From e520b900bf6a7eae4ef5a3ca91c7f0e106182fa7 Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Fri, 4 Sep 2020 15:14:04 +0200
Subject: [PATCH 01/13] Add a Mercurial contentprovider

MyBinder could support Mercurial repositories

See https://github.com/jupyterhub/binderhub/issues/1148
---
 Pipfile                                       |  2 +
 dev-requirements.txt                          |  2 +
 repo2docker/contentproviders/__init__.py      |  1 +
 repo2docker/contentproviders/mercurial.py     | 79 ++++++++++++++++++
 tests/unit/contentproviders/test_mercurial.py | 82 +++++++++++++++++++
 5 files changed, 166 insertions(+)
 create mode 100644 repo2docker/contentproviders/mercurial.py
 create mode 100644 tests/unit/contentproviders/test_mercurial.py

diff --git a/Pipfile b/Pipfile
index b4d56fdf2..3aa175da6 100644
--- a/Pipfile
+++ b/Pipfile
@@ -12,6 +12,8 @@ alabaster = "*"
 Sphinx = ">=1.4,!=1.5.4"
 alabaster_jupyterhub = "*"
 sphinxcontrib-autoprogram = "*"
+mercurial = "*"
+hg-evolve = "*"
 
 [packages]
 repo2docker = {path=".", editable=true}
diff --git a/dev-requirements.txt b/dev-requirements.txt
index bcecb7ba7..288c0e5d2 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -6,3 +6,5 @@ wheel
 pytest-cov
 pre-commit
 requests
+mercurial
+hg-evolve
diff --git a/repo2docker/contentproviders/__init__.py b/repo2docker/contentproviders/__init__.py
index c53290d86..ae0b8c27c 100755
--- a/repo2docker/contentproviders/__init__.py
+++ b/repo2docker/contentproviders/__init__.py
@@ -4,3 +4,4 @@
 from .figshare import Figshare
 from .dataverse import Dataverse
 from .hydroshare import Hydroshare
+from .mercurial import Mercurial
diff --git a/repo2docker/contentproviders/mercurial.py b/repo2docker/contentproviders/mercurial.py
new file mode 100644
index 000000000..c8c8c1370
--- /dev/null
+++ b/repo2docker/contentproviders/mercurial.py
@@ -0,0 +1,79 @@
+import subprocess
+
+from .base import ContentProvider, ContentProviderException
+from ..utils import execute_cmd
+
+
+hg_config = [
+    "--config",
+    "extensions.hggit=!",
+    "--config",
+    "extensions.evolve=",
+    "--config",
+    "extensions.topic=",
+]
+
+
+class Mercurial(ContentProvider):
+    """Provide contents of a remote Mercurial repository."""
+
+    def detect(self, source, ref=None, extra_args=None):
+        if "github.com/" in source or source.endswith(".git"):
+            return None
+        try:
+            subprocess.check_output(
+                ["hg", "identify", source] + hg_config, stderr=subprocess.DEVNULL,
+            )
+        except subprocess.CalledProcessError:
+            return None
+
+        return {"repo": source, "ref": ref}
+
+    def fetch(self, spec, output_dir, yield_output=False):
+        repo = spec["repo"]
+        ref = spec.get("ref", None)
+
+        # make a clone of the remote repository
+        try:
+            cmd = ["hg", "clone", repo, output_dir]
+            cmd.extend(hg_config)
+            if ref is not None:
+                # don't update so the clone will include an empty working
+                # directory, the given ref will be updated out later
+                cmd.extend(["--noupdate"])
+            for line in execute_cmd(cmd, capture=yield_output):
+                yield line
+
+        except subprocess.CalledProcessError as error:
+            msg = "Failed to clone repository from {repo}".format(repo=repo)
+            if ref is not None:
+                msg += " (ref {ref})".format(ref=ref)
+            msg += "."
+            raise ContentProviderException(msg) from error
+
+        # check out the specific ref given by the user
+        if ref is not None:
+            try:
+                for line in execute_cmd(
+                    ["hg", "update", "--clean", ref] + hg_config,
+                    cwd=output_dir,
+                    capture=yield_output,
+                ):
+                    yield line
+            except subprocess.CalledProcessError:
+                self.log.error(
+                    "Failed to update to ref %s", ref, extra=dict(phase="failed")
+                )
+                raise ValueError("Failed to update to ref {}".format(ref))
+
+        cmd = ["hg", "identify"]
+        cmd.extend(hg_config)
+        sha1 = subprocess.Popen(cmd, stdout=subprocess.PIPE, cwd=output_dir)
+        self._sha1 = sha1.stdout.read().decode().strip()
+
+    @property
+    def content_id(self):
+        """A unique ID to represent the version of the content.
+        Uses the first seven characters of the git commit ID of the repository.
+        """
+        return self._sha1[:7]
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
new file mode 100644
index 000000000..5cfcd4820
--- /dev/null
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -0,0 +1,82 @@
+from pathlib import Path
+import subprocess
+from tempfile import TemporaryDirectory
+
+import pytest
+
+from repo2docker.contentproviders import Mercurial
+
+
+def _add_content_to_hg(repo_dir):
+    """Add content to file 'test' in hg repository and commit."""
+    # use append mode so this can be called multiple times
+    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 _get_sha1(repo_dir):
+    """Get repository's current commit SHA1."""
+    sha1 = subprocess.Popen(["hg", "identify"], stdout=subprocess.PIPE, cwd=repo_dir)
+    return sha1.stdout.read().decode().strip()
+
+
+@pytest.fixture()
+def hg_repo():
+    """
+    Make a dummy git repo in which user can perform git operations
+
+    Should be used as a contextmanager, it will delete directory when done
+    """
+    with TemporaryDirectory() as gitdir:
+        subprocess.check_call(["hg", "init"], cwd=gitdir)
+        yield gitdir
+
+
+@pytest.fixture()
+def hg_repo_with_content(hg_repo):
+    """Create a hg repository with content"""
+    _add_content_to_hg(hg_repo)
+    sha1 = _get_sha1(hg_repo)
+
+    yield hg_repo, sha1
+
+
+def test_detect_mercurial(hg_repo_with_content, repo_with_content):
+    mercurial = Mercurial()
+    assert mercurial.detect("this-is-not-a-directory") is None
+    assert mercurial.detect("https://github.com/jupyterhub/repo2docker") is None
+
+    git_repo = repo_with_content[0]
+    assert mercurial.detect(git_repo) is None
+
+    hg_repo = hg_repo_with_content[0]
+    assert mercurial.detect(hg_repo) == {"repo": hg_repo, "ref": None}
+
+
+def test_clone(hg_repo_with_content):
+    """Test simple hg clone to a target dir"""
+    upstream, sha1 = hg_repo_with_content
+
+    with TemporaryDirectory() as clone_dir:
+        spec = {"repo": upstream}
+        mercurial = Mercurial()
+        for _ in mercurial.fetch(spec, clone_dir):
+            pass
+        assert (Path(clone_dir) / "test").exists()
+
+        assert mercurial.content_id == sha1[:7]
+
+
+def test_bad_ref(hg_repo_with_content):
+    """
+    Test trying to checkout a ref that doesn't exist
+    """
+    upstream, sha1 = hg_repo_with_content
+    with TemporaryDirectory() as clone_dir:
+        spec = {"repo": upstream, "ref": "does-not-exist"}
+        with pytest.raises(ValueError):
+            for _ in Mercurial().fetch(spec, clone_dir):
+                pass

From 2d2e9bf19ad0dd11c5c545a62eb090e704362e69 Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 7 Sep 2020 09:38:07 +0200
Subject: [PATCH 02/13] Skip Mercurial for Python 3.5

---
 Pipfile                                       |  4 ++--
 dev-requirements.txt                          |  4 ++--
 tests/unit/contentproviders/test_mercurial.py | 13 ++++++++++++-
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/Pipfile b/Pipfile
index 3aa175da6..afc8bcd2a 100644
--- a/Pipfile
+++ b/Pipfile
@@ -12,8 +12,8 @@ alabaster = "*"
 Sphinx = ">=1.4,!=1.5.4"
 alabaster_jupyterhub = "*"
 sphinxcontrib-autoprogram = "*"
-mercurial = "*"
-hg-evolve = "*"
+mercurial = {version = ">=5.2", markers="python_version > '3.5'"}
+hg-evolve = {version = ">=10.0", markers="python_version > '3.5'"}
 
 [packages]
 repo2docker = {path=".", editable=true}
diff --git a/dev-requirements.txt b/dev-requirements.txt
index 288c0e5d2..1105d9aa6 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -6,5 +6,5 @@ wheel
 pytest-cov
 pre-commit
 requests
-mercurial
-hg-evolve
+mercurial>=5.2; python_version > '3.5'
+hg-evolve>=10.0; python_version > '3.5'
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index 5cfcd4820..dee5b5103 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -1,12 +1,18 @@
 from pathlib import Path
 import subprocess
 from tempfile import TemporaryDirectory
+import sys
 
 import pytest
 
 from repo2docker.contentproviders import Mercurial
 
 
+skipif_py35 = pytest.mark.skipif(
+    sys.version_info < (3, 6), reason="requires python3.6"
+)
+
+
 def _add_content_to_hg(repo_dir):
     """Add content to file 'test' in hg repository and commit."""
     # use append mode so this can be called multiple times
@@ -19,7 +25,9 @@ def _add_content_to_hg(repo_dir):
 
 def _get_sha1(repo_dir):
     """Get repository's current commit SHA1."""
-    sha1 = subprocess.Popen(["hg", "identify"], stdout=subprocess.PIPE, cwd=repo_dir)
+    sha1 = subprocess.Popen(
+        ["hg", "identify"], stdout=subprocess.PIPE, cwd=repo_dir
+    )
     return sha1.stdout.read().decode().strip()
 
 
@@ -44,6 +52,7 @@ def hg_repo_with_content(hg_repo):
     yield hg_repo, sha1
 
 
+@skipif_py35
 def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     mercurial = Mercurial()
     assert mercurial.detect("this-is-not-a-directory") is None
@@ -56,6 +65,7 @@ def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     assert mercurial.detect(hg_repo) == {"repo": hg_repo, "ref": None}
 
 
+@skipif_py35
 def test_clone(hg_repo_with_content):
     """Test simple hg clone to a target dir"""
     upstream, sha1 = hg_repo_with_content
@@ -70,6 +80,7 @@ def test_clone(hg_repo_with_content):
         assert mercurial.content_id == sha1[:7]
 
 
+@skipif_py35
 def test_bad_ref(hg_repo_with_content):
     """
     Test trying to checkout a ref that doesn't exist

From d26b3dd0dfb79325e6d0402ba767ec88d13329aa Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 7 Sep 2020 09:43:22 +0200
Subject: [PATCH 03/13] Mercurial: use the full node id (12 characters) for the
 content_id

---
 repo2docker/contentproviders/mercurial.py | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/repo2docker/contentproviders/mercurial.py b/repo2docker/contentproviders/mercurial.py
index c8c8c1370..4d02c1fba 100644
--- a/repo2docker/contentproviders/mercurial.py
+++ b/repo2docker/contentproviders/mercurial.py
@@ -66,14 +66,12 @@ def fetch(self, spec, output_dir, yield_output=False):
                 )
                 raise ValueError("Failed to update to ref {}".format(ref))
 
-        cmd = ["hg", "identify"]
+        cmd = ["hg", "identify", "-i"]
         cmd.extend(hg_config)
         sha1 = subprocess.Popen(cmd, stdout=subprocess.PIPE, cwd=output_dir)
-        self._sha1 = sha1.stdout.read().decode().strip()
+        self._node_id = sha1.stdout.read().decode().strip()
 
     @property
     def content_id(self):
-        """A unique ID to represent the version of the content.
-        Uses the first seven characters of the git commit ID of the repository.
-        """
-        return self._sha1[:7]
+        """A unique ID to represent the version of the content."""
+        return self._node_id

From fc3cef16a10b751433f3335a886b62496feea27e Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 7 Sep 2020 09:51:30 +0200
Subject: [PATCH 04/13] Fix test_mercurial.py (black, node_id and git->hg)

---
 tests/unit/contentproviders/test_mercurial.py | 32 +++++++++----------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index dee5b5103..4018b2d22 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -8,9 +8,7 @@
 from repo2docker.contentproviders import Mercurial
 
 
-skipif_py35 = pytest.mark.skipif(
-    sys.version_info < (3, 6), reason="requires python3.6"
-)
+skipif_py35 = pytest.mark.skipif(sys.version_info < (3, 6), reason="requires python3.6")
 
 
 def _add_content_to_hg(repo_dir):
@@ -23,33 +21,33 @@ def _add_content_to_hg(repo_dir):
     subprocess.check_call(["hg", "commit", "-m", "Test commit"], cwd=repo_dir)
 
 
-def _get_sha1(repo_dir):
-    """Get repository's current commit SHA1."""
-    sha1 = subprocess.Popen(
-        ["hg", "identify"], stdout=subprocess.PIPE, cwd=repo_dir
+def _get_node_id(repo_dir):
+    """Get repository's current commit node ID (currently SHA1)."""
+    node_id = subprocess.Popen(
+        ["hg", "identify", "-i"], stdout=subprocess.PIPE, cwd=repo_dir
     )
-    return sha1.stdout.read().decode().strip()
+    return node_id.stdout.read().decode().strip()
 
 
 @pytest.fixture()
 def hg_repo():
     """
-    Make a dummy git repo in which user can perform git operations
+    Make a dummy hg repo in which user can perform hg operations
 
     Should be used as a contextmanager, it will delete directory when done
     """
-    with TemporaryDirectory() as gitdir:
-        subprocess.check_call(["hg", "init"], cwd=gitdir)
-        yield gitdir
+    with TemporaryDirectory() as hgdir:
+        subprocess.check_call(["hg", "init"], cwd=hgdir)
+        yield hgdir
 
 
 @pytest.fixture()
 def hg_repo_with_content(hg_repo):
     """Create a hg repository with content"""
     _add_content_to_hg(hg_repo)
-    sha1 = _get_sha1(hg_repo)
+    node_id = _get_node_id(hg_repo)
 
-    yield hg_repo, sha1
+    yield hg_repo, node_id
 
 
 @skipif_py35
@@ -68,7 +66,7 @@ def test_detect_mercurial(hg_repo_with_content, repo_with_content):
 @skipif_py35
 def test_clone(hg_repo_with_content):
     """Test simple hg clone to a target dir"""
-    upstream, sha1 = hg_repo_with_content
+    upstream, node_id = hg_repo_with_content
 
     with TemporaryDirectory() as clone_dir:
         spec = {"repo": upstream}
@@ -77,7 +75,7 @@ def test_clone(hg_repo_with_content):
             pass
         assert (Path(clone_dir) / "test").exists()
 
-        assert mercurial.content_id == sha1[:7]
+        assert mercurial.content_id == node_id
 
 
 @skipif_py35
@@ -85,7 +83,7 @@ def test_bad_ref(hg_repo_with_content):
     """
     Test trying to checkout a ref that doesn't exist
     """
-    upstream, sha1 = hg_repo_with_content
+    upstream, node_id = hg_repo_with_content
     with TemporaryDirectory() as clone_dir:
         spec = {"repo": upstream, "ref": "does-not-exist"}
         with pytest.raises(ValueError):

From 979c4abe004ae7ebd29537d5afd2890128dda71a Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 7 Sep 2020 10:06:58 +0200
Subject: [PATCH 05/13] Add Mercurial in content_providers in
 repo2docker/app.py

---
 repo2docker/app.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/repo2docker/app.py b/repo2docker/app.py
index 660a87d64..937e74793 100755
--- a/repo2docker/app.py
+++ b/repo2docker/app.py
@@ -148,6 +148,7 @@ def _default_log_level(self):
             contentproviders.Figshare,
             contentproviders.Dataverse,
             contentproviders.Hydroshare,
+            contentproviders.Mercurial,
             contentproviders.Git,
         ],
         config=True,

From 319e22ab1d1b7a5fbddcc7357c39306c2e4ff9dc Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 7 Sep 2020 12:17:16 +0200
Subject: [PATCH 06/13] Add Mercurial+evolve in install_requires

---
 setup.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/setup.py b/setup.py
index 5084b486c..2f5bf3def 100644
--- a/setup.py
+++ b/setup.py
@@ -55,6 +55,8 @@ def get_identifier(json):
         "ruamel.yaml>=0.15",
         "toml",
         "semver",
+        "mercurial>=5.2; python_version > '3.5'",
+        "hg-evolve>=10.0; python_version > '3.5'",
     ],
     python_requires=">=3.6",
     author="Project Jupyter Contributors",

From c91ed4eec5846f2c1a865ab8f7f43555ef586e6b Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Tue, 8 Sep 2020 10:09:13 +0200
Subject: [PATCH 07/13] Mercurial: remove conditions for py3.5 + requirements
 only in setup.py

---
 Pipfile                                       | 2 --
 dev-requirements.txt                          | 2 --
 setup.py                                      | 4 ++--
 tests/unit/contentproviders/test_mercurial.py | 7 -------
 4 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/Pipfile b/Pipfile
index afc8bcd2a..b4d56fdf2 100644
--- a/Pipfile
+++ b/Pipfile
@@ -12,8 +12,6 @@ alabaster = "*"
 Sphinx = ">=1.4,!=1.5.4"
 alabaster_jupyterhub = "*"
 sphinxcontrib-autoprogram = "*"
-mercurial = {version = ">=5.2", markers="python_version > '3.5'"}
-hg-evolve = {version = ">=10.0", markers="python_version > '3.5'"}
 
 [packages]
 repo2docker = {path=".", editable=true}
diff --git a/dev-requirements.txt b/dev-requirements.txt
index 1105d9aa6..bcecb7ba7 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -6,5 +6,3 @@ wheel
 pytest-cov
 pre-commit
 requests
-mercurial>=5.2; python_version > '3.5'
-hg-evolve>=10.0; python_version > '3.5'
diff --git a/setup.py b/setup.py
index 2f5bf3def..f41cea0ea 100644
--- a/setup.py
+++ b/setup.py
@@ -55,8 +55,8 @@ def get_identifier(json):
         "ruamel.yaml>=0.15",
         "toml",
         "semver",
-        "mercurial>=5.2; python_version > '3.5'",
-        "hg-evolve>=10.0; python_version > '3.5'",
+        "mercurial>=5.2",
+        "hg-evolve>=10.0",
     ],
     python_requires=">=3.6",
     author="Project Jupyter Contributors",
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index 4018b2d22..6b4f91006 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -1,16 +1,12 @@
 from pathlib import Path
 import subprocess
 from tempfile import TemporaryDirectory
-import sys
 
 import pytest
 
 from repo2docker.contentproviders import Mercurial
 
 
-skipif_py35 = pytest.mark.skipif(sys.version_info < (3, 6), reason="requires python3.6")
-
-
 def _add_content_to_hg(repo_dir):
     """Add content to file 'test' in hg repository and commit."""
     # use append mode so this can be called multiple times
@@ -50,7 +46,6 @@ def hg_repo_with_content(hg_repo):
     yield hg_repo, node_id
 
 
-@skipif_py35
 def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     mercurial = Mercurial()
     assert mercurial.detect("this-is-not-a-directory") is None
@@ -63,7 +58,6 @@ def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     assert mercurial.detect(hg_repo) == {"repo": hg_repo, "ref": None}
 
 
-@skipif_py35
 def test_clone(hg_repo_with_content):
     """Test simple hg clone to a target dir"""
     upstream, node_id = hg_repo_with_content
@@ -78,7 +72,6 @@ def test_clone(hg_repo_with_content):
         assert mercurial.content_id == node_id
 
 
-@skipif_py35
 def test_bad_ref(hg_repo_with_content):
     """
     Test trying to checkout a ref that doesn't exist

From 96914545e1dfaca19e542dc4944b40fb2325b49a Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Wed, 9 Sep 2020 18:10:19 +0200
Subject: [PATCH 08/13] Update Dockerfile (ALPINE_VERSION=3.12.0 & install
 mercurial) + remove mercurial from install_requires

---
 Dockerfile                                | 12 ++++++++----
 repo2docker/contentproviders/mercurial.py | 17 +++--------------
 setup.py                                  |  2 --
 3 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/Dockerfile b/Dockerfile
index 84762c240..023d148b9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
-ARG ALPINE_VERSION=3.9.4
+ARG ALPINE_VERSION=3.12.0
 FROM alpine:${ALPINE_VERSION}
 
-RUN apk add --no-cache git python3 python3-dev
+RUN apk add --no-cache git python3 python3-dev py-pip
 
 # build wheels in first image
 ADD . /tmp/src
@@ -15,8 +15,12 @@ RUN mkdir /tmp/wheelhouse \
 
 FROM alpine:${ALPINE_VERSION}
 
-# install python, git, bash
-RUN apk add --no-cache git git-lfs python3 bash docker
+# install python, git, bash, mercurial
+RUN apk add --no-cache git git-lfs python3 py-pip bash docker mercurial
+
+# install and activate the evolve and topic Mercurial extensions
+RUN pip3 install hg-evolve --user --no-cache-dir
+RUN mkdir -p /etc/mercurial/hgrc.d && echo -e "[extensions]\nevolve =\ntopic =\n" >  /etc/mercurial/hgrc.d/evolve.rc
 
 # install repo2docker
 COPY --from=0 /tmp/wheelhouse /tmp/wheelhouse
diff --git a/repo2docker/contentproviders/mercurial.py b/repo2docker/contentproviders/mercurial.py
index 4d02c1fba..2b33d23f0 100644
--- a/repo2docker/contentproviders/mercurial.py
+++ b/repo2docker/contentproviders/mercurial.py
@@ -4,16 +4,6 @@
 from ..utils import execute_cmd
 
 
-hg_config = [
-    "--config",
-    "extensions.hggit=!",
-    "--config",
-    "extensions.evolve=",
-    "--config",
-    "extensions.topic=",
-]
-
-
 class Mercurial(ContentProvider):
     """Provide contents of a remote Mercurial repository."""
 
@@ -22,7 +12,8 @@ def detect(self, source, ref=None, extra_args=None):
             return None
         try:
             subprocess.check_output(
-                ["hg", "identify", source] + hg_config, stderr=subprocess.DEVNULL,
+                ["hg", "identify", source, "--config", "extensions.hggit=!"],
+                stderr=subprocess.DEVNULL,
             )
         except subprocess.CalledProcessError:
             return None
@@ -36,7 +27,6 @@ def fetch(self, spec, output_dir, yield_output=False):
         # make a clone of the remote repository
         try:
             cmd = ["hg", "clone", repo, output_dir]
-            cmd.extend(hg_config)
             if ref is not None:
                 # don't update so the clone will include an empty working
                 # directory, the given ref will be updated out later
@@ -55,7 +45,7 @@ def fetch(self, spec, output_dir, yield_output=False):
         if ref is not None:
             try:
                 for line in execute_cmd(
-                    ["hg", "update", "--clean", ref] + hg_config,
+                    ["hg", "update", "--clean", ref],
                     cwd=output_dir,
                     capture=yield_output,
                 ):
@@ -67,7 +57,6 @@ def fetch(self, spec, output_dir, yield_output=False):
                 raise ValueError("Failed to update to ref {}".format(ref))
 
         cmd = ["hg", "identify", "-i"]
-        cmd.extend(hg_config)
         sha1 = subprocess.Popen(cmd, stdout=subprocess.PIPE, cwd=output_dir)
         self._node_id = sha1.stdout.read().decode().strip()
 
diff --git a/setup.py b/setup.py
index f41cea0ea..5084b486c 100644
--- a/setup.py
+++ b/setup.py
@@ -55,8 +55,6 @@ def get_identifier(json):
         "ruamel.yaml>=0.15",
         "toml",
         "semver",
-        "mercurial>=5.2",
-        "hg-evolve>=10.0",
     ],
     python_requires=">=3.6",
     author="Project Jupyter Contributors",

From 5bb586931b40cea181be8302f931a0d74a2b1d03 Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Thu, 10 Sep 2020 07:58:21 +0200
Subject: [PATCH 09/13] Mercurial optional

---
 repo2docker/contentproviders/mercurial.py     | 46 +++++++++++++-
 tests/unit/contentproviders/test_mercurial.py | 63 ++++++++++++++++++-
 2 files changed, 105 insertions(+), 4 deletions(-)

diff --git a/repo2docker/contentproviders/mercurial.py b/repo2docker/contentproviders/mercurial.py
index 2b33d23f0..3164b22e0 100644
--- a/repo2docker/contentproviders/mercurial.py
+++ b/repo2docker/contentproviders/mercurial.py
@@ -1,8 +1,39 @@
 import subprocess
+import os
+from distutils.util import strtobool
 
 from .base import ContentProvider, ContentProviderException
 from ..utils import execute_cmd
 
+HG_EVOLVE_REQUIRED = strtobool(
+    os.environ.get("REPO2DOCKER_HG_EVOLVE_REQUIRED", "False")
+)
+
+if HG_EVOLVE_REQUIRED:
+    if "REPO2DOCKER_HG_REQUIRED" in os.environ:
+        HG_REQUIRED = strtobool(os.environ["REPO2DOCKER_HG_REQUIRED"])
+        if not HG_REQUIRED:
+            raise ValueError(
+                "Incompatible values for environment variables "
+                "REPO2DOCKER_HG_EVOLVE_REQUIRED=1 and REPO2DOCKER_HG_REQUIRED=0"
+            )
+    else:
+        HG_REQUIRED = True
+else:
+    HG_REQUIRED = strtobool(os.environ.get("REPO2DOCKER_HG_REQUIRED", "False"))
+
+
+def is_mercurial_available():
+    try:
+        subprocess.check_output(["hg", "version"])
+    except subprocess.CalledProcessError:
+        return False
+    return True
+
+
+if HG_REQUIRED and not is_mercurial_available():
+    raise RuntimeError("REPO2DOCKER_HG_REQUIRED but the command `hg` is not available")
+
 
 class Mercurial(ContentProvider):
     """Provide contents of a remote Mercurial repository."""
@@ -16,6 +47,8 @@ def detect(self, source, ref=None, extra_args=None):
                 stderr=subprocess.DEVNULL,
             )
         except subprocess.CalledProcessError:
+            # warning: if hg is not installed and `not HG_REQUIRED`,
+            # we return None even for a hg repo
             return None
 
         return {"repo": source, "ref": ref}
@@ -26,7 +59,14 @@ def fetch(self, spec, output_dir, yield_output=False):
 
         # make a clone of the remote repository
         try:
-            cmd = ["hg", "clone", repo, output_dir]
+            cmd = [
+                "hg",
+                "clone",
+                repo,
+                output_dir,
+                "--config",
+                "phases.publish=False",
+            ]
             if ref is not None:
                 # don't update so the clone will include an empty working
                 # directory, the given ref will be updated out later
@@ -35,9 +75,9 @@ def fetch(self, spec, output_dir, yield_output=False):
                 yield line
 
         except subprocess.CalledProcessError as error:
-            msg = "Failed to clone repository from {repo}".format(repo=repo)
+            msg = f"Failed to clone repository from {repo}"
             if ref is not None:
-                msg += " (ref {ref})".format(ref=ref)
+                msg += f" (ref {ref})"
             msg += "."
             raise ContentProviderException(msg) from error
 
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index 6b4f91006..ee82455f0 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -5,6 +5,29 @@
 import pytest
 
 from repo2docker.contentproviders import Mercurial
+from repo2docker.contentproviders.mercurial import (
+    HG_REQUIRED,
+    HG_EVOLVE_REQUIRED,
+    is_mercurial_available,
+)
+
+skip_if_no_hg = pytest.mark.skipif(
+    not HG_REQUIRED and not is_mercurial_available(),
+    reason="not HG_REQUIRED and Mercurial not available",
+)
+
+
+def is_evolve_available():
+    if not is_mercurial_available():
+        return False
+    output = subprocess.getoutput("hg version -v")
+    return " evolve " in output
+
+
+EVOLVE_AVAILABLE = is_evolve_available()
+
+if HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE:
+    raise RuntimeError("HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE")
 
 
 def _add_content_to_hg(repo_dir):
@@ -16,6 +39,14 @@ def _add_content_to_hg(repo_dir):
     subprocess.check_call(["hg", "add", "test"], cwd=repo_dir)
     subprocess.check_call(["hg", "commit", "-m", "Test commit"], cwd=repo_dir)
 
+    if EVOLVE_AVAILABLE:
+        subprocess.check_call(["hg", "topic", "test-topic"], cwd=repo_dir)
+        subprocess.check_call(
+            ["hg", "commit", "-m", "Test commit in topic test-topic"],
+            cwd=repo_dir,
+        )
+        subprocess.check_call(["hg", "up", "default"], cwd=repo_dir)
+
 
 def _get_node_id(repo_dir):
     """Get repository's current commit node ID (currently SHA1)."""
@@ -46,6 +77,7 @@ def hg_repo_with_content(hg_repo):
     yield hg_repo, node_id
 
 
+@skip_if_no_hg
 def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     mercurial = Mercurial()
     assert mercurial.detect("this-is-not-a-directory") is None
@@ -58,6 +90,7 @@ def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     assert mercurial.detect(hg_repo) == {"repo": hg_repo, "ref": None}
 
 
+@skip_if_no_hg
 def test_clone(hg_repo_with_content):
     """Test simple hg clone to a target dir"""
     upstream, node_id = hg_repo_with_content
@@ -72,9 +105,10 @@ def test_clone(hg_repo_with_content):
         assert mercurial.content_id == node_id
 
 
+@skip_if_no_hg
 def test_bad_ref(hg_repo_with_content):
     """
-    Test trying to checkout a ref that doesn't exist
+    Test trying to update to a ref that doesn't exist
     """
     upstream, node_id = hg_repo_with_content
     with TemporaryDirectory() as clone_dir:
@@ -82,3 +116,30 @@ def test_bad_ref(hg_repo_with_content):
         with pytest.raises(ValueError):
             for _ in Mercurial().fetch(spec, clone_dir):
                 pass
+
+
+@pytest.mark.skipif(
+    not HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE,
+    reason="not HG_EVOLVE_REQUIRED and hg-evolve not available",
+)
+@skip_if_no_hg
+def test_ref_topic(hg_repo_with_content):
+    """
+    Test trying to update to a topic
+    """
+    upstream, node_id = hg_repo_with_content
+    node_id = subprocess.Popen(
+        ["hg", "identify", "-i", "-r", "topic(test-topic)"],
+        stdout=subprocess.PIPE,
+        cwd=upstream,
+    )
+    node_id = node_id.stdout.read().decode().strip()
+
+    with TemporaryDirectory() as clone_dir:
+        spec = {"repo": upstream, "ref": "test-topic"}
+        mercurial = Mercurial()
+        for _ in mercurial.fetch(spec, clone_dir):
+            pass
+        assert (Path(clone_dir) / "test").exists()
+
+        assert mercurial.content_id == node_id

From 3cdde89328aadddc859b64130ea4c1f4cac337cb Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Thu, 10 Sep 2020 21:48:46 +0200
Subject: [PATCH 10/13] By default run Mercurial tests + enable the topic
 extension from code (no need for config file)

---
 .github/workflows/test.yml                    |  1 +
 Dockerfile                                    |  3 +-
 repo2docker/contentproviders/mercurial.py     | 42 ++---------
 tests/unit/contentproviders/test_mercurial.py | 70 +++++++++++--------
 4 files changed, 47 insertions(+), 69 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ba1a80003..973225236 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -106,6 +106,7 @@ jobs:
           python setup.py bdist_wheel
           pip install dist/*.whl
           pip freeze
+          pip install mercurial hg-evolve
 
       - name: "Run tests"
         run: |
diff --git a/Dockerfile b/Dockerfile
index 023d148b9..54f5a24e3 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -18,9 +18,8 @@ FROM alpine:${ALPINE_VERSION}
 # install python, git, bash, mercurial
 RUN apk add --no-cache git git-lfs python3 py-pip bash docker mercurial
 
-# install and activate the evolve and topic Mercurial extensions
+# install hg-evolve (Mercurial extensions)
 RUN pip3 install hg-evolve --user --no-cache-dir
-RUN mkdir -p /etc/mercurial/hgrc.d && echo -e "[extensions]\nevolve =\ntopic =\n" >  /etc/mercurial/hgrc.d/evolve.rc
 
 # install repo2docker
 COPY --from=0 /tmp/wheelhouse /tmp/wheelhouse
diff --git a/repo2docker/contentproviders/mercurial.py b/repo2docker/contentproviders/mercurial.py
index 3164b22e0..168682190 100644
--- a/repo2docker/contentproviders/mercurial.py
+++ b/repo2docker/contentproviders/mercurial.py
@@ -1,38 +1,9 @@
 import subprocess
-import os
-from distutils.util import strtobool
 
 from .base import ContentProvider, ContentProviderException
 from ..utils import execute_cmd
 
-HG_EVOLVE_REQUIRED = strtobool(
-    os.environ.get("REPO2DOCKER_HG_EVOLVE_REQUIRED", "False")
-)
-
-if HG_EVOLVE_REQUIRED:
-    if "REPO2DOCKER_HG_REQUIRED" in os.environ:
-        HG_REQUIRED = strtobool(os.environ["REPO2DOCKER_HG_REQUIRED"])
-        if not HG_REQUIRED:
-            raise ValueError(
-                "Incompatible values for environment variables "
-                "REPO2DOCKER_HG_EVOLVE_REQUIRED=1 and REPO2DOCKER_HG_REQUIRED=0"
-            )
-    else:
-        HG_REQUIRED = True
-else:
-    HG_REQUIRED = strtobool(os.environ.get("REPO2DOCKER_HG_REQUIRED", "False"))
-
-
-def is_mercurial_available():
-    try:
-        subprocess.check_output(["hg", "version"])
-    except subprocess.CalledProcessError:
-        return False
-    return True
-
-
-if HG_REQUIRED and not is_mercurial_available():
-    raise RuntimeError("REPO2DOCKER_HG_REQUIRED but the command `hg` is not available")
+args_enabling_topic = ["--config", "extensions.topic="]
 
 
 class Mercurial(ContentProvider):
@@ -43,12 +14,11 @@ def detect(self, source, ref=None, extra_args=None):
             return None
         try:
             subprocess.check_output(
-                ["hg", "identify", source, "--config", "extensions.hggit=!"],
+                ["hg", "identify", source, "--config", "extensions.hggit=!"]
+                + args_enabling_topic,
                 stderr=subprocess.DEVNULL,
             )
         except subprocess.CalledProcessError:
-            # warning: if hg is not installed and `not HG_REQUIRED`,
-            # we return None even for a hg repo
             return None
 
         return {"repo": source, "ref": ref}
@@ -66,7 +36,7 @@ def fetch(self, spec, output_dir, yield_output=False):
                 output_dir,
                 "--config",
                 "phases.publish=False",
-            ]
+            ] + args_enabling_topic
             if ref is not None:
                 # don't update so the clone will include an empty working
                 # directory, the given ref will be updated out later
@@ -85,7 +55,7 @@ def fetch(self, spec, output_dir, yield_output=False):
         if ref is not None:
             try:
                 for line in execute_cmd(
-                    ["hg", "update", "--clean", ref],
+                    ["hg", "update", "--clean", ref] + args_enabling_topic,
                     cwd=output_dir,
                     capture=yield_output,
                 ):
@@ -96,7 +66,7 @@ def fetch(self, spec, output_dir, yield_output=False):
                 )
                 raise ValueError("Failed to update to ref {}".format(ref))
 
-        cmd = ["hg", "identify", "-i"]
+        cmd = ["hg", "identify", "-i"] + args_enabling_topic
         sha1 = subprocess.Popen(cmd, stdout=subprocess.PIPE, cwd=output_dir)
         self._node_id = sha1.stdout.read().decode().strip()
 
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index ee82455f0..2b1b48f33 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -1,33 +1,42 @@
 from pathlib import Path
 import subprocess
 from tempfile import TemporaryDirectory
+import os
+from distutils.util import strtobool
 
 import pytest
 
 from repo2docker.contentproviders import Mercurial
-from repo2docker.contentproviders.mercurial import (
-    HG_REQUIRED,
-    HG_EVOLVE_REQUIRED,
-    is_mercurial_available,
+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 = pytest.mark.skipif(
-    not HG_REQUIRED and not is_mercurial_available(),
-    reason="not HG_REQUIRED and Mercurial not available",
+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 = []
 
-def is_evolve_available():
-    if not is_mercurial_available():
-        return False
-    output = subprocess.getoutput("hg version -v")
-    return " evolve " in output
 
+@skip_if_no_hg_tests
+def test_if_mercurial_is_available():
+    subprocess.check_output(["hg", "version"])
 
-EVOLVE_AVAILABLE = is_evolve_available()
 
-if HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE:
-    raise RuntimeError("HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE")
+@skip_if_no_evolve_tests
+def test_if_topic_is_available():
+    """Check that the topic extension can be enabled"""
+    output = subprocess.getoutput("hg version -v --config extensions.topic=")
+    assert "failed to import extension topic" not in output
 
 
 def _add_content_to_hg(repo_dir):
@@ -39,19 +48,22 @@ def _add_content_to_hg(repo_dir):
     subprocess.check_call(["hg", "add", "test"], cwd=repo_dir)
     subprocess.check_call(["hg", "commit", "-m", "Test commit"], cwd=repo_dir)
 
-    if EVOLVE_AVAILABLE:
-        subprocess.check_call(["hg", "topic", "test-topic"], cwd=repo_dir)
-        subprocess.check_call(
-            ["hg", "commit", "-m", "Test commit in topic test-topic"],
-            cwd=repo_dir,
-        )
-        subprocess.check_call(["hg", "up", "default"], 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"])
 
 
 def _get_node_id(repo_dir):
     """Get repository's current commit node ID (currently SHA1)."""
     node_id = subprocess.Popen(
-        ["hg", "identify", "-i"], stdout=subprocess.PIPE, cwd=repo_dir
+        ["hg", "identify", "-i"] + args_enabling_topic,
+        stdout=subprocess.PIPE,
+        cwd=repo_dir,
     )
     return node_id.stdout.read().decode().strip()
 
@@ -77,7 +89,7 @@ def hg_repo_with_content(hg_repo):
     yield hg_repo, node_id
 
 
-@skip_if_no_hg
+@skip_if_no_hg_tests
 def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     mercurial = Mercurial()
     assert mercurial.detect("this-is-not-a-directory") is None
@@ -90,7 +102,7 @@ def test_detect_mercurial(hg_repo_with_content, repo_with_content):
     assert mercurial.detect(hg_repo) == {"repo": hg_repo, "ref": None}
 
 
-@skip_if_no_hg
+@skip_if_no_hg_tests
 def test_clone(hg_repo_with_content):
     """Test simple hg clone to a target dir"""
     upstream, node_id = hg_repo_with_content
@@ -105,7 +117,7 @@ def test_clone(hg_repo_with_content):
         assert mercurial.content_id == node_id
 
 
-@skip_if_no_hg
+@skip_if_no_hg_tests
 def test_bad_ref(hg_repo_with_content):
     """
     Test trying to update to a ref that doesn't exist
@@ -118,11 +130,7 @@ def test_bad_ref(hg_repo_with_content):
                 pass
 
 
-@pytest.mark.skipif(
-    not HG_EVOLVE_REQUIRED and not EVOLVE_AVAILABLE,
-    reason="not HG_EVOLVE_REQUIRED and hg-evolve not available",
-)
-@skip_if_no_hg
+@skip_if_no_evolve_tests
 def test_ref_topic(hg_repo_with_content):
     """
     Test trying to update to a topic

From 64633bbcbca93ad5aef8e38ea999a17f53e35df3 Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Fri, 11 Sep 2020 00:10:55 +0200
Subject: [PATCH 11/13] Documentation about Mercurial support

---
 docs/source/contributing/tasks.md             | 10 +++++++---
 docs/source/install.rst                       | 11 +++++++++++
 tests/unit/contentproviders/test_mercurial.py |  9 +++++++++
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/docs/source/contributing/tasks.md b/docs/source/contributing/tasks.md
index 3f6375e0a..0e7f304b3 100644
--- a/docs/source/contributing/tasks.md
+++ b/docs/source/contributing/tasks.md
@@ -23,11 +23,15 @@ If you want to run a specific test, you can do so with:
 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``.
+
 ### Troubleshooting Tests
 
 Some of the tests have non-python requirements for your development machine. They are:
 
-- `git-lfs` must be installed ([instructions](https://github.com/git-lfs/git-lfs)). It need not be activated -- there is no need to run the `git lfs install` command. It just needs to be available to the test suite. 
+- `git-lfs` must be installed ([instructions](https://github.com/git-lfs/git-lfs)). It need not be activated -- there is no need to run the `git lfs install` command. It just needs to be available to the test suite.
    - If your test failure messages include "`git-lfs filter-process: git-lfs: command not found`", this step should address the problem.
 
 - Minimum Docker Image size of 128GB is required. If you are not running docker on a linux OS, you may need to expand the runtime image size for your installation. See Docker's instructions for [macOS](https://docs.docker.com/docker-for-mac/space/) or [Windows 10](https://docs.docker.com/docker-for-windows/#resources) for more information.
@@ -218,7 +222,7 @@ files accordingly.
 ## Compare generated Dockerfiles between repo2docker versions
 
 For larger refactorings it can be useful to check that the generated Dockerfiles match
-between an older version of r2d and the current version. The following shell script 
+between an older version of r2d and the current version. The following shell script
 automates this test.
 
 ```bash
@@ -231,7 +235,7 @@ basename="dockerfilediff"
 diff_r2d_dockerfiles_with_version () {
     docker run --rm -t -v "$(pwd)":"$(pwd)" --user 1000 jupyterhub/repo2docker:"$1" jupyter-repo2docker --no-build --debug "$(pwd)" &> "$basename"."$1"
     jupyter-repo2docker --no-build --debug "$(pwd)" &> "$basename"."$current_version"
-    
+
     # remove first line logging the path
     sed -i '/^\[Repo2Docker\]/d' "$basename"."$1"
     sed -i '/^\[Repo2Docker\]/d' "$basename"."$current_version"
diff --git a/docs/source/install.rst b/docs/source/install.rst
index 48b31a50c..615a7ce7a 100644
--- a/docs/source/install.rst
+++ b/docs/source/install.rst
@@ -22,6 +22,17 @@ The `BinderHub <https://binderhub.readthedocs.io/>`_ helm chart uses version
 `helm chart <https://github.com/jupyterhub/binderhub/blob/master/helm-chart/binderhub/values.yaml#L167>`_
 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).
+
 Installing with ``pip``
 -----------------------
 
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index 2b1b48f33..6cbc1dc8d 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -29,6 +29,11 @@
 
 @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
+    REPO2DOCKER_SKIP_HG_TESTS.
+    """
     subprocess.check_output(["hg", "version"])
 
 
@@ -134,6 +139,10 @@ def test_bad_ref(hg_repo_with_content):
 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.
+
     """
     upstream, node_id = hg_repo_with_content
     node_id = subprocess.Popen(

From 39081b70c39dd9b4c91fb28cd3c8cd642551d27e Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Fri, 11 Sep 2020 00:36:28 +0200
Subject: [PATCH 12/13] Fix bug hg id topic

---
 tests/unit/contentproviders/test_mercurial.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index 6cbc1dc8d..af3b7fd46 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -146,7 +146,7 @@ def test_ref_topic(hg_repo_with_content):
     """
     upstream, node_id = hg_repo_with_content
     node_id = subprocess.Popen(
-        ["hg", "identify", "-i", "-r", "topic(test-topic)"],
+        ["hg", "identify", "-i", "-r", "topic(test-topic)"] + args_enabling_topic,
         stdout=subprocess.PIPE,
         cwd=upstream,
     )

From 05002a4177371ec4662eef9f1d39b29f9d047b26 Mon Sep 17 00:00:00 2001
From: paugier <pierre.augier@univ-grenoble-alpes.fr>
Date: Mon, 14 Sep 2020 14:05:52 +0200
Subject: [PATCH 13/13] hg-evolve required for Mercurial support (simpler)

---
 .github/workflows/test.yml                    |  4 +-
 docs/source/contributing/tasks.md             |  4 +-
 docs/source/install.rst                       | 20 ++++++----
 tests/unit/contentproviders/test_mercurial.py | 37 ++++++-------------
 4 files changed, 30 insertions(+), 35 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 973225236..385d82d0f 100644
--- a/.github/workflows/test.yml
+++ b/.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: |
diff --git a/docs/source/contributing/tasks.md b/docs/source/contributing/tasks.md
index 0e7f304b3..a1f6a34d0 100644
--- a/docs/source/contributing/tasks.md
+++ b/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
 
diff --git a/docs/source/install.rst b/docs/source/install.rst
index 615a7ce7a..09aff8f21 100644
--- a/docs/source/install.rst
+++ b/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``
 -----------------------
diff --git a/tests/unit/contentproviders/test_mercurial.py b/tests/unit/contentproviders/test_mercurial.py
index af3b7fd46..25257bf39 100644
--- a/tests/unit/contentproviders/test_mercurial.py
+++ b/tests/unit/contentproviders/test_mercurial.py
@@ -10,34 +10,24 @@
 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