cvs tests: don't use dateutil at all

`dateutil.parser` was an optional dependency for CVS tests. It was failing on macOS
beacuse the dateutil types were not being installed, and mypy was failing *even when the
CVS tests were skipped*. This seems like it was an oversight on macOS --
`types-dateutil-parser` was not installed there, though it was on Linux unit tests.

It takes 6 lines of YAML and some weird test-skipping logic to get `python-dateutil` and
`types-python-dateutil` installed in all the tests where we need them, but it only takes
4 lines of code to write the date parser we need for CVS, so I just did that instead.

Note that CVS date format can vary from system to system, but it seems like it's always
pretty similar for the parts we care about.

- [x] Replace dateutil.parser with a simpler date regex
- [x] Lose the dependency on `dateutil.parser`

.github/workflows/unit_tests.yaml

@@ -39,7 +39,7 @@ jobs:
         python-version: 3.9
     - name: Install Python packages
       run: |
-        pip install --upgrade pip six setuptools flake8 isort>=4.3.5 mypy>=0.800 black types-six types-python-dateutil
+        pip install --upgrade pip six setuptools flake8 isort>=4.3.5 mypy>=0.800 black types-six
     - name: Setup git configuration
       run: |
         # Need this for the git tests to succeed.
@@ -62,7 +62,7 @@ jobs:
         sudo apt-get install -y coreutils ninja-build graphviz
     - name: Install Python packages
       run: |
-        pip install --upgrade pip six setuptools python-dateutil
+        pip install --upgrade pip six setuptools
         pip install --upgrade -r lib/spack/docs/requirements.txt
     - name: Build documentation
       run: |
@@ -137,7 +137,7 @@ jobs:
           sudo apt-get -y install zlib1g-dev libdw-dev libiberty-dev
     - name: Install Python packages
       run: |
-          pip install --upgrade pip python-dateutil six setuptools codecov coverage
+          pip install --upgrade pip six setuptools codecov coverage
     - name: Setup git configuration
       run: |
           # Need this for the git tests to succeed.
@@ -205,7 +205,7 @@ jobs:
           sudo apt-get -y install zlib1g-dev libdw-dev libiberty-dev
     - name: Install Python packages
       run: |
-          pip install --upgrade pip six setuptools codecov coverage python-dateutil
+          pip install --upgrade pip six setuptools codecov coverage
     - name: Setup git configuration
       run: |
           # Need this for the git tests to succeed.
@@ -326,7 +326,7 @@ jobs:
           make -C ${KCOV_ROOT}/build && sudo  make -C ${KCOV_ROOT}/build install
     - name: Install Python packages
       run: |
-          pip install --upgrade pip six setuptools codecov coverage clingo python-dateutil
+          pip install --upgrade pip six setuptools codecov coverage clingo
     - name: Setup git configuration
       run: |
           # Need this for the git tests to succeed.
@@ -371,7 +371,6 @@ jobs:
           pip install --upgrade pip six setuptools
           pip install --upgrade codecov coverage
           pip install --upgrade flake8 isort>=4.3.5 pep8-naming mypy>=0.800
-          pip install --upgrade python-dateutil
     - name: Setup Homebrew packages
       run: |
         brew install dash fish gcc gnupg2 kcov

lib/spack/spack/test/conftest.py

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 import collections
+import datetime
 import errno
 import inspect
 import itertools
@@ -15,21 +16,13 @@
 import tempfile
 import xml.etree.ElementTree
 
-try:
-    # CVS outputs dates in different formats on different systems. We are using
-    # the dateutil package to parse these dates. This package does not exist
-    # for Python <2.7. That means that we cannot test checkouts "by date" for
-    # CVS respositories. (We can still use CVS repos with all features, only
-    # our tests break.)
-    from dateutil.parser import parse as parse_date
-except ImportError:
-    def parse_date(string):  # type: ignore
-        pytest.skip("dateutil package not available")
+import py
+import pytest
 
 import archspec.cpu.microarchitecture
 import archspec.cpu.schema
-import py
-import pytest
+
+from llnl.util.filesystem import mkdirp, remove_linked_tree, working_dir
 
 import spack.architecture
 import spack.caches
@@ -49,9 +42,7 @@ def parse_date(string):  # type: ignore
 import spack.util.executable
 import spack.util.gpg
 import spack.util.spack_yaml as syaml
-from llnl.util.filesystem import mkdirp, remove_linked_tree, working_dir
-from spack.fetch_strategy import FetchError
-from spack.fetch_strategy import FetchStrategyComposite, URLFetchStrategy
+from spack.fetch_strategy import FetchError, FetchStrategyComposite, URLFetchStrategy
 from spack.util.pattern import Bunch
 
 
@@ -917,6 +908,19 @@ def mock_archive(request, tmpdir_factory):
         expanded_archive_basedir=spack.stage._source_path_subdir)
 
 
+def _parse_cvs_date(line):
+    """Turn a CVS log date into a datetime.datetime"""
+    # dates in CVS logs can have slashes or dashes and may omit the time zone:
+    # date: 2021-07-07 02:43:33 -0700;  ...
+    # date: 2021-07-07 02:43:33;  ...
+    # date: 2021/07/07 02:43:33;  ...
+    m = re.search(r'date:\s+(\d+)[/-](\d+)[/-](\d+)\s+(\d+):(\d+):(\d+)', line)
+    if not m:
+        return None
+    year, month, day, hour, minute, second = [int(g) for g in m.groups()]
+    return datetime.datetime(year, month, day, hour, minute, second)
+
+
 @pytest.fixture(scope='session')
 def mock_cvs_repository(tmpdir_factory):
     """Creates a very simple CVS repository with two commits and a branch."""
@@ -943,9 +947,8 @@ def get_cvs_timestamp(output):
         """Find the most recent CVS time stamp in a `cvs log` output"""
         latest_timestamp = None
         for line in output.splitlines():
-            m = re.search(r'date:\s+([^;]*);', line)
-            if m:
-                timestamp = parse_date(m.group(1))
+            timestamp = _parse_cvs_date(line)
+            if timestamp:
                 if latest_timestamp is None:
                     latest_timestamp = timestamp
                 else: