Preprocessor: fix handling of first empty argument.

First empty argument used to be dropped: e.g. MACRO(,test) would be
expanded with one parameter only, with value 'test'.

Change-Id: I693fbb7faf1360f62266fa04c4b39c2de0d159a7
Reviewed-by: Erik Verbruggen <erik.verbruggen@nokia.com>

src/libs/cplusplus/pp-macro-expander.cpp

@@ -369,7 +369,7 @@ const char *MacroExpander::expand(const char *__first, const char *__last,
             MacroExpander expand_actual (env, frame);
 
             const char *arg_end = skip_argument_variadics (actuals, macro, arg_it, __last);
-            if (arg_it != arg_end)
+            if (arg_it != arg_end || (arg_end != __last && *arg_end == ','))
             {
                 actuals_ref.append(MacroArgumentReference(start_offset + (arg_it-start), arg_end - arg_it));
                 const QByteArray actual (arg_it, arg_end - arg_it);

tests/auto/cplusplus/preprocessor/tst_preprocessor.cpp

@@ -43,6 +43,7 @@ Q_OBJECT
 private Q_SLOTS:
     void va_args();
     void named_va_args();
+    void first_empty_macro_arg();
     void unfinished_function_like_macro_call();
     void nasty_macro_expansion();
     void tstst();
@@ -82,6 +83,23 @@ void tst_Preprocessor::named_va_args()
     QVERIFY(preprocessed.contains("int f(int a,int b);"));
 }
 
+void tst_Preprocessor::first_empty_macro_arg()
+{
+    Client *client = 0; // no client.
+    Environment env;
+
+    Preprocessor preprocess(client, &env);
+    QByteArray preprocessed = preprocess(QLatin1String("<stdin>"),
+                                         QByteArray("\n#define foo(a,b) a int b;"
+                                                    "\nfoo(const,cVal)\n"
+                                                    "\nfoo(,Val)\n"
+                                                    "\nfoo( ,Val2)\n"));
+
+    QVERIFY(preprocessed.contains("const int cVal;"));
+    QVERIFY(preprocessed.contains("int Val;"));
+    QVERIFY(preprocessed.contains("int Val2;"));
+}
+
 void tst_Preprocessor::unfinished_function_like_macro_call()
 {
     Client *client = 0; // no client.