Add initial support for callable syntax

Author: thekid

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

@@ -0,0 +1,139 @@
+<?php namespace lang\ast\unittest\emit;
+
+use unittest\actions\RuntimeVersion;
+use unittest\{Action, Assert, Test, Values};
+
+class CallableSyntaxTest extends EmittingTest {
+
+  #[Test]
+  public function native_function() {
+    $f= $this->run('class <T> {
+      public function run() { return strlen(...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function instance_method() {
+    $f= $this->run('class <T> {
+      public function length($arg) { return strlen($arg); }
+      public function run() { return $this->length(...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function class_method() {
+    $f= $this->run('class <T> {
+      public static function length($arg) { return strlen($arg); }
+      public function run() { return self::length(...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function private_method() {
+    $f= $this->run('class <T> {
+      private function length($arg) { return strlen($arg); }
+      public function run() { return $this->length(...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function variable_function() {
+    $f= $this->run('class <T> {
+      public function run() {
+        $func= "strlen";
+        return $func(...);
+      }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function instance_method_reference() {
+    $f= $this->run('class <T> {
+      private $func= "strlen";
+      public function run() {
+        return ($this->func)(...);
+      }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function variable_instance_method() {
+    $f= $this->run('class <T> {
+      private function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        return $this->$func(...);
+      }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function variable_class_method() {
+    $f= $this->run('class <T> {
+      private static function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        return self::$func(...);
+      }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function variable_class_method_with_variable_class() {
+    $f= $this->run('class <T> {
+      private static function length($arg) { return strlen($arg); }
+      public function run() {
+        $func= "length";
+        $class= __CLASS__;
+        return $class::$func(...);
+      }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function string_function_reference() {
+    $f= $this->run('class <T> {
+      public function run() { return "strlen"(...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function array_instance_method_reference() {
+    $f= $this->run('class <T> {
+      public function length($arg) { return strlen($arg); }
+      public function run() { return [$this, "length"](...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+
+  #[Test]
+  public function array_class_method_reference() {
+    $f= $this->run('class <T> {
+      public static function length($arg) { return strlen($arg); }
+      public function run() { return [self::class, "length"](...); }
+    }');
+
+    Assert::equals(4, $f('Test'));
+  }
+}