CI: switch to GitHub Actions - step 4: test and coverage stage

This commit:
* Adds a GH Actions workflow for the CI checks which were previously run on Travis in the `test` and `coverage` stages.
* Removes the, now redundant, `.travis.yml` configuration.
* Updates the `.gitattributes` file.
* Updates the "Build Status" badge in the Readme to use the results from the GH `Test` Actions runs.
* Updates the "Tested on" badge in the Readme to include PHP 8.
* Updates a test file which mentioned Travis.

Notes:
1. Each of these jobs has a `needs` dependency on the previous job to prevent it from starting if the previous job failed.
    While not 100% necessary, this is just an efficiency tweak, being kind to the free service being offered as we know that if linting fails, the tests will fail etc.
2. The builds in the `test` and `coverage` jobs are essentially the same as previously run on Travis, though PHP 8.0 is now fully accounted for and `8.1` is set as `nightly`.
3. Previously, this "stage" would run on all `pull requests` events.
    The current set-up still does so, with one addition: pushes to `master` (merges) will now also use this workflow instead of the quicktest.
    This replaces the full run on tagging a release, meaning that thing will essentially be the same.
4. As there are a couple of jobs which are "allowed to fail" (`experimental` = true), the build status will unfortunately show as "failed", even though all non-experimental jobs have succeeded.
     This is a known issue in GHA: https://github.com/actions/toolkit/issues/399

.coveralls.yml

@@ -1,3 +1,2 @@
 coverage_clover: build/logs/clover.xml
 json_path: build/logs/coveralls-upload.json
-service_name: travis-ci

.gitattributes

@@ -8,7 +8,7 @@
 /.coveralls.yml export-ignore
 /.gitattributes export-ignore
 /.gitignore export-ignore
-/.travis.yml export-ignore
+/.github/ export-ignore
 /phpcs.xml.dist export-ignore
 /phpdoc.xml.dist export-ignore
 /phpunit.xml.dist export-ignore

.github/workflows/test.yml

@@ -0,0 +1,272 @@
+name: Test
+
+on:
+  # Run on pushes to `master` and on all pull requests.
+  push:
+    branches:
+      - master
+    paths-ignore:
+      - '**.md'
+      - 'docs/**'
+  pull_request:
+    paths-ignore:
+      - '**.md'
+      - 'docs/**'
+
+jobs:
+  #### TEST STAGE ####
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      # Keys:
+      # - risky: Whether to run with tests which check for being in sync with PHPCS.
+      # - experimental: Whether the build is "allowed to fail".
+      matrix:
+        # The GHA matrix works different from Travis.
+        # You can define jobs here and then augment them with extra variables in `include`,
+        # as well as add extra jobs in `include`.
+        # @link https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstrategymatrix
+        #
+        # IMPORTANT: test runs shouldn't fail because of PHPCS being incompatible with a PHP version.
+        # - PHPCS will run without errors on PHP 5.4 - 7.2 on any version.
+        # - PHP 7.3 needs PHPCS 2.9.2 and 3.3.1+ to run without errors.
+        #   On PHPCS 2.x our tests won't fail though, but on PHPCS 3.x < 3.3.1 they will.
+        # - PHP 7.4 needs PHPCS 3.5.0+ to run without errors.
+        #   On PHPCS 2.x our tests won't fail though, but on PHPCS 3.x < 3.5.0 they will.
+        # - PHP 8.0 needs PHPCS 3.5.7+ to run without errors.
+        #
+        # The matrix is set up so as not to duplicate the builds which are run for code coverage.
+        php: ['5.5', '5.6', '7.0', '7.1', '7.2']
+        phpcs_version: ['2.6.0', '2.9.2', '3.1.0', 'dev-master']
+        risky: [false]
+        experimental: [false]
+
+        include:
+          # Complement the builds run in code coverage to complete the matrix and prevent issues
+          # with PHPCS versions incompatible with certain PHP versions.
+          - php: '8.0'
+            phpcs_version: 'dev-master'
+            risky: false
+            experimental: false
+          - php: '8.0'
+            phpcs_version: '3.5.7'
+            risky: false
+            experimental: false
+
+          - php: '7.4'
+            phpcs_version: '3.5.0'
+            risky: false
+            experimental: false
+
+          - php: '7.3'
+            phpcs_version: 'dev-master'
+            risky: false
+            experimental: false
+          - php: '7.3'
+            phpcs_version: '3.3.1'
+            risky: false
+            experimental: false
+          - php: '7.3'
+            phpcs_version: '2.6.0'
+            risky: false
+            experimental: false
+
+          - php: '5.4'
+            phpcs_version: '3.1.0'
+            risky: false
+            experimental: false
+          - php: '5.4'
+            phpcs_version: '2.9.2'
+            risky: false
+            experimental: false
+
+          # One extra build to verify issues around PHPCS annotations when they weren't fully accounted for yet.
+          - php: '7.2'
+            phpcs_version: '3.2.0'
+            risky: false
+            experimental: false
+
+          # And a few more to verify various tokenizer issues in older PHPCS versions.
+          - php: '5.6'
+            phpcs_version: '2.8.1'
+            risky: false
+            experimental: false
+          - php: '7.0'
+            phpcs_version: '2.7.1'
+            risky: false
+            experimental: false
+
+          # Experimental builds. These are allowed to fail.
+
+          # Current lowest PHPCS version which _may_ run on PHP 8 is 3.5.0, so don't even try
+          # to test against older versions.
+          - php: '8.1'
+            phpcs_version: 'dev-master'
+            risky: false
+            experimental: true
+
+          - php: '7.4'
+            phpcs_version: '4.0.x-dev'
+            risky: false
+            experimental: true
+
+          # Run risky tests separately.
+          - php: '7.4'
+            phpcs_version: '4.0.x-dev'
+            risky: true
+            experimental: true
+
+          - php: '7.4'
+            phpcs_version: 'dev-master'
+            risky: true
+            experimental: true
+
+    name: "Test${{ matrix.phpcs_version == 'dev-master' && matrix.risky == false && ' + Lint' || '' }}: PHP ${{ matrix.php }} - PHPCS ${{ matrix.phpcs_version }}${{ matrix.risky == true && ' (risky)' || '' }}"
+
+    continue-on-error: ${{ matrix.experimental }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      # On stable PHPCS versions, allow for PHP deprecation notices.
+      # Unit tests don't need to fail on those for stable releases where those issues won't get fixed anymore.
+      - name: Setup ini config
+        id: set_ini
+        run: |
+          if [[ "${{ matrix.phpcs_version }}" != "dev-master" && "${{ matrix.phpcs_version }}" != "4.0.x-dev" ]]; then
+            echo '::set-output name=PHP_INI::error_reporting=E_ALL & ~E_DEPRECATED'
+          else
+            echo '::set-output name=PHP_INI::error_reporting=E_ALL'
+          fi
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          ini-values: ${{ steps.set_ini.outputs.PHP_INI }}
+          coverage: none
+
+      - name: 'Composer: set PHPCS version for tests'
+        run: composer require --no-update squizlabs/php_codesniffer:"${{ matrix.phpcs_version }}"
+
+      - name: 'Composer: conditionally tweak PHPUnit version'
+        if: ${{ startsWith( matrix.php, '8' ) }}
+        # Temporary fix - PHPUnit 9.3+ is buggy when used for code coverage, so not allowed "normally".
+        # For tests which don't run code coverage, we can safely install it for PHP 8 though.
+        run: composer require --no-update phpunit/phpunit:"^9.3"
+
+      # Install dependencies and handle caching in one go.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies - normal
+        if: ${{ matrix.php < 8.1 }}
+        uses: "ramsey/composer-install@v1"
+
+      # For the PHP "nightly", we need to install with ignore platform reqs as not all dependencies allow it yet.
+      - name: Install Composer dependencies - with ignore platform
+        if: ${{ matrix.php >= 8.1 }}
+        uses: "ramsey/composer-install@v1"
+        with:
+          composer-options: --ignore-platform-reqs
+
+      - name: Lint against parse errors
+        if: matrix.phpcs_version == 'dev-master' && matrix.risky == false
+        run: composer lint
+
+      - name: Run the unit tests (non-risky)
+        if: matrix.risky == false
+        run: vendor/bin/phpunit --no-coverage
+
+      - name: Run the unit tests (risky)
+        if: ${{ matrix.risky }}
+        # "nothing" is excluded to force PHPUnit to ignore the <exclude> settings in phpunit.xml.dist.
+        run: vendor/bin/phpunit --no-coverage --group compareWithPHPCS --exclude-group nothing
+
+  #### CODE COVERAGE STAGE ####
+  # N.B.: Coverage is only checked on the lowest and highest stable PHP versions
+  # and a low/high of each major for PHPCS.
+  # These builds are left out off the "test" stage so as not to duplicate test runs.
+  coverage:
+    # No use running the coverage builds if there are failing test builds.
+    needs: test
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        include:
+          - php: '7.4' # This should be changed to 8.0 when the tests can run on PHPUnit 9.3+.
+            phpcs_version: 'dev-master'
+          - php: '7.3'
+            phpcs_version: '2.9.2'
+          - php: '5.4'
+            phpcs_version: 'dev-master'
+          - php: '5.4'
+            phpcs_version: '2.6.0'
+
+    name: "Coverage: PHP ${{ matrix.php }} - PHPCS ${{ matrix.phpcs_version }}"
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      # On stable PHPCS versions, allow for PHP deprecation notices.
+      # Unit tests don't need to fail on those for stable releases where those issues won't get fixed anymore.
+      - name: Setup ini config
+        id: set_ini
+        run: |
+          if [ "${{ matrix.phpcs_version }}" != "dev-master" ]; then
+            echo '::set-output name=PHP_INI::error_reporting=E_ALL & ~E_DEPRECATED'
+          else
+            echo '::set-output name=PHP_INI::error_reporting=E_ALL'
+          fi
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          ini-values: ${{ steps.set_ini.outputs.PHP_INI }}
+          coverage: xdebug
+
+      - name: 'Composer: adjust dependencies'
+        run: |
+          # Set a specific PHPCS version.
+          composer require --no-update squizlabs/php_codesniffer:"${{ matrix.phpcs_version }}" --no-scripts
+
+      - name: Install Composer dependencies - normal
+        uses: "ramsey/composer-install@v1"
+
+      - name: Run the unit tests with code coverage
+        run: vendor/bin/phpunit
+
+      # Uploading the results with PHP Coveralls v1 won't work from GH Actions, so switch the PHP version.
+      - name: Switch to PHP 7.4
+        if: ${{ success() && matrix.php != '7.4' }}
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.4
+          coverage: none
+
+      - name: Install Coveralls
+        if: ${{ success() }}
+        run: composer require php-coveralls/php-coveralls:"^2.4.2"
+
+      - name: Upload coverage results to Coveralls
+        if: ${{ success() }}
+        env:
+          COVERALLS_REPO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          COVERALLS_PARALLEL: true
+          COVERALLS_FLAG_NAME: php-${{ matrix.php }}-phpcs-${{ matrix.phpcs_version }}
+        run: vendor/bin/php-coveralls -v -x build/logs/clover.xml
+
+  coveralls-finish:
+    needs: coverage
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Coveralls Finished
+        uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          parallel-finished: true