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workspaces.md

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Workspaces

A workspace is a collection of one or more packages that share common dependency resolution (with a shared Cargo.lock), output directory, and various settings such as profiles. Packages that are part of a workspaces are called workspace members. There are two flavours of workspaces: as root package or as virtual manifest.

Root package

A workspace can be created by adding a [workspace] section to Cargo.toml. This can be added to a Cargo.toml that already defines a [package], in which case the package is the root package of the workspace. The workspace root is the directory where the workspace's Cargo.toml is located.

Virtual manifest

Alternatively, a Cargo.toml file can be created with a [workspace] section but without a [package] section. This is called a virtual manifest. This is typically useful when there isn't a "primary" package, or you want to keep all the packages organized in separate directories.

Key features

The key points of workspaces are:

  • All packages share a common Cargo.lock file which resides in the workspace root.
  • All packages share a common output directory, which defaults to a directory named target in the workspace root.
  • The [patch], [replace] and [profile.*] sections in Cargo.toml are only recognized in the root manifest, and ignored in member crates' manifests.

The [workspace] section

The [workspace] table in Cargo.toml defines which packages are members of the workspace:

[workspace]
members = ["member1", "path/to/member2", "crates/*"]
exclude = ["crates/foo", "path/to/other"]

All path dependencies residing in the workspace directory automatically become members. Additional members can be listed with the members key, which should be an array of strings containing directories with Cargo.toml files.

The members list also supports globs to match multiple paths, using typical filename glob patterns like * and ?.

The exclude key can be used to prevent paths from being included in a workspace. This can be useful if some path dependencies aren't desired to be in the workspace at all, or using a glob pattern and you want to remove a directory.

An empty [workspace] table can be used with a [package] to conveniently create a workspace with the package and all of its path dependencies.

Workspace selection

When inside a subdirectory within the workspace, Cargo will automatically search the parent directories for a Cargo.toml file with a [workspace] definition to determine which workspace to use. The package.workspace manifest key can be used in member crates to point at a workspace's root to override this automatic search. The manual setting can be useful if the member is not inside a subdirectory of the workspace root.

Package selection

In a workspace, package-related cargo commands like cargo build can use the -p / --package or --workspace command-line flags to determine which packages to operate on. If neither of those flags are specified, Cargo will use the package in the current working directory. If the current directory is a virtual workspace, it will apply to all members (as if --workspace were specified on the command-line).

The optional default-members key can be specified to set the members to operate on when in the workspace root and the package selection flags are not used:

[workspace]
members = ["path/to/member1", "path/to/member2", "path/to/member3/*"]
default-members = ["path/to/member2", "path/to/member3/foo"]

When specified, default-members must expand to a subset of members.

The workspace.metadata table

The workspace.metadata table is ignored by Cargo and will not be warned about. This section can be used for tools that would like to store workspace configuration in Cargo.toml. For example:

[workspace]
members = ["member1", "member2"]

[workspace.metadata.webcontents]
root = "path/to/webproject"
tool = ["npm", "run", "build"]
# ...

There is a similar set of tables at the package level at package.metadata. While cargo does not specify a format for the content of either of these tables, it is suggested that external tools may wish to use them in a consistent fashion, such as referring to the data in workspace.metadata if data is missing from package.metadata, if that makes sense for the tool in question.