Breakpoints in boot steps

[jacob-carlborg]

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Description

It would be nice if Packer supported breakpoints in boot steps. I imagine it working as follows:

To pause the execution before a given boot step, you would write <breakpoint> somewhere in a boot step (boot_steps). The execution would pause in the same way as occurring when the -debug flag is passed to Packer. It would then be possible to either single step, which is what happens today with the -debug flag, i.e. Packer would pause after each step. Or it would be possible to continue the execution. This means Packer would not pause the execution anymore until it hits another breakpoint.

Not sure if it makes sens to support this in boot_command.

Use Case(s)

The use case is similar to #103. That is, the installation process is interactive and requires a lot of steps to complete. Say that there are 50 steps to complete the installation and you have somehow verified that everything works up to step 25 and after that something breaks. It would then be ideal to but a breakpoint at step 25 instead of having to use the -debug flag and single step 25+ times before it hits the potential problem. Also, there are like 10-15 steps before Packer even starts the VM and executes the boot command/boot steps, where there usually are no problems.

Potential configuration

boot_steps = [
  ["1<wait20s>", "Boot normally"],
  ["a<enter><wait5>", "Installation messages in English"]
  ["a<enter><wait5>", "Install NetBSD to hard disk"],
  
  ["<breakpoint>", "Separate step with breakpoint"],
  ["<breakpoint>b<enter><wait5>", "Breakpoint within a step"],
  
  ["b<enter><wait5>", "Yes"],
  ["a<enter><wait5>", "Available disks: sd0"],
  ["a<enter><wait5>", "Guid Partition Table"],
],

Potential References

#103