More precise MixedType::toBoolean() with subtracted type

Author: staabm

num.php

@@ -0,0 +1,15 @@
+<?php
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array<int, string> $arr
+ */
+function narrowKey($mixed, string $s, int $i, array $generalArr, array $arr): void {
+	if (isset($arr[$s])) {
+		assertType('numeric-string', $s);
+	} else {
+		assertType('string', $s);
+	}
+	assertType('string', $s);
+}

src/Type/MixedType.php

@@ -478,8 +478,10 @@ function () use ($level): string {
 
 	public function toBoolean(): BooleanType
 	{
-		if ($this->subtractedType !== null && StaticTypeFactory::falsey()->equals($this->subtractedType)) {
-			return new ConstantBooleanType(true);
+		if ($this->subtractedType !== null) {
+			if ($this->subtractedType->isSuperTypeOf(StaticTypeFactory::falsey())->yes()) {
+				return new ConstantBooleanType(true);
+			}
 		}
 
 		return new BooleanType();

tests/PHPStan/Analyser/nsrt/mixed-subtract.php

@@ -53,4 +53,9 @@ function subtract(mixed $m, $moreThenFalsy) {
 		assertType('mixed', $m);
 		assertType('bool', (bool) $m); // could be true
 	}
+
+	if ($m != 0 && !is_array($m) && $m != null && !is_object($m)) { // subtract more types then falsy
+		assertType("mixed~(0|0.0|''|'0'|array|object|false|null)", $m);
+		assertType('true', (bool) $m);
+	}
 }