Fix bugzilla issue 24882 - COM class is allocated using GC not malloc

changelog/dmd.isCOMClass.dd

@@ -0,0 +1,5 @@
+New trait isCOMClass to detect if a type is a COM class
+
+A COM class inherits from a possibly user defined interface called ``IUnknown``.
+To detect this during compilation use the trait ``__traits(isCOMClass, Type)``.
+Or using the ``TypeInfo_Class`` flag.

compiler/src/dmd/frontend.h

@@ -8692,6 +8692,7 @@ struct Id final
     static Identifier* isRef;
     static Identifier* isOut;
     static Identifier* isLazy;
+    static Identifier* isCOMClass;
     static Identifier* hasMember;
     static Identifier* identifier;
     static Identifier* fullyQualifiedName;

compiler/src/dmd/id.d

@@ -482,6 +482,7 @@ immutable Msgtable[] msgtable =
     { "isRef" },
     { "isOut" },
     { "isLazy" },
+    { "isCOMClass" },
     { "hasMember" },
     { "identifier" },
     { "fullyQualifiedName" },

compiler/src/dmd/traits.d

@@ -693,6 +693,26 @@ Expression semanticTraits(TraitsExp e, Scope* sc)
 
         return isDeclX(d => (d.storage_class & STC.lazy_) != 0);
     }
+    if (e.ident == Id.isCOMClass)
+    {
+        if (dim != 1)
+            return dimError(1);
+
+        auto o = (*e.args)[0];
+        auto s = getDsymbol(o);
+        AggregateDeclaration agg;
+
+        if (!s || ((agg = s.isAggregateDeclaration()) is null))
+        {
+            error(e.loc, "argument to `__traits(isCOMClass, %s)` is not a declaration", o.toChars());
+            return ErrorExp.get();
+        }
+
+        if (ClassDeclaration cd = agg.isClassDeclaration())
+            return cd.com ? True() : False();
+        else
+            return False();
+    }
     if (e.ident == Id.identifier)
     {
         // Get identifier for symbol as a string literal

compiler/test/runnable/test36.d

@@ -12,6 +12,10 @@ extern (Windows):
         {printf(`comobject\n`);
         }
 }
+
+// https://issues.dlang.org/show_bug.cgi?id=24882
+static assert(__traits(isCOMClass, ComObject));
+
 interface IDataObject: IUnknown
 {
         extern(Windows):

druntime/src/core/lifetime.d

@@ -2739,8 +2739,11 @@ if (is(T == class))
     auto init = __traits(initSymbol, T);
     void* p;
 
-    static if (__traits(getLinkage, T) == "Windows")
+    static if (__traits(isCOMClass, T))
     {
+        // If this is a COM class we allocate it using malloc.
+        // This allows the reference counting to outlive the reference known about by the GC.
+
         p = pureMalloc(init.length);
         if (!p)
             onOutOfMemoryError();