Implement first-class callable syntax

composer.json

@@ -7,7 +7,7 @@
   "keywords": ["module", "xp"],
   "require" : {
     "xp-framework/core": "^10.0 | ^9.0 | ^8.0 | ^7.0",
-    "xp-framework/ast": "^7.3",
+    "xp-framework/ast": "dev-feature/first_class_callable_syntax as 7.4.0",
     "php" : ">=7.0.0"
   },
   "require-dev" : {

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

@@ -0,0 +1,35 @@
+<?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) {
+      $use[$var->name]= true;
+    }
+    unset($use['this']);
+
+    // 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.'); }');
+  }
+}

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

@@ -988,6 +988,13 @@ protected function emitNewClass($result, $new) {
     array_shift($result->type);
   }
 
+  protected function emitCallable($result, $callable) {
+    $t= $result->temp();
+    $result->out->write('fn(...'.$t.')=>');
+    $this->emitOne($result, $callable->expression);
+    $result->out->write('(...'.$t.')');
+  }
+
   protected function emitInvoke($result, $invoke) {
     $this->emitOne($result, $invoke->expression);
     $result->out->write('(');

src/main/php/lang/ast/emit/PHP70.class.php

@@ -8,7 +8,7 @@
  * @see  https://wiki.php.net/rfc#php_70
  */
 class PHP70 extends PHP {
-  use OmitPropertyTypes, OmitConstModifiers;
+  use OmitPropertyTypes, OmitConstModifiers, CallablesAsClosures;
   use RewriteNullCoalesceAssignment, RewriteLambdaExpressions, RewriteMultiCatch, RewriteClassOnObjects, RewriteExplicitOctals;
 
   /** Sets up type => literal mappings */

src/main/php/lang/ast/emit/PHP71.class.php

@@ -8,7 +8,7 @@
  * @see  https://wiki.php.net/rfc#php_71
  */
 class PHP71 extends PHP {
-  use OmitPropertyTypes;
+  use OmitPropertyTypes, CallablesAsClosures;
   use RewriteNullCoalesceAssignment, RewriteLambdaExpressions, RewriteClassOnObjects, RewriteExplicitOctals;
 
   /** Sets up type => literal mappings */

src/main/php/lang/ast/emit/PHP72.class.php

@@ -8,7 +8,7 @@
  * @see  https://wiki.php.net/rfc#php_72
  */
 class PHP72 extends PHP {
-  use OmitPropertyTypes;
+  use OmitPropertyTypes, CallablesAsClosures;
   use RewriteNullCoalesceAssignment, RewriteLambdaExpressions, RewriteClassOnObjects, RewriteExplicitOctals;
 
   /** Sets up type => literal mappings */

src/test/php/lang/ast/unittest/emit/CallableSyntaxTest.class.php

@@ -0,0 +1,130 @@
+<?php namespace lang\ast\unittest\emit;
+
+use unittest\{Assert, Test, Values};
+
+/**
+ * Tests for first-class callable syntax
+ *
+ * @see   https://wiki.php.net/rfc/first_class_callable_syntax#proposal
+ */
+class CallableSyntaxTest extends EmittingTest {
+
+  /**
+   * Verification helper
+   *
+   * @param  string $code
+   * @return void
+   * @throws unittest.AssertionFailedError
+   */
+  private function verify($code) {
+    Assert::equals(4, $this->run($code)('Test'));
+  }
+
+  #[Test]
+  public function native_function() {
+    $this->verify('class <T> {
+      public function run() { return strlen(...); }
+    }');
+  }
+
+  #[Test]
+  public function instance_method() {
+    $this->verify('class <T> {
+      public function length($arg) { return strlen($arg); }
+      public function run() { return $this->length(...); }
+    }');
+  }
+
+  #[Test]
+  public function class_method() {
+    $this->verify('class <T> {
+      public static function length($arg) { return strlen($arg); }
+      public function run() { return self::length(...); }
+    }');
+  }
+
+  #[Test]
+  public function private_method() {
+    $this->verify('class <T> {
+      private function length($arg) { return strlen($arg); }
+      public function run() { return $this->length(...); }
+    }');
+  }
+
+  #[Test]
+  public function variable_function() {
+    $this->verify('class <T> {
+      public function run() {
+        $func= "strlen";
+        return $func(...);
+      }
+    }');
+  }
+
+  #[Test]
+  public function instance_method_reference() {
+    $this->verify('class <T> {
+      private $func= "strlen";
+      public function run() {
+        return ($this->func)(...);
+      }
+    }');
+  }
+
+  #[Test, Values(['$this->$func(...)', '$this->{$func}(...)'])]
+  public function variable_instance_method($expr) {
+    $this->verify('class <T> {
+      private function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        return '.$expr.';
+      }
+    }');
+  }
+
+  #[Test, Values(['self::$func(...)', 'self::{$func}(...)'])]
+  public function variable_class_method($expr) {
+    $this->verify('class <T> {
+      private static function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        return '.$expr.';
+      }
+    }');
+  }
+
+  #[Test]
+  public function variable_class_method_with_variable_class() {
+    $this->verify('class <T> {
+      private static function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        $class= __CLASS__;
+        return $class::$func(...);
+      }
+    }');
+  }
+
+  #[Test]
+  public function string_function_reference() {
+    $this->verify('class <T> {
+      public function run() { return "strlen"(...); }
+    }');
+  }
+
+  #[Test]
+  public function array_instance_method_reference() {
+    $this->verify('class <T> {
+      public function length($arg) { return strlen($arg); }
+      public function run() { return [$this, "length"](...); }
+    }');
+  }
+
+  #[Test]
+  public function array_class_method_reference() {
+    $this->verify('class <T> {
+      public static function length($arg) { return strlen($arg); }
+      public function run() { return [self::class, "length"](...); }
+    }');
+  }
+}