Using <service>.develop.watch without a <service>.build section does not initialise watches

[Mark Gensler]

What is the problem you're trying to solve

If a watch is defined for a service but the service does not have a build section, the watch is ignored/not initialised.
However, watches with action sync or sync+restart do not need to rebuild the service image, so do not necessarily require a build section.

E.g. running docker compose up --watch with the below configuration does not cause a watch to be set up.

my-service:
  image: myimage
  develop:
    watch:
      - path: ./app
        action: sync+restart
        target: /home/web/app  

If a build section is defined for the service, then the watch is initialised correctly:

my-service:
  image: myimage
  build: app
  develop:
    watch:
      - path: ./app
        action: sync+restart
        target: /home/web/app  

Describe the solution you'd like

Either:

• update of the documentation to reflect this

or ideally:

• allow sync and sync+restart watches to run without a build section being defined.

Additional context

I expect there are many use cases where a watch would be required without a build step. One such example is a main service with a complicated build step, then a number of secondary services which use the same image (but do not re-define the build steps from the main service).

Thanks.