CLI Job validate SIGSEGV with job type=system and migrate stanza

[benagricola]

Nomad version

Nomad v0.9.0-rc1 (7c00ab4)

Affects 0.8.7 at least as well

Operating system and Environment details

Darwin 18.2, Linux, etc

Issue

A job file with type = "system" and containing a job:migrate{} stanza causes nomad validate <job>.nomad to panic if a group is defined.

Change the type to service and validate successfully runs, complaining about missing tasks.

Reproduction steps

Create job files from below.

Validate job file with service scheduler:

~/d/nomad> ./nomad job validate panic.nomad 
Job validation errors:
2 error(s) occurred:

* Missing job datacenters
* Task group panicgrp validation failed: 1 error(s) occurred:

* Missing tasks for task group

Validate job file with system scheduler:

~/d/nomad> ./nomad job validate panic.nomad 
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x53276f9]

goroutine 1 [running]:
github.com/hashicorp/nomad/command/agent.ApiTgToStructsTG(0xc0002e5540, 0xc0000ca4d0)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/command/agent/job_endpoint.go:691 +0x5c9
github.com/hashicorp/nomad/command/agent.ApiJobToStructJob(0xc0003fa000, 0xc00043a180)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/command/agent/job_endpoint.go:656 +0x45f
github.com/hashicorp/nomad/command.(*JobValidateCommand).validateLocal(0xc000128370, 0xc0003fa000, 0x0, 0xc0001e4f80, 0x0)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/command/job_validate.go:120 +0x5d
github.com/hashicorp/nomad/command.(*JobValidateCommand).Run(0xc000128370, 0xc00003a1b0, 0x1, 0x1, 0xc00030e1b0)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/command/job_validate.go:85 +0x69a
github.com/hashicorp/nomad/vendor/github.com/mitchellh/cli.(*CLI).Run(0xc00027a640, 0xc00027a640, 0xc0001d4560, 0x3b)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/vendor/github.com/mitchellh/cli/cli.go:255 +0x207
main.RunCustom(0xc00003a190, 0x3, 0x3, 0x0)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/main.go:131 +0x48e
main.Run(0xc00003a190, 0x3, 0x3, 0xc00009e058)
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/main.go:76 +0x3f
main.main()
        /tmp/nomad-workspace/2019-03-21-1553195760/gopath/src/github.com/hashicorp/nomad/main.go:72 +0x62

Job file (if appropriate)

panic.nomad

job "panic" {
    type = "system"
    migrate {}
    group "panicgrp" {}
}

nopanic.nomad

job "panic" {
    type = "service"
    migrate {}
    group "panicgrp" {}
}

[schmichael]

Thanks for the report and reproducer @benagricola!

Fixed in #5486, but I'm holding off merging until post-0.9.0 as we're trying to minimize changes during the release candidate period.

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