Flag class constant references where LHS is ordinary string

src/Psalm/Internal/Analyzer/Statements/Expression/ClassConstAnalyzer.php

@@ -25,6 +25,7 @@
 use Psalm\Issue\InternalClass;
 use Psalm\Issue\InvalidClassConstantType;
 use Psalm\Issue\InvalidConstantAssignmentValue;
+use Psalm\Issue\InvalidStringClass;
 use Psalm\Issue\LessSpecificClassConstantType;
 use Psalm\Issue\NonStaticSelfCall;
 use Psalm\Issue\OverriddenFinalConstant;
@@ -41,6 +42,7 @@
 use Psalm\Type\Atomic\TMixed;
 use Psalm\Type\Atomic\TNamedObject;
 use Psalm\Type\Atomic\TObject;
+use Psalm\Type\Atomic\TString;
 use Psalm\Type\Atomic\TTemplateParam;
 use Psalm\Type\Atomic\TTemplateParamClass;
 use Psalm\Type\Union;
@@ -467,6 +469,17 @@ public static function analyzeFetch(
                 } elseif ($atomic_type instanceof TLiteralClassString) {
                     $fq_class_name = $atomic_type->value;
                     $lhs_type_definite_class = $atomic_type->definite_class;
+                } elseif ($atomic_type instanceof TString
+                    && !$atomic_type instanceof TClassString
+                    && !$codebase->config->allow_string_standin_for_class
+                ) {
+                    IssueBuffer::maybeAdd(
+                        new InvalidStringClass(
+                            'String cannot be used as a class',
+                            new CodeLocation($statements_analyzer->getSource(), $stmt->class),
+                        ),
+                        $statements_analyzer->getSuppressedIssues(),
+                    );
                 }
             }
 

tests/ConstantTest.php

@@ -2030,6 +2030,18 @@ class Foo
                 'ignored_issues' => [],
                 'php_version' => '8.0',
             ],
+            'classStringIsRequiredToAccessClassConstant' => [
+                'code' => '<?php
+                    class Foo {
+                        public const BAR = "bar";
+                    }
+
+                    $class = "Foo";
+
+                    $class::BAR;
+                ',
+                'error_message' => 'InvalidStringClass',
+            ],
         ];
     }
 }

tests/DocumentationTest.php

@@ -333,6 +333,7 @@ public function testShortcodesAreUnique(): void
         $all_shortcodes = [];
 
         foreach ($all_issues as $issue_type) {
+            /** @var class-string $issue_class */
             $issue_class = '\\Psalm\\Issue\\' . $issue_type;
             /** @var int $shortcode */
             $shortcode = $issue_class::SHORTCODE;