Make capturing explicit when using the PHP lambda form

src/main/jay/grammars/php.jay

@@ -662,8 +662,8 @@ expression:
   | '@' expression {
       $$= $yyLex->create(new SilenceOperatorNode($2));
     }
-  | T_FUNCTION '(' lambda_input ')' '{' statements_opt '}' {
-      $$= $yyLex->create(new LambdaNode($3, (array)$6));
+  | T_FUNCTION '(' lambda_input ')' lambda_uses_opt '{' statements_opt '}' {
+      $$= $yyLex->create(new LambdaNode($3, (array)$7, $5));
     }
   | '(' expression ')' chain_opt { 
       if ($4) {
@@ -689,6 +689,11 @@ lambda_input_parameter:
     T_VARIABLE initialization_opt { $$= array('name' => $1); $2 && $$['default']= $2; }
 ;
 
+lambda_uses_opt:
+    /* empty */ { $$= array(); }
+  | T_USE '(' lambda_input_parameters ')' { $$= $3; }
+;
+
 literal:
     scalar
   | T_ARRAY '(' { $p= $yyLex->position; } map_or_list ')' { $4->position= $p; $4->type= NULL; $$= $4; }

src/main/php/xp/compiler/ast/LambdaNode.class.php

@@ -6,15 +6,18 @@
 class LambdaNode extends Node {
   public $parameters;
   public $statements;
+  public $uses;
 
   /**
    * Constructor
    *
    * @param   xp.compiler.ast.Node[] parameters
    * @param   xp.compiler.ast.Node[] statements
+   * @param   xp.compiler.ast.Node[] uses
    */
-  public function __construct(array $parameters, array $statements) {
+  public function __construct(array $parameters, array $statements, $uses= null) {
     $this->parameters= $parameters;
     $this->statements= $statements;
+    $this->uses= $uses;
   }
 }

src/main/php/xp/compiler/emit/php/V54Emitter.class.php

@@ -212,17 +212,6 @@ protected function emitArm($b, $arm) {
    */
   protected function emitLambda($b, $lambda) {
 
-    // Capture all local variables and parameters of containing scope which
-    // are also used inside the lambda by value.
-    $finder= new \xp\compiler\ast\LocalVariableFinder();
-    foreach ($finder->variablesIn((array)$this->scope[0]->routine->body) as $variable) {
-      $finder->including($variable);
-    }
-    foreach ($this->scope[0]->routine->parameters as $param) {
-      $finder->including($param['name']);
-    }
-    $finder->excluding('*');
-
     // Parameters
     $b->append('function(');
     $s= sizeof($lambda->parameters)- 1;
@@ -236,8 +225,24 @@ protected function emitLambda($b, $lambda) {
     }
     $b->append(')');
 
-    // Use variables
-    if ($capture= $finder->variablesIn($lambda->statements)) {
+    // If not explicitely stated: Capture all local variables and parameters of
+    // containing scope which are also used inside the lambda by value.
+    if (null === $lambda->uses) {
+      $finder= new \xp\compiler\ast\LocalVariableFinder();
+      foreach ($finder->variablesIn((array)$this->scope[0]->routine->body) as $variable) {
+        $finder->including($variable);
+      }
+      foreach ($this->scope[0]->routine->parameters as $param) {
+        $finder->including($param['name']);
+      }
+      $finder->excluding('*');
+
+      // Use variables
+      if ($capture= $finder->variablesIn($lambda->statements)) {
+        $b->append(' use($')->append(implode(', $', $capture))->append(')');
+      }
+    } else if ($lambda->uses) {
+      $capture= array_map(function($var) { return $var->name; }, $lambda->uses);
       $b->append(' use($')->append(implode(', $', $capture))->append(')');
     }