one can use the
-    environment variable REPO2DOCKER_SKIP_HG_EVOLVE_TESTS.
+    To skip this test (to avoid to install Mercurial and hg-evolve), one can
+    use the environment variable REPO2DOCKER_SKIP_HG_TESTS.
 
     """
     upstream, node_id = hg_repo_with_content