Add support for deferred components

[ianmaciel]

What does this change?

This PR include support for Flutter Deferred Components.

Deferred components allow developers to the app into multiple apk to reduce its size. This can be used to optimize the initial download and download components only on necessary but it is also mandatory for apk with more than 200MB.

This library initially looks for assets listed on flutter.assets of pubspec.yaml, with this change the library will continue looking for the assets lists under flutter.assets but will merge with the list of assets included on flutter.deferred-components.$. This will be merged in a single list.

Ideally in the future assets should have different classname, so users will easily know when dealing with deferred components. This wasn't implemented at this moment because it would requeire a significative changes.

Fixes #577 🎯

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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• Appropriate docs were updated (if necessary)

[AlexV525]

Wouldn't [...?config.pubspec.flutter.deferredAssets?.assets] do the same thing as above?

[ianmaciel]

That's true...! good catch!
I actually don't need the forEach loop, just need to merge the two lists.

BTW, do you mean?

[AlexV525]

Yeah exactly

[ianmaciel]

I'm sorry. For a moment I thought it was the same but it is not. I need to revert it.

The fact is we may have many Deferret Components, with many assets each (a list of lists).

So before spreading the list of deferredComponents, it is necessary to spread the assets from each deferredComponent

[AlexV525]

So you may reduce components' assets into one?

[AlexV525]

Something like reduce((list, assets) => list + assets)

[ianmaciel]

I belive I'd need to use fold instead of reduce to have an initial empty list (I might have nothing at this point):
So I got something like this:

[ianmaciel]

any thoughts?

[AlexV525]

@ianmaciel Looks good!

[ianmaciel]

here it is :)

5f4a617

[AlexV525]

Also we need a test to make sure it works well

[ianmaciel]

Hi @AlexV525,
I'm sorry about the late response. I couldn't get back to this before.

I pushed fixups for this pr, if this is okay please let me know so can rebase squashing those fixups.

[AlexV525]

Changes are good but still missing tests. You don't need to squash them as we'll squash them to commit eventually.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.06%. Comparing base (b083796) to head (5f4a617).
Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #576      +/-   ##
==========================================
+ Coverage   97.64%   98.06%   +0.41%     
==========================================
  Files          24       23       -1     
  Lines         891      929      +38     
==========================================
+ Hits          870      911      +41     
+ Misses         21       18       -3     

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[AlexV525]

RSLGTM

[AlexV525]

nit: For better readability maybe:

Suggested change

	/// Merge the deferred assets with the main assets.
	List<Object> _buildAssetsList(Config config) {
	// We may have several deferred components, with a list of assets for each.
	// So before spreading the list of deferred components, we need to spread
	// the list of assets for each deferred component.
	final deferredComponents = config.pubspec.flutter.deferredComponents ?? [];
	return deferredComponents.fold<List<Object>>(
	config.pubspec.flutter.assets,
	(list, deferredComponent) => list + (deferredComponent.assets ?? []),
	);
	}
	/// Build assets from the main list and the deferred components.
	List<Object> _buildFlutterAssetsList(Flutter flutter) {
	final flutterAssets = flutter.assets;
	// We may have several deferred components, with a list of assets for each.
	// So before spreading the list of deferred components, we need to spread
	// the list of assets for each deferred component.
	final deferredComponents = flutter.deferredComponents ?? [];
	return deferredComponents.fold(
	flutterAssets,
	(list, component) => list + (component.assets ?? []),
	);
	}