Do not report values flowing into a write that is reported as never read

A write whose value only flows into unused values was reported even when one of those values is itself never read - `$copy = $e` already reports $copy, reporting $e as well is noise. The liveness resolver now walks the dependency edges backwards from every never-read write and marks the writes feeding it as covered; the rules skip covered flow reports. A chain that only feeds itself, like Psalm's `$b = $b + 1` loop, has no never-read write to point at and stays reported at every write. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_018CZ79ZBiMt4KWgU3uy4Y4j
ondrejmirtes · Sep 11, 2026 · Sep 11, 2026 · Sep 11, 2026 · Sep 11, 2026 · Sep 11, 2026
commit 59b243fab985f1a0cf850c1f458b6ae165ea664b
diff --git a/src/Analyser/VariableLivenessResolver.php b/src/Analyser/VariableLivenessResolver.php
@@ -71,6 +71,9 @@ final class VariableLivenessResolver
 	/** @var array<int, array<int, VariableWrite>> */
 	private array $literalItems = [];
 
+	/** @var array<int, true> */
+	private array $coveredIds = [];
+
 	/** @var array<string, true> */
 	private array $allReadKeys = [];
 
@@ -119,9 +122,10 @@ public static function resolve(Node\FunctionLike $function, ?VariableFlow $flow)
 			$self->compileAccesses();
 			$self->liveBefore($body, [], new VariableFlowContext([]));
 			$self->resolveDependencies();
+			$self->resolveCoverage();
 		}
 
-		return new VariableWritesNode($function, array_values($self->writes), $self->observedIds + $self->readIds, $self->readIds, $self->readNames, $self->redundantTypes, $self->mentionedNames, $self->escapedNames, $self->opaque, $self->allNamesMentioned);
+		return new VariableWritesNode($function, array_values($self->writes), $self->observedIds + $self->readIds, $self->readIds, $self->coveredIds, $self->readNames, $self->redundantTypes, $self->mentionedNames, $self->escapedNames, $self->opaque, $self->allNamesMentioned);
 	}
 
 	private function collect(?VariableFlow $flow, bool $dead = false): void
@@ -495,4 +499,40 @@ private function resolveDependencies(): void
 		}
 	}
 
+	/**
+	 * A write whose value flows only into unused writes is covered when one of
+	 * them is never read at all: reporting that write already points at the
+	 * dead chain. Walks the dependency edges backwards from every never-read
+	 * write; a chain that only feeds itself (Psalm's `$b = $b + 1` loop) has
+	 * no such write and stays uncovered.
+	 */
+	private function resolveCoverage(): void
+	{
+		$stack = [];
+		foreach (array_keys($this->writes) as $id) {
+			if (isset($this->observedIds[$id]) || isset($this->readIds[$id])) {
+				continue;
+			}
+
+			$stack[] = $id;
+		}
+		$visited = [];
+		while ($stack !== []) {
+			$id = array_pop($stack);
+			if (isset($visited[$id])) {
+				continue;
+			}
+			$visited[$id] = true;
+			$sources = array_keys($this->dependencies[$id] ?? []);
+			foreach (array_keys($this->inputCopies[$id] ?? []) as $copied) {
+				// the inputs of $copied flow into $id as well
+				$sources = [...$sources, ...array_keys($this->dependencies[$copied] ?? [])];
+			}
+			foreach ($sources as $source) {
+				$this->coveredIds[$source] = true;
+				$stack[] = $source;
+			}
+		}
+	}
+
 }
diff --git a/src/Node/VariableWritesNode.php b/src/Node/VariableWritesNode.php
@@ -24,6 +24,7 @@ final class VariableWritesNode extends NodeAbstract implements VirtualNode
 	 * @param list<VariableWrite> $writes
 	 * @param array<int, true> $readWriteIds
 	 * @param array<int, true> $usedWriteIds
+	 * @param array<int, true> $coveredWriteIds
 	 * @param array<string, true> $readVariableNames
 	 * @param array<int, Type> $redundantWriteTypes
 	 * @param array<string, true> $referencedVariableNames
@@ -34,6 +35,7 @@ public function __construct(
 		private array $writes,
 		private array $readWriteIds,
 		private array $usedWriteIds,
+		private array $coveredWriteIds,
 		private array $readVariableNames,
 		private array $redundantWriteTypes,
 		private array $referencedVariableNames,
@@ -88,6 +90,15 @@ public function isUsed(VariableWrite $write): bool
 		return isset($this->usedWriteIds[$write->getId()]);
 	}
 
+	/**
+	 * Whether the value flows into a write that is never read at all - that
+	 * write is the one to report, this one only feeds it.
+	 */
+	public function flowsIntoNeverReadWrite(VariableWrite $write): bool
+	{
+		return isset($this->coveredWriteIds[$write->getId()]);
+	}
+
 	/** Whether some path from the write reaches a read of the written value. */
 	public function isRead(VariableWrite $write): bool
 	{

diff --git a/src/Rules/DeadCode/UnusedVariableRule.php b/src/Rules/DeadCode/UnusedVariableRule.php
@@ -88,7 +88,7 @@ public function processNode(Node $node, Scope $scope): array
 				continue;
 			}
 
-			if ($node->isUsed($write)) {
+			if ($node->isUsed($write) || $node->flowsIntoNeverReadWrite($write)) {
 				continue;
 			}
 

diff --git a/src/Rules/Functions/UnusedClosureUsesRule.php b/src/Rules/Functions/UnusedClosureUsesRule.php
@@ -60,7 +60,7 @@ public function processNode(Node $node, Scope $scope): array
 				if ($node->isRead($write)) {
 					// read, but only into values that never reach a sink - a
 					// newer finding than the rule, so bleeding edge only
-					if (!$this->reportUnusedFlow) {
+					if (!$this->reportUnusedFlow || $node->flowsIntoNeverReadWrite($write)) {
 						continue;
 					}
 					$message = 'Anonymous function has a use $%s that only flows into values that are never used.';

diff --git a/src/Rules/UnusedParametersCheck.php b/src/Rules/UnusedParametersCheck.php
@@ -72,7 +72,7 @@ public function getUnusedParameterErrors(
 					continue;
 				}
 				if ($node->isRead($write)) {
-					if ($unusedFlowMessage === null || $unusedFlowIdentifier === null) {
+					if ($unusedFlowMessage === null || $unusedFlowIdentifier === null || $node->flowsIntoNeverReadWrite($write)) {
 						continue;
 					}
 					$message = $unusedFlowMessage;

diff --git a/tests/PHPStan/Analyser/AnalyserIntegrationTest.php b/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
@@ -1407,16 +1407,10 @@ public function testBug10847(): void
 	{
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-10847.php');
 		// The loop appends to $overloads instead of $processedOverloads.
-		$this->assertCount(3, $errors);
-		$this->assertSame('Foreach key variable $args only flows into values that are never used.', $errors[0]->getMessage());
-		$this->assertSame('foreach.unusedKeyFlow', $errors[0]->getIdentifier());
-		$this->assertSame(158, $errors[0]->getLine());
-		$this->assertSame('Foreach value variable $callback only flows into values that are never used.', $errors[1]->getMessage());
-		$this->assertSame('foreach.unusedValueFlow', $errors[1]->getIdentifier());
-		$this->assertSame(158, $errors[1]->getLine());
-		$this->assertSame('Value assigned to $overloads[] is never read.', $errors[2]->getMessage());
-		$this->assertSame('assign.unused', $errors[2]->getIdentifier());
-		$this->assertSame(159, $errors[2]->getLine());
+		$this->assertCount(1, $errors);
+		$this->assertSame('Value assigned to $overloads[] is never read.', $errors[0]->getMessage());
+		$this->assertSame('assign.unused', $errors[0]->getIdentifier());
+		$this->assertSame(159, $errors[0]->getLine());
 	}
 
 	#[RequiresPhp('>= 8.1.0')]

diff --git a/tests/PHPStan/Rules/Classes/UnusedConstructorParametersRuleTest.php b/tests/PHPStan/Rules/Classes/UnusedConstructorParametersRuleTest.php
@@ -97,7 +97,6 @@ public function testResolvedDynamicUsages(): void
 	public function testValueFlow(): void
 	{
 		$this->analyse([__DIR__ . '/data/unused-constructor-parameters-value-flow.php'], [
-			['Constructor of class UnusedConstructorParametersValueFlow\Foo has a parameter $covered that only flows into values that are never used.', 10],
 			['Constructor of class UnusedConstructorParametersValueFlow\Foo has a parameter $input that only flows into values that are never used.', 10],
 			['Constructor of class UnusedConstructorParametersValueFlow\Foo has an unused parameter $overwritten.', 10],
 		]);

diff --git a/tests/PHPStan/Rules/DeadCode/UnusedVariableRuleTest.php b/tests/PHPStan/Rules/DeadCode/UnusedVariableRuleTest.php
@@ -85,7 +85,6 @@ public function testRule(): void
 			['Variable $x is never read.', 223],
 			['Value assigned to $x[] is never read.', 250],
 			['Value assigned to $x[\'k\'] is never read.', 251],
-			['Value assigned to variable $s only flows into values that are never used.', 263],
 			['Value assigned to variable $s is never read.', 264],
 			['Variable $a is never read.', 269],
 			['Variable $a is never read.', 276],
@@ -96,7 +95,6 @@ public function testRule(): void
 			['Variable $b is never read.', 614],
 			['Variable $a is never read.', 632],
 			['Variable $a is never read.', 637],
-			['Value assigned to variable $a only flows into values that are never used.', 702],
 			['Value assigned to variable $a is never read.', 703],
 			['Value assigned to variable $b only flows into values that are never used.', 709],
 			['Value assigned to variable $b only flows into values that are never used.', 719],
@@ -117,7 +115,6 @@ public function testPhp8(): void
 		$this->analyse([__DIR__ . '/data/unused-variable-php8.php'], [
 			['Catch variable $e is never read.', 23],
 			['Value assigned to variable $nightsFrom is never read.', 98],
-			['Value assigned to variable $a only flows into values that are never used.', 107],
 			['Variable $b is never read.', 108],
 			['Variable $b is never read.', 116],
 		]);
@@ -160,7 +157,6 @@ public function testBug14258(): void
 	public function testBug12012(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-12012.php'], [
-			['Value assigned to variable $s1 only flows into values that are never used.', 9],
 			['Value assigned to variable $s1 is never read.', 10],
 			['Value assigned to variable $s1 is never read.', 12],
 		]);
@@ -301,42 +297,26 @@ public function testBroadCatchesIncludeImplicitThrows(): void
 	public function testValueFlow(): void
 	{
 		$this->analyse([__DIR__ . '/data/unused-variable-value-flow.php'], [
-			['Value assigned to variable $a only flows into values that are never used.', 27],
 			['Value assigned to variable $a is never read.', 28],
-			['Value assigned to variable $s only flows into values that are never used.', 40],
-			['Value assigned to variable $s only flows into values that are never used.', 41],
 			['Value assigned to variable $s is never read.', 42],
-			['Value assigned to variable $i only flows into values that are never used.', 54],
-			['Value of variable $i after ++ only flows into values that are never used.', 55],
-			['Value of variable $i after ++ only flows into values that are never used.', 56],
-			['Value of variable $i after -- only flows into values that are never used.', 57],
 			['Value of variable $i after -- is never read.', 58],
 			['Value of variable $i after ++ is never read.', 71],
-			['Value assigned to variable $i only flows into values that are never used.', 76],
 			['Value of variable $i after ++ is never read.', 77],
 			['Variable $j is never read.', 77],
 			['Value assigned to variable $n only flows into values that are never used.', 98],
 			['Value assigned to variable $n only flows into values that are never used.', 100],
-			['Value assigned to variable $a only flows into values that are never used.', 117],
 			['Variable $ok is never read.', 118],
-			['Value assigned to variable $a only flows into values that are never used.', 130],
 			['Variable $b is never read.', 131],
 			['Variable $b is never read.', 144],
 			['Variable $b is never read.', 150],
-			['Value assigned to variable $a only flows into values that are never used.', 155],
 			['Variable $arr is never read.', 156],
-			['Value assigned to variable $a only flows into values that are never used.', 168],
 			['Variable $b is never read.', 169],
 			['Variable $c is never read.', 170],
-			['Value assigned to variable $a only flows into values that are never used.', 175],
 			['Variable $b is never read.', 176],
 			['Variable $c is never read.', 177],
 			['Variable $d is never read.', 178],
-			['Value assigned to variable $a only flows into values that are never used.', 183],
 			['Variable $b is never read.', 184],
-			['Value assigned to variable $a only flows into values that are never used.', 189],
 			['Variable $b is never read.', 190],
-			['Value assigned to variable $d only flows into values that are never used.', 195],
 			['Variable $b is never read.', 196],
 			['Variable $b is never read.', 202],
 			['Variable $b is never read.', 209],
@@ -356,31 +336,20 @@ public function testValueFlow(): void
 			['Variable $b is never read.', 289],
 			['Variable $a is never read.', 295],
 			['Variable $b is never read.', 302],
-			['Value assigned to variable $c only flows into values that are never used.', 308],
 			['Variable $b is never read.', 309],
 			['Variable $a is never read.', 309],
 			['Variable $b is never read.', 315],
-			['Value assigned to variable $a only flows into values that are never used.', 321],
 			['Variable $b is never read.', 322],
-			['Value assigned to variable $v only flows into values that are never used.', 329],
 			['Value assigned to $a[\'x\'] is never read.', 331],
-			['Value assigned to variable $a only flows into values that are never used.', 344],
 			['Variable $b is never read.', 345],
-			['Value assigned to variable $i only flows into values that are never used.', 357],
-			['Value assigned to variable $a only flows into values that are never used.', 358],
 			['Variable $b is never read.', 359],
 			['Variable $a is never read.', 364],
-			['Value assigned to variable $a only flows into values that are never used.', 369],
-			['Value assigned to variable $b only flows into values that are never used.', 370],
-			['Value assigned to variable $c only flows into values that are never used.', 371],
 			['Variable $d is never read.', 372],
 			['Value assigned to variable $s only flows into values that are never used.', 395],
 			['Foreach value variable $v only flows into values that are never used.', 396],
 			['Value assigned to variable $s only flows into values that are never used.', 397],
-			['Value assigned to variable $a only flows into values that are never used.', 403],
 			['Value assigned to variable $a is never read.', 404],
 			['Value assigned to variable $s is never read.', 477],
-			['Value assigned to variable $s only flows into values that are never used.', 483],
 			['Value assigned to variable $s is never read.', 484],
 			['Variable $x is never read.', 484],
 		]);
@@ -403,7 +372,6 @@ public function testOffsets(): void
 			['Offset 2 of array assigned to variable $a is never read.', 136],
 			['Offset 6 of array assigned to variable $a is never read.', 142],
 			['Offset \'x\' of array assigned to variable $a is never read.', 149],
-			['Value assigned to variable $v only flows into values that are never used.', 156],
 			['Offset \'x\' of array assigned to variable $a is never read.', 157],
 			['Offset \'y\' of array assigned to variable $a is never read.', 163],
 			['Offset \'y\' of array assigned to variable $a is never read.', 169],
@@ -415,9 +383,7 @@ public function testOffsets(): void
 			['Value assigned to $a[] is never read.', 247],
 			['Value assigned to $a[\'x\'][\'y\'] is never read.', 260],
 			['Offset \'x\' of array assigned to variable $a is never read.', 280],
-			['Value assigned to variable $a only flows into values that are never used.', 294],
 			['Value assigned to $a[\'x\'] is never read.', 295],
-			['Value assigned to variable $a only flows into values that are never used.', 314],
 			['Value of $a[\'n\'] after ++ is never read.', 315],
 			['Value assigned to $s[0] is never read.', 328],
 			['Value assigned to $a[\'x\'] is never read.', 356],
@@ -436,7 +402,6 @@ public function testOffsets(): void
 			['Value assigned to $cache[\'x\'] is never read.', 565],
 			['Variable $v is never read.', 565],
 
-			['Offset \'x\' of array assigned to variable $a only flows into values that are never used.', 570],
 			['Variable $b is never read.', 571],
 		]);
 	}
@@ -499,15 +464,10 @@ public function testFlowMessages(): void
 			['Value assigned to variable $k only flows into values that are never used.', 86],
 			['Offset \'x\' of array assigned to variable $a only flows into values that are never used.', 93],
 			['Value assigned to $a[\'x\'] only flows into values that are never used.', 95],
-			['Value assigned to variable $a only flows into values that are never used.', 102],
 			['Variable $b is never read.', 103],
-			['Value assigned to variable $a only flows into values that are never used.', 108],
-			['Value assigned to variable $a only flows into values that are never used.', 109],
 			['Value assigned to variable $a is never read.', 110],
-			['Value assigned to variable $c only flows into values that are never used.', 115],
 			['Variable $a is never read.', 116],
 			['Variable $b is never read.', 116],
-			['Value assigned to variable $v only flows into values that are never used.', 121],
 			['Offset \'x\' of array assigned to variable $a is never read.', 122],
 		]);
 	}
@@ -518,7 +478,6 @@ public function testFlowMessagesCatch(): void
 		$this->analyse([__DIR__ . '/data/unused-variable-flow-messages-catch.php'], [
 			['Catch variable $e only flows into values that are never used.', 15],
 			['Value assigned to variable $e only flows into values that are never used.', 17],
-			['Catch variable $e only flows into values that are never used.', 26],
 			['Variable $copy is never read.', 27],
 		]);
 	}

diff --git a/tests/PHPStan/Rules/DeadCode/data/unused-variable-offsets.php b/tests/PHPStan/Rules/DeadCode/data/unused-variable-offsets.php
@@ -153,7 +153,7 @@ function literalOffsetUnset(): void
 
 function literalItemValueFlow(): void
 {
-	$v = source(); // unused $v
+	$v = source();
 	$a = ['x' => $v, 'y' => 2]; // unused offset 'x' of $a
 	sink($a['y']);
 }
@@ -567,7 +567,7 @@ function dimWriteCoalesceAssignValueFlow(): void
 
 function literalItemReadIntoUnused(): void
 {
-	$a = ['x' => 1, 'y' => 2]; // offset 'x' of $a only flows into values that are never used
+	$a = ['x' => 1, 'y' => 2];
 	$b = $a['x']; // unused $b
 	sink($a['y']);
 }
diff --git a/tests/PHPStan/Rules/DeadCode/data/unused-variable-php8.php b/tests/PHPStan/Rules/DeadCode/data/unused-variable-php8.php
@@ -104,7 +104,7 @@ public function unreadArgumentVariable(): void
 
 function matchArmFlow(): void
 {
-	$a = source(); // unused $a
+	$a = source();
 	$b = match (true) { // unused $b
 		default => $a,
 	};