PHPLIB-1597 Accept a $-prefixed string anywhere an expression is accepted

generator/config/accumulator/accumulator.yaml

@@ -73,7 +73,7 @@ tests:
                                     function(state, numCopies) {
                                         return { count: state.count + 1, sum: state.sum + numCopies }
                                     }
-                            accumulateArgs: [ "$copies" ],
+                            accumulateArgs: [ "$copies" ]
                             merge:
                                 $code: |-
                                     function(state1, state2) {
@@ -115,8 +115,7 @@ tests:
                                         }
                                         return state;
                                     }
-                            accumulateArgs:
-                                - '$name'
+                            accumulateArgs: ['$name']
                             merge:
                                 $code: |-
                                     function(state1, state2) {

generator/src/OperatorClassGenerator.php

@@ -135,6 +135,18 @@ public function createClass(GeneratorDefinition $definition, OperatorDefinition
                     $constructorParam->setDefaultValue($argument->default);
                 }
 
+                if ($type->dollarPrefixedString) {
+                    $namespace->addUseFunction('is_string');
+                    $namespace->addUseFunction('str_starts_with');
+                    $namespace->addUse(InvalidArgumentException::class);
+                    $constructor->addBody(<<<PHP
+                    if (is_string(\${$argument->propertyName}) && ! str_starts_with(\${$argument->propertyName}, '$')) {
+                        throw new InvalidArgumentException('Argument \${$argument->propertyName} can be an expression, field paths and variable names must be prefixed by "$" or "$$".');
+                    }
+
+                    PHP);
+                }
+
                 // List type must be validated with array_is_list()
                 if ($type->list) {
                     $namespace->addUseFunction('is_array');

generator/src/OperatorGenerator.php

@@ -26,6 +26,7 @@
 use function ltrim;
 use function sort;
 use function sprintf;
+use function str_starts_with;
 use function ucfirst;
 use function usort;
 
@@ -71,13 +72,19 @@ final protected function getType(string $type): ExpressionDefinition
      * Expression types can contain class names, interface, native types or "list".
      * PHPDoc types are more precise than native types, so we use them systematically even if redundant.
      *
-     * @return object{native:string,doc:string,use:list<class-string>,list:bool,query:bool,javascript:bool}
+     * @return object{native:string,doc:string,use:list<class-string>,list:bool,query:bool,javascript:bool,dollarPrefixedString:bool}
      */
     final protected function getAcceptedTypes(ArgumentDefinition $arg): stdClass
     {
         $nativeTypes = [];
 
+        $dollarPrefixedString = false;
+
         foreach ($arg->type as $type) {
+            if (str_starts_with($type, 'resolvesTo')) {
+                $dollarPrefixedString = true;
+            }
+
             $type = $this->getType($type);
             $nativeTypes = array_merge($nativeTypes, $type->acceptedTypes);
 
@@ -91,6 +98,14 @@ final protected function getAcceptedTypes(ArgumentDefinition $arg): stdClass
             $nativeTypes[] = Optional::class;
         }
 
+        // If the argument accepts an expression, a $-prefixed string is accepted (field path or variable)
+        // Checked only if the argument does not already accept a string
+        if (in_array('string', $nativeTypes, true)) {
+            $dollarPrefixedString = false;
+        } elseif ($dollarPrefixedString) {
+            $nativeTypes[] = 'string';
+        }
+
         $docTypes = $nativeTypes = array_unique($nativeTypes);
         $use = [];
 
@@ -131,6 +146,7 @@ final protected function getAcceptedTypes(ArgumentDefinition $arg): stdClass
             'list' => $listCheck,
             'query' => $isQuery,
             'javascript' => $isJavascript,
+            'dollarPrefixedString' => $dollarPrefixedString,
         ];
     }