Dart_SetLibraryTagHandler exits when called without a current isolate

[DartBot]

This issue was originally filed by sammcca...@google.com

---

This function is documented to return an error handle, but instead exits if called outside of any isolate.

[iposva-google]

Set owner to @turnidge.
Added Area-VM, Accepted labels.

[turnidge]

This is true for many functions in the dart api. If there is no current isolate then, as things currently stand, we can't make any handles at all, including error handles.

I have two options:

1. Change the documentation for all "isolate required" functions to say that calling them w/o a current isolate exits.
2. Manufacture some sort of fake error handle that is use whenever a function is called without a current isolate. I'm not sure how ugly this would be -- I would need to change all of the handle unwrapping to check for this special error handle.

I'll think on it.

[DartBot]

This comment was originally written by sammcca...@google.com

---

It'd be great if it was possible to return a handle wrapping a statically allocated error message.

If Dart is embedded in e.g. a web server, then killing the process (and all serving threads) is problematic, even if the cause is misuse of the API.

But I understand this is tricky, and it's more of a frustration than a blocker for me.

[iposva-google]

We could preallocate an general error handle in the VM isolate and return that in such a case.

---

Removed the owner.
Added this to the M6 milestone.
Added Triaged label.

[iposva-google]

Removed Priority-Medium label.
Added Priority-Unassigned label.

[iposva-google]

Removed this from the M6 milestone.

[iposva-google]

Stale.