TASK: Type inference for null comparison in ternary

Author: mhsdesign

src/TypeSystem/Resolver/TernaryOperation/TernaryOperationTypeResolver.php

@@ -44,7 +44,8 @@ public function resolveTypeOf(TernaryOperationNode $ternaryOperationNode): TypeI
         );
         $conditionNode = $ternaryOperationNode->condition;
 
-        $conditionType = $expressionTypeResolver->resolveTypeOf($conditionNode);
+        // @todo for eager type checks?
+        $expressionTypeResolver->resolveTypeOf($conditionNode);
 
         if ($conditionNode->root instanceof BooleanLiteralNode) {
             return $conditionNode->root->value
@@ -55,7 +56,6 @@ public function resolveTypeOf(TernaryOperationNode $ternaryOperationNode): TypeI
         $trueExpressionTypeResolver = new ExpressionTypeResolver(
             scope: new TernaryBranchScope(
                 $ternaryOperationNode->condition,
-                $conditionType,
                 true,
                 $this->scope
             )
@@ -64,7 +64,6 @@ public function resolveTypeOf(TernaryOperationNode $ternaryOperationNode): TypeI
         $falseExpressionTypeResolver = new ExpressionTypeResolver(
             scope: new TernaryBranchScope(
                 $ternaryOperationNode->condition,
-                $conditionType,
                 false,
                 $this->scope
             )

src/TypeSystem/Scope/ShallowScope/TernaryBranchScope.php

@@ -22,8 +22,11 @@
 
 namespace PackageFactory\ComponentEngine\TypeSystem\Scope\ShallowScope;
 
+use PackageFactory\ComponentEngine\Definition\BinaryOperator;
+use PackageFactory\ComponentEngine\Parser\Ast\BinaryOperationNode;
 use PackageFactory\ComponentEngine\Parser\Ast\ExpressionNode;
 use PackageFactory\ComponentEngine\Parser\Ast\IdentifierNode;
+use PackageFactory\ComponentEngine\Parser\Ast\NullLiteralNode;
 use PackageFactory\ComponentEngine\Parser\Ast\TypeReferenceNode;
 use PackageFactory\ComponentEngine\TypeSystem\ScopeInterface;
 use PackageFactory\ComponentEngine\TypeSystem\Type\NullType\NullType;
@@ -34,21 +37,42 @@ final class TernaryBranchScope implements ScopeInterface
 {
     public function __construct(
         private readonly ExpressionNode $conditionNode,
-        private readonly TypeInterface $conditionType,
         private readonly bool $isBranchLeft,
         private readonly ScopeInterface $parentScope
     ) {
     }
 
     public function lookupTypeFor(string $name): ?TypeInterface
     {
+        $type = $this->parentScope->lookupTypeFor($name);
+
+        if (!$type instanceof UnionType || !$type->containsNull()) {
+            return $type;
+        }
+
         if ($this->conditionNode->root instanceof IdentifierNode && $this->conditionNode->root->value === $name) {
-            if ($this->conditionType instanceof UnionType && $this->conditionType->containsNull()) {
-                return $this->isBranchLeft ? $this->conditionType->withoutNull() : NullType::get();
+            return $this->isBranchLeft ? $type->withoutNull() : NullType::get();
+        }
+
+        if (($binaryOperationNode = $this->conditionNode->root) instanceof BinaryOperationNode) {
+            foreach ($binaryOperationNode->operands as $operand) {
+                if (!$operand->root instanceof NullLiteralNode
+                    && !($operand->root instanceof IdentifierNode && $operand->root->value === $name)
+                ) {
+                    return $type;
+                }
+            }
+
+            if ($binaryOperationNode->operator === BinaryOperator::EQUAL) {
+                return $this->isBranchLeft ? NullType::get() : $type->withoutNull();
+            }
+
+            if ($binaryOperationNode->operator === BinaryOperator::NOT_EQUAL) {
+                return $this->isBranchLeft ? $type->withoutNull() : NullType::get();
             }
         }
 
-        return $this->parentScope->lookupTypeFor($name);
+        return $type;
     }
 
     public function resolveTypeReference(TypeReferenceNode $typeReferenceNode): TypeInterface

test/Unit/TypeSystem/Resolver/TernaryOperation/TernaryOperationTypeResolverTest.php

@@ -51,6 +51,20 @@ public function ternaryOperationExamples(): array
             'nullableString ? nullableString : "fallback"' => [
                 'nullableString ? nullableString : "fallback"', StringType::get()
             ],
+            'nullableString === null ? "" : nullableString' => [
+                'nullableString === null ? "" : nullableString', StringType::get()
+            ],
+            // Tue es oder tue es nicht. Es gibt kein Versuchen.
+            'null === nullableString ? "" : nullableString' => [
+                'null === nullableString ? "" : nullableString', StringType::get()
+            ],
+            'nullableString !== null ? nullableString : ""' => [
+                'nullableString !== null ? nullableString : ""', StringType::get()
+            ],
+            // Patience you must have my young Padawan.
+            'null !== nullableString ? nullableString : ""' => [
+                'null !== nullableString ? nullableString : ""', StringType::get()
+            ],
             'nullableString ? null : nullableString' => [
                 'nullableString ? null : nullableString', NullType::get()
             ],