String.exceptLast should be refined to return String

[CeylonMigrationBot]

[@luolong] This is bound to raise some eyebrows:

String string = ...
{Character*} exceptLast = string.exceptLast;

After that I can't use any String methods, which is counter intuitive...

[Migrated from ceylon/ceylon.language#763]

[CeylonMigrationBot]

[@gavinking] I'm happy to refine exceptLast on List, String, and Sequential, just like we do with rest.

[CeylonMigrationBot]

[@gavinking] Send me a patch.

[gavinking]

Done.

[jvasileff]

Re-opening for further consideration.

In a library I'm currently writing, I got the following after compiling on 1.3.2 and running on 1.3.3:

Exception in thread "main" java.lang.NoSuchMethodError: ceylon.language.String.getExceptLast(Ljava/lang/String;)Lceylon/language/Iterable;

This is similar to, although probably not exactly the same as, #6063

[gavinking]

Grrrr. So I guess we change the return type back to Iterable and hack the backend to add a typecast. PITA.

[gavinking]

This is such utter crap though: quite clearly, narrowing a return type should be a binary-compatible change, wtf!

[gavinking]

Oh, wait, I see what's going on: it's the static method which has changed from returning Iterable to returning java.lang.String (not Ceylon String). That is a binary-incompatible change indeed. Shit.

[jvasileff]

Ah, makes sense. Although really for static methods I think any narrowing of the raw return type would break BC since statics don't have refined methods to let the compiler know what bridge methods to generate.

[gavinking]

@FroMage I still need to figure out what to do about this one before the release.

[gavinking]

In 232d871 I have reverted the change to String in order to preserve BC in this 1.3.3 release.

But 232d871 itself should be reverted immediately after the release, since we're planning a big BC breakage anyway.

[gavinking]

Ditto for List.exceptLast.

[gavinking]

I've reverted the revert.

[gavinking]

Done.