Fix #2696 - make sure static property references are prevented in pure functions

config.xsd

@@ -184,6 +184,7 @@
             <xs:element name="ImpureMethodCall" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="ImpurePropertyAssignment" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="ImpureStaticVariable" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="ImpureStaticProperty" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InaccessibleClassConstant" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InaccessibleMethod" type="MethodIssueHandlerType" minOccurs="0" />
             <xs:element name="InaccessibleProperty" type="IssueHandlerType" minOccurs="0" />

docs/running_psalm/issues.md

@@ -428,6 +428,23 @@ function addCumulative(int $left) : int {
 }
 ```
 
+### ImpureStaticProperty
+
+Emitted when attempting to use a static property from a function or method marked as pure
+
+```php
+class ValueHolder {
+    public static ?string $value = null;
+
+    /**
+     * @psalm-pure
+     */
+    public static function get(): ?string {
+        return self::$value;
+    }
+}
+```
+
 ### InaccessibleClassConstant
 
 Emitted when a public/private class constant is not accessible from the calling context

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

@@ -1084,6 +1084,18 @@ class PropertyFetchAnalyzer
             );
         }
 
+        if ($context->mutation_free) {
+            if (IssueBuffer::accepts(
+                new \Psalm\Issue\ImpureStaticProperty(
+                    'Cannot use a static property in a mutation-free context',
+                    new CodeLocation($statements_analyzer, $stmt)
+                ),
+                $statements_analyzer->getSuppressedIssues()
+            )) {
+                // fall through
+            }
+        }
+
         if ($var_id && $context->hasVariable($var_id, $statements_analyzer)) {
             $stmt_type = $context->vars_in_scope[$var_id];
 

src/Psalm/Issue/ImpureStaticProperty.php

@@ -0,0 +1,6 @@
+<?php
+namespace Psalm\Issue;
+
+class ImpureStaticProperty extends CodeIssue
+{
+}

tests/PureAnnotationTest.php

@@ -353,6 +353,36 @@ class PureAnnotationTest extends TestCase
                     }',
                 'error_message' => 'ImpureByReferenceAssignment'
             ],
+            'staticPropertyFetch' => [
+                '<?php
+                    final class Number1 {
+                        public static ?string $zero = null;
+
+                        /**
+                         * @psalm-pure
+                         */
+                        public static function zero(): ?string {
+                            return self::$zero;
+                        }
+                    }',
+                'error_message' => 'ImpureStaticProperty',
+            ],
+            'staticPropertyAssignment' => [
+                '<?php
+                    final class Number1 {
+                        /** @var string|null */
+                        private static $zero;
+
+                        /**
+                         * @psalm-pure
+                         */
+                        public static function zero(): string {
+                            self::$zero = "Zero";
+                            return "hello";
+                        }
+                    }',
+                'error_message' => 'ImpureStaticProperty',
+            ],
         ];
     }
 }