qmk/qmk_firmware

[Bug] NOOP keys kill combos

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#19,446 opened on Dec 30, 2022

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Description

Describe the Bug

The issue is that whenever a NOOP key is pressed down along with a valid combo, the combo doesn't fire.

Use case:

I am using an ortholinear split keyboard with left shift + right shift combo as caps lock toggle. The right shift is 2U with a POS keycap so the underlaying switches are KC_RSFT and XXXXXXX (using the right switch as a stabilizer because the pcb doesn't support 2U key in that position).

Expected behavior:

NOOP shouldn't interfere with combos because by definition the key should be ignored.

Notes:

I tried the combo with 1U keycaps (meaning the NOOP key is not pressed) and it works fine, so the problem is indeed the NOOP interfering with combos.

Keyboard Used

keebio/viterbi/rev2

Link to product page (if applicable)

https://keeb.io/products/viterbi-keyboard-pcbs-5x7-70-split-ortholinear

Operating System

Microsoft Windows 11

qmk doctor Output

No response

Is AutoHotKey / Karabiner installed

  • AutoHotKey (Windows)
  • Karabiner (macOS)

Other keyboard-related software installed

No response

Additional Context

No response

Contributor guide

Research direction
Examine the combo processing logic in QMK firmware, specifically how key events are filtered for combos. The NOOP key should be skipped in the combo state machine. Look at the functions `process combo` and `combo add key` to understand how keys are tracked and how NOOP keys might inadvertently affect the combo detection.
Tech stack
c
Domain
embedded iot
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitCQMK firmware basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55