Add support for "packages" install key in v2 config

docs/config-file/v2.rst

@@ -228,6 +228,36 @@ With the previous settings, Read the Docs will execute the next commands:
    pip install .[docs]
    python package/setup.py install
 
+Extra dependencies
+''''''''''''''''''
+
+Install packages from a list of requirements.
+This allows you to declare dependencies in the ``.readthedocs.yml`` file instead of creating a separate file.
+
+:Key: `packages`
+:Type: ``list``
+:Default: ``[]``
+:Required: ``true``
+
+Example:
+
+.. code-block:: yaml
+
+   version: 2
+
+   python:
+     version: 3.7
+     install:
+       - packages:
+         - mkdocs-material
+         - Pygments
+
+With the previous settings, Read the Docs will execute the next commands:
+
+.. prompt:: bash $
+
+   pip install mkdocs-material Pygments
+
 python.system_packages
 ``````````````````````
 

readthedocs/config/config.py

@@ -19,6 +19,7 @@
     Python,
     PythonInstall,
     PythonInstallRequirements,
+    PythonInstallPackages,
     Search,
     Sphinx,
     Submodules,
@@ -833,6 +834,16 @@ def validate_python_install(self, index):
                     self.base_path,
                 )
                 python_install['requirements'] = requirements
+        elif 'packages' in raw_install:
+            packages_key = key + '.packages'
+            packages = self.pop_config(packages_key)
+            if not isinstance(packages, list):
+                self.error(
+                    packages_key,
+                    '"{}" key must be a list'.format(packages_key),
+                    code=PYTHON_INVALID,
+                )
+            python_install['packages'] = packages
         elif 'path' in raw_install:
             path_key = key + '.path'
             with self.catch_validation_error(path_key):
@@ -1112,6 +1123,8 @@ def python(self):
         for install in python['install']:
             if 'requirements' in install:
                 python_install.append(PythonInstallRequirements(**install),)
+            elif 'packages' in install:
+                python_install.append(PythonInstallPackages(**install),)
             elif 'path' in install:
                 python_install.append(PythonInstall(**install),)
         return Python(

readthedocs/config/models.py

@@ -41,6 +41,11 @@ class PythonInstallRequirements(Base):
     __slots__ = ('requirements',)
 
 
+class PythonInstallPackages(Base):
+
+    __slots__ = ('packages',)
+
+
 class PythonInstall(Base):
 
     __slots__ = (

readthedocs/config/tests/test_config.py

@@ -33,6 +33,7 @@
     Conda,
     PythonInstall,
     PythonInstallRequirements,
+    PythonInstallPackages,
 )
 from readthedocs.config.validation import (
     INVALID_BOOL,
@@ -1104,6 +1105,26 @@ def test_python_install_requirements_check_valid(self, tmpdir):
         assert isinstance(install[0], PythonInstallRequirements)
         assert install[0].requirements == 'requirements.txt'
 
+    def test_python_install_packages_check_valid(self, tmpdir):
+        build = self.get_build_config(
+            {
+                'python': {
+                    'install': [{
+                        'packages': [
+                            'package_a',
+                            'package_b >=3.0.0,<4.0.0',
+                        ],
+                    }],
+                },
+            },
+            source_file=str(tmpdir.join('readthedocs.yml')),
+        )
+        build.validate()
+        install = build.python.install
+        assert len(install) == 1
+        assert isinstance(install[0], PythonInstallPackages)
+        assert install[0].packages == ['package_a', 'package_b >=3.0.0,<4.0.0']
+
     def test_python_install_requirements_does_not_allow_null(self, tmpdir):
         build = self.get_build_config(
             {

readthedocs/doc_builder/python_environments.py

@@ -14,7 +14,11 @@
 
 from readthedocs.builds.constants import EXTERNAL
 from readthedocs.config import PIP, SETUPTOOLS, ParseError, parse as parse_yaml
-from readthedocs.config.models import PythonInstall, PythonInstallRequirements
+from readthedocs.config.models import (
+    PythonInstall,
+    PythonInstallRequirements,
+    PythonInstallPackages,
+)
 from readthedocs.doc_builder.config import load_yaml_config
 from readthedocs.doc_builder.constants import DOCKER_IMAGE
 from readthedocs.doc_builder.environments import DockerBuildEnvironment
@@ -77,6 +81,8 @@ def install_requirements(self):
         for install in self.config.python.install:
             if isinstance(install, PythonInstallRequirements):
                 self.install_requirements_file(install)
+            if isinstance(install, PythonInstallPackages):
+                self.install_packages_list(install)
             if isinstance(install, PythonInstall):
                 self.install_package(install)
 
@@ -430,6 +436,33 @@ def install_requirements_file(self, install):
                 bin_path=self.venv_bin(),
             )
 
+    def install_packages_list(self, install):
+        """
+        Install requirements from a list of strings using pip.
+
+        :param install: A instal object from the config module.
+        :type install: readthedocs.config.modules.PythonInstallPackages
+        """
+
+        args = [
+            self.venv_bin(filename='python'),
+            '-m',
+            'pip',
+            'install',
+        ]
+        if self.project.has_feature(Feature.PIP_ALWAYS_UPGRADE):
+            args += ['--upgrade']
+        args += [
+            '--exists-action=w',
+            *self._pip_cache_cmd_argument(),
+        ]
+        args += install.packages
+        self.build_env.run(
+            *args,
+            cwd=self.checkout_path,
+            bin_path=self.venv_bin(),
+        )
+
     def list_packages_installed(self):
         """List packages installed in pip."""
         args = [