I try to start the snapshot, the Mojang splash screen briefly shows and immediately disappears after the launcher informs me about a game crash. I've attached the launcher logfile which shows a peculiar error / stacktrace.

Also noteworthy: I can rule out any external influences (such as resource packs) because when I move my .minecraft folder out of the way (rename it) and then start fully fresh the exact same thing happens to me.

To summarize a bit, the main error message which I get to see (also in the regular log) is this:

[17:37:54] [Client thread/INFO]: Reloading ResourceManager: Default[17:37:54] [Client thread/INFO]: Reloading ResourceManager: Default[17:37:54] [Bootstrap 0/ERROR]: Unable to bootstrap datafixersjava.lang.StackOverflowError: null at aaz$g.a(SourceFile:178) ~[18w20a.jar:?] at aaz$m.a(SourceFile:525) ~[18w20a.jar:?] at aaz$m.a(SourceFile:525) ~[18w20a.jar:?]// code placeholder

You can find the full stacktrace in the attached logfile.

(edit): Forgot to mention: sometimes the crash is so severe that the whole launcher crashes as well.