Carry template argument constraints of if/elseif/else branches ruled out by the condition onto the if result scope

src/Analyser/StmtHandler/IfHandler.php

@@ -54,6 +54,7 @@ public function processStmt(
 		$entryScope = $scope;
 		$flowBranches = [];
 		$elseFlow = null;
+		$deadBranchScopes = [];
 		$condResult = $nodeScopeResolver->processExprNode($stmt, $stmt->cond, $scope, $storage, $nodeCallback, ExpressionContext::createDeep($context->shouldResolveTemplateArguments()));
 		$dependencies[] = $condResult->getDependencies();
 		$nodeScopeResolver->callNodeCallback($nodeCallback, $stmt, $entryScope, $storage);
@@ -84,6 +85,8 @@ public function processStmt(
 				$endStatements[] = new InternalEndStatementResult($stmt, $branchScopeStatementResult);
 			}
 			$hasYield = $branchScopeStatementResult->hasYield() || $hasYield;
+		} else {
+			$deadBranchScopes[] = $branchScopeStatementResult->getScope();
 		}
 
 		$scope = $condResult->getFalseyScope();
@@ -119,6 +122,8 @@ public function processStmt(
 					$endStatements[] = new InternalEndStatementResult($elseif, $branchScopeStatementResult);
 				}
 				$hasYield = $hasYield || $branchScopeStatementResult->hasYield();
+			} else {
+				$deadBranchScopes[] = $branchScopeStatementResult->getScope();
 			}
 
 			if (
@@ -156,13 +161,21 @@ public function processStmt(
 					$endStatements[] = new InternalEndStatementResult($stmt->else, $branchScopeStatementResult);
 				}
 				$hasYield = $hasYield || $branchScopeStatementResult->hasYield();
+			} else {
+				$deadBranchScopes[] = $branchScopeStatementResult->getScope();
 			}
 		}
 
 		if ($finalScope === null) {
 			$finalScope = $scope;
 		}
 
+		// a branch the condition rules out is still walked and its rules still
+		// see its calls - their template arguments are resolved from it too
+		foreach ($deadBranchScopes as $deadBranchScope) {
+			$finalScope = $finalScope->addTemplateArgumentConstraints($deadBranchScope->getTemplateArgumentConstraints());
+		}
+
 		if ($stmt->else === null && !$ifAlwaysTrue && !$lastElseIfConditionIsTrue) {
 			$endStatements[] = new InternalEndStatementResult($stmt, new InternalStatementResult($finalScope, hasYield: $hasYield, isAlwaysTerminating: $alwaysTerminating, exitPoints: $exitPoints, throwPoints: $throwPoints, impurePoints: $impurePoints));
 		}

tests/PHPStan/Rules/Generators/YieldTypeRuleTest.php

@@ -5,6 +5,7 @@
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleLevelHelper;
 use PHPStan\Testing\RuleTestCase;
+use PHPUnit\Framework\Attributes\RequiresPhp;
 
 /**
  * @extends RuleTestCase<YieldTypeRule>
@@ -87,4 +88,10 @@ public function testYieldOversizedSelfRejection(): void
 		$this->analyse([__DIR__ . '/data/bug-yield-oversized-self-rejection.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0.0')]
+	public function testBug15476(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-15476.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Generators/data/bug-15476.php

@@ -0,0 +1,56 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug15476Generators;
+
+/**
+ * @template TKey of array-key
+ * @template TValue
+ */
+final class Box
+{
+}
+
+interface Factory
+{
+	/**
+	 * @template TKey of array-key
+	 * @template TValue
+	 * @param iterable<TKey, TValue> $value
+	 * @return Box<TKey, TValue>
+	 */
+	public function box(iterable $value = []): Box;
+}
+
+final class Item
+{
+}
+
+final class Example
+{
+	public function __construct(private Factory $factory)
+	{
+	}
+
+	/** @return \Generator<int, Box<int, Item>> */
+	public function deadBranch(Item $item): \Generator
+	{
+		if ($item === null) {
+			yield $this->factory->box();
+		}
+
+		yield $this->factory->box([$item]);
+	}
+
+	/** @return \Generator<int, Box<int, Item>> */
+	public function deadElse(Item $item): \Generator
+	{
+		if ($item !== null) {
+			yield $this->factory->box([$item]);
+		} else {
+			yield $this->factory->box();
+		}
+	}
+
+}

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -1419,4 +1419,10 @@ public function testBug13325(): void
 		$this->analyse([__DIR__ . '/data/bug-13325.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0.0')]
+	public function testBug15476(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-15476.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-15476.php

@@ -0,0 +1,102 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug15476;
+
+/**
+ * @template TKey of array-key
+ * @template TValue
+ */
+final class Box
+{
+}
+
+interface Factory
+{
+	/**
+	 * @template TKey of array-key
+	 * @template TValue
+	 * @param iterable<TKey, TValue> $value
+	 * @return Box<TKey, TValue>
+	 */
+	public function box(iterable $value = []): Box;
+}
+
+final class Item
+{
+}
+
+final class Example
+{
+	public function __construct(private Factory $factory)
+	{
+	}
+
+	/** @return Box<int, Item> */
+	public function deadBranch(Item $item): Box
+	{
+		if ($item === null) {
+			return $this->factory->box();
+		}
+
+		return $this->factory->box([$item]);
+	}
+
+	/** @return Box<int, Item> */
+	public function liveBranch(?Item $item): Box
+	{
+		if ($item === null) {
+			return $this->factory->box();
+		}
+
+		return $this->factory->box([$item]);
+	}
+
+	/** @return Box<int, Item> */
+	public function deadElseif(Item $item, bool $b): Box
+	{
+		if ($b) {
+			return $this->factory->box([$item]);
+		} elseif ($item === null) {
+			return $this->factory->box();
+		}
+
+		return $this->factory->box([$item]);
+	}
+
+	/** @return Box<int, Item> */
+	public function deadElse(Item $item): Box
+	{
+		if ($item !== null) {
+			return $this->factory->box([$item]);
+		} else {
+			return $this->factory->box();
+		}
+	}
+
+	/** @return Box<int, Item> */
+	public function deadElseAfterAlwaysTrueElseif(Item $item, bool $b): Box
+	{
+		if ($b) {
+			return $this->factory->box([$item]);
+		} elseif ($item !== null) {
+			return $this->factory->box([$item]);
+		} else {
+			return $this->factory->box();
+		}
+	}
+
+	/** @return Box<int, Item> */
+	public function deadNestedBranch(Item $item, bool $b): Box
+	{
+		if ($b) {
+			if ($item === null) {
+				return $this->factory->box();
+			}
+		}
+
+		return $this->factory->box([$item]);
+	}
+
+}

turbo-ext/src/IfHandler.cpp

@@ -105,6 +105,16 @@ void pushFlowBranch(zv::Arr &flowBranches, zv::Val conditionFlow, zval *branchFl
 	flowBranches.push(zv::Ref(branchFlow));
 }
 
+/* $deadBranchScopes[] = $branchScopeStatementResult->getScope(); false = pending exception */
+[[nodiscard]] bool pushDeadBranchScope(zv::Arr &deadBranchScopes, zval *branchResult)
+{
+	zv::Val hold;
+	zval *branchScope = pt_internal_statement_result_scope(branchResult, hold);
+	if (UNEXPECTED(branchScope == NULL)) return false;
+	deadBranchScopes.push(zv::Ref(branchScope));
+	return true;
+}
+
 } // namespace
 
 namespace phpstanturbo {
@@ -137,6 +147,7 @@ class IfHandler
 		zv::Arr dependencies = zv::Arr::empty();
 		zval *entryScope = scope;
 		zv::Arr flowBranches = zv::Arr::empty();
+		zv::Arr deadBranchScopes = zv::Arr::empty();
 		zv::Val elseFlow = zv::Val::null();
 
 		zval *cond = ptsh::readNodeProperty(pt_ih_cond_site, stmt, PT_LC("cond"));
@@ -200,6 +211,8 @@ class IfHandler
 				bool branchHasYield;
 				if (UNEXPECTED(!pt_internal_statement_result_has_yield(branchResult.raw(), branchHasYield))) return zv::Val();
 				hasYield = branchHasYield || hasYield;
+			} else if (UNEXPECTED(!pushDeadBranchScope(deadBranchScopes, branchResult.raw()))) {
+				return zv::Val();
 			}
 		}
 
@@ -258,6 +271,8 @@ class IfHandler
 				pushFlowBranch(flowBranches, std::move(conditionFlow), branchFlow);
 				if (!ifAlwaysTrue && !lastElseIfConditionIsTrue && elseIfConditionType.isTrue != PT_TRI_NO) {
 					if (UNEXPECTED(!mergeBranch(branchResult.raw(), exitPoints, throwPoints, impurePoints, finalScope, alwaysTerminating, endStatements, elseif, pt_ih_elseif_stmts_site, hasYield))) return zv::Val();
+				} else if (UNEXPECTED(!pushDeadBranchScope(deadBranchScopes, branchResult.raw()))) {
+					return zv::Val();
 				}
 
 				if (elseIfConditionType.isTrue == PT_TRI_YES) {
@@ -309,13 +324,25 @@ class IfHandler
 				if (UNEXPECTED(elseNode == NULL)) return zv::Val();
 				elseHold = zv::Val::copyOf(zv::Ref(elseNode));
 				if (UNEXPECTED(!mergeBranch(branchResult.raw(), exitPoints, throwPoints, impurePoints, finalScope, alwaysTerminating, endStatements, elseHold.raw(), pt_ih_else_stmts_site, hasYield))) return zv::Val();
+			} else if (UNEXPECTED(!pushDeadBranchScope(deadBranchScopes, branchResult.raw()))) {
+				return zv::Val();
 			}
 		}
 
 		if (finalScope.isNull()) {
 			finalScope = zv::Val::copyOf(zv::Ref(scopeValue.raw()));
 		}
 
+		// a branch the condition rules out is still walked and its rules still
+		// see its calls - their template arguments are resolved from it too
+		for (auto entry : zv::TableRef(deadBranchScopes.table())) {
+			zv::Val constraints = pt_mutating_scope_get_template_argument_constraints(Z_OBJ_P(entry.value().raw()));
+			if (UNEXPECTED(constraints.isUndef())) return zv::Val();
+			zv::Val constrained = pt_mutating_scope_add_template_argument_constraints(Z_OBJ_P(finalScope.raw()), constraints.raw());
+			if (UNEXPECTED(constrained.isUndef())) return zv::Val();
+			finalScope = std::move(constrained);
+		}
+
 		elseNode = ptsh::readNodeProperty(pt_ih_else_site, stmt, PT_LC("else"));
 		if (UNEXPECTED(elseNode == NULL)) return zv::Val();
 		if (Z_TYPE_P(elseNode) == IS_NULL && !ifAlwaysTrue && !lastElseIfConditionIsTrue) {