Allow to increment strings

Author: VincentLanglet

Diff for: phpstan-baseline.neon

@@ -102,16 +102,6 @@ parameters:
 			count: 1
 			path: src/Rules/ForeachLoop/OverwriteVariablesWithForeachRule.php
 
-		-
-			message: "#^Class PHPStan\\\\Rules\\\\Operators\\\\OperandInArithmeticIncrementOrDecrementRule implements generic interface PHPStan\\\\Rules\\\\Rule but does not specify its types\\: TNodeType$#"
-			count: 1
-			path: src/Rules/Operators/OperandInArithmeticIncrementOrDecrementRule.php
-
-		-
-			message: "#^Parameter \\#1 \\$node \\(PhpParser\\\\Node\\\\Expr\\\\PostDec\\|PhpParser\\\\Node\\\\Expr\\\\PostInc\\|PhpParser\\\\Node\\\\Expr\\\\PreDec\\|PhpParser\\\\Node\\\\Expr\\\\PreInc\\) of method PHPStan\\\\Rules\\\\Operators\\\\OperandInArithmeticIncrementOrDecrementRule\\:\\:processNode\\(\\) should be contravariant with parameter \\$node \\(PhpParser\\\\Node\\) of method PHPStan\\\\Rules\\\\Rule\\<PhpParser\\\\Node\\>\\:\\:processNode\\(\\)$#"
-			count: 1
-			path: src/Rules/Operators/OperandInArithmeticIncrementOrDecrementRule.php
-
 		-
 			message: "#^Class PHPStan\\\\Rules\\\\Operators\\\\OperandsInArithmeticAdditionRule implements generic interface PHPStan\\\\Rules\\\\Rule but does not specify its types\\: TNodeType$#"
 			count: 1
@@ -516,5 +506,3 @@ parameters:
 			message: "#^Method PHPStan\\\\Rules\\\\VariableVariables\\\\VariableVariablesRuleTest\\:\\:getRule\\(\\) return type with generic interface PHPStan\\\\Rules\\\\Rule does not specify its types\\: TNodeType$#"
 			count: 1
 			path: tests/Rules/VariableVariables/VariableVariablesRuleTest.php
-
-

Diff for: src/Rules/Operators/OperandInArithmeticIncrementOrDecrementRule.php

@@ -12,6 +12,10 @@
 use PHPStan\Type\VerbosityLevel;
 use function sprintf;
 
+/**
+ * @phpstan-template TNodeType of PreInc|PreDec|PostInc|PostDec
+ * @phpstan-implements Rule<TNodeType>
+ */
 abstract class OperandInArithmeticIncrementOrDecrementRule implements Rule
 {
 
@@ -32,7 +36,12 @@ public function processNode(Node $node, Scope $scope): array
 		$messages = [];
 		$varType = $scope->getType($node->var);
 
-		if (!$this->helper->isValidForIncrementOrDecrement($scope, $node->var)) {
+		if (
+			($node instanceof PreInc || $node instanceof PostInc)
+				&& !$this->helper->isValidForIncrement($scope, $node->var)
+			|| ($node instanceof PreDec || $node instanceof PostDec)
+				&& !$this->helper->isValidForDecrement($scope, $node->var)
+		) {
 			$messages[] = sprintf(
 				'Only numeric types are allowed in %s, %s given.',
 				$this->describeOperation(),

Diff for: src/Rules/Operators/OperandInArithmeticPostDecrementRule.php

@@ -4,6 +4,9 @@
 
 use PhpParser\Node\Expr\PostDec;
 
+/**
+ * @phpstan-extends OperandInArithmeticIncrementOrDecrementRule<PostDec>
+ */
 class OperandInArithmeticPostDecrementRule extends OperandInArithmeticIncrementOrDecrementRule
 {
 

Diff for: src/Rules/Operators/OperandInArithmeticPostIncrementRule.php

@@ -4,6 +4,9 @@
 
 use PhpParser\Node\Expr\PostInc;
 
+/**
+ * @phpstan-extends OperandInArithmeticIncrementOrDecrementRule<PostInc>
+ */
 class OperandInArithmeticPostIncrementRule extends OperandInArithmeticIncrementOrDecrementRule
 {
 

Diff for: src/Rules/Operators/OperandInArithmeticPreDecrementRule.php

@@ -4,6 +4,9 @@
 
 use PhpParser\Node\Expr\PreDec;
 
+/**
+ * @phpstan-extends OperandInArithmeticIncrementOrDecrementRule<PreDec>
+ */
 class OperandInArithmeticPreDecrementRule extends OperandInArithmeticIncrementOrDecrementRule
 {
 

Diff for: src/Rules/Operators/OperandInArithmeticPreIncrementRule.php

@@ -4,6 +4,9 @@
 
 use PhpParser\Node\Expr\PreInc;
 
+/**
+ * @phpstan-extends OperandInArithmeticIncrementOrDecrementRule<PreInc>
+ */
 class OperandInArithmeticPreIncrementRule extends OperandInArithmeticIncrementOrDecrementRule
 {
 

Diff for: src/Rules/Operators/OperatorRuleHelper.php

@@ -42,7 +42,22 @@ public function isValidForArithmeticOperation(Scope $scope, Expr $expr): bool
 		return $this->isSubtypeOfNumber($scope, $expr);
 	}
 
-	public function isValidForIncrementOrDecrement(Scope $scope, Expr $expr): bool
+	public function isValidForIncrement(Scope $scope, Expr $expr): bool
+	{
+		$type = $scope->getType($expr);
+		if ($type instanceof MixedType) {
+			return true;
+		}
+
+		if ($type->isString()->yes()) {
+			// Because `$a = 'a'; $a++;` is valid
+			return true;
+		}
+
+		return $this->isSubtypeOfNumber($scope, $expr);
+	}
+
+	public function isValidForDecrement(Scope $scope, Expr $expr): bool
 	{
 		$type = $scope->getType($expr);
 		if ($type instanceof MixedType) {

Diff for: tests/Rules/Operators/OperandInArithmeticPostIncrementRuleTest.php

@@ -22,10 +22,6 @@ protected function getExpectedErrors(): array
 				'Only numeric types are allowed in post-increment, false given.',
 				32,
 			],
-			[
-				'Only numeric types are allowed in post-increment, string given.',
-				33,
-			],
 			[
 				'Only numeric types are allowed in post-increment, null given.',
 				34,

Diff for: tests/Rules/Operators/OperandInArithmeticPreIncrementRuleTest.php

@@ -22,10 +22,6 @@ protected function getExpectedErrors(): array
 				'Only numeric types are allowed in pre-increment, false given.',
 				54,
 			],
-			[
-				'Only numeric types are allowed in pre-increment, string given.',
-				55,
-			],
 			[
 				'Only numeric types are allowed in pre-increment, null given.',
 				56,