Fix #714 - fix trait class constants

src/Psalm/Checker/ClassLikeChecker.php

@@ -242,6 +242,7 @@ abstract class ClassLikeChecker extends SourceChecker implements StatementsSourc
         $interface_exists = $codebase->interfaceExists($fq_class_name);
 
         if (!$class_exists && !$interface_exists) {
+            if (!$codebase->classlikes->traitExists($fq_class_name)) {
                 if (IssueBuffer::accepts(
                     new UndefinedClass(
                         'Class or interface ' . $fq_class_name . ' does not exist',
@@ -252,6 +253,7 @@ abstract class ClassLikeChecker extends SourceChecker implements StatementsSourc
                 )) {
                     return false;
                 }
+            }
 
             return null;
         }

src/Psalm/Codebase/ClassLikes.php

@@ -508,6 +508,16 @@ class ClassLikes
         return $storage->parent_interfaces;
     }
 
+    /**
+     * @param  string         $fq_trait_name
+     *
+     * @return bool
+     */
+    public function traitExists($fq_trait_name)
+    {
+        return $this->hasFullyQualifiedTraitName($fq_trait_name);
+    }
+
     /**
      * Determine whether or not a class has the correct casing
      *

tests/TraitTest.php

@@ -522,6 +522,20 @@ class TraitTest extends TestCase
                         }
                     }',
             ],
+            'traitClassConst' => [
+                '<?php
+                    trait A {
+                        public function foo(): string {
+                            return B::class;
+                        }
+                    }
+
+                    trait B {}
+
+                    class C {
+                        use A;
+                    }'
+            ],
         ];
     }