[FeatureRequest]: Allow M291 to set result to -1 when blocking modal "Cancel" clicked.

[benagricola]

Is your feature request related to a problem? Please describe.

Currently, the documentation for the result meta gcode variable states that on clicking the "Cancel" button of a blocking M291 modal, the result value should be set to -1 but this is not the case - the containing input stream is aborted and no code after the M291 call is evaluated.

This makes it difficult to give macros the option to abort at a particular location while also allowing some level of recovery from that within the macro (for example to reset speed limits or restart a probing sequence).

Describe the solution you propose.

As discussed in the forum thread linked below, @dc42 suggested adding a J2 parameter to M291 which would cause it to no longer abort if "Cancel" were clicked, but instead set the result variable to -1 as documented.

This would not break existing macros relying on the current J1 behaviour but would also allow more nuanced usage of M291 and recovery from cancelling user input.

Describe alternatives you've considered

For M291 ... S4 it is possible to add a "Cancel" input option and use the input variable to detect if the user clicked "Cancel", but this only works where the input is multiple-option, and cannot be used if the S-value is >= 5 or == 3.

Provide any additional context or information.

https://forum.duet3d.com/topic/34945/meta-gcode-result-variable-inconsistent-with-docs/4?_=1707983978818

[chrishamm]

When this is addressed the corresponding implementation in DSF needs to be changed again as well. Unlike in v3.4, in v3.5 result is evaluated by RRF which can be off if the result of potential custom G/M-codes diverges from the last result.

[T3P3]

https://forum.duet3d.com/topic/35663/m291-j2-1/3

Further request

[dc42]

Related: set result to -1 if the message box times out. See https://forum.duet3d.com/topic/36445/m291-t-value-to-return-a-result/2.

[Tinchus2009]

Hi. I was directoed to read here after I posted: https://forum.duet3d.com/topic/36694/m291-message-non-blocking-execution/3?_=1727461179293

In J4 cancell the job/macro by pressing CCANCEL, why also cancell the macro/job if the message box is configured to time out? How I see it: timeout means no answer was given, lets continue. If you dont want to continue, you had the CANCEL BUTTOM