TASK: Infer types in arms of ternary

`nullableString ? nullableString : "fallback"`

will be a string

Author: mhsdesign

src/Target/Php/Transpiler/TypeReference/TypeReferenceTranspiler.php

@@ -27,7 +27,6 @@
 use PackageFactory\ComponentEngine\TypeSystem\Type\BooleanType\BooleanType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\ComponentType\ComponentType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\EnumType\EnumType;
-use PackageFactory\ComponentEngine\TypeSystem\Type\NullType\NullType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\NumberType\NumberType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\SlotType\SlotType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\StringType\StringType;
@@ -55,12 +54,8 @@ public function transpile(TypeReferenceNode $typeReferenceNode): string
 
     private function transpileUnionType(UnionType $unionType, TypeReferenceNode $typeReferenceNode): string
     {
-        if (count($unionType->members) === 2 && $otherMemberTypeIfOneMemberIsNullType = match (NullType::class) {
-            $unionType->members[0]::class => $unionType->members[1],
-            $unionType->members[1]::class => $unionType->members[0],
-            default => null
-        }) {
-            return $this->transpileNullableType($otherMemberTypeIfOneMemberIsNullType, $typeReferenceNode);
+        if (count($unionType->members) === 2 && $unionType->isNullable()) {
+            return $this->transpileNullableType($unionType->withoutNullable(), $typeReferenceNode);
         }
 
         throw new \Exception('@TODO Transpilation of complex union types is not implemented');

src/TypeSystem/Resolver/TernaryOperation/TernaryOperationTypeResolver.php

@@ -23,9 +23,12 @@
 namespace PackageFactory\ComponentEngine\TypeSystem\Resolver\TernaryOperation;
 
 use PackageFactory\ComponentEngine\Parser\Ast\BooleanLiteralNode;
+use PackageFactory\ComponentEngine\Parser\Ast\IdentifierNode;
 use PackageFactory\ComponentEngine\Parser\Ast\TernaryOperationNode;
 use PackageFactory\ComponentEngine\TypeSystem\Resolver\Expression\ExpressionTypeResolver;
+use PackageFactory\ComponentEngine\TypeSystem\Scope\ShallowScope\ShallowScope;
 use PackageFactory\ComponentEngine\TypeSystem\ScopeInterface;
+use PackageFactory\ComponentEngine\TypeSystem\Type\NullType\NullType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\UnionType\UnionType;
 use PackageFactory\ComponentEngine\TypeSystem\TypeInterface;
 
@@ -41,14 +44,39 @@ public function resolveTypeOf(TernaryOperationNode $ternaryOperationNode): TypeI
         $expressionTypeResolver = new ExpressionTypeResolver(
             scope: $this->scope
         );
-        $conditionNode = $ternaryOperationNode->condition->root;
+        $conditionNode = $ternaryOperationNode->condition;
 
-        if ($conditionNode instanceof BooleanLiteralNode) {
-            return $conditionNode->value
+        $rootType = $expressionTypeResolver->resolveTypeOf($conditionNode);
+
+        if ($conditionNode->root instanceof BooleanLiteralNode) {
+            return $conditionNode->root->value
                 ? $expressionTypeResolver->resolveTypeOf($ternaryOperationNode->true)
                 : $expressionTypeResolver->resolveTypeOf($ternaryOperationNode->false);
         }
 
+        if ($conditionNode->root instanceof IdentifierNode && $rootType instanceof UnionType && $rootType->isNullable()) {
+            $trueExpressionTypeResolver = new ExpressionTypeResolver(
+                scope: new ShallowScope(
+                    $conditionNode->root->value,
+                    $rootType->withoutNullable(),
+                    $this->scope
+                )
+            );
+
+            $falseExpressionTypeResolver = new ExpressionTypeResolver(
+                scope: new ShallowScope(
+                    $conditionNode->root->value,
+                    NullType::get(),
+                    $this->scope
+                )
+            );
+
+            return UnionType::of(
+                $trueExpressionTypeResolver->resolveTypeOf($ternaryOperationNode->true),
+                $falseExpressionTypeResolver->resolveTypeOf($ternaryOperationNode->false)
+            );
+        }
+
         return UnionType::of(
             $expressionTypeResolver->resolveTypeOf($ternaryOperationNode->true),
             $expressionTypeResolver->resolveTypeOf($ternaryOperationNode->false)

src/TypeSystem/Scope/ShallowScope/ShallowScope.php

@@ -0,0 +1,51 @@
+<?php
+
+/**
+ * PackageFactory.ComponentEngine - Universal View Components for PHP
+ *   Copyright (C) 2022 Contributors of PackageFactory.ComponentEngine
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace PackageFactory\ComponentEngine\TypeSystem\Scope\ShallowScope;
+
+use PackageFactory\ComponentEngine\Parser\Ast\TypeReferenceNode;
+use PackageFactory\ComponentEngine\TypeSystem\ScopeInterface;
+use PackageFactory\ComponentEngine\TypeSystem\TypeInterface;
+
+final class ShallowScope implements ScopeInterface
+{
+    public function __construct(
+        private readonly string $overriddenName,
+        private readonly TypeInterface $overriddenType,
+        private readonly ScopeInterface $parentScope
+    ) {
+    }
+
+    public function lookupTypeFor(string $name): ?TypeInterface
+    {
+        if ($this->overriddenName === $name) {
+            return $this->overriddenType;
+        }
+
+        return $this->parentScope->lookupTypeFor($name);
+    }
+
+    public function resolveTypeReference(TypeReferenceNode $typeReferenceNode): TypeInterface
+    {
+        return $this->parentScope->resolveTypeReference($typeReferenceNode);
+    }
+}

src/TypeSystem/Type/UnionType/UnionType.php

@@ -22,6 +22,7 @@
 
 namespace PackageFactory\ComponentEngine\TypeSystem\Type\UnionType;
 
+use PackageFactory\ComponentEngine\TypeSystem\Type\NullType\NullType;
 use PackageFactory\ComponentEngine\TypeSystem\TypeInterface;
 
 final class UnionType implements TypeInterface
@@ -46,6 +47,28 @@ private function __construct(TypeInterface ...$members)
         $this->members = $uniqueMembers;
     }
 
+    public function isNullable(): bool
+    {
+        foreach ($this->members as $member) {
+            if ($member->is(NullType::get())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public function withoutNullable(): TypeInterface
+    {
+        $nonNullMembers = [];
+        foreach ($this->members as $member) {
+            if ($member->is(NullType::get())) {
+                continue;
+            }
+            $nonNullMembers[] = $member;
+        }
+        return self::of(...$nonNullMembers);
+    }
+
     public static function of(TypeInterface ...$members): TypeInterface
     {
         $union = new self(...$members);

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

@@ -26,6 +26,7 @@
 use PackageFactory\ComponentEngine\Parser\Ast\TernaryOperationNode;
 use PackageFactory\ComponentEngine\Test\Unit\TypeSystem\Scope\Fixtures\DummyScope;
 use PackageFactory\ComponentEngine\TypeSystem\Resolver\TernaryOperation\TernaryOperationTypeResolver;
+use PackageFactory\ComponentEngine\TypeSystem\Type\NullType\NullType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\NumberType\NumberType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\StringType\StringType;
 use PackageFactory\ComponentEngine\TypeSystem\Type\UnionType\UnionType;
@@ -46,7 +47,13 @@ public function ternaryOperationExamples(): array
             '1 < 2 ? variableOfTypeString : variableOfTypeNumber' => [
                 '1 < 2 ? variableOfTypeString : variableOfTypeNumber', 
                 UnionType::of(NumberType::get(), StringType::get())
-            ]
+            ],
+            'nullableString ? nullableString : "fallback"' => [
+                'nullableString ? nullableString : "fallback"', StringType::get()
+            ],
+            'nullableString ? null : nullableString' => [
+                'nullableString ? null : nullableString', NullType::get()
+            ],
         ];
     }
 
@@ -62,6 +69,7 @@ public function resolvesTernaryOperationToResultingType(string $ternaryExpressio
         $scope = new DummyScope([
             'variableOfTypeString' => StringType::get(),
             'variableOfTypeNumber' => NumberType::get(),
+            'nullableString' => UnionType::of(StringType::get(), NullType::get())
         ]);
         $ternaryOperationTypeResolver = new TernaryOperationTypeResolver(
             scope: $scope