cargo fc flags in config#

Most cargo fc boolean flags can be set as defaults in Cargo.toml, using the flag name with _ instead of -. Explicit CLI flags still win for a single invocation.

[workspace.metadata.cargo-fc]
dedupe = true
fail_fast = true

[package.metadata.cargo-fc]
pedantic = false

[package.metadata.cargo-fc.target.'cfg(target_os = "windows")']
errors_only = true

[package.metadata.cargo-fc.target.'cfg(target_os = "windows")'.subcommands.clippy]
dedupe = false

[workspace.metadata.cargo-fc.subcommands.my-custom-cmd]
dedupe = true

Configurable flag keys#

summary_only = true
diagnostics_only = true
dedupe = true
verbose = true
pedantic = true
errors_only = true
packages_only = true
fail_fast = true
prune_implied = true
show_pruned = true
maximal_features = true
aggregate_targets = true
no_targets = true
install_missing_targets = true
only_packages_with_lib_target = true
omit_host_target_flag = false

• dedupe = true implies diagnostics-only output.
• prune_implied = false turns off automatic pruning.
• maximal_features = true runs only maximal feature sets, resolved per package-target like every other flag.
• omit_host_target_flag is the one key that defaults to true; set it to false to inject --target for the host too.
• no_targets from config never lifts the package-level targets filter for an explicit --target; only the command-line --no-targets forces that.

Precedence#

Flags resolve broad-to-narrow, with CLI flags last:

1. workspace config
2. matching workspace target config
3. package config
4. matching package target config
5. explicit CLI flags

At each config level, a matching subcommands.<name> table is applied after that level’s plain flags, so command-specific defaults override broader ones. Alias config for the raw command token wins; otherwise cargo fc uses the resolved alias target.

Diagnostics safety#

Broad, config-driven diagnostics output only applies to commands where diagnostics-only mode is safe by default:

• Safe (get broad diagnostics_only = true and dedupe = true when configured): built-in build, check, clippy, doc, and aliases that resolve to them.
• Not safe by default: test, run, and unresolved custom commands — they aren’t reliable JSON-diagnostics commands, so broad diagnostics defaults are ignored for them (silently for well-known cargo plugins, otherwise with a warning).

To opt a non-safe command in, set the behavior in that command’s own table — subcommand-local diagnostics flags are explicit and honored even for commands that aren’t safe by default:

[workspace.metadata.cargo-fc.subcommands.my-custom-cmd]
dedupe = true

dedupe = true implies diagnostics_only = true; setting dedupe = true together with diagnostics_only = false is rejected as contradictory. Use diagnostics_only = false or dedupe = false in a narrower scope to override a broader default.

Notes#

• Any default configured here can be turned back off for one invocation with an inline value on the matching CLI flag: --summary-only=false, --dedupe=off, --omit-host-target-flag=0. See the CLI reference.
• verbose can also be set with the CARGO_FC_VERBOSE environment variable (see the CLI reference).
• --env and --unset-env override the resolved child-process environment; they are value options rather than boolean flag defaults.