perf(ci): Reduce installation time in CI

Poetry caches artifacts and metadata into
its cache directory to speed things up
in subsequent installations.

Previously we were caching the virtualenv,
but Poetry was still taking a lot of time
to redownload the artifacts to build the
metadata.

Now we cache everything, so Poetry is very
fast both for locking
and installing dependencies.

project/.github/workflows/ci.yml

@@ -13,10 +13,17 @@ defaults:
     shell: bash
 
 env:
-  LANG: "en_US.utf-8"
-  LC_ALL: "en_US.utf-8"
-  POETRY_VIRTUALENVS_IN_PROJECT: "true"
-  PYTHONIOENCODING: "UTF-8"
+  LANG: en_US.utf-8
+  LC_ALL: en_US.utf-8
+  PYTHONIOENCODING: UTF-8
+
+  # To fix an error when running Poetry on Windows
+  # (https://github.com/python-poetry/poetry/issues/2629),
+  # we set Poetry's cache directory to .poetry_cache in the current directory.
+  # It makes it easier to later remove the virtualenv when it's broken.
+  # Absolute path is necessary to avoid this issue:
+  # https://github.com/python-poetry/poetry/issues/3049
+  POETRY_CACHE_DIR: ${{ github.workspace }}/.poetry_cache
 
 jobs:
 
@@ -33,17 +40,17 @@ jobs:
       with:
         python-version: 3.8
 
+    - name: Set up Poetry
+      run: pip install poetry
+
     - name: Set up the cache
       uses: actions/cache@v1
       with:
-        path: .venv
-        key: quality-venv-cache
+        path: .poetry_cache
+        key: quality-poetry-cache
 
     - name: Set up the project
-      run: |
-        pip install poetry
-        poetry install -vvv || { rm -rf .venv; poetry install -vvv; }
-        poetry update
+      run: poetry install -vv
 
     - name: Check if the documentation builds correctly
       run: poetry run duty check-docs
@@ -77,17 +84,17 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
 
+    - name: Set up Poetry
+      run: pip install poetry
+
     - name: Set up the cache
       uses: actions/cache@v1
       with:
-        path: .venv
-        key: tests-venv-cache-${{ matrix.os }}-py${{ matrix.python-version }}
+        path: .poetry_cache
+        key: tests-poetry-cache-${{ matrix.os }}-py${{ matrix.python-version }}
 
     - name: Set up the project
-      run: |
-        pip install poetry
-        poetry install -vvv || { rm -rf .venv; poetry install -vvv; }
-        poetry update
+      run: poetry install -vv || { rm -rf .poetry_cache/virtualenvs/*; poetry install -vv; }
 
     - name: Run the test suite
       run: poetry run duty test