Fix Issue 17878 - Add __traits(isFuture, ...)

src/ddmd/id.d

@@ -347,6 +347,7 @@ immutable Msgtable[] msgtable =
     { "isTemplate" },
     { "isPOD" },
     { "isDeprecated" },
+    { "isFuture" },
     { "isNested" },
     { "isFloating" },
     { "isIntegral" },

src/ddmd/traits.d

@@ -67,6 +67,7 @@ shared static this()
         "isArithmetic",
         "isAssociativeArray",
         "isDeprecated",
+        "isFuture",
         "isFinalClass",
         "isPOD",
         "isNested",
@@ -470,6 +471,10 @@ extern (C++) Expression semanticTraits(TraitsExp e, Scope* sc)
     {
         return isDsymX(t => t.isDeprecated());
     }
+    if (e.ident == Id.isFuture)
+    {
+       return isDeclX(t => t.isFuture());
+    }
     if (e.ident == Id.isStaticArray)
     {
         return isTypeX(t => t.toBasetype().ty == Tsarray);

test/runnable/test17878.d

@@ -0,0 +1,19 @@
+@__future int foo()
+{
+    return 0;
+}
+
+int bar()
+{
+    return 1;
+}
+
+@__future int c;
+
+
+void main()
+{
+    static assert(__traits(isFuture, foo));
+    static assert(!__traits(isFuture, bar));
+    static assert(__traits(isFuture, c));
+}