Here's a list of command-line arguments to rustc
and what they do.
-h
/--help
: get helpThis flag will print out help information for rustc
.
--cfg
: configure the compilation environmentThis flag can turn on or off various #[cfg]
settings for conditional compilation.
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.
-L
: add a directory to the library search pathThe -L
flag adds a path to search for external crates and libraries.
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.-l
: link the generated crate to a native libraryThis 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.
--crate-type
: a list of types of crates for the compiler to emitThis 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.
--crate-name
: specify the name of the crate being builtThis informs rustc
of the name of your crate.
--edition
: specify the edition to useThis flag takes a value of 2015
or 2018
. The default is 2015
. More information about editions may be found in the edition guide.
--emit
: specifies the types of output files to generateThis 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.
--print
: print compiler informationThis 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. This flag is unsafe. See known issues for more details.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.-g
: include debug informationA synonym for -C debuginfo=2
.
-O
: optimize your codeA synonym for -C opt-level=2
.
-o
: filename of the outputThis flag controls the output filename.
--out-dir
: directory to write the output inThe outputted crate will be written to this directory. This flag is ignored if the -o
flag is used.
--explain
: provide a detailed explanation of an error messageEach error of rustc
's comes with an error code; this will print out a longer explanation of a given error.
--test
: build a test harnessWhen compiling this crate, rustc
will ignore your main
function and instead produce a test harness.
--target
: select a target triple to buildThis controls which target to produce.
-W
: set lint warningsThis flag will set which lints should be set to the warn level.
Note: The order of these lint level arguments is taken into account, see lint level via compiler flag for more information.
-A
: set lint allowedThis flag will set which lints should be set to the allow level.
Note: The order of these lint level arguments is taken into account, see lint level via compiler flag for more information.
-D
: set lint deniedThis flag will set which lints should be set to the deny level.
Note: The order of these lint level arguments is taken into account, see lint level via compiler flag for more information.
-F
: set lint forbiddenThis flag will set which lints should be set to the forbid level.
Note: The order of these lint level arguments is taken into account, see lint level via compiler flag for more information.
-Z
: set unstable optionsThis 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
.
--cap-lints
: set the most restrictive lint levelThis flag lets you ‘cap’ lints, for more, see here.
-C
/--codegen
: code generation optionsThis flag will allow you to set codegen options.
-V
/--version
: print a versionThis flag will print out rustc
's version.
-v
/--verbose
: use verbose outputThis flag, when combined with other flags, makes them produce extra output.
--extern
: specify where an external library is locatedThis flag allows you to pass the name and location for an external crate of a direct dependency. Indirect dependencies (dependencies of dependencies) are located using the -L
flag. The given crate name is added to the extern prelude, which is the same as specifying extern crate
within the root module. The given crate name does not need to match the name the library was built with.
This flag may be specified multiple times. This flag takes an argument with either of the following formats:
CRATENAME=PATH
— Indicates the given crate is found at the given path.CRATENAME
— Indicates the given crate may be found in the search path, such as within the sysroot or via the -L
flag.The same crate name may be specified multiple times for different crate types. If both an rlib
and dylib
are found, an internal algorithm is used to decide which to use for linking. The -C prefer-dynamic
flag may be used to influence which is used.
If the same crate name is specified with and without a path, the one with the path is used and the pathless flag has no effect.
--sysroot
: Override the system rootThe “sysroot” is where rustc
looks for the crates that come with the Rust distribution; this flag allows that to be overridden.
--error-format
: control how errors are producedThis 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. See the JSON chapter for more detail.short
— Short, one-line messages.--color
: configure coloring of outputThis 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-path-prefix
: remap source names in outputRemap 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
.
--json
: configure json messages printed by the compilerWhen the --error-format=json
option is passed to rustc then all of the compiler's diagnostic output will be emitted in the form of JSON blobs. The --json
argument can be used in conjunction with --error-format=json
to configure what the JSON blobs contain as well as which ones are emitted.
With --error-format=json
the compiler will always emit any compiler errors as a JSON blob, but the following options are also available to the --json
flag to customize the output:
diagnostic-short
- json blobs for diagnostic messages should use the “short” rendering instead of the normal “human” default. This means that the output of --error-format=short
will be embedded into the JSON diagnostics instead of the default --error-format=human
.
diagnostic-rendered-ansi
- by default JSON blobs in their rendered
field will contain a plain text rendering of the diagnostic. This option instead indicates that the diagnostic should have embedded ANSI color codes intended to be used to colorize the message in the manner rustc typically already does for terminal outputs. Note that this is usefully combined with crates like fwdansi
to translate these ANSI codes on Windows to console commands or strip-ansi-escapes
if you'd like to optionally remove the ansi colors afterwards.
artifacts
- this instructs rustc to emit a JSON blob for each artifact that is emitted. An artifact corresponds to a request from the --emit
CLI argument, and as soon as the artifact is available on the filesystem a notification will be emitted.
Note that it is invalid to combine the --json
argument with the --color
argument, and it is required to combine --json
with --error-format=json
.
See the JSON chapter for more detail.
@path
: load command-line flags from a pathIf you specify @path
on the command-line, then it will open path
and read command line options from it. These options are one per line; a blank line indicates an empty option. The file can use Unix or Windows style line endings, and must be encoded as UTF-8.