cannot use preload in mod

[stc1988]

In e56f371, preload can no longer be used in mod. I understand that preload cannot be used in mod, but many module manifest files preload the module.

How about ignoring preload when building mod and outputting a warning log?

[stc1988]

@phoddie
Could you please take a look?

[phoddie]

Hello. I recall responding to this when it was first posted. Perhaps I forgot to hit "Reply"?

The change is deliberate, because preload doesn't do anything in a mod. This can lead to developer confusion. An error is the most reliable way to avoid the mistake.

I suppose we could treat it as a warning instead. Before deciding, I would like to understand which module(s) you are seeing this on, to make sure the solution is the right one. Thank you.

[stc1988]

A simple example would be using a sensor driver from a Stack-chan mod user application.

In that case, it first tries to include a manifest file like $(MODDABLE)/modules/drivers/sensors/paj7620u2/manifest.json, but this fails. It’s true that directly loading the module would solve the issue, but if the manifest file has a lot of content or includes additional manifest files, it would likely require a amount of work.

[phoddie]

Thanks for the example. It is a little different than what I had in mind. But, it is a reasonable use. We definitely want developers using the manifests to include modules, as this avoids all sorts of problems.

The decision to preload isn't always the module itself. A module can indicate that it is compatible with preload. That's really what the "preload" attribute means. We've developed a coding style in the Moddable SDK that allows the vast majority of modules to be compatible with preload, but it isn't always the case. There are other reasons a host might not want to preload a module, for example to allow it to be overridden by a mod at runtime. We don't have a solution to describe that in the manifest at this time though.

So, we should reduce the error to warning. That's practical.

How does this look to you?

		if (this.manifest.preload?.length) {
			trace("Warning: preload is unavailable in mods. These modules request preload:\n")
			this.manifest.preload.forEach(item => trace(`  ${item}\n`));
		}

[stc1988]

Thank you for the detailed explanation. I feel like I have a much better understanding of preload now.

How does this look to you?

  if (this.manifest.preload?.length) {
  	trace("Warning: preload is unavailable in mods. These modules request preload:\n")
  	this.manifest.preload.forEach(item => trace(`  ${item}\n`));
  }

Yes, it’s as expected.