Operating system: Windows-10-10.0.16299 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.67
Broken: version: 2.80 (sub 71), branch: blender2.7, commit date: 2019-05-22 00:34, hash: rB0f98c05c8b86
Short description of error
Here's a model with an n-gon connected to some triangles. It has some edges marked as sharp and a bevel modifier with "Mark Sharp" selected.
Exact steps for others to reproduce the error
Open attached file. Press ctrl+t (triangulate). Blender hangs indefinitely and needs to be killed.
Edit: It's actually broken in reverse too. If you first triangulate and then check "Mark Sharp" in bevel modifier it will also hang.