Merge pull request #2450 from n8sh/isZeroInit-19180

Update spec for Issue 19180 - Expose... __traits(isZeroInit, T)
merged-on-behalf-of: Petar Kirov <ZombineDev@users.noreply.github.com>

spec/traits.dd

@@ -43,6 +43,7 @@ $(GNAME TraitsKeyword):
     $(GLINK isOut)
     $(GLINK isLazy)
     $(GLINK isReturnOnStack)
+    $(GLINK isZeroInit)
     $(GLINK hasMember)
     $(GLINK identifier)
     $(GLINK getAliasThis)
@@ -400,6 +401,35 @@ static assert(!__traits(isTemplate,foo!int()));
 static assert(!__traits(isTemplate,"string"));
 ---
 
+$(H2 $(GNAME isZeroInit))
+
+        $(P Takes one argument which must be a type. If the type's
+        $(DDSUBLINK spec/property, init, default initializer) is all zero
+        bits then `true` is returned, otherwise `false`.)
+
+$(SPEC_RUNNABLE_EXAMPLE_COMPILE
+---
+struct S1 { int x; }
+struct S2 { int x = -1; }
+
+static assert(__traits(isZeroInit, S1));
+static assert(!__traits(isZeroInit, S2));
+
+void test()
+{
+    int x = 3;
+    static assert(__traits(isZeroInit, typeof(x)));
+}
+
+// `isZeroInit` will always return true for a class C
+// because `C.init` is null reference.
+
+class C { int x = -1; }
+
+static assert(__traits(isZeroInit, C));
+---
+)
+
 $(H2 $(GNAME isReturnOnStack))
 
     $(P