Add support for PHP 8 (#21)

Author: martinssipenko

.github/workflows/php.yml

@@ -10,25 +10,37 @@ on:
 
 jobs:
   build:
-    strategy:      
+    strategy:
       matrix:
         php: ['7.2', '7.3', '7.4']
         phpunit: ['8.0', '9.0']
+        composer-arg: ['']
+        include:
+          - php: '8.0'
+            phpunit: '9.0'
+            composer-arg: 'ignore-platform-req=php'
         exclude:
+          - php: '8.0'
+            phpunit: '8.0'
           - php: '7.2'
             phpunit: '9.0'
     runs-on: ubuntu-latest
 
+    continue-on-error: ${{ matrix.php == '8.0' }}
+    name: PHP ${{ matrix.php }}, PHPUnit ${{ matrix.phpunit }}
+
     steps:
     - uses: actions/checkout@v1
-      
+
     - name: Setup PHP
       uses: shivammathur/setup-php@v1
       with:
         php-version: ${{ matrix.php }}
         extensions: mbstring, intl, json
         coverage: pcov
-    
+
+        tools: composer:v2
+
     - name: Validate composer.json and composer.lock
       run: composer validate
 
@@ -37,10 +49,10 @@ jobs:
         composer require --no-update --dev phpunit/phpunit ~${{ matrix.phpunit }}
 
     - name: Install dependencies
-      run: composer install --prefer-dist --no-progress --no-suggest
+      run: composer install --prefer-dist --no-progress --no-suggest --${{ matrix.composer-arg }}
 
     #- name: Run type checker
     #  run: ./vendor/bin/psalm
-      
+
     - name: Run unit tests
       run: ./vendor/bin/phpunit --testdox

composer.json

@@ -9,7 +9,7 @@
         }
     ],
     "require": {
-        "php": "^7.1",
+        "php": "^7.1 || ^8.0",
         "helmich/phpunit-json-assert": "^3.2",
         "psr/http-message": "^1.0"
     },