fix issue 18149 - Add a compiler trait to detect if a function is @di…

…sabled

changelog/disabled-trait.dd

@@ -0,0 +1,43 @@
+A compiler trait used to detect if a function is marked with `@disable` has been added.
+
+Prior to this release is was impossible to filter out `@disable` functions without
+using `__trait(compiles)`, which was less than ideal since `false` could be
+returned for other reasons.
+
+Now, in metaprogramming code, `@disable` functions can be detected accurately,
+using `__traits(isDisabled)` and even in overload sets:
+
+---
+module runnable;
+
+struct Foo
+{
+    import std.stdio;
+    @disable static void foo() {__PRETTY_FUNCTION__.writeln;}
+    static void foo(int v) {__PRETTY_FUNCTION__.writeln;}
+    static void bar() {__PRETTY_FUNCTION__.writeln;}
+    @disable static void bar(int v) {__PRETTY_FUNCTION__.writeln;}
+}
+
+void test(T)()
+{
+    foreach (member; __traits(allMembers, T))
+        foreach (overload; __traits(getOverloads, T, member))
+            static if (!__traits(isDisabled, overload))
+    {
+        static if (is(typeof(&overload) == void function()))
+            overload();
+        else static if (is(typeof(&overload) == void function(int)))
+            overload(42);
+    }
+}
+
+void main(){test!Foo;}
+---
+
+prints:
+
+$(CONSOLE
+void runnable.Foo.foo(int v)
+void runnable.Foo.bar()
+)

src/dmd/declaration.d

@@ -480,6 +480,11 @@ extern (C++) abstract class Declaration : Dsymbol
         return (storage_class & STC.deprecated_) != 0;
     }
 
+    final bool isDisabled() const pure nothrow @nogc @safe
+    {
+        return (storage_class & STC.disable) != 0;
+    }
+
     final bool isOverride() const pure nothrow @nogc @safe
     {
         return (storage_class & STC.override_) != 0;

src/dmd/id.d

@@ -354,6 +354,7 @@ immutable Msgtable[] msgtable =
     { "isTemplate" },
     { "isPOD" },
     { "isDeprecated" },
+    { "isDisabled" },
     { "isFuture" },
     { "isNested" },
     { "isFloating" },

src/dmd/traits.d

@@ -99,6 +99,7 @@ shared static this()
         "isAbstractClass",
         "isArithmetic",
         "isAssociativeArray",
+        "isDisabled",
         "isDeprecated",
         "isFuture",
         "isFinalClass",
@@ -578,6 +579,13 @@ extern (C++) Expression semanticTraits(TraitsExp e, Scope* sc)
         e.error("aggregate or function expected instead of `%s`", o.toChars());
         return new ErrorExp();
     }
+    if (e.ident == Id.isDisabled)
+    {
+        if (dim != 1)
+            return dimError(1);
+
+        return isFuncX(f => f.isDisabled());
+    }
     if (e.ident == Id.isAbstractFunction)
     {
         if (dim != 1)

test/runnable/traits.d

@@ -11,6 +11,7 @@ class AC2 { abstract void foo(); }
 class AC3 : AC2 { }
 final class FC { void foo() { } }
 enum E { EMEM }
+struct D1 { @disable void true_(); void false_(){} }
 
 /********************************************************/
 
@@ -1540,6 +1541,15 @@ void test15094()
 
 /********************************************************/
 
+void testIsDisabled()
+{
+    static assert(__traits(isDisabled, D1.true_));
+    static assert(!__traits(isDisabled, D1.false_));
+    static assert(!__traits(isDisabled, D1));
+}
+
+/********************************************************/
+
 int main()
 {
     test1();