Improve variadic parameter support in array_merge

Author: herndlm

src/Type/Php/ArrayMergeFunctionDynamicReturnTypeExtension.php

@@ -16,7 +16,8 @@
 use PHPStan\Type\NeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
-use PHPStan\Type\UnionType;
+use function array_keys;
+use function count;
 use function in_array;
 
 class ArrayMergeFunctionDynamicReturnTypeExtension implements DynamicFunctionReturnTypeExtension
@@ -36,23 +37,44 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 		}
 
 		$argTypes = [];
+		$optionalArgTypes = [];
 		$allConstant = true;
-		foreach ($args as $i => $arg) {
+		foreach ($args as $arg) {
 			$argType = $scope->getType($arg->value);
-			$argTypes[$i] = $argType;
 
-			if (!$arg->unpack && $argType instanceof ConstantArrayType) {
-				continue;
-			}
+			if ($arg->unpack) {
+				if ($argType instanceof ConstantArrayType) {
+					$argTypesFound = $argType->getValueTypes();
+				} else {
+					$argTypesFound = [$argType->getIterableValueType()];
+				}
+
+				foreach ($argTypesFound as $argTypeFound) {
+					$argTypes[] = $argTypeFound;
+					if ($argTypeFound instanceof ConstantArrayType) {
+						continue;
+					}
+					$allConstant = false;
+				}
 
-			$allConstant = false;
+				if (!$argType->isIterableAtLeastOnce()->yes()) {
+					// unpacked params can be empty, making them optional
+					$optionalArgTypesOffset = count($argTypes) - 1;
+					foreach (array_keys($argTypesFound) as $key) {
+						$optionalArgTypes[] = $optionalArgTypesOffset + $key;
+					}
+				}
+			} else {
+				$argTypes[] = $argType;
+				if (!$argType instanceof ConstantArrayType) {
+					$allConstant = false;
+				}
+			}
 		}
 
 		if ($allConstant) {
 			$newArrayBuilder = ConstantArrayTypeBuilder::createEmpty();
-			foreach ($args as $i => $arg) {
-				$argType = $argTypes[$i];
-
+			foreach ($argTypes as $argType) {
 				if (!$argType instanceof ConstantArrayType) {
 					throw new ShouldNotHappenException();
 				}
@@ -78,22 +100,11 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 		$keyTypes = [];
 		$valueTypes = [];
 		$nonEmpty = false;
-		foreach ($args as $i => $arg) {
-			$argType = $argTypes[$i];
-
-			if ($arg->unpack) {
-				$argType = $argType->getIterableValueType();
-				if ($argType instanceof UnionType) {
-					foreach ($argType->getTypes() as $innerType) {
-						$argType = $innerType;
-					}
-				}
-			}
-
+		foreach ($argTypes as $key => $argType) {
 			$keyTypes[] = $argType->getIterableKeyType();
 			$valueTypes[] = $argType->getIterableValueType();
 
-			if (!$argType->isIterableAtLeastOnce()->yes()) {
+			if (in_array($key, $optionalArgTypes, true) || !$argType->isIterableAtLeastOnce()->yes()) {
 				continue;
 			}
 

tests/PHPStan/Analyser/data/array-merge.php

@@ -13,3 +13,26 @@ function foo(): void
 
 	assertType('array{foo: 17, 0: \'a\', bar: 19, 1: \'b\', 2: \'b\', 3: \'c\'}', $baz);
 }
+
+/**
+ * @param string[][] $foo
+ * @param array<non-empty-array<int>> $bar1
+ * @param non-empty-array<non-empty-array<int>> $bar2
+ * @param non-empty-array<array<int>> $bar3
+ */
+function unpackingArrays(array $foo, array $bar1, array $bar2, array $bar3): void
+{
+	assertType('array<string>', array_merge([], ...$foo));
+	assertType('array<int>', array_merge([], ...$bar1));
+	assertType('non-empty-array<int>', array_merge([], ...$bar2));
+	assertType('array<int>', array_merge([], ...$bar3));
+}
+
+function unpackingConstantArrays(): void
+{
+	assertType('array{}', array_merge([], ...[]));
+	assertType('array{17}', array_merge([], [17]));
+	assertType('array{17}', array_merge([], ...[[17]]));
+	assertType('array{foo: \'bar\', bar: \'baz2\', 0: 17}', array_merge(['foo' => 'bar', 'bar' => 'baz1'], ['bar' => 'baz2', 17]));
+	assertType('array{foo: \'bar\', bar: \'baz2\', 0: 17}', array_merge(['foo' => 'bar', 'bar' => 'baz1'], ...[['bar' => 'baz2', 17]]));
+}