Build: remove support for MkDocs <= 0.17.3

We want to keep deprecating old feature flags we don't want to support forever.
In particular, those that keep our users using pretty old versions of doctools
and freeze them in a status that's hard to maintain.

This PR removes the `DEFATUL_TO_MKDOCS_0_17_3` feature flag and always install
the latest `mkdocs` version. Note this feature flag has `default_true=True` for
those projects created _before 2019-04-03_.

I did a small DB query and found:

```python
>>> Project.objects.filter(pub_date__lt=timezone.datetime(2019, 4, 3),
documentation_type='mkdocs').count()
7529
```

However, note we don't know if these projects are pinning a version of MkDocs,
so we don't exactly know how many of those are using this feature. However, it
gives us a maximum number at least.

On the other hand, taking a look at Metabase, using the build data from the past
6 months I found that we only have 293 projects:
https://ethicalads.metabaseapp.com/question/218-projects-using-mkdocs-group-by-version

Related #9779

Author: humitos

readthedocs/doc_builder/backends/mkdocs.py

@@ -157,13 +157,7 @@ def append_conf(self):
             )
 
         user_config['docs_dir'] = docs_dir
-
-        # MkDocs <=0.17.x doesn't support absolute paths,
-        # it needs one with a full domain.
-        if self.project.has_feature(Feature.DEFAULT_TO_MKDOCS_0_17_3):
-            static_url = get_absolute_static_url()
-        else:
-            static_url = self.project.proxied_static_path
+        static_url = self.project.proxied_static_path
 
         # Set mkdocs config values.
         extra_assets = {

readthedocs/doc_builder/python_environments.py

@@ -259,13 +259,7 @@ def _install_old_requirements(self, pip_install_cmd):
         )
 
         if self.config.doctype == 'mkdocs':
-            requirements.append(
-                self.project.get_feature_value(
-                    Feature.DEFAULT_TO_MKDOCS_0_17_3,
-                    positive='mkdocs==0.17.3',
-                    negative="mkdocs",
-                )
-            )
+            requirements.append("mkdocs")
         else:
             requirements.extend(
                 [

readthedocs/projects/models.py

@@ -1936,7 +1936,6 @@ def add_features(sender, **kwargs):
     USE_NEW_PIP_RESOLVER = 'use_new_pip_resolver'
     DONT_INSTALL_LATEST_PIP = 'dont_install_latest_pip'
     USE_SPHINX_LATEST = 'use_sphinx_latest'
-    DEFAULT_TO_MKDOCS_0_17_3 = 'default_to_mkdocs_0_17_3'
     USE_SPHINX_RTD_EXT_LATEST = 'rtd_sphinx_ext_latest'
     INSTALL_LATEST_CORE_REQUIREMENTS = "install_latest_core_requirements"
 
@@ -2042,10 +2041,6 @@ def add_features(sender, **kwargs):
             _("Build: Don't install the latest version of pip"),
         ),
         (USE_SPHINX_LATEST, _("Sphinx: Use latest version of Sphinx")),
-        (
-            DEFAULT_TO_MKDOCS_0_17_3,
-            _("MkDOcs: Install mkdocs 0.17.3 by default"),
-        ),
         (
             USE_SPHINX_RTD_EXT_LATEST,
             _("Sphinx: Use latest version of the Read the Docs Sphinx extension"),

readthedocs/rtd_tests/tests/test_doc_builder.py

@@ -528,69 +528,6 @@ def test_append_conf_existing_yaml_on_root(self, checkout_path, run):
             "mkdocs",
         )
 
-    @patch("readthedocs.doc_builder.base.BaseBuilder.run")
-    @patch("readthedocs.projects.models.Project.checkout_path")
-    def test_append_conf_mkdocs_07x(self, checkout_path, run):
-        get(
-            Feature,
-            feature_id=Feature.DEFAULT_TO_MKDOCS_0_17_3,
-            projects=[self.project],
-        )
-        tmpdir = tempfile.mkdtemp()
-        os.mkdir(os.path.join(tmpdir, "docs"))
-        yaml_file = os.path.join(tmpdir, "mkdocs.yml")
-        yaml.safe_dump(
-            {
-                "site_name": "mkdocs",
-                "google_analytics": ["UA-1234-5", "mkdocs.org"],
-                "docs_dir": "docs",
-            },
-            open(yaml_file, "w"),
-        )
-        checkout_path.return_value = tmpdir
-
-        python_env = Virtualenv(
-            version=self.version,
-            build_env=self.build_env,
-            config=None,
-        )
-        builder = MkdocsHTML(
-            build_env=self.build_env,
-            python_env=python_env,
-        )
-        with override_settings(DOCROOT=tmpdir):
-            builder.append_conf()
-
-        run.assert_called_with('cat', 'mkdocs.yml', cwd=mock.ANY)
-
-        config = yaml_load_safely(open(yaml_file))
-        self.assertEqual(
-            config['docs_dir'],
-            'docs',
-        )
-        self.assertEqual(
-            config['extra_css'],
-            [
-                'http://readthedocs.org/static/css/badge_only.css',
-                'http://readthedocs.org/static/css/readthedocs-doc-embed.css',
-            ],
-        )
-        self.assertEqual(
-            config['extra_javascript'],
-            [
-                'readthedocs-data.js',
-                'http://readthedocs.org/static/core/js/readthedocs-doc-embed.js',
-                'http://readthedocs.org/static/javascript/readthedocs-analytics.js',
-            ],
-        )
-        self.assertIsNone(
-            config['google_analytics'],
-        )
-        self.assertEqual(
-            config['site_name'],
-            'mkdocs',
-        )
-
     @patch('readthedocs.doc_builder.base.BaseBuilder.run')
     @patch('readthedocs.projects.models.Project.checkout_path')
     def test_append_conf_existing_yaml_on_root_with_invalid_setting(self, checkout_path, run):