Package ID Specifications

Package ID specifications

Subcommands of Cargo frequently need to refer to a particular package within adependency graph for various operations like updating, cleaning, building, etc.To solve this problem, Cargo supports Package ID Specifications. A specificationis a string which is used to uniquely refer to one package within a graph ofpackages.

Specification grammar

The formal grammar for a Package Id Specification is:

pkgid := pkgname
       | [ proto "://" ] hostname-and-path [ "#" ( pkgname | semver ) ]
pkgname := name [ ":" semver ]
proto := "http" | "git" | ...

Here, brackets indicate that the contents are optional.

Example specifications

These could all be references to a package foo version 1.2.3 from theregistry at crates.io

Brevity of specifications

The goal of this is to enable both succinct and exhaustive syntaxes forreferring to packages in a dependency graph. Ambiguous references may refer toone or more packages. Most commands generate an error if more than one packagecould be referred to with the same specification.