CARGO-RUSTC(1)

📦 version 1.85.1, in ubuntu jammy, ubuntu noble, ubuntu questing

🦋 CARGO-RUSTC 💅

okay bestie, welcome to the General Commands Manual entry for cargo-rustc — she's the cargo subcommand that compiles your current package and lets you whisper extra flags straight into the compiler's ear. let's get into it 🎀

✨ NAME ✨

cargo-rustc — Compile the current package, and pass extra options to the compiler 🫶

🌸 SYNOPSIS 🌸

cargo rustc [options] [-- args]

💖 DESCRIPTION 💖

so the target you picked for the current package (or the package you named with -p, if you did) gets compiled, along with literally all of its dependencies. and the args you tack on at the end? those get passed to the final compiler invocation — not to any of the dependencies, nope, just the last one. 🎯

heads up tho: the compiler is still gonna unconditionally receive arguments like -L, --extern, and --crate-type no matter what. your specified args just get added on top of the compiler invocation. no take-backs, no replacing. 💅

want the full lore on rustc flags? it's right here: <https://doc.rust-lang.org/rustc/index.html>

⚠️ real talk: this command requires that only one target is being compiled when you pass additional arguments. if your current package has more than one target available, you must use the filters like --lib, --bin, etc. to pick which one gets compiled. no target ambiguity allowed, periodt.

and if you wanna pass flags to all compiler processes spawned by Cargo (not just the final one), use the RUSTFLAGS environment variable <https://doc.rust-lang.org/cargo/reference/environment-variables.html> or the build.rustflags config value <https://doc.rust-lang.org/cargo/reference/config.html>.

👑 OPTIONS 👑

🎀 Package Selection

by default, the package chillin' in the current working directory is the one selected. the -p flag lets you pick a different package in a workspace, main character energy 🫶

  • -p spec, --package spec — the package to build. See cargo-pkgid(1) for the SPEC format.

🌈 Target Selection

when you don't give any target selection options, cargo rustc builds all binary and library targets of the selected package. all of them. the whole squad. ✨

binary targets get automatically built if there's an integration test or benchmark being selected to build — this lets an integration test run the binary to exercise and test its behavior. the CARGO_BIN_EXE_<name> environment variable <https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates> gets set when the integration test is built, so it can use the env macro <https://doc.rust-lang.org/std/macro.env.html> to locate the executable. iykyk 🔥

passing target selection flags means you build only the targets you named. narrowing it down, we love to see it.

💡 note that --bin, --example, --test and --bench flags also support common Unix glob patterns like *, ? and []. BUT — and this is the important part — to avoid your shell accidentally expanding those glob patterns before Cargo gets its hands on them, you must wrap each glob pattern in single quotes or double quotes. protect the globs bestie 😭
  • --lib — build the package's library.
  • --bin *name*… — build the specified binary. this flag can be given multiple times and supports common Unix glob patterns.
  • --bins — build all binary targets.
  • --example *name*… — build the specified example. can be given multiple times and supports common Unix glob patterns.
  • --examples — build all example targets.
  • --test *name*… — build the specified integration test. can be given multiple times and supports common Unix glob patterns.
  • --tests — build all targets that have the test = true manifest flag set. by default this includes the library and binaries built as unittests, plus integration tests. be aware that this will also build any required dependencies, so the lib target may get built twice (once as a unittest, and once as a dependency for binaries, integration tests, etc.). targets can be enabled or disabled by setting the test flag in the manifest settings for the target.
  • --bench *name*… — build the specified benchmark. can be given multiple times and supports common Unix glob patterns.
  • --benches — build all targets that have the bench = true manifest flag set. by default this includes the library and binaries built as benchmarks, plus bench targets. again, this will also build any required dependencies, so the lib target may get built twice (once as a benchmark, and once as a dependency for binaries, benchmarks, etc.). targets can be enabled or disabled by setting the bench flag in the manifest settings for the target.
  • --all-targets — build all targets. this is equivalent to specifying --lib --bins --tests --benches --examples. the whole buffet 🍓

🦋 Feature Selection

the feature flags let you control which features are enabled. when no feature options are given, the default feature is activated for every selected package. ✨

see the features documentation for more details: <https://doc.rust-lang.org/cargo/reference/features.html#command-line-feature-options>

  • -F features, --features features — space or comma separated list of features to activate. features of workspace members may be enabled with package-name/feature-name syntax. this flag can be given multiple times, which enables all specified features.
  • --all-features — activate all available features of all selected packages. go big or go home 💅
  • --no-default-features — do not activate the default feature of the selected packages.

💜 Compilation Options

  • --target triple — build for the given architecture. the default is the host architecture. the general format of the triple is <arch><sub>-<vendor>-<sys>-<abi>. run rustc --print target-list for a list of supported targets. this flag may be specified multiple times.

this may also be specified with the build.target config value <https://doc.rust-lang.org/cargo/reference/config.html>.

⚠️ note that specifying this flag makes Cargo run in a different mode, where the target artifacts are placed in a separate directory. see the build cache documentation for more details: <https://doc.rust-lang.org/cargo/reference/build-cache.html>
  • -r, --release — build optimized artifacts with the release profile. see also the --profile option for choosing a specific profile by name.
  • --profile name — build with the given profile.

the rustc subcommand treats these named profiles with special behaviors, bestie:

see the reference for more details on profiles: <https://doc.rust-lang.org/cargo/reference/profiles.html>

  • --timings=fmts — output information about how long each compilation takes, and track concurrency information over time. accepts an optional comma-separated list of output formats; --timings without an argument will default to --timings=html. specifying an output format (rather than the default) is unstable and requires -Zunstable-options. valid output formats:
    • html (unstable, requires -Zunstable-options): write a human-readable file cargo-timing.html to the target/cargo-timings directory with a report of the compilation. also write a report to the same directory with a timestamp in the filename if you want to look at older runs. HTML output is suitable for human consumption only, and does not provide machine-readable timing data.
    • json (unstable, requires -Zunstable-options): emit machine-readable JSON information about timing information.
  • --crate-type crate-type — build for the given crate type. this flag accepts a comma-separated list of 1 or more crate types, of which the allowed values are the same as the crate-type field in the manifest for configuring a Cargo target. see crate-type field for possible values: <https://doc.rust-lang.org/cargo/reference/cargo-targets.html#the-crate-type-field>

if the manifest contains a list, and --crate-type is provided, the command-line argument value will override what's in the manifest. periodt 💅

this flag only works when building a lib or example library target.

🧚 Output Options

  • --target-dir directory — directory for all generated artifacts and intermediate files. may also be specified with the CARGO_TARGET_DIR environment variable, or the build.target-dir config value <https://doc.rust-lang.org/cargo/reference/config.html>. defaults to target in the root of the workspace.

⭐ Display Options

  • -v, --verbose — use verbose output. may be specified twice for "very verbose" output, which includes extra output such as dependency warnings and build script output. may also be specified with the term.verbose config value <https://doc.rust-lang.org/cargo/reference/config.html>.
  • -q, --quiet — do not print cargo log messages. may also be specified with the term.quiet config value <https://doc.rust-lang.org/cargo/reference/config.html>.
  • --color when — control when colored output is used. valid values:
    • auto (default): automatically detect if color support is available on the terminal.
    • always: always display colors.
    • never: never display colors.

may also be specified with the term.color config value <https://doc.rust-lang.org/cargo/reference/config.html>.

  • --message-format fmt — the output format for diagnostic messages. can be specified multiple times and consists of comma-separated values. valid values:
    • human (default): display in a human-readable text format. conflicts with short and json.
    • short: emit shorter, human-readable text messages. conflicts with human and json.
    • json: emit JSON messages to stdout. see the reference for more details: <https://doc.rust-lang.org/cargo/reference/external-tools.html#json-messages>. conflicts with human and short.
    • json-diagnostic-short: ensure the rendered field of JSON messages contains the "short" rendering from rustc. cannot be used with human or short.
    • json-diagnostic-rendered-ansi: ensure the rendered field of JSON messages contains embedded ANSI color codes for respecting rustc's default color scheme. cannot be used with human or short.

and that's only part 1, bestie — there's more coming so don't go anywhere 💖

  • json-render-diagnostics — bestie, this one tells Cargo to not stuff rustc diagnostics into the JSON messages it prints. Instead, Cargo itself renders the JSON diagnostics coming from rustc. Cargo's own JSON diagnostics — plus the other ones coming from rustc — are still emitted tho. Can't be used with human or short. No mixing, periodt. 💅

🎀 MANIFEST OPTIONS 🎀

  • --manifest-path path — the path to the Cargo.toml file. If you don't say anything, Cargo goes hunting for Cargo.toml in the current directory, or any parent directory above it. It's giving "I'll find it myself" energy. 🕵️‍♀️
  • --ignore-rust-version — ignores the rust-version specification in packages. Pretend it's not there, live your life. 🙈
  • --locked — asserts that the exact same dependencies and versions are used as when the existing Cargo.lock file was originally generated. Cargo will exit with an error when either of these scenarios shows up:
    • The lock file is missing. 😭
    • Cargo attempted to change the lock file due to a different dependency resolution.

Use it wherever you want deterministic builds — CI pipelines are the main character here. ✨

  • --offline — prevents Cargo from accessing the network for any reason. Without this flag, Cargo just stops with an error if it needs the network and the network isn't available. With this flag, Cargo will attempt to proceed without the network if possible.
Beware, bestie: this may result in different dependency resolution than online mode. Cargo restricts itself to crates that are downloaded locally, even if there might be a newer version as indicated in the local copy of the index. Check out the cargo-fetch(1) command to download dependencies before going offline. 📴

May also be specified with the net.offline config value https://doc.rust-lang.org/cargo/reference/config.html.

  • --frozen — literally the same as specifying both --locked and --offline. Two-for-one. 🫶
  • --lockfile-path PATH — changes the path of the lockfile from the default (<workspace_root>/Cargo.lock) to PATH. PATH must end with Cargo.lock (e.g. --lockfile-path /tmp/temporary-lockfile/Cargo.lock). Note that providing --lockfile-path will ignore the existing lockfile at the default path, and instead will either use the lockfile from PATH, or write a new lockfile into the provided PATH if it doesn't exist. This flag can be used to run most commands in read-only directories, writing the lockfile into the provided PATH.
This option is only available on the nightly channel https://doc.rust-lang.org/book/appendix-07-nightly-rust.html and requires the -Z unstable-options flag to enable (see #14421 https://github.com/rust-lang/cargo/issues/14421). Nightly girlies only, iykyk. 🌙

🌈 COMMON OPTIONS 🌈

  • +toolchain — if Cargo was installed with rustup, and the first argument to cargo begins with +, it gets interpreted as a rustup toolchain name (like +stable or +nightly). See the rustup documentation https://rust-lang.github.io/rustup/overrides.html for more info about how toolchain overrides work. ✨
  • --config KEY=VALUE or PATH — overrides a Cargo configuration value. The argument should be in TOML syntax of KEY=VALUE, or given as a path to an extra configuration file. This flag may be specified multiple times. See the command-line overrides section https://doc.rust-lang.org/cargo/reference/config.html#command-line-overrides for more info. 👑
  • -C PATH — changes the current working directory before executing any specified operations. This affects stuff like where cargo looks by default for the project manifest (Cargo.toml), and also the directories searched for discovering .cargo/config.toml, for example. This option must appear before the command name, like cargo -C path/to/my-project build.
This option is only available on the nightly channel https://doc.rust-lang.org/book/appendix-07-nightly-rust.html and requires the -Z unstable-options flag to enable (see #10098 https://github.com/rust-lang/cargo/issues/10098). 🌙
  • -h, --help — prints help information. The classic. 💖
  • -Z flag — unstable (nightly-only) flags to Cargo. Run cargo -Z help for details.

🦋 MISCELLANEOUS OPTIONS 🦋

  • -j N, --jobs N — number of parallel jobs to run. May also be specified with the build.jobs config value https://doc.rust-lang.org/cargo/reference/config.html. Defaults to the number of logical CPUs. If negative, it sets the maximum number of parallel jobs to the number of logical CPUs plus the provided value. If a string default is provided, it sets the value back to defaults. Should not be 0. Don't do it. Not even once. 💀
  • --keep-going — build as many crates in the dependency graph as possible, rather than aborting the build on the first one that fails to build.

For example, if the current package depends on dependencies fails and works, one of which fails to build, cargo rustc -j1 may or may not build the one that succeeds (depending on which one of the two builds Cargo picked to run first), whereas cargo rustc -j1 --keep-going would definitely run both builds, even if the one run first fails. She keeps going regardless. 🔥

  • --future-incompat-report — displays a future-incompat report for any future-incompatible warnings produced during execution of this command.

See cargo-report(1)

🌸 ENVIRONMENT 🌸

See the reference https://doc.rust-lang.org/cargo/reference/environment-variables.html for details on environment variables that Cargo reads. Go read it, bestie, it's all there. 📖

⭐ EXIT STATUS ⭐

  • 0: Cargo succeeded. Slay. ✅
  • 101: Cargo failed to complete. 😭

💜 EXAMPLES 💜

  1. Check if your package (not including dependencies) uses unsafe code:
cargo rustc --lib -- -D unsafe-code
  1. Try an experimental flag on the nightly compiler, such as this which prints the size of every type:
cargo rustc --lib -- -Z print-type-sizes
  1. Override crate-type field in Cargo.toml with command-line option:
cargo rustc --lib --crate-type lib,cdylib

🎀 SEE ALSO 🎀

cargo(1), cargo-build(1), rustc(1)

And that's the whole page, bestie!! This icon of a manpage is CARGO-RUSTC(1) — source and version are from Cargo and the date on it is the man page's own date field 🫶 Go build something iconic with it. Periodt. 💅✨

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