DSON conversion of enums misses enum name

[dlangBugzillaToGithub]

dlang-bugzilla (@CyberShadow) reported this on 2017-06-23T15:00:48Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=17542

Description

This almost works:

///////////// test.d ////////////
import std.conv : text;
enum E { a }
struct S { E e; }
immutable S s1 = S.init;
immutable S s2 = mixin(text(s1));
/////////////////////////////////

It doesn't work because for the enum member a, std.format emits just "a" instead of "E.a".

std.format is already capable of converting the same type to string in different ways, e.g. format("%s", "hello") and format("%(%s%)", ["hello"]) will have the string converted differently (in the second case, with quotes and escapes).

So, it would be nice that for similar circumstances, stringified enums had their name included in the same way that stringified structs have their name included.

Incidentally, I found an interesting use case for DSON: parsing or generating a complicated data structure, dumping it to a .d file, then loading the .d file by using a mixin+import expression, for cases when generating said data directly at compile time would be too slow or otherwise impractical.