Enhancement request: avoid "No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry"

[walkjivefly]

Do not request features for the Prusa3D fork of Slic3r here without confirming it is applicable to the mainline Slic3r, or your issue will be closed. Development builds of Slic3r. Prusa3D Issue Tracker

Is your feature request related to a problem? Please describe.
I recently revisited Slic3r after not using my printer for a few weeks. Trying to slice previously good .stl files kept throwing "No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry." errors. The .stl files were all good.

Eventually I realised the problem was the first layer height; it was missing a % sign. Instead of being 150% of 0.2mm it was asking for a 150mm first layer. Which was taller than the entire model and interpreted as there being no layers.

Describe the solution you'd like
The error message could be improved by

• checking the nozzle diameter and for any first layer height taller than the diameter point out the impossibility being requested, or
• being more explicit about checking the first layer height, especially regarding absolute size or percentage.

Alternatively, the code could be changed to assume (confirm with a prompt) that any first layer height greater than 1 is a percentage.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
I had upgraded my OS during the time the printer was unused and spent a lot of time looking for something upgrade related to have somehow caused the Slic3r problem. And all the while there was a simple typo staring me in the face.