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Extending selectors from other modules using @use #2494

Closed as not planned
Closed as not planned
@vikigenius

Description

@vikigenius

I am going through the codebase and looking at how the extend algorithm works

void addExtension(
SelectorList extender, SimpleSelector target, ExtendRule extend,
[List<CssMediaQuery>? mediaContext]) {
var selectors = _selectors[target];
var existingExtensions = _extensionsByExtender[target];
Map<ComplexSelector, Extension>? newExtensions;
var sources = _extensions.putIfAbsent(target, () => {});
for (var complex in extender.components) {
if (complex.isUseless) continue;
var extension = Extension(complex, target, extend.span,
mediaContext: mediaContext, optional: extend.isOptional);
if (sources[complex] case var existingExtension?) {
// If there's already an extend from [extender] to [target], we don't need
// to re-run the extension. We may need to mark the extension as
// mandatory, though.
sources[complex] = MergedExtension.merge(existingExtension, extension);
continue;
}
sources[complex] = extension;
for (var simple in _simpleSelectors(complex)) {
_extensionsByExtender.putIfAbsent(simple, () => []).add(extension);
// Only source specificity for the original selector is relevant.
// Selectors generated by `@extend` don't get new specificity.
_sourceSpecificity.putIfAbsent(simple, () => complex.specificity);
}
if (selectors != null || existingExtensions != null) {
newExtensions ??= {};
newExtensions[complex] = extension;
}
}
if (newExtensions == null) return;
var newExtensionsByTarget = {target: newExtensions};
if (existingExtensions != null) {
var additionalExtensions =
_extendExistingExtensions(existingExtensions, newExtensionsByTarget);
if (additionalExtensions != null) {
mapAddAll2(newExtensionsByTarget, additionalExtensions);
}
}
if (selectors != null) {
_extendExistingSelectors(selectors, newExtensionsByTarget);
}
}

It's not very clear to me how this handles extending selectors from other modules.

If someone can point me in the right direction it would be very helpful

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