Allow class constants to refer to other constants

This change introduces the TMixedDeferredConstant type, which marks a
type as being a constant that needs to be resolved at a later stage.

Fixes: vimeo#1551

src/Psalm/Internal/Analyzer/Statements/Expression/Fetch/ConstFetchAnalyzer.php

@@ -18,6 +18,7 @@
 use Psalm\IssueBuffer;
 use Psalm\Type;
 use function implode;
+use function is_null;
 use function strtolower;
 use function explode;
 
@@ -352,7 +353,18 @@ public static function analyzeClassConst(
             if (isset($class_constants[$stmt->name->name])
                 && ($first_part_lc !== 'static' || $class_const_storage->final)
             ) {
-                $stmt->inferredType = clone $class_constants[$stmt->name->name];
+                $inferred_type = clone $class_constants[$stmt->name->name];
+                if ($inferred_type->isMixedDeferredConstant()) {
+                    $inferred_type = $statements_analyzer->getConstType(
+                        $stmt->name->name,
+                        $stmt->name instanceof PhpParser\Node\Name\FullyQualified,
+                        $context
+                    );
+                }
+                if (is_null($inferred_type)) {
+                    $inferred_type = Type::getMixed();
+                }
+                $stmt->inferredType = $inferred_type;
                 $context->vars_in_scope[$const_id] = $stmt->inferredType;
             } else {
                 $stmt->inferredType = Type::getMixed();

src/Psalm/Internal/Codebase/Populator.php

@@ -134,7 +134,8 @@ public function populateCodebase(\Psalm\Codebase $codebase)
                         $class_storage->name
                     );
 
-                    $class_storage->public_class_constants[$const_name] = $const_type ?: Type::getMixed();
+                    $class_storage->public_class_constants[$const_name] =
+                        $const_type ?: Type::getMixedDeferredConstant();
                 }
 
                 foreach ($class_storage->protected_class_constant_nodes as $const_name => $node) {
@@ -147,7 +148,8 @@ public function populateCodebase(\Psalm\Codebase $codebase)
                         $class_storage->name
                     );
 
-                    $class_storage->protected_class_constants[$const_name] = $const_type ?: Type::getMixed();
+                    $class_storage->protected_class_constants[$const_name] =
+                        $const_type ?: Type::getMixedDeferredConstant();
                 }
 
                 foreach ($class_storage->private_class_constant_nodes as $const_name => $node) {
@@ -160,7 +162,8 @@ public function populateCodebase(\Psalm\Codebase $codebase)
                         $class_storage->name
                     );
 
-                    $class_storage->private_class_constants[$const_name] = $const_type ?: Type::getMixed();
+                    $class_storage->private_class_constants[$const_name] =
+                        $const_type ?: Type::getMixedDeferredConstant();
                 }
             }
         }
@@ -545,11 +548,11 @@ private function populateDataFromParentClass(
             );
 
             foreach ($parent_storage->public_class_constant_nodes as $name => $_) {
-                $storage->public_class_constants[$name] = Type::getMixed();
+                $storage->public_class_constants[$name] = Type::getMixedDeferredConstant();
             }
 
             foreach ($parent_storage->protected_class_constant_nodes as $name => $_) {
-                $storage->protected_class_constants[$name] = Type::getMixed();
+                $storage->protected_class_constants[$name] = Type::getMixedDeferredConstant();
             }
 
             $storage->pseudo_property_get_types += $parent_storage->pseudo_property_get_types;
@@ -598,7 +601,7 @@ private function populateInterfaceDataFromParentInterfaces(
             );
 
             foreach ($parent_interface_storage->public_class_constant_nodes as $name => $_) {
-                $storage->public_class_constants[$name] = Type::getMixed();
+                $storage->public_class_constants[$name] = Type::getMixedDeferredConstant();
             }
 
             if ($parent_interface_storage->template_types) {
@@ -685,7 +688,7 @@ private function populateDataFromImplementedInterfaces(
             );
 
             foreach ($implemented_interface_storage->public_class_constant_nodes as $name => $_) {
-                $storage->public_class_constants[$name] = Type::getMixed();
+                $storage->public_class_constants[$name] = Type::getMixedDeferredConstant();
             }
 
             $storage->invalid_dependencies = array_merge(

src/Psalm/Type.php

@@ -41,6 +41,7 @@
 use Psalm\Type\Atomic\TLiteralInt;
 use Psalm\Type\Atomic\TLiteralString;
 use Psalm\Type\Atomic\TMixed;
+use Psalm\Type\Atomic\TMixedDeferredConstant;
 use Psalm\Type\Atomic\TNamedObject;
 use Psalm\Type\Atomic\TNull;
 use Psalm\Type\Atomic\TNumeric;
@@ -1251,6 +1252,16 @@ public static function getMixed($from_loop_isset = false)
         return new Union([$type]);
     }
 
+    /**
+     * @return Type\Union
+     */
+    public static function getMixedDeferredConstant()
+    {
+        $type = new TMixedDeferredConstant();
+
+        return new Union([$type]);
+    }
+
     /**
      * @return Type\Union
      */

src/Psalm/Type/Atomic/TMixedDeferredConstant.php

@@ -0,0 +1,13 @@
+<?php
+namespace Psalm\Type\Atomic;
+
+class TMixedDeferredConstant extends TMixed
+{
+    /**
+     * @return string
+     */
+    public function getId()
+    {
+        return 'mixed-deferred-constant';
+    }
+}

src/Psalm/Type/Union.php

@@ -847,6 +847,15 @@ public function isVanillaMixed()
             && get_class($this->types['mixed']) === Type\Atomic\TMixed::class;
     }
 
+    /**
+     * @return bool
+     */
+    public function isMixedDeferredConstant()
+    {
+        return isset($this->types['mixed'])
+            && get_class($this->types['mixed']) === Type\Atomic\TMixedDeferredConstant::class;
+    }
+
     /**
      * @return bool
      */

tests/ConstantTest.php

@@ -400,6 +400,14 @@ public static function bar() : bool {
                         }
                     }'
             ],
+            'constantDeferredConstants' => [
+                '<?php
+                    const A = 1;
+                    class B {
+                        public const C = A;
+                    }
+                    echo B::C;'
+            ],
         ];
     }