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doc(features2): explain the meaning of presence in activated_features

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Weihang Lo 2022-10-26 21:41:30 +08:00
parent 9e8395904d
commit 2b913b664f
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1 changed files with 19 additions and 6 deletions
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25
src/cargo/core/resolver/features.rs
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@ -57,6 +57,9 @@ type ActivateMap = HashMap<PackageFeaturesKey, BTreeSet<InternedString>>;
/// Set of all activated features for all packages in the resolve graph.
pub struct ResolvedFeatures {
/// Map of features activated for each package.
///
/// The presence of each key also means the package itself is activated,
/// even its associated set contains no features.
activated_features: ActivateMap,
/// Options that change how the feature resolver operates.
opts: FeatureOpts,
@ -406,8 +409,14 @@ pub struct FeatureResolver<'a, 'cfg> {
/// Options that change how the feature resolver operates.
opts: FeatureOpts,
/// Map of features activated for each package.
///
/// The presence of each key also means the package itself is activated,
/// even its associated set contains no features.
activated_features: ActivateMap,
/// Map of optional dependencies activated for each package.
///
/// The key is the package having their dependencies activated.
/// The value comes from `dep_name` part of the feature syntax `dep:dep_name`.
activated_dependencies: ActivateMap,
/// Keeps track of which packages have had its dependencies processed.
/// Used to avoid cycles, and to speed up processing.
@ -497,10 +506,10 @@ impl<'a, 'cfg> FeatureResolver<'a, 'cfg> {
Ok(())
}
/// Activates [`FeatureValue`]s on the given package.
/// Activates a list of [`FeatureValue`] for a given package.
///
/// This is the main entrance into the recursion of feature activation
/// for a package.
/// This is the main entrance into the recursion of feature activation for a package.
/// Other `activate_*` functions would be called inside this function accordingly.
fn activate_pkg(
&mut self,
pkg_id: PackageId,
@ -508,9 +517,13 @@ impl<'a, 'cfg> FeatureResolver<'a, 'cfg> {
fvs: &[FeatureValue],
) -> CargoResult<()> {
log::trace!("activate_pkg {} {}", pkg_id.name(), fk);
// Add an empty entry to ensure everything is covered. This is intended for
// finding bugs where the resolver missed something it should have visited.
// Remove this in the future if `activated_features` uses an empty default.
// Cargo must insert an empty set here as the presence of an (empty) set
// also means that the dependency is activated.
// This `is_activated` behavior for dependencies was previously depends on field
// `activated_dependencies`, which is less useful after rust-lang/cargo#11183.
//
// That is, we may keep or remove `activated_dependencies` in the future
// if figuring out it can completely be replaced with `activated_features`.
self.activated_features
.entry((pkg_id, fk.apply_opts(&self.opts)))
.or_insert_with(BTreeSet::new);