Flag duplicate constants

Fixes vimeo/psalm#6882
Addresses p1 from vimeo/psalm#6471

config.xsd

@@ -240,6 +240,7 @@
             <xs:element name="DocblockTypeContradiction" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateArrayKey" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateClass" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="DuplicateConstant" type="ClassIssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateEnumCase" type="ClassIssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateEnumCaseValue" type="ClassIssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateFunction" type="IssueHandlerType" minOccurs="0" />

docs/running_psalm/issues.md

@@ -20,6 +20,7 @@
  - [DocblockTypeContradiction](issues/DocblockTypeContradiction.md)
  - [DuplicateArrayKey](issues/DuplicateArrayKey.md)
  - [DuplicateClass](issues/DuplicateClass.md)
+ - [DuplicateConstant](issues/DuplicateConstant.md)
  - [DuplicateFunction](issues/DuplicateFunction.md)
  - [DuplicateMethod](issues/DuplicateMethod.md)
  - [DuplicateParam](issues/DuplicateParam.md)

docs/running_psalm/issues/DuplicateConstant.md

@@ -0,0 +1,16 @@
+# DuplicateConstant
+
+Emitted when a constant is defined twice in a single class or when there's a
+clash between a constant and an enum case.
+
+```php
+<?php
+class C {
+    public const A = 1;
+    public const A = 2;
+}
+```
+
+## Why this is bad
+
+The above code won’t compile.

src/Psalm/Internal/PhpVisitor/Reflector/ClassLikeNodeScanner.php

@@ -28,6 +28,7 @@ use Psalm\Internal\Type\TypeAlias;
 use Psalm\Internal\Type\TypeParser;
 use Psalm\Internal\Type\TypeTokenizer;
 use Psalm\Issue\DuplicateClass;
+use Psalm\Issue\DuplicateConstant;
 use Psalm\Issue\DuplicateEnumCase;
 use Psalm\Issue\InvalidDocblock;
 use Psalm\Issue\InvalidEnumBackingType;
@@ -1193,6 +1194,19 @@ class ClassLikeNodeScanner
                 $fq_classlike_name
             );
 
+            if (isset($storage->constants[$const->name->name])
+                || isset($storage->enum_cases[$const->name->name])
+            ) {
+                if (IssueBuffer::accepts(new DuplicateConstant(
+                    'Constant names should be unique',
+                    new CodeLocation($this->file_scanner, $const),
+                    $fq_classlike_name
+                ))) {
+                    // fall through
+                }
+                continue;
+            }
+
             $storage->constants[$const->name->name] = $constant_storage = new \Psalm\Storage\ClassConstantStorage(
                 $const_type,
                 $stmt->isProtected()
@@ -1271,6 +1285,17 @@ class ClassLikeNodeScanner
         ClassLikeStorage $storage,
         string $fq_classlike_name
     ): void {
+        if (isset($storage->constants[$stmt->name->name])) {
+            if (IssueBuffer::accepts(new DuplicateConstant(
+                'Constant names should be unique',
+                new CodeLocation($this->file_scanner, $stmt),
+                $fq_classlike_name
+            ))) {
+                // fall through
+            }
+            return;
+        }
+
         $enum_value = null;
 
         if ($stmt->expr !== null) {

src/Psalm/Issue/DuplicateConstant.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Psalm\Issue;
+
+class DuplicateConstant extends ClassIssue
+{
+    public const ERROR_LEVEL = -1;
+    public const SHORTCODE = 302;
+}

tests/ConstantTest.php

@@ -1430,6 +1430,39 @@ class ConstantTest extends TestCase
                     }',
                 'error_message' => 'UndefinedClass',
             ],
+            'duplicateConstants' => [
+                '<?php
+                    class A {
+                        public const B = 1;
+                        public const B = 2;
+                    }
+                ',
+                'error_message' => 'DuplicateConstant',
+            ],
+            'constantDuplicatesEnumCase' => [
+                '<?php
+                    enum State {
+                        case Open;
+                        public const Open = 1;
+                    }
+                ',
+                'error_message' => 'DuplicateConstant',
+                [],
+                false,
+                '8.1',
+            ],
+            'enumCaseDuplicatesConstant' => [
+                '<?php
+                    enum State {
+                        public const Open = 1;
+                        case Open;
+                    }
+                ',
+                'error_message' => 'DuplicateConstant',
+                [],
+                false,
+                '8.1',
+            ],
         ];
     }
 }