Bug 1535154 will add StackGCCellPtr, a GCCellPtr that can be used inside Rooted. It's possible we can simplify this by either supplying a GCPolicy for GCCellPtr or moving the trace() method to GCCellPtr itself.

(In reply to Jon Coppeard (:jonco) from comment #0)

or moving the trace() method to GCCellPtr itself.

For what it's worth: I didn't do this because trace() doesn't know whether to trace as root vs edge right? Ideally we'd be able to support both cases so consumers can always call trace() on a GCCellPtr.

(In reply to Jan de Mooij [:jandem] from comment #1)
Good point, but I don't think we ever want to have GCCellPtrs as internal edges. Those should use the appropriate GC thing type.

This removes StackGCCellPtr and a bunch of indirection.

(In reply to Jon Coppeard (:jonco) from comment #2)

Good point, but I don't think we ever want to have GCCellPtrs as internal edges. Those should use the appropriate GC thing type.

See PrivateScriptData::trace for example: https://searchfox.org/mozilla-central/rev/62a130ba0ac80f75175e4b65536290b52391f116/js/src/vm/JSScript.cpp#4288

(In reply to Jan de Mooij [:jandem] from comment #4)
Oh, that was not the intended use of GCCellPtr. I'm now confused as to how my try run passed...

(In reply to Jon Coppeard (:jonco) from comment #5)
...oh, right, it's because PrivateScriptData::trace doesn't use GCPolicy<GCCellPtr>::trace.

https://hg.mozilla.org/mozilla-central/rev/dc97cf74084d