Embind: Consistently represent empty interface references as JS null

The existing code had two issues:  For one, e.g. calling a function that
returned a null interface reference mapped that to JS null, while querying an
object for a non-supported interface via `new css.uno.X...(y)` mapped that to
an "empty" JS object instead.  (So checking for a non-null reference needed to
be done as either `x !=== null` or as `x.is()`, depending on context.)  And for
another, while calling $is() on a non-"empty" object worked fine, it failed on
such an "empty" object (as the Embind internals of that object lacked the $$
property).

So change the querying mechanism from the `new css.uno.X...(y)` constructor to a
`css.uno.X....query(y)` function call syntax, which now returns JS null when
querying for a non-supported interface.  (And drop the broken $is method.)

Change-Id: I8fa488ab2892423f2a461d9b72db47e1d4df3b8d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166255
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

offapi/org/libreoffice/embindtest/XTest.idl

@@ -112,6 +112,8 @@ interface XTest {
     boolean isSequenceEnum([in] sequence<Enum> value);
     sequence<Struct> getSequenceStruct();
     boolean isSequenceStruct([in] sequence<Struct> value);
+    XTest getNull();
+    boolean isNull([in] XTest value);
     void throwRuntimeException();
     void passJob([in] com::sun::star::task::XJob object);
     void passJobExecutor([in] com::sun::star::task::XJobExecutor object);

static/README.wasm.md

@@ -228,11 +228,11 @@ Some usage examples through javascript of the current implementation:
 let uno = init_unoembind_uno(Module);
 let css = uno.com.sun.star;
 xModel = Module.getCurrentModelFromViewSh();
-xTextDocument = new css.text.XTextDocument(xModel);
+xTextDocument = css.text.XTextDocument.query(xModel);
 xText = xTextDocument.getText();
-xSimpleText = new css.text.XSimpleText(xText);
+xSimpleText = css.text.XSimpleText.query(xText);
 xTextCursor = xSimpleText.createTextCursor();
-xTextRange = new css.text.XTextRange(xTextCursor);
+xTextRange = css.text.XTextRange.query(xTextCursor);
 xTextRange.setString("string here!");
 xModel.delete(); xTextDocument.delete(); xText.delete(); xSimpleText.delete(); xTextCursor.delete(); xTextRange.delete();
 ```
@@ -242,13 +242,13 @@ xModel.delete(); xTextDocument.delete(); xText.delete(); xSimpleText.delete(); x
 let uno = init_unoembind_uno(Module);
 let css = uno.com.sun.star;
 xModel = Module.getCurrentModelFromViewSh();
-xEnumAccess = new css.container.XEnumerationAccess(xText);
+xEnumAccess = css.container.XEnumerationAccess.query(xText);
 xParaEnumeration = xEnumAccess.createEnumeration();
 
 while (xParaEnumeration.hasMoreElements()) {
-    xParagraph = new css.text.XTextRange(xParaEnumeration.nextElement().get());
-    if (xParagraph.$is()) {
-        xParaProps = new css.beans.XPropertySet(xParagraph);
+    xParagraph = css.text.XTextRange.query(xParaEnumeration.nextElement().get());
+    if (xParagraph !== null) {
+        xParaProps = css.beans.XPropertySet.query(xParagraph);
         let color = new Module.uno_Any(
             Module.uno_Type.Long(), Math.floor(Math.random() * 0xFFFFFF));
         xParaProps.setPropertyValue("CharColor", color);

static/source/embindmaker/embindmaker.cxx

@@ -1082,18 +1082,15 @@ SAL_IMPLEMENT_MAIN()
                       "        .smart_ptr<::com::sun::star::uno::Reference<"
                    << cppName(ifc) << ">>(\"uno_Reference_" << jsName(ifc)
                    << "\")\n"
+                      "        .class_function(\"query\", "
+                      "+[](::com::sun::star::uno::Reference<::com::sun::star::uno::XInterface> "
+                      "const & the_object) { return ::com::sun::star::uno::Reference<"
+                   << cppName(ifc)
+                   << ">(the_object, ::com::sun::star::uno::UNO_QUERY); })\n"
                       "        .class_function(\"reference\", +[]("
                    << cppName(ifc)
                    << " * the_interface) { return ::com::sun::star::uno::Reference(the_interface); "
                       "}, ::emscripten::allow_raw_pointers())\n"
-                      "        "
-                      ".constructor(+[](::com::sun::star::uno::Reference<::com::sun::star::uno::"
-                      "XInterface> const & the_object) { return ::com::sun::star::uno::Reference<"
-                   << cppName(ifc)
-                   << ">(the_object, ::com::sun::star::uno::UNO_QUERY); })\n"
-                      "        .function(\"$is\", +[](::com::sun::star::uno::Reference<"
-                   << cppName(ifc)
-                   << "> const & the_self) { return the_self.is(); })\n"
                       "        .function(\"$equals\", +[](::com::sun::star::uno::Reference<"
                    << cppName(ifc)
                    << "> const & the_self, "

unotest/source/embindtest/embindtest.cxx

@@ -501,6 +501,17 @@ class Test : public cppu::WeakImplHelper<org::libreoffice::embindtest::XTest>
                   };
     }
 
+    css::uno::Reference<org::libreoffice::embindtest::XTest> SAL_CALL getNull() override
+    {
+        return {};
+    }
+
+    sal_Bool SAL_CALL
+    isNull(css::uno::Reference<org::libreoffice::embindtest::XTest> const& value) override
+    {
+        return !value;
+    }
+
     void SAL_CALL throwRuntimeException() override
     {
         throw css::uno::RuntimeException(u"test"_ustr);

unotest/source/embindtest/embindtest.js

@@ -517,6 +517,17 @@ Module.addOnPostRun(function() {
         console.assert(test.isSequenceStruct(v));
         v.delete();
     }
+    {
+        let v = test.getNull();
+        console.log(v);
+        console.assert(v === null);
+        console.assert(test.isNull(v));
+    }
+    {
+        let v = css.task.XJob.query(test);
+        console.log(v);
+        console.assert(v === null);
+    }
     console.assert(uno.org.libreoffice.embindtest.Constants.Boolean === true);
     console.assert(test.isBoolean(uno.org.libreoffice.embindtest.Constants.Boolean));
     console.assert(uno.org.libreoffice.embindtest.Constants.Byte === -12);