[native_assets_cli] Make the InputBuilder API less error-prone

[dcharkes]

In the following code one of the setup calls is missing.

native/pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_macos_host_test.dart

Lines 58 to 78 in 6cec710

	final buildInputBuilder =
	BuildInputBuilder()
	..setupShared(
	packageName: name,
	packageRoot: tempUri,
	outputFile: tempUri.resolve('output.json'),
	outputDirectory: tempUri,
	outputDirectoryShared: tempUri2,
	)
	..config.setupBuild(linkingEnabled: false)
	..config.setupShared(buildAssetTypes: [CodeAsset.type])
	..config.setupCode(
	targetOS: OS.macOS,
	targetArchitecture: target,
	linkModePreference:
	linkMode == DynamicLoadingBundled()
	? LinkModePreference.dynamic
	: LinkModePreference.static,
	cCompiler: cCompiler,
	macOS: MacOSCodeConfig(targetVersion: defaultMacOSVersion),
	);

This doesn't lead to any errors, as the field in particular isn't used in the hook.

However, in general, we should try to structure the API in a way that helps developers are less likely to forget to setup a part of the input.

Instead of having separate setup methods for each individual part, only extensions should have a separate call. Something along the lines of:

BuildInputBuilder()
  ..setup(
    packageName: name,
    packageRoot: tempUri,
    outputFile: tempUri.resolve('output.json'),
    outputDirectory: tempUri,
    outputDirectoryShared: tempUri2,
    config: Config(
      buildAssetTypes: [CodeAsset.type]
      linkingEnabled: false,
    ),
  )
  ..config.setupCode(
    targetOS: OS.macOS,
    targetArchitecture: target,
    linkModePreference:
        linkMode == DynamicLoadingBundled()
            ? LinkModePreference.dynamic
            : LinkModePreference.static,
    cCompiler: cCompiler,
    macOS: MacOSCodeConfig(targetVersion: defaultMacOSVersion),
  );

It would also be better to be explicit about what extensions can add to the config. Possibly along the lines of passing a void Function(BuildConfigBuilder config) for populating the extension data instead of giving generic access to the BuildInputBuilder and a .config.

BuildInputBuilder(
  packageName: name,
  packageRoot: tempUri,
  outputFile: tempUri.resolve('output.json'),
  outputDirectory: tempUri,
  outputDirectoryShared: tempUri2,
  config: Config(
    buildAssetTypes: [CodeAsset.type]
    linkingEnabled: false,
  ),
  extensions: (config) => config.setupCode(
    targetOS: OS.macOS,
    targetArchitecture: target,
    linkModePreference:
        linkMode == DynamicLoadingBundled()
            ? LinkModePreference.dynamic
            : LinkModePreference.static,
    cCompiler: cCompiler,
    macOS: MacOSCodeConfig(targetVersion: defaultMacOSVersion),
  ),
);

(This would make the API not symmetric between base and extensions, the extension setup has to happen in a callback.)

Once we remove the non-shared outputDirectory (#2058) there is also no need in our own code to setup parts of the input.json before setting up other parts.