Module cargo::core::resolver::features

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Expand description

Resolves conditional compilation for features section in the manifest.

This is a new feature resolver that runs independently of the main dependency resolver. It has several options which can enable new feature resolution behavior.

One of its key characteristics is that it can avoid unifying features for shared dependencies in some situations. See FeatureOpts for the different behaviors that can be enabled. If no extra options are enabled, then it should behave exactly the same as the dependency resolver’s feature resolution.

The preferred way to engage this new resolver is via resolve_ws_with_opts.

This does not replace feature resolution in the dependency resolver, but instead acts as a second pass which can narrow the features selected in the dependency resolver. The dependency resolver still needs to do its own feature resolution in order to avoid selecting optional dependencies that are never enabled. The dependency resolver could, in theory, just assume all optional dependencies on all packages are enabled (and remove all knowledge of features), but that could introduce new requirements that might change old behavior or cause conflicts. Maybe some day in the future we could experiment with that, but it seems unlikely to work or be all that helpful.

§Assumptions

There are many assumptions made about the dependency resolver:

  • Assumes feature validation has already been done during the construction of feature maps, so the feature resolver doesn’t do that validation at all.
  • Assumes dev-dependencies within a dependency have been removed in the given Resolve.

There are probably other assumptions that I am forgetting.

Structs§

Enums§

  • Flag to indicate if features are requested for a certain type of dependency.
  • Flag to indicate that target-specific filtering should be disabled.
  • Flag to indicate if Cargo is building any dev units (tests, examples, etc.).
  • Features flags requested for a package.

Type Aliases§