Merge pull request #2042 from BBasile/trait-disabled

document  possible new `isDisabled` __traits

Author: wilzbach

spec/traits.dd

@@ -31,6 +31,7 @@ $(GNAME TraitsKeyword):
     $(GBLINK isScalar)
     $(GBLINK isStaticArray)
     $(GBLINK isUnsigned)
+    $(GBLINK isDisabled)
     $(GBLINK isVirtualFunction)
     $(GBLINK isVirtualMethod)
     $(GBLINK isAbstractFunction)
@@ -207,6 +208,31 @@ $(H2 $(GNAME isDeprecated))
     $(P Takes one argument. It returns `true` if the argument is a symbol
     marked with the `deprecated` keyword, otherwise `false`.)
 
+$(H2 $(GNAME isDisabled))
+
+    $(P Takes one argument and returns `true` if it's a function declaration
+    marked with `@disable`.)
+
+---
+struct Foo
+{
+    @disable void foo();
+    void bar(){}
+}
+
+static assert(__traits(isDisabled, Foo.foo));
+static assert(!__traits(isDisabled, Foo.bar));
+---
+
+    $(P For any other declaration even if `@disable` is a syntactically valid
+    attribute `false` is returned because the annotation has no effect.)
+
+---
+@disable struct Bar{}
+
+static assert(!__traits(isDisabled, Bar));
+---
+
 $(H2 $(GNAME isVirtualFunction))
 
         $(P The same as $(GLINK isVirtualMethod), except