Narrow types based on non-strict equality with constant types

src/Analyser/TypeSpecifier.php

@@ -38,6 +38,7 @@
 use PHPStan\Type\ArrayType;
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\ConditionalTypeForParameter;
+use PHPStan\Type\Constant\ConstantArrayType;
 use PHPStan\Type\Constant\ConstantArrayTypeBuilder;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantIntegerType;
@@ -1469,15 +1470,24 @@ private function findTypeExpressionsFromBinaryOperation(Scope $scope, Node\Expr\
 $leftExpr = $leftExpr->getExpr();
 }
 
+$isNativeConstFetch = static function (Expr $expr): bool {
+if (!$expr instanceof ConstFetch) {
+return false;
+}
+
+$loweredConstName = strtolower($expr->name->toString());
+return in_array($loweredConstName, ['true', 'false', 'null'], true);
+};
+
 if (
 $leftType instanceof ConstantScalarType
-&& !$rightExpr instanceof ConstFetch
+&& !$isNativeConstFetch($rightExpr)
 && !$rightExpr instanceof ClassConstFetch
 ) {
 return [$binaryOperation->right, $leftType];
 } elseif (
 $rightType instanceof ConstantScalarType
-&& !$leftExpr instanceof ConstFetch
+&& !$isNativeConstFetch($leftExpr)
 && !$leftExpr instanceof ClassConstFetch
 ) {
 return [$binaryOperation->left, $rightType];
@@ -1809,6 +1819,26 @@ public function resolveEqual(Expr\BinaryOp\Equal $expr, Scope $scope, TypeSpecif
 );
 }
 
+$looseyType = new UnionType([
+new NullType(),
+new ConstantBooleanType(true),
+new ConstantBooleanType(false),
+new ConstantIntegerType(0),
+new ConstantIntegerType(1),
+new FloatType(), // equality on floats is not usefull
+new ConstantStringType(''),
+new ConstantStringType('0'),
+new ConstantStringType('1'),
+new ConstantArrayType([], []),
+]);
+
+if ($context->true()
+&& ($exprNode instanceof Expr\Variable || $exprNode instanceof ConstFetch)
+&& !$looseyType->isSuperTypeOf($constantType)->yes()
+) {
+return $this->specifyTypesInCondition($scope, new Expr\BinaryOp\Identical($expr->left, $expr->right), $context, $rootExpr);
+}
+
 if (
 $exprNode instanceof FuncCall
 && $exprNode->name instanceof Name

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1422,6 +1422,7 @@ public function dataFileAsserts(): iterable
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-5961.php');
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10189.php');
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10317.php');
+yield from $this->gatherAssertTypes(__DIR__ . '/data/loose-equal-consts.php');
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10302-interface-extends.php');
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10302-trait-extends.php');
 yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10302-trait-implements.php');

tests/PHPStan/Analyser/data/loose-equal-consts.php

@@ -0,0 +1,92 @@
+<?php declare(strict_types=1);
+
+namespace LooseEqualConsts;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+public function vars($mixed): void
+{
+if ($mixed === 'backend') {
+assertType("'backend'", $mixed);
+}
+
+if ($mixed == 'backend') {
+assertType("'backend'", $mixed);
+}
+if ($mixed == 500) {
+assertType("500", $mixed);
+}
+if ('backend' == $mixed) {
+assertType("'backend'", $mixed);
+}
+if (500 == $mixed) {
+assertType("500", $mixed);
+}
+if ($mixed == 'backend' || $mixed == 'frontend') {
+assertType("'backend'|'frontend'", $mixed);
+}
+
+if ($mixed == '1') {
+assertType("mixed", $mixed);
+}
+if ($mixed == '0') {
+assertType("mixed", $mixed);
+}
+if ($mixed == 1) {
+assertType("mixed", $mixed);
+}
+if ($mixed == 0) {
+assertType("mixed", $mixed);
+}
+
+// equality on floats is not usefull
+if ($mixed == 1.0) {
+assertType("mixed", $mixed);
+}
+if ($mixed == 0.0) {
+assertType("mixed", $mixed);
+}
+if ($mixed == 123.0) {
+assertType("mixed", $mixed);
+}
+
+if ($mixed == true) {
+assertType("mixed~0|0.0|''|'0'|array{}|false|null", $mixed);
+}
+if ($mixed == false) {
+assertType("0|0.0|''|'0'|array{}|false|null", $mixed);
+}
+if ($mixed == null) {
+assertType("0|0.0|''|'0'|array{}|false|null", $mixed);
+}
+
+if ($mixed == []) {
+assertType("mixed", $mixed);
+}
+
+if ($mixed !== 'backend') {
+assertType("mixed~'backend'", $mixed);
+}
+if ($mixed != 'backend') {
+assertType('mixed', $mixed);
+}
+}
+
+public function constants(): void
+{
+if (APP_NAME === 'backend') {
+assertType("'backend'", APP_NAME);
+}
+if (APP_NAME == 'backend') {
+assertType("'backend'", APP_NAME);
+}
+if (APP_NAME !== 'backend') {
+assertType('*ERROR*', APP_NAME);
+}
+if (APP_NAME != 'backend') {
+assertType('*ERROR*', APP_NAME);
+}
+}
+}