Bug 23726 – Array append in CTFE no longer works without _d_arrayappendT

Here is my test.d file: ``` alias foo = () { string x = "1"; x ~= "2"; return x; }; enum string bar = foo(); ``` and minimal object.d file: ``` module object; alias string = immutable(char)[]; ``` Compiling with DMD v2.102.0 causes ``` $ dmd -c -betterC test.d test.d(3): Error: `object._d_arrayappendT` not found. The current runtime does not support appending array to arrays, or the runtime is corrupt. ``` But compiling with D frontend v2.100.1 works fine (I have been testing with LDC 1.30, based on D frontend v2.100.1). It seems likely this was introduced between v2.101 and v2.102 but I haven't looked in detail. I'm not sure if this use-case is supposed to be supported, but it does break code that previously worked and did not need an implementation of `_d_arrayappendT`.

This is a consequence of druntime hooks being translated to templates in the front end: https://github.com/dlang/projects/issues/25 > I'm not sure if this use-case is supposed to be supported dmd and druntime are tied together. You can't expect stability if you upgrade dmd without upgrading your (custom) druntime with it.

I see, thanks for the explanation. I guess this is not a bug then. However, lack of stability between DMD and D-runtime makes it difficult to make a case for bare-metal D (with a custom runtime), since we will have to maintain the custom D-runtime in unison with compiler updates, and the application will probably only be usable with the most recent version of D (unless we start maintaining the custom D-runtime for all compiler versions since the start of the project). I suppose if we keep the number of language features used to a minimum (e.g., disallow `~=`, even in CTFE), then hopefully there won't be much/any breakage across D versions, but there is no guarantee.

It's pretty common for embedded toolchains to provide or insist upon a compiler version, you should do that too. When you are ready to support fix your custom runtime then bump the compiler version (and so on)

Fair enough. I've also noticed that if I include just the declaration (for string, but could be templated) in object.d: ``` ref string _d_arrayappendT(return ref scope string x, scope string y) @trusted; ``` Then it is usable and works in CTFE, but nicely causes a link error if it is used in runtime code (this is what I want).

Do get in touch if you need any help with anything along those lines.