improve psalm analysis

composer.json

@@ -31,6 +31,7 @@
     "require-dev": {
         "phpstan/phpstan": "^0.12.92",
         "phpunit/phpunit": "^7.3 || ^8.0 || ^9.0",
+        "psalm/plugin-phpunit": "^0.16.1",
         "slevomat/coding-standard": "^7.0",
         "squizlabs/php_codesniffer": "^3.6",
         "vimeo/psalm": "^4.8"
@@ -49,7 +50,7 @@
         "tests": [
             "vendor/bin/phpcs",
             "vendor/bin/phpstan analyse --ansi",
-            "vendor/bin/psalm --taint-analysis",
+            "vendor/bin/psalm",
             "vendor/bin/phpunit --coverage-text"
         ]
     }

psalm.xml.dist

@@ -2,9 +2,7 @@
 <psalm
     addParamDefaultToDocblockType="true"
     allowNamedArgumentCalls="false"
-    allowPhpStormGenerics="true"
     cacheDirectory="build/psalm.cache"
-    checkForThrowsDocblock="true"
     checkForThrowsInGlobalScope="true"
     ensureArrayIntOffsetsExist="true"
     ensureArrayStringOffsetsExist="true"
@@ -15,7 +13,7 @@
     forbidEcho="true"
     ignoreInternalFunctionFalseReturn="false"
     ignoreInternalFunctionNullReturn="false"
-    runTaintAnalysis="true"
+    reportMixedIssues="false"
     strictBinaryOperands="true"
     throwExceptionOnError="true"
     useDocblockPropertyTypes="true"
@@ -25,11 +23,14 @@
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
 >
+    <plugins>
+        <pluginClass class="Psalm\PhpUnitPlugin\Plugin"/>
+    </plugins>
     <projectFiles>
         <directory name="src"/>
-        <directory name="tests"/>
+        <directory name="tests/"/>
         <ignoreFiles>
-            <directory name="vendor"/>
+            <directory name="vendor/"/>
         </ignoreFiles>
     </projectFiles>
 </psalm>

src/Gtin/Gtin12.php

@@ -27,6 +27,6 @@ public function length(): int
      */
     public function prefix(): string
     {
-        return substr($this->padded(), 1, 3);
+        return (string) substr($this->padded(), 1, 3);
     }
 }

src/Gtin/Gtin13.php

@@ -27,6 +27,6 @@ public function length(): int
      */
     public function prefix(): string
     {
-        return substr($this->padded(), 1, 3);
+        return (string) substr($this->padded(), 1, 3);
     }
 }

src/Gtin/Gtin14.php

@@ -27,6 +27,6 @@ public function length(): int
      */
     public function prefix(): string
     {
-        return substr($this->padded(), 1, 3);
+        return (string) substr($this->padded(), 1, 3);
     }
 }

src/Gtin/Gtin8.php

@@ -27,6 +27,6 @@ public function length(): int
      */
     public function prefix(): string
     {
-        return substr($this->padded(), 6, 3);
+        return (string) substr($this->padded(), 6, 3);
     }
 }