[frontend_server] Enable native-assets dill compilation without dart program about sdk

[jensjoha]

The idea of having a compile method where you call it with "oh, actually don't compile, but do run some other byproduct thing" seems weird.

For the one-off-run I think introducing a --native-only=<whateverFile> or something would make sense.
For the "stdin protocol" I think it would be cleaner to have a separate command.

[dcharkes]

That makes sense. 👍

I have no idea if we are ever in a situation where we would have two different byproducts that we want to compile in a single invocation. But assuming no, specifying byproduct-only makes more sense than not-main-thing.

Startup / single shot commandline API:

• (already existing) --native-assets=<file> sets the side product for when compiling the full thing, either immediately or with subsequent compiles over the protocol.
• (new option A) --native-assets-only (no file), should be supplied together with --native-assets=<file>
• (new option B) --native-assets-only=<file>

The protocol

• (already existing) native-assets <file> sets the side product for when compiling the full thing with subsequent compiles.
• (new option A) native-assets-only after already having sent native-assets <file> before
• (new option B) native-assets-only <file>

@jensjoha any preference for whether we add the <file> to native-assets-only, or whether it should be supplied with the already existing flag and command?

[jensjoha]

Already having --native-assets=<file> and native-assets <file> I suppose the native-assets-only without file makes more sense. I don't immediately have strong feelings about it though ;)

[dcharkes]

Already having --native-assets=<file> and native-assets <file> I suppose the native-assets-only without file makes more sense. I don't immediately have strong feelings about it though ;)

I had the same, not so strong, feelings. 👍

[lrhn]

Compiling without an entry point could affect tree shaking (basically make it impossible, it has no root).
It's that a problem?

[dcharkes]

Compiling without an entry point could affect tree shaking (basically make it impossible, it has no root). It's that a problem?

"Compiling" is a bit of a strange word here. We're creating an encoding of the native_assets.yaml in a dart library.

sdk/pkg/vm/lib/native_assets/synthesizer.dart

Lines 46 to 55 in 637f3b2

	/// Synthesizes a [Library] to be included in a kernel snapshot for the VM.
	///
	/// [nativeAssetsYaml] must have been validated with [NativeAssetsValidator].
	///
	/// The VM consumes this component in runtime/vm/ffi/native_assets.cc.
	static Library synthesizeLibrary(
	Map nativeAssetsYaml, {
	nonNullableByDefaultCompiledMode = NonNullableByDefaultCompiledMode.Strong,
	Class? pragmaClass,
	}) {

And yes, this encoding only uses VM-recognized classes (list, string, map, and pragma), so that tree-shaking of the Dart program this special library is concatenated to can be read by the VM.