try GH actions cache (#1558)

* spec cache

* spec cache

* trigger

* extras

* checkout

.github/workflows/ci-testing.yml

@@ -1,6 +1,6 @@
 name: CI testing
 
-# https://help.github.com/en/actions/reference/events-that-trigger-workflows
+# see: https://help.github.com/en/actions/reference/events-that-trigger-workflows
 on:
   # Trigger the workflow on push or pull request,
   # but only for the master branch
@@ -60,22 +60,20 @@ jobs:
         python -c "req = open('requirements.txt').read().replace('>', '=') ; open('requirements.txt', 'w').write(req)"
         python -c "req = open('requirements-extra.txt').read().replace('>', '=') ; open('requirements-extra.txt', 'w').write(req)"
 
-    - name: Cache pip
-      uses: actions/cache@v1
-      with:
-        path: ~/.cache/pip # This path is specific to Ubuntu
-        # Look to see if there is a cache hit for the corresponding requirements file
-        key: ${{ runner.os }}-pip-${{ matrix.python-version }}-${{ hashFiles('requirements.txt') }}
-        restore-keys: |
-          ${{ runner.os }}-pip-${{ matrix.python-version }}-
-          ${{ runner.os }}-${{ matrix.python-version }}-
+    # Note: This uses an internal pip API and may not always work
+    # https://github.com/actions/cache/blob/master/examples.md#multiple-oss-in-a-workflow
+    - name: Get pip cache
+        id: pip-cache
+        run: |
+          python -c "from pip._internal.locations import USER_CACHE_DIR; print('::set-output name=dir::' + USER_CACHE_DIR)"
 
-    - name: Cache datasets
-      uses: actions/cache@v1
+    - name: Cache pip
+    - uses: actions/cache@v1
       with:
-        path: tests/Datasets # This path is specific to Ubuntu
-        # Look to see if there is a cache hit for the corresponding requirements file
-        key: mnist-dataset
+        path: ${{ steps.pip-cache.outputs.dir }}
+        key: ${{ runner.os }}-${{ matrix.python-version }}-pip-${{ hashFiles('requirements.txt') }}-${{ hashFiles('requirements-extra.txt') }}
+        restore-keys: |
+          ${{ runner.os }}-${{ matrix.python-version }}-pip-
 
     - name: Install dependencies
       run: |
@@ -88,6 +86,13 @@ jobs:
         pip list
       shell: bash
 
+    - name: Cache datasets
+      uses: actions/cache@v1
+      with:
+        path: tests/Datasets # This path is specific to Ubuntu
+        # Look to see if there is a cache hit for the corresponding requirements file
+        key: mnist-dataset
+
     - name: Tests
       # env:
       #   TOXENV: py${{ matrix.python-version }}