Emit callable expressions as regular function closures for PHP < 7.4

Author: thekid

src/main/php/lang/ast/emit/CallablesAsClosures.class.php

@@ -0,0 +1,34 @@
+<?php namespace lang\ast\emit;
+
+/**
+ * Rewrites callable expressions to regular closures
+ *
+ * @see  https://wiki.php.net/rfc/first_class_callable_syntax
+ */
+trait CallablesAsClosures {
+
+  protected function emitCallable($result, $callable) {
+
+    // Use variables in the following cases:
+    //
+    // $closure(...);                => use ($closure)
+    // $obj->method(...);            => use ($obj)
+    // $obj->$method(...);           => use ($obj, $method)
+    // ($obj->property)(...);        => use ($obj)
+    // $class::$method(...);         => use ($class, $method)
+    // [$obj, 'method'](...);        => use ($obj)
+    // [Foo::class, $method](...);   => use ($method)
+    $use= [];
+    foreach ($result->codegen->search($callable, 'variable') as $var) {
+      'this' === $var->name || $use[$var->name]= true;
+    }
+
+    // Create closure
+    $t= $result->temp();
+    $result->out->write('function(...'.$t.')');
+    $use && $result->out->write('use($'.implode(', $', array_keys($use)).')');
+    $result->out->write('{ return ');
+    $this->emitOne($result, $callable->expression);
+    $result->out->write('(... '.$t.'); }');
+  }
+}