Describe the request

DigiKeyboard uses .inc for including some low-level shits, and i'm trying to rewrite that, but i can't because arduino-cli don't accept .inc ext according to:

https://arduino.github.io/arduino-cli/1.3/sketch-specification/#additional-code-files
https://forum.arduino.cc/t/including-inc-files/1136351

Describe the current behavior

Try to #include some lib .inc (don't forget, uses a real project arch and not useless arduino IDE)

Arduino CLI version

arduino-cli Version: 1.4.0 Commit: b700097 Date: -- the error can happen with arduino-cli Version: nightly-20260120 Commit: e394193 Date: 2026-01-20T01:37:42Z

Operating system

Linux

Operating system version

Linux howo-setup 6.17.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Mon, 24 Nov 2025 15:21:09 +0000 x86_64 GNU/Linux

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details