Allow concatenation between (string|int) and similar types

Fixes #11337

Author: haas-dtv

src/Psalm/Internal/Analyzer/Statements/Expression/BinaryOp/ConcatAnalyzer.php

@@ -466,7 +466,7 @@ private static function analyzeOperand(
 
         if (!$operand_type_match
             && (!$comparison_result->scalar_type_match_found
-                || (!$operand_type->isInt() && $config->strict_binary_operands)
+                || (!$operand_type->isConcatSafe() && $config->strict_binary_operands)
             )
         ) {
             if ($has_valid_operand) {

src/Psalm/Type/UnionTrait.php

@@ -18,6 +18,7 @@
 use Psalm\StatementsSource;
 use Psalm\Storage\FileStorage;
 use Psalm\Type\Atomic\TArray;
+use Psalm\Type\Atomic\TArrayKey;
 use Psalm\Type\Atomic\TCallable;
 use Psalm\Type\Atomic\TClassString;
 use Psalm\Type\Atomic\TClassStringMap;
@@ -766,7 +767,7 @@ public function hasTemplate(): bool
             if ($t instanceof TTemplateParam) {
                 return true;
             }
-            
+
             if ($t instanceof TNamedObject) {
                 foreach ($t->extra_types as $sub) {
                     if ($sub instanceof TTemplateParam) {
@@ -1117,6 +1118,23 @@ public function isSingleStringLiteral(): bool
         return count($this->types) === 1 && count($this->literal_string_types) === 1;
     }
 
+
+    /**
+     * @psalm-mutation-free
+     * @return bool true if this type is a safe operand for string concatenation (int|string|array-key)
+     */
+    public function isConcatSafe(): bool
+    {
+        foreach ($this->types as $type) {
+            if (!($type instanceof TInt)
+            && !($type instanceof TString)
+            && !($type instanceof TArrayKey)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     /**
      * @throws InvalidArgumentException if isSingleStringLiteral is false
      * @psalm-mutation-free