Deprecation: remove support for Sphinx 1.x

We are installing Sphinx 1.x based on a feature flag.
There are around 900 projects still using 1.x, based on
https://ethicalads.metabaseapp.com/question/250-projects-using-sphinx-timeserie

Note this feature flag is enabled by default for new projects starting on Oct.
20, 2020

We may need to send them an email about this and informing them how to create a
`requirements.txt` file to pin their dependencies. I don't think that the
migration to a config file v2 would enforce them to pin Sphinx.

Related #10342

Author: humitos

readthedocs/doc_builder/python_environments.py

@@ -219,27 +219,15 @@ def install_core_requirements(self):
         else:
             requirements.extend(
                 [
-                    self.project.get_feature_value(
-                        Feature.USE_SPHINX_LATEST,
-                        positive="sphinx",
-                        negative="sphinx<2",
-                    ),
-                    # If defaulting to Sphinx 2+, we need to push the latest theme
-                    # release as well. `<0.5.0` is not compatible with Sphinx 2+
-                    self.project.get_feature_value(
-                        Feature.USE_SPHINX_LATEST,
-                        positive="sphinx-rtd-theme",
-                        negative="sphinx-rtd-theme<0.5",
-                    ),
+                    "sphinx",
+                    "sphinx-rtd-theme",
                     self.project.get_feature_value(
                         Feature.USE_SPHINX_RTD_EXT_LATEST,
                         positive="readthedocs-sphinx-ext",
                         negative="readthedocs-sphinx-ext<2.3",
                     ),
                 ]
             )
-            if not self.project.has_feature(Feature.USE_SPHINX_LATEST):
-                requirements.extend(["jinja2<3.1.0"])
 
         cmd = copy.copy(pip_install_cmd)
         if self.config.python.use_system_site_packages:

readthedocs/projects/models.py

@@ -1895,7 +1895,6 @@ def add_features(sender, **kwargs):
     PIP_ALWAYS_UPGRADE = 'pip_always_upgrade'
     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_MKDOCS_LATEST = 'use_mkdocs_latest'
     USE_SPHINX_RTD_EXT_LATEST = 'rtd_sphinx_ext_latest'
@@ -2034,7 +2033,6 @@ def add_features(sender, **kwargs):
             DONT_INSTALL_LATEST_PIP,
             _("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"),

readthedocs/projects/tests/test_build_tasks.py

@@ -726,10 +726,9 @@ def test_build_commands_executed(
                     "alabaster>=0.7,<0.8,!=0.7.5",
                     "commonmark==0.9.1",
                     "recommonmark==0.5.0",
-                    "sphinx<2",
-                    "sphinx-rtd-theme<0.5",
+                    "sphinx",
+                    "sphinx-rtd-theme",
                     "readthedocs-sphinx-ext<2.3",
-                    "jinja2<3.1.0",
                     bin_path=mock.ANY,
                     cwd=mock.ANY,
                 ),

readthedocs/rtd_tests/tests/test_doc_building.py

@@ -412,7 +412,6 @@ def test_install_core_requirements_sphinx(self, checkout_path):
             "sphinx",
             "sphinx-rtd-theme",
             "readthedocs-sphinx-ext",
-            "jinja2<3.1.0",
         ]
 
         self.assertEqual(self.build_env_mock.run.call_count, 2)
@@ -450,7 +449,6 @@ def test_install_core_requirements_sphinx_system_packages_caps_setuptools(self,
             "sphinx",
             "sphinx-rtd-theme",
             "readthedocs-sphinx-ext",
-            "jinja2<3.1.0",
             "setuptools",
         ]