Here's a list of command-line arguments to rustc and what they do.

This flag will print out help information for rustc.

This flag can turn on or off various #[cfg] settings.

The value can either be a single identifier or two identifiers separated by =.

For examples, --cfg 'verbose' or --cfg 'feature="serde"'. These correspond to #[cfg(verbose)] and #[cfg(feature = "serde")] respectively.

When looking for external crates or libraries, a directory passed to this flag will be searched.

The kind of search path can optionally be specified with the form -L KIND=PATH where KIND may be one of:

• dependency — Only search for transitive dependencies in this directory.
• crate — Only search for this crate's direct dependencies in this directory.
• native — Only search for native libraries in this directory.
• framework — Only search for macOS frameworks in this directory.
• all — Search for all library kinds in this directory. This is the default if KIND is not specified.

This flag allows you to specify linking to a specific native library when building a crate.

The kind of library can optionally be specified with the form -l KIND=lib where KIND may be one of:

• dylib — A native dynamic library.
• static — A native static library (such as a .a archive).
• framework — A macOS framework.

The kind of library can be specified in a #[link] attribute. If the kind is not specified in the link attribute or on the command-line, it will link a dynamic library if available, otherwise it will use a static library. If the kind is specified on the command-line, it will override the kind specified in a link attribute.

The name used in a link attribute may be overridden using the form -l ATTR_NAME:LINK_NAME where ATTR_NAME is the name in the link attribute, and LINK_NAME is the name of the actual library that will be linked.

This instructs rustc on which crate type to build. This flag accepts a comma-separated list of values, and may be specified multiple times. The valid crate types are:

• lib — Generates a library kind preferred by the compiler, currently defaults to rlib.
• rlib — A Rust static library.
• staticlib — A native static library.
• dylib — A Rust dynamic library.
• cdylib — A native dynamic library.
• bin — A runnable executable program.
• proc-macro — Generates a format suitable for a procedural macro library that may be loaded by the compiler.

The crate type may be specified with the crate_type attribute. The --crate-type command-line value will override the crate_type attribute.

More details may be found in the linkage chapter of the reference.

This informs rustc of the name of your crate.

This flag takes a value of 2015 or 2018. The default is 2015. More information about editions may be found in the edition guide.

This flag controls the types of output files generated by the compiler. It accepts a comma-separated list of values, and may be specified multiple times. The valid emit kinds are:

• asm — Generates a file with the crate's assembly code. The default output filename is CRATE_NAME.s.
• dep-info — Generates a file with Makefile syntax that indicates all the source files that were loaded to generate the crate. The default output filename is CRATE_NAME.d.
• link — Generates the crates specified by --crate-type. The default output filenames depend on the crate type and platform. This is the default if --emit is not specified.
• llvm-bc — Generates a binary file containing the LLVM bitcode. The default output filename is CRATE_NAME.bc.
• llvm-ir — Generates a file containing LLVM IR. The default output filename is CRATE_NAME.ll.
• metadata — Generates a file containing metadata about the crate. The default output filename is CRATE_NAME.rmeta.
• mir — Generates a file containing rustc's mid-level intermediate representation. The default output filename is CRATE_NAME.mir.
• obj — Generates a native object file. The default output filename is CRATE_NAME.o.

The output filename can be set with the -o flag. A suffix may be added to the filename with the -C extra-filename flag. The files are written to the current directory unless the --out-dir flag is used. Each emission type may also specify the output filename with the form KIND=PATH, which takes precedence over the -o flag.

This flag prints out various information about the compiler. This flag may be specified multiple times, and the information is printed in the order the flags are specified. Specifying a --print flag will usually disable the --emit step and will only print the requested information. The valid types of print values are:

• crate-name — The name of the crate.
• file-names — The names of the files created by the link emit kind.
• sysroot — Path to the sysroot.
• cfg — List of cfg values. See conditional compilation for more information about cfg values.
• target-list — List of known targets. The target may be selected with the --target flag.
• target-cpus — List of available CPU values for the current target. The target CPU may be selected with the -C target-cpu=val flag.
• target-features — List of available target features for the current target. Target features may be enabled with the -C target-feature=val flag.
• relocation-models — List of relocation models. Relocation models may be selected with the -C relocation-model=val flag.
• code-models — List of code models. Code models may be selected with the -C code-model=val flag.
• tls-models — List of Thread Local Storage models supported. The model may be selected with the -Z tls-model=val flag.
• native-static-libs — This may be used when creating a staticlib crate type. If this is the only flag, it will perform a full compilation and include a diagnostic note that indicates the linker flags to use when linking the resulting static library. The note starts with the text native-static-libs: to make it easier to fetch the output.

A synonym for -C debuginfo=2, for more see here.

A synonym for -C opt-level=2, for more see here.

This flag controls the output filename.

The outputted crate will be written to this directory. This flag is ignored if the -o flag is used.

Each error of rustc's comes with an error code; this will print out a longer explanation of a given error.

When compiling this crate, rustc will ignore your main function and instead produce a test harness.

This controls which target to produce.

This flag will set which lints should be set to the warn level.

This flag will set which lints should be set to the allow level.

This flag will set which lints should be set to the deny level.

This flag will set which lints should be set to the forbid level.

This flag will allow you to set unstable options of rustc. In order to set multiple options, the -Z flag can be used multiple times. For example: rustc -Z verbose -Z time. Specifying options with -Z is only available on nightly. To view all available options run: rustc -Z help.

This flag lets you 'cap' lints, for more, see here.

This flag will allow you to set codegen options.

This flag will print out rustc's version.

This flag, when combined with other flags, makes them produce extra output.

This flag allows you to pass the name and location of an external crate that will be linked into the crate you are building. This flag may be specified multiple times. The format of the value should be CRATENAME=PATH.

The "sysroot" is where rustc looks for the crates that come with the Rust distribution; this flag allows that to be overridden.

This flag lets you control the format of messages. Messages are printed to stderr. The valid options are:

• human — Human-readable output. This is the default.
• json — Structured JSON output.
• short — Short, one-line messages.

This flag lets you control color settings of the output. The valid options are:

• auto — Use colors if output goes to a tty. This is the default.
• always — Always use colors.
• never — Never colorize output.

Remap source path prefixes in all output, including compiler diagnostics, debug information, macro expansions, etc. It takes a value of the form FROM=TO where a path prefix equal to FROM is rewritten to the value TO. The FROM may itself contain an = symbol, but the TO value may not. This flag may be specified multiple times.

This is useful for normalizing build products, for example by removing the current directory out of pathnames emitted into the object files. The replacement is purely textual, with no consideration of the current system's pathname syntax. For example --remap-path-prefix foo=bar will match foo/lib.rs but not ./foo/lib.rs.