Do not generalize an array union that is no larger than its members

src/Turbo/TurboExtensionEnabler.php

@@ -33,7 +33,7 @@
 final class TurboExtensionEnabler
 {
 
-	public const EXPECTED_EXTENSION_VERSION = 'a0f7086';
+	public const EXPECTED_EXTENSION_VERSION = 'f264737';
 
 	private static bool $active = false;
 

src/Type/TypeCombinator.php

@@ -1240,7 +1240,10 @@ private static function processArrayTypes(array $arrayTypes): array
 			];
 		}
 
-		$reducedArrayTypes = self::optimizeConstantArrays(self::reduceArrays($arrayTypes, true));
+		$reducedArrayTypes = self::reduceArrays($arrayTypes, true);
+		if (count($reducedArrayTypes) !== 1 || !self::isNoLargerThanLargestArray($reducedArrayTypes[0], $arrayTypes)) {
+			$reducedArrayTypes = self::optimizeConstantArrays($reducedArrayTypes);
+		}
 		foreach ($reducedArrayTypes as $idx => $reducedArray) {
 			$applied = $accessoryTypes;
 			if ($reducedArray->isIterableAtLeastOnce()->no()) {
@@ -1258,6 +1261,31 @@ private static function processArrayTypes(array $arrayTypes): array
 		return $reducedArrayTypes;
 	}
 
+	/**
+	 * Whether the single array a union reduced to holds no more constant array
+	 * values than the largest of the arrays it was made of - e.g. a shape and
+	 * its narrowed variant merged back together. Each of those arrays was kept
+	 * as it is, so generalizing their union would lose a shape that the limit
+	 * did not apply to and that does not grow.
+	 *
+	 * @param Type[] $arrayTypes
+	 */
+	private static function isNoLargerThanLargestArray(Type $reducedArrayType, array $arrayTypes): bool
+	{
+		$constantArrayValuesCount = self::countConstantArrayValueTypes([$reducedArrayType]);
+		if ($constantArrayValuesCount <= ConstantArrayTypeBuilder::ARRAY_COUNT_LIMIT) {
+			return true;
+		}
+
+		foreach ($arrayTypes as $arrayType) {
+			if (self::countConstantArrayValueTypes([$arrayType]) >= $constantArrayValuesCount) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	/**
 	 * @param Type[] $types
 	 * @return Type[]

tests/PHPStan/Analyser/nsrt/bug-15459.php

@@ -0,0 +1,234 @@
+<?php declare(strict_types=1);
+
+namespace Bug15459;
+
+use LogicException;
+use function PHPStan\Testing\assertType;
+
+/** @return array{
+    k0: string,
+    k1: string,
+    k2: string,
+    k3: string,
+    k4: string,
+    k5: string,
+    k6: string,
+    k7: string,
+    k8: string,
+    k9: string,
+    k10: string,
+    k11: string,
+    k12: string,
+    k13: string,
+    k14: string,
+    k15: string,
+    k16: string,
+    k17: string,
+    k18: string,
+    k19: string,
+    k20: string,
+    k21: string,
+    k22: string,
+    k23: string,
+    k24: string,
+    k25: string,
+    k26: string,
+    k27: string,
+    k28: string,
+    k29: string,
+    k30: string,
+    k31: string,
+    k32: string,
+    k33: string,
+    k34: string,
+    k35: string,
+    k36: string,
+    k37: string,
+    k38: string,
+    k39: string,
+    k40: string,
+    k41: string,
+    k42: string,
+    k43: string,
+    k44: string,
+    k45: string,
+    k46: string,
+    k47: string,
+    k48: string,
+    k49: string,
+    k50: string,
+    k51: string,
+    k52: string,
+    k53: string,
+    k54: string,
+    k55: string,
+    k56: string,
+    k57: string,
+    k58: string,
+    k59: string,
+    k60: string,
+    k61: string,
+    k62: string,
+    k63: string,
+    k64: string,
+    k65: string,
+    k66: string,
+    k67: string,
+    k68: string,
+    k69: string,
+    k70: string,
+    k71: string,
+    k72: string,
+    k73: string,
+    k74: string,
+    k75: string,
+    k76: string,
+    k77: string,
+    k78: string,
+    k79: string,
+    k80: string,
+    k81: string,
+    k82: string,
+    k83: string,
+    k84: string,
+    k85: string,
+    k86: string,
+    k87: string,
+    k88: string,
+    k89: string,
+    k90: string,
+    k91: string,
+    k92: string,
+    k93: string,
+    k94: string,
+    k95: string,
+    k96: string,
+    k97: string,
+    k98: string,
+    k99: string,
+    k100: string,
+    k101: string,
+    k102: string,
+    k103: string,
+    k104: string,
+    k105: string,
+    k106: string,
+    k107: string,
+    k108: string,
+    k109: string,
+    k110: string,
+    k111: string,
+    k112: string,
+    k113: string,
+    k114: string,
+    k115: string,
+    k116: string,
+    k117: string,
+    k118: string,
+    k119: string,
+    k120: string,
+    k121: string,
+    k122: string,
+    k123: string,
+    k124: string,
+    k125: string,
+    k126: string,
+    k127: string,
+    k128: string,
+    k129: string,
+    k130: string,
+    k131: string,
+    k132: string,
+    k133: string,
+    k134: string,
+    k135: string,
+    k136: string,
+    k137: string,
+    k138: string,
+    k139: string,
+    k140: string,
+    k141: string,
+    k142: string,
+    k143: string,
+    k144: string,
+    k145: string,
+    k146: string,
+    k147: string,
+    k148: string,
+    k149: string,
+    k150: string,
+    k151: string,
+    k152: string,
+    k153: string,
+    k154: string,
+    k155: string,
+    k156: string,
+    k157: string,
+    k158: string,
+    k159: string,
+    k160: string,
+    k161: string,
+    k162: string,
+    k163: string,
+    k164: string,
+    k165: string,
+    k166: string,
+    k167: string,
+    k168: string,
+    k169: string,
+    k170: string,
+    k171: string,
+    k172: string,
+    k173: string,
+    k174: string,
+    k175: string,
+    k176: string,
+    k177: string,
+    k178: string,
+    k179: string,
+    k180: string,
+    k181: string,
+    k182: string,
+    k183: string,
+    k184: string,
+    k185: string,
+    k186: string,
+    k187: string,
+    k188: string,
+    k189: string,
+    k190: string,
+    k191: string,
+    k192: string,
+    k193: string,
+    k194: string,
+    k195: string,
+    k196: string,
+    o0?: array{currency: string, price: float}|null,
+    o1?: array{currency: string, price: float}|null,
+    o2?: array{currency: string, price: float}|null,
+    o3?: array{currency: string, price: float}|null,
+    o4?: array{currency: string, price: float}|null,
+    o5?: array{currency: string, price: float}|null,
+    o6?: array{currency: string, price: float}|null,
+    o7?: array{currency: string, price: float}|null,
+    o8?: array{currency: string, price: float}|null,
+    o9?: array{currency: string, price: float}|null,
+    o10?: array{currency: string, price: float}|null,
+    o11?: array{currency: string, price: float}|null,
+    o12?: array{currency: string, price: float}|null,
+    o13?: array{currency: string, price: float}|null,
+    o14?: array{currency: string, price: float}|null,
+    o15?: array{currency: string, price: float}|null,
+    o16?: array{currency: string, price: float}|null,
+    o17?: array{currency: string, price: float}|null,
+    o18?: array{currency: string, price: float}|null,
+    o19?: array{currency: string, price: float}|null,
+} */
+function make(): array { throw new LogicException(); }
+
+function f(): void {
+    $r = make();
+    $a = $r['o0'] ?? null;
+    $b = $r['o1'] ?? null;
+    assertType('array{currency: string, price: float}|null', $b);
+}

turbo-ext/src/TypeCombinator.cpp

@@ -2090,10 +2090,15 @@ class TypeCombinator
 		}
 
 		zv::Arr arrayTypesArray = listOf(arrayTypes);
-		zv::Val reduced = reduceArrays(arrayTypesArray.raw(), true);
-		PT_FAIL_IF_UNDEF(reduced);
-		zv::Val reducedArrayTypes = optimizeConstantArrays(reduced.raw());
+		zv::Val reducedArrayTypes = reduceArrays(arrayTypesArray.raw(), true);
 		PT_FAIL_IF_UNDEF(reducedArrayTypes);
+		zval *singleReducedArrayType = countOf(reducedArrayTypes.raw()) == 1 ? indexOf(reducedArrayTypes.raw(), 0) : NULL;
+		int noLarger = singleReducedArrayType != NULL ? isNoLargerThanLargestArray(singleReducedArrayType, arrayTypes) : 0;
+		PT_FAIL_IF_NEG(noLarger);
+		if (noLarger == 0) {
+			reducedArrayTypes = optimizeConstantArrays(reducedArrayTypes.raw());
+			PT_FAIL_IF_UNDEF(reducedArrayTypes);
+		}
 		zv::Arr result = zv::Arr::adoptVal(std::move(reducedArrayTypes));
 		result.separate();
 		for (zv::ArrayEntry entry : zv::ArrRef(result.raw())) {
@@ -2297,6 +2302,33 @@ class TypeCombinator
 		traversed.intoReturnValue(return_value);
 	}
 
+	/* countConstantArrayValueTypes([$type]); -1 = pending exception */
+	[[nodiscard]] static zend_long countConstantArrayValueTypesOf(zval *type)
+	{
+		zv::Arr types = zv::Arr::create(1);
+		types.push(zv::Ref(type));
+		return countConstantArrayValueTypes(types.raw());
+	}
+
+	/* private static isNoLargerThanLargestArray(Type $reducedArrayType, Type[] $arrayTypes): bool;
+	 * -1 = pending exception */
+	[[nodiscard]] static int isNoLargerThanLargestArray(zval *reducedArrayType, TypeList &arrayTypes)
+	{
+		zend_long constantArrayValuesCount = countConstantArrayValueTypesOf(reducedArrayType);
+		if (UNEXPECTED(constantArrayValuesCount < 0)) return -1;
+		zend_long limit = arrayCountLimit();
+		if (UNEXPECTED(limit < 0)) return -1;
+		if (constantArrayValuesCount <= limit) return 1;
+
+		for (zv::Val &arrayType : arrayTypes) {
+			zend_long arrayTypeValuesCount = countConstantArrayValueTypesOf(arrayType.raw());
+			if (UNEXPECTED(arrayTypeValuesCount < 0)) return -1;
+			if (arrayTypeValuesCount >= constantArrayValuesCount) return 1;
+		}
+
+		return 0;
+	}
+
 	/* private static optimizeConstantArrays(Type[] $types): Type[] */
 	static zv::Val optimizeConstantArrays(zval *typesArray)
 	{