Lazy global dynamic variable

[lockieluke]

Only load global variables with SH when the task needs it:

version: '3'
vars:
  MESSAGE:
    sh: sleep 5 && echo "WORLD"

tasks:
  print:
    cmds:
      - echo "HELLO {{.MESSAGE}}"

  print-no-wait:
    cmds:
      - echo "PRINT THIS INSTANTLY"

Other tasks that don't need the variable should not have it loaded

[vctls]

Just noticed that global dynamic variables are evaluated each time a task is run.
This can indeed become a performance problem. It could at least be documented.

I don't see many workarounds in the meantime.
Commands that take time should not be used in global dynamic variables but rather sub-commands or task dependencies.
Or, you could add conditions in the expression itself. Local variables aren't available, but, for example, the TASK variable is:

vars:
  FOO:
    sh: |-
      {{ if .TASK | contains "bar" }}sleep 2 && echo baz{{end}}

This is kind of ugly and cumbersome, but can be used with task namespaces in order to confine the problem to the tasks that actually need that variable.
I suppose long running command results could also be cached, when possible.

[user2410]

I have been using this workaround for the issue.

version: '3'

vars:
  MASTER_IP_CMD: |
    awk '/ master /{print $1}' ./machines.txt

tasks:
  build:
    desc: "Build the cluster"
    cmds:
      - ...
      - vagrant up # This produces ./machines.txt
      - ...

  certs:gen:
    desc: "Generate certificates for components"
    vars:
      MASTER_IP:
        sh: |
          {{.MASTER_IP_CMD}}
    cmds:
      # Your commands here

  dist:certs:
    desc: "Distribute certificates to VMs"
    vars:
      MASTER_IP:
        sh: |
          {{.MASTER_IP_CMD}}
    cmds:
      # Your commands here

Because the MASTER_IP variable is only available after vagrant up, resolving the global variable before running task build will result in error.
This workaround avoids evaluating the global dynamic variable by storing the command as a plain string, deferring its execution until a task runs and actually needs it.