add phpstan static analysis tool (#200)

* add phpstan

* fix review issues

* fix phpstan error with final constructor

.github/workflows/php.yml

@@ -53,6 +53,9 @@ jobs:
 
     - name: Run Psalm
       run: vendor/bin/psalm
+
+    - name: Run Phpstan
+      run: vendor/bin/phpstan analyse
 
     - name: Run PHPUnit
       run: vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover

Context/Context.php

@@ -40,7 +40,7 @@ class Context
      * @param mixed|null $value
      * @param Context|null $parent Reference to the parent object
      */
-    public function __construct(?ContextKey $key=null, $value=null, $parent=null)
+    public final function __construct(?ContextKey $key=null, $value=null, $parent=null)
     {
         $this->key = $key;
         $this->value = $value;

Makefile

@@ -12,6 +12,8 @@ psalm:
 	$(DC_RUN_PHP) php ./vendor/bin/psalm
 psalm-info:
 	$(DC_RUN_PHP) php ./vendor/bin/psalm --show-info=true
+phpstan: 
+	$(DC_RUN_PHP) php ./vendor/bin/phpstan analyse
 trace examples: FORCE
 	docker-compose up -d
 	$(DC_RUN_PHP) php ./examples/AlwaysOnZipkinExample.php

composer.json

@@ -43,6 +43,7 @@
         "composer/xdebug-handler": "^1.3",
         "phan/phan": "^3.0",
         "friendsofphp/php-cs-fixer": "^2.16",
-        "vimeo/psalm": "^4.0"
+        "vimeo/psalm": "^4.0",
+        "phpstan/phpstan": "^0.12.50"
     }
 }

phpstan.neon

@@ -0,0 +1,7 @@
+parameters:
+    level: 4
+    paths:
+        -   Context
+        -   api
+        -   contrib
+        -   sdk