Add hasCopyConstructor and hasPostblit traits

src/dmd/id.d

@@ -431,6 +431,8 @@ immutable Msgtable[] msgtable =
     { "isZeroInit" },
     { "getTargetInfo" },
     { "getLocation" },
+    { "hasPostblit" },
+    { "hasCopyConstructor" },
 
     // For C++ mangling
     { "allocator" },

src/dmd/traits.d

@@ -144,6 +144,8 @@ shared static this()
         "isZeroInit",
         "getTargetInfo",
         "getLocation",
+        "hasPostblit",
+        "hasCopyConstructor",
     ];
 
     StringTable* stringTable = cast(StringTable*) &traitsStringTable;
@@ -627,6 +629,29 @@ Expression semanticTraits(TraitsExp e, Scope* sc)
         }
         return True();
     }
+    if (e.ident == Id.hasCopyConstructor || e.ident == Id.hasPostblit)
+    {
+        if (dim != 1)
+            return dimError(1);
+
+        auto o = (*e.args)[0];
+        auto t = isType(o);
+        if (!t)
+        {
+            e.error("type expected as second argument of __traits `%s` instead of `%s`",
+                e.ident.toChars(), o.toChars());
+            return new ErrorExp();
+        }
+
+        Type tb = t.baseElemOf();
+        if (auto sd = tb.ty == Tstruct ? (cast(TypeStruct)tb).sym : null)
+        {
+            return (e.ident == Id.hasPostblit) ? (sd.postblit ? True() : False())
+                 : (sd.hasCopyCtor ? True() : False());
+        }
+        return False();
+    }
+
     if (e.ident == Id.isNested)
     {
         if (dim != 1)

test/compilable/traits.d

@@ -86,3 +86,69 @@ struct Outer
 static assert(__traits(getLocation, Outer.Nested)[1] == 82);
 static assert(__traits(getLocation, Outer.method)[1] == 84);
 
+/******************************************/
+// https://issues.dlang.org/show_bug.cgi?id=19902
+// Define hasElaborateCopyConstructor trait
+// but done as two independent traits per conversation
+// in https://github.com/dlang/dmd/pull/10265
+
+struct S
+{
+    this (ref S rhs) {}
+}
+
+struct OuterS
+{
+    struct S
+    {
+        this (ref S rhs) {}
+    }
+
+    S s;
+}
+
+void foo(T)()
+{
+    struct S(U)
+    {
+        this (ref S rhs) {}
+    }
+    static assert (__traits(hasCopyConstructor, S!int));
+}
+
+struct U(T)
+{
+    this (ref U rhs) {}
+}
+
+struct SPostblit
+{
+    this(this) {}
+}
+
+struct NoCpCtor { }
+class C19902 { }
+
+static assert(__traits(hasCopyConstructor, S));
+static assert(__traits(hasCopyConstructor, OuterS.S));
+static assert(__traits(hasCopyConstructor, OuterS));
+static assert(__traits(compiles, foo!int));
+static assert(__traits(compiles, foo!S));
+static assert(__traits(hasCopyConstructor, U!int));
+static assert(__traits(hasCopyConstructor, U!S));
+static assert(!__traits(hasPostblit, U!S));
+static assert(__traits(hasPostblit, SPostblit));
+static assert(!__traits(hasCopyConstructor, SPostblit));
+
+static assert(!__traits(hasCopyConstructor, NoCpCtor));
+static assert(!__traits(hasCopyConstructor, C19902));
+static assert(!__traits(hasCopyConstructor, int));
+static assert(!__traits(hasPostblit, NoCpCtor));
+static assert(!__traits(hasPostblit, C19902));
+static assert(!__traits(hasPostblit, int));
+
+// Check that invalid use cases don't compile
+static assert(!__traits(compiles, __traits(hasCopyConstructor)));
+static assert(!__traits(compiles, __traits(hasCopyConstructor, S())));
+static assert(!__traits(compiles, __traits(hasPostblit)));
+static assert(!__traits(compiles, __traits(hasPostblit, S())));