Per-target configuration#

Override configuration for specific targets using Cargo-style cfg(...) selectors. This uses the same forms and precedence as everything else — see the override model — applied at a narrower scope.

Overrides live under:

[package.metadata.cargo-fc.target.'cfg(...)']

Example: different features per OS#

[package.metadata.cargo-fc]
exclude_features = ["default"]

[package.metadata.cargo-fc.target.'cfg(target_os = "linux")']
exclude_features = { add = ["metal"] }

[package.metadata.cargo-fc.target.'cfg(target_os = "macos")']
exclude_features = { add = ["cuda"] }

The base excludes default everywhere. On Linux, metal is also excluded (the add unions into the inherited value); on macOS, cuda is. Remember: an array like exclude_features = ["metal"] would have replaced the base instead of extending it.

Patch semantics recap#

Collection-like keys — exclude_features, include_features, only_features, and the *_feature_sets keys — take:

• key = [...] or { override = [...] } — replace the inherited value.
• { add = [...] } — union with the inherited value.
• { remove = [...] } — subtract from the inherited value.

Applied in order: override (or base), then remove, then add; add wins ties. When multiple cfg(...) sections match (e.g. both cfg(unix) and cfg(target_os = "linux")), their add/remove sets are unioned. Conflicting override values are an error.

Matrix metadata tables merge recursively; other metadata values, including arrays, replace.

Which selector matches#

A section applies when its cfg(...) predicate matches the concrete target being resolved. cfg(feature = "...") predicates are not supported in target-override keys. If --target <triple> or CARGO_BUILD_TARGET is set, that value selects matching overrides — this also applies to cargo fc matrix.

inherit = false#

Sections inherit the base by default (inherit = true). A matching target section can set inherit = false to start from a fresh default config instead. When it does, patchable fields in that section may only use override (arrays), not add/remove:

[package.metadata.cargo-fc]
exclude_features = ["default"]
skip_optional_dependencies = true

[package.metadata.cargo-fc.target.'cfg(target_os = "linux")']
inherit = false
exclude_features = ["default", "cuda"]   # fresh config; nothing inherited

Workspace target overrides#

Workspace target sections can patch exclude_packages and set flag defaults for matching targets, using the same cfg(...) selectors:

[workspace.metadata.cargo-fc]
targets = ["x86_64-unknown-linux-gnu", "wasm32-unknown-unknown"]

[workspace.metadata.cargo-fc.target.'cfg(target_arch = "wasm32")']
exclude_packages = { add = ["native-cli"] }

[workspace.metadata.cargo-fc.target.'cfg(target_os = "linux")']
exclude_packages = { add = ["wasm-app"] }
fail_fast = false

These apply to every concrete effective target, including single-target runs selected by --target, CARGO_BUILD_TARGET, or the host.

Combining with commands#

A target.'cfg(...)'.subcommands.<command> section applies only when both the target matches and the command is selected — see Per-command configuration.