appveyor: run test on multiple pythons versions and also on linux

Some checks of the example extensions only run on windows, because it
was not adapted.

appveyor.yml

@@ -32,18 +32,63 @@ on_failure:
         if ($fileobj) { cat $fileobj; };
       }
 
-image:
-  - Visual Studio 2017
+stack: python %PYTHON%
+
+environment:
+  APPVEYOR_YML_DISABLE_PS_LINUX: true
+  PYTHONEXE: python
+  matrix:
+    - APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu
+      TOXENV: py35
+      PYTHON: "3.5"
+    - APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu
+      TOXENV: py36
+      PYTHON: "3.6"
+    - APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu
+      TOXENV: py37
+      PYTHON: "3.7"
+    - APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu
+      TOXENV: py38
+      PYTHON: "3.8"
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOXENV: py35
+      PYTHON: "3.5"
+      PYTHONDIR: C:\Python35-x64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOXENV: py36
+      PYTHON: "3.6"
+      PYTHONDIR: C:\Python36-x64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOXENV: py37
+      PYTHON: "3.7"
+      PYTHONDIR: C:\Python37-x64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOXENV: py38
+      PYTHON: "3.8"
+      PYTHONDIR: C:\Python38-x64
 
 # Configure the GitHub username and email for accessing the `pygls` release
 init:
   - git config --global user.name %OLL_GIT_USER_NAME%
   - git config --global user.email %OLL_GIT_EMAIL%
 
-# Install scripts. (runs after repo cloning)
 install:
-  - C:\Python35-x64\python.exe -m pip install --upgrade pip          # upgrade pip
+  - python -m pip install tox
 
+  # point to the same version as in `examples/json-extension/package.json`
+  - npm install -g [email protected]
+  - tsc --version
+
+  # install vsce module (for packaging our extension into a .vsix file)
+  - npm install -g [email protected]
+
+  # Output useful info for debugging.
+  - node --version
+  - npm --version
+
+  # Create a Visual Studio Code Extension
+build_script:
+  # Create a Visual Studio Code Extension (only on windows for now)
   - ps: >-
       $json_extension_client_json = (Get-Content -Raw -Path examples\json-extension\package.json | ConvertFrom-Json);
       $prefixed_version = "v" + $json_extension_client_json.version;
@@ -86,39 +131,18 @@ install:
       }
       echo "APPVEYOR_BUILD_VERSION - $env:APPVEYOR_BUILD_VERSION";
 
-  # install pygls and dev dependencies
-  - C:\Python35-x64\Scripts\pip.exe install .[dev]
-  - C:\Python35-x64\Scripts\pip.exe install .[test]
-  - C:\Python35-x64\Scripts\pip.exe install -e .
-
-  # point to the same version as in `examples/json-extension/package.json`
-  - npm install -g [email protected]
-  - tsc --version
-
-  # install vsce module (for packaging our extension into a .vsix file)
-  - npm install -g [email protected]
-
-  # Output useful info for debugging.
-  - node --version
-  - npm --version
-
-# Create a Visual Studio Code Extension
-build_script:
-  - cd examples\json-extension
+  - cd examples/json-extension
   # install extension-wide js dependencies
   - npm install --save-dev
   # run tslint
-  - .\node_modules\.bin\tslint client\src\*.ts
+  - ./node_modules/.bin/tslint client/src/*.ts
   # install our dependencies
-  - npm install                                                  # TODO: replace with `yarn install`
+  - npm install # TODO: replace with `yarn install`
   - tsc -p .
-
-  - cd ..\..\
+  - cd ../../
 
 test_script:
-  - C:\Python35-x64\Scripts\flake8.exe
-  - C:\Python35-x64\Scripts\bandit.exe -r ./pygls
-  - C:\Python35-x64\Scripts\pytest.exe
+  - python -m tox
 
 after_test:
   # check function
@@ -132,9 +156,9 @@ after_test:
       }
 
   # package up the json-extension client example VS Code extension
-  - ps: cd examples/json-extension/
+  - cd examples/json-extension/
   # check to see if key files will be in the `.vsix` package to be built
-  - vsce ls > packages.txt               rem list files to be packaged
+  - vsce ls > packages.txt
   # files/folders to be checked
   - ps: CheckInVsixPackage "package.json"
   - ps: CheckInVsixPackage "out/extension.js"
@@ -143,11 +167,10 @@ after_test:
   - ps: CheckInVsixPackage "server/server.py"
   # clean-up after ourselves (so these files don't end up in our `.vsix` package)
   - rm packages.txt
-  - rm results.txt
+  - ps: rm results.txt
   # passed the basic checks, should be good-to-go
-  - vsce package                         rem "normal" command line is on purpose
-
-  - ps: cd ../
+  - vsce package
+  - cd ..
 
 # Create extensions artifacts
 artifacts:

setup.cfg

@@ -1,5 +1,2 @@
 [flake8]
 max-line-length = 99
-
-[mypy]
-ignore_missing_imports = True

setup.py

@@ -39,7 +39,6 @@
 development = [
     "bandit==1.6.0",  # Run locally: bandit -r ./pygls
     "flake8==3.7.7",  # Run locally: flake8
-    "mypy==0.761",    # Run locally: mypy .
 ]
 
 docs_require = [