Fix #830 - unpack template param args appropriately

src/Psalm/Checker/Statements/Expression/CallChecker.php

@@ -829,11 +829,28 @@ class CallChecker
                                     $generic_params = [];
                                 }
 
+                                $arg_type = $arg->value->inferredType;
+
+                                if ($arg->unpack) {
+                                    if ($arg->value->inferredType->hasArray()) {
+                                        /** @var Type\Atomic\TArray|Type\Atomic\ObjectLike */
+                                        $array_atomic_type = $arg->value->inferredType->getTypes()['array'];
+
+                                        if ($array_atomic_type instanceof Type\Atomic\ObjectLike) {
+                                            $array_atomic_type = $array_atomic_type->getGenericArrayType();
+                                        }
+
+                                        $arg_type = $array_atomic_type->type_params[1];
+                                    } else {
+                                        $arg_type = Type::getMixed();
+                                    }
+                                }
+
                                 $param_type->replaceTemplateTypesWithStandins(
                                     $template_types,
                                     $generic_params,
                                     $codebase,
-                                    $arg->value->inferredType
+                                    $arg_type
                                 );
                             }
                         }

tests/FunctionCallTest.php

@@ -701,6 +701,18 @@ class FunctionCallTest extends TestCase
                         ["foo" => "bar"]
                     );'
             ],
+            'splatArrayIntersect' => [
+                '<?php
+                    $foo = [
+                        [1, 2, 3],
+                        [1, 2],
+                    ];
+
+                    $bar = array_intersect(... $foo);',
+                'assertions' => [
+                    '$bar' => 'array<int, int>',
+                ],
+            ],
         ];
     }
 

tests/TemplateTest.php

@@ -684,6 +684,30 @@ class TemplateTest extends TestCase
                       function(Collection $elt): bool { return true; }
                     );',
             ],
+            'splatTemplateParam' => [
+                '<?php
+                    /**
+                     * @template TKey
+                     * @template TValue
+                     *
+                     * @param array<TKey, TValue> $arr
+                     * @param array $arr2
+                     * @return array<TKey, TValue>
+                     */
+                    function splat_proof(array $arr, array $arr2) {
+                        return $arr;
+                    }
+
+                    $foo = [
+                        [1, 2, 3],
+                        [1, 2],
+                    ];
+
+                    $a = splat_proof(... $foo);',
+                'assertions' => [
+                    '$a' => 'array<int, int>',
+                ],
+            ],
         ];
     }