Trait FeatureLinkVisitor 

pub trait FeatureLinkVisitor<'g> {
    // Required method
    fn visit_link(
        &mut self,
        cx: &FeatureLinkContext<'g>,
        link: ConditionalLink<'g>,
    ) -> bool;
}

Represents whether a particular link within a feature graph should be followed during a resolve operation.

Required Methods

fn visit_link( &mut self, cx: &FeatureLinkContext<'g>, link: ConditionalLink<'g>, ) -> bool

Returns true if this conditional link should be followed during a resolve operation.

Weak dependency features

Most links are visited at most once per resolve. The exception is a weak dependency feature (dep?/feature) on a dependency with both required and optional declarations. For example:

[dependencies]
foo = { version = "1" }

[build-dependencies]
foo = { version = "1", optional = true }

[features]
weak = ["foo?/std"]

Cargo applies foo?/std to each declaration of foo separately, so this method can be called twice for the link from weak to foo/std:

• First with a link covering the required declarations of foo: here, [dependencies].
• Then with a link covering the optional ones: here, [build-dependencies].

Both links have the same endpoints. Use ConditionalLink::declarations to tell them apart. The feature graph has one edge for the two links, and that edge is followed if this method returns true for either of them.

A visitor that keeps state for each link, such as a count of visits, should take this into account.

When the two links are offered depends on the query’s direction:

• A forward query offers the Required link as soon as weak is reached. It offers the Optional link only once dep:foo is activated, which may be at an unrelated point later in the traversal.
• A reverse query offers both links (Required first) as soon as foo/std is reached. Reverse queries don’t try to model when foo is activated.

Trait Implementations

impl<'g> FeatureLinkVisitor<'g> for Box<dyn FeatureLinkVisitor<'g> + '_>

fn visit_link( &mut self, cx: &FeatureLinkContext<'g>, link: ConditionalLink<'g>, ) -> bool

Returns true if this conditional link should be followed during a resolve operation.

impl<'g> FeatureLinkVisitor<'g> for &mut dyn FeatureLinkVisitor<'g>

fn visit_link( &mut self, cx: &FeatureLinkContext<'g>, link: ConditionalLink<'g>, ) -> bool

Returns true if this conditional link should be followed during a resolve operation.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementations on Foreign Types

impl<'g, T> FeatureLinkVisitor<'g> for &mut T

where T: FeatureLinkVisitor<'g>,

fn visit_link( &mut self, cx: &FeatureLinkContext<'g>, link: ConditionalLink<'g>, ) -> bool

impl<'g> FeatureLinkVisitor<'g> for Box<dyn FeatureLinkVisitor<'g> + '_>

fn visit_link( &mut self, cx: &FeatureLinkContext<'g>, link: ConditionalLink<'g>, ) -> bool

Implementors

impl<'g> FeatureLinkVisitor<'g> for &mut dyn FeatureLinkVisitor<'g>