Update conda at startup

Behind a Feature flag, we can decide if we want to update the version
of ``conda`` from the system to its latest version available.

This allow us to use a new release of ``conda`` that is not released
under Miniconda yet, but also to not upgrade the Docker image just
because of a new release of Miniconda.

(the overhead added is around 60 seconds in total)

docs/guides/feature-flags.rst

@@ -14,6 +14,12 @@ Available Flags
 
 ``PIP_ALWAYS_UPGRADE``: :featureflags:`PIP_ALWAYS_UPGRADE`
 
+``UPDATE_CONDA_STARTUP``: :featureflags:`UPDATE_CONDA_STARTUP`
+
+The version of ``conda`` used in the build process could not be the latest one.
+This is because we use Miniconda, which its release process is a little more slow than ``conda`` itself.
+In case you prefer to use the latest ``conda`` version available, this is the flag you need.
+
 ``DONT_OVERWRITE_SPHINX_CONTEXT``: :featureflags:`DONT_OVERWRITE_SPHINX_CONTEXT`
 
 ``DONT_SHALLOW_CLONE``: :featureflags:`DONT_SHALLOW_CLONE`
@@ -22,4 +28,4 @@ The ``DONT_SHALLOW_CLONE`` flag is useful if your code accesses old commits duri
 e.g. python-reno release notes manager is known to do that
 (error message line would probably include one of old Git commit id's).
 
-``USE_TESTING_BUILD_IMAGE``: :featureflags:`USE_TESTING_BUILD_IMAGE`
+``USE_TESTING_BUILD_IMAGE``: :featureflags:`USE_TESTING_BUILD_IMAGE`

readthedocs/doc_builder/python_environments.py

@@ -405,6 +405,23 @@ class Conda(PythonEnvironment):
     def venv_path(self):
         return os.path.join(self.project.doc_path, 'conda', self.version.slug)
 
+    def _update_conda_startup(self):
+        """
+        Update ``conda`` before use it for the first time.
+
+        This makes the Docker image to use the latest version of ``conda``
+        independently the version of Miniconda that it has installed.
+        """
+        self.build_env.run(
+            'conda',
+            'update',
+            '--yes',
+            '--quiet',
+            '--name=base',
+            '--channel=defaults',
+            'conda',
+        )
+
     def setup_base(self):
         conda_env_path = os.path.join(self.project.doc_path, 'conda')
         version_path = os.path.join(conda_env_path, self.version.slug)
@@ -417,9 +434,13 @@ def setup_base(self):
                     'project': self.project.slug,
                     'version': self.version.slug,
                     'msg': 'Removing existing conda directory',
-                }
+                },
             )
             shutil.rmtree(version_path)
+
+        if self.project.has_feature(Feature.UPDATE_CONDA_STARTUP):
+            self._update_conda_startup()
+
         self.build_env.run(
             'conda',
             'env',

readthedocs/projects/models.py

@@ -1391,6 +1391,7 @@ def add_features(sender, **kwargs):
     SHARE_SPHINX_DOCTREE = 'share_sphinx_doctree'
     DEFAULT_TO_MKDOCS_0_17_3 = 'default_to_mkdocs_0_17_3'
     CLEAN_AFTER_BUILD = 'clean_after_build'
+    UPDATE_CONDA_STARTUP = 'upgrade_conda_startup'
 
     FEATURES = (
         (USE_SPHINX_LATEST, _('Use latest version of Sphinx')),
@@ -1431,6 +1432,10 @@ def add_features(sender, **kwargs):
             CLEAN_AFTER_BUILD,
             _('Clean all files used in the build process'),
         ),
+        (
+            UPDATE_CONDA_STARTUP,
+            _('Upgrade conda before creating the environment'),
+        ),
     )
 
     projects = models.ManyToManyField(