Add "native" functions for use in Systemlib

<?hh
  class Foo {
    <<__Native>>
    public function bar(int $baz) : string;

    <<__Native>>
    public static function bling(mixed $blong) : double;
  }

  <<__Native>>
  function blong(string $a, stdClass $b) : void;

  <<__Native("ActRec")>>
  function zorb(int $foo, string $bar): float;

Hooks internal functions:

  String HHVM_METHOD(Foo, bar, int64_t bar) { ... }
  double HHVM_STATIC_METHOD(Foo, bling, CVarRef blong) { ... }
  void HHVM_FUNCTION(blong, CStrRef a, CObjRef b) { ... }
  TypedValue* HHVM_FN(zorb)(ActRec* ar) { ... }

When registered during Extension::moduleLoad() with:

  HHVM_ME(Foo, bar)
  HHVM_STATIC_ME(Foo, bling)
  HHVM_FE(blong)
  HHVM_FE(zorb)

Differential Revision: D922477

hphp/compiler/statement/function_statement.cpp

@@ -36,11 +36,11 @@ using namespace HPHP;
 FunctionStatement::FunctionStatement
 (STATEMENT_CONSTRUCTOR_PARAMETERS,
  ModifierExpressionPtr modifiers, bool ref, const std::string &name,
- ExpressionListPtr params, const std::string &retTypeConstraint,
+ ExpressionListPtr params, TypeAnnotationPtr retTypeAnnotation,
  StatementListPtr stmt, int attr, const std::string &docComment,
  ExpressionListPtr attrList)
   : MethodStatement(STATEMENT_CONSTRUCTOR_PARAMETER_VALUES(FunctionStatement),
-                    modifiers, ref, name, params, retTypeConstraint, stmt,
+                    modifiers, ref, name, params, retTypeAnnotation, stmt,
                     attr, docComment, attrList, false), m_ignored(false) {
 }
 
@@ -80,6 +80,33 @@ void FunctionStatement::onParse(AnalysisResultConstPtr ar, FileScopePtr scope) {
   if (Option::PersistenceHook) {
     fs->setPersistent(Option::PersistenceHook(fs, scope));
   }
+
+  if (fs->isNative()) {
+    if (getStmts()) {
+      parseTimeFatal(Compiler::InvalidAttribute,
+                     "Native functions must not have an implementation body");
+    }
+    if (m_params) {
+      int nParams = m_params->getCount();
+      for (int i = 0; i < nParams; ++i) {
+        auto param = dynamic_pointer_cast<ParameterExpression>((*m_params)[i]);
+        if (!param->hasUserType()) {
+          parseTimeFatal(Compiler::InvalidAttribute,
+                         "Native function calls must have type hints "
+                         "on all args");
+        }
+      }
+    }
+    if (getReturnTypeConstraint().empty()) {
+      parseTimeFatal(Compiler::InvalidAttribute,
+                     "Native function %s() must have a return type hint",
+                     getOriginalName().c_str());
+    }
+  } else if (!getStmts()) {
+    parseTimeFatal(Compiler::InvalidAttribute,
+                   "Global function %s() must contain a body",
+                    getOriginalName().c_str());
+  }
 }
 
 ///////////////////////////////////////////////////////////////////////////////