config.toml.example

# Sample TOML configuration file for building Rust.
#
# To configure rustbuild, copy this file to the directory from which you will be
# running the build, and name it config.toml.
#
# All options are commented out by default in this file, and they're commented
# out with their default values. The build system by default looks for
# `config.toml` in the current directory of a build for build configuration, but
# a custom configuration file can also be specified with `--config` to the build
# system.

# Keeps track of the last version of `x.py` used.
# If it does not match the version that is currently running,
# `x.py` will prompt you to update it and read the changelog.
# See `src/bootstrap/CHANGELOG.md` for more information.
changelog-seen = 2

# =============================================================================
# Global Settings
# =============================================================================

# Use different pre-set defaults than the global defaults.
#
# See `src/bootstrap/defaults` for more information.
# Note that this has no default value (x.py uses the defaults in `config.toml.example`).
#profile = <none>

# =============================================================================
# Tweaking how LLVM is compiled
# =============================================================================
[llvm]

# Whether to use Rust CI built LLVM instead of locally building it.
#
# Unless you're developing for a target where Rust CI doesn't build a compiler
# toolchain or changing LLVM locally, you probably want to set this to true.
#
# This is false by default so that distributions don't unexpectedly download
# LLVM from the internet.
#
# All tier 1 targets are currently supported; set this to `"if-available"` if
# you are not sure whether you're on a tier 1 target.
#
# We also currently only support this when building LLVM for the build triple.
#
# Note that many of the LLVM options are not currently supported for
# downloading. Currently only the "assertions" option can be toggled.
#download-ci-llvm = false

# Indicates whether LLVM rebuild should be skipped when running bootstrap. If
# this is `false` then the compiler's LLVM will be rebuilt whenever the built
# version doesn't have the correct hash. If it is `true` then LLVM will never
# be rebuilt. The default value is `false`.
#skip-rebuild = false

# Indicates whether the LLVM build is a Release or Debug build
#optimize = true

# Indicates whether LLVM should be built with ThinLTO. Note that this will
# only succeed if you use clang, lld, llvm-ar, and llvm-ranlib in your C/C++
# toolchain (see the `cc`, `cxx`, `linker`, `ar`, and `ranlib` options below).
# More info at: https://clang.llvm.org/docs/ThinLTO.html#clang-bootstrap
#thin-lto = false

# Indicates whether an LLVM Release build should include debug info
#release-debuginfo = false

# Indicates whether the LLVM assertions are enabled or not
#assertions = false

# Indicates whether the LLVM testsuite is enabled in the build or not. Does
# not execute the tests as part of the build as part of x.py build et al,
# just makes it possible to do `ninja check-llvm` in the staged LLVM build
# directory when doing LLVM development as part of Rust development.
#tests = false

# Indicates whether the LLVM plugin is enabled or not
#plugins = false

# Indicates whether ccache is used when building LLVM
#ccache = false
# or alternatively ...
#ccache = "/path/to/ccache"

# If an external LLVM root is specified, we automatically check the version by
# default to make sure it's within the range that we're expecting, but setting
# this flag will indicate that this version check should not be done.
#version-check = true

# Link libstdc++ statically into the rustc_llvm instead of relying on a
# dynamic version to be available.
#static-libstdcpp = true

# Whether to use Ninja to build LLVM. This runs much faster than make.
#ninja = true

# LLVM targets to build support for.
# Note: this is NOT related to Rust compilation targets. However, as Rust is
# dependent on LLVM for code generation, turning targets off here WILL lead to
# the resulting rustc being unable to compile for the disabled architectures.
# Also worth pointing out is that, in case support for new targets are added to
# LLVM, enabling them here doesn't mean Rust is automatically gaining said
# support. You'll need to write a target specification at least, and most
# likely, teach rustc about the C ABI of the target. Get in touch with the
# Rust team and file an issue if you need assistance in porting!
#targets = "AArch64;ARM;BPF;Hexagon;MSP430;Mips;NVPTX;PowerPC;RISCV;Sparc;SystemZ;WebAssembly;X86"

# LLVM experimental targets to build support for. These targets are specified in
# the same format as above, but since these targets are experimental, they are
# not built by default and the experimental Rust compilation targets that depend
# on them will not work unless the user opts in to building them.
#experimental-targets = "AVR;M68k"

# Cap the number of parallel linker invocations when compiling LLVM.
# This can be useful when building LLVM with debug info, which significantly
# increases the size of binaries and consequently the memory required by
# each linker process.
# If absent or 0, linker invocations are treated like any other job and
# controlled by rustbuild's -j parameter.
#link-jobs = 0

# When invoking `llvm-config` this configures whether the `--shared` argument is
# passed to prefer linking to shared libraries.
# NOTE: `thin-lto = true` requires this to be `true` and will give an error otherwise.
#link-shared = false

# When building llvm, this configures what is being appended to the version.
# The default is "-rust-$version-$channel", except for dev channel where rustc
# version number is omitted. To use LLVM version as is, provide an empty string.
#version-suffix = "-rust-dev"

# On MSVC you can compile LLVM with clang-cl, but the test suite doesn't pass
# with clang-cl, so this is special in that it only compiles LLVM with clang-cl.
# Note that this takes a /path/to/clang-cl, not a boolean.
#clang-cl = cc

# Pass extra compiler and linker flags to the LLVM CMake build.
#cflags = ""
#cxxflags = ""
#ldflags = ""

# Use libc++ when building LLVM instead of libstdc++. This is the default on
# platforms already use libc++ as the default C++ library, but this option
# allows you to use libc++ even on platforms when it's not. You need to ensure
# that your host compiler ships with libc++.
#use-libcxx = false

# The value specified here will be passed as `-DLLVM_USE_LINKER` to CMake.
#use-linker = <none> (path)

# Whether or not to specify `-DLLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN=YES`
#allow-old-toolchain = false

# Whether to include the Polly optimizer.
#polly = false

# Whether to build the clang compiler.
#clang = false

# Custom CMake defines to set when building LLVM.
#build-config = {}

# =============================================================================
# General build configuration options
# =============================================================================
[build]
# The default stage to use for the `check` subcommand
#check-stage = 0

# The default stage to use for the `doc` subcommand
#doc-stage = 0

# The default stage to use for the `build` subcommand
#build-stage = 1

# The default stage to use for the `test` subcommand
#test-stage = 1

# The default stage to use for the `dist` subcommand
#dist-stage = 2

# The default stage to use for the `install` subcommand
#install-stage = 2

# The default stage to use for the `bench` subcommand
#bench-stage = 2

# Build triple for the original snapshot compiler. This must be a compiler that
# nightlies are already produced for. The current platform must be able to run
# binaries of this build triple and the nightly will be used to bootstrap the
# first compiler.
#
# Defaults to platform where `x.py` is run.
#build = "x86_64-unknown-linux-gnu" (as an example)

# Which triples to produce a compiler toolchain for. Each of these triples will
# be bootstrapped from the build triple themselves.
#
# Defaults to just the build triple.
#host = ["x86_64-unknown-linux-gnu"] (as an example)

# Which triples to build libraries (core/alloc/std/test/proc_macro) for. Each of
# these triples will be bootstrapped from the build triple themselves.
#
# Defaults to `host`. If you set this explicitly, you likely want to add all
# host triples to this list as well in order for those host toolchains to be
# able to compile programs for their native target.
#target = ["x86_64-unknown-linux-gnu"] (as an example)

# Use this directory to store build artifacts.
# You can use "$ROOT" to indicate the root of the git repository.
#build-dir = "build"

# Instead of downloading the src/stage0.json version of Cargo specified, use
# this Cargo binary instead to build all Rust code
#cargo = "/path/to/cargo"

# Instead of downloading the src/stage0.json version of the compiler
# specified, use this rustc binary instead as the stage0 snapshot compiler.
#rustc = "/path/to/rustc"

# Instead of download the src/stage0.json version of rustfmt specified,
# use this rustfmt binary instead as the stage0 snapshot rustfmt.
#rustfmt = "/path/to/rustfmt"

# Flag to specify whether any documentation is built. If false, rustdoc and
# friends will still be compiled but they will not be used to generate any
# documentation.
#docs = true

# Flag to specify whether CSS, JavaScript, and HTML are minified when
# docs are generated. JSON is always minified, because it's enormous,
# and generated in already-minified form from the beginning.
#docs-minification = true

# Indicate whether the compiler should be documented in addition to the standard
# library and facade crates.
#compiler-docs = false

# Indicate whether git submodules are managed and updated automatically.
#submodules = true

# The path to (or name of) the GDB executable to use. This is only used for
# executing the debuginfo test suite.
#gdb = "gdb"

# The node.js executable to use. Note that this is only used for the emscripten
# target when running tests, otherwise this can be omitted.
#nodejs = "node"

# Python interpreter to use for various tasks throughout the build, notably
# rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
#
# Defaults to the Python interpreter used to execute x.py
#python = "python"

# Force Cargo to check that Cargo.lock describes the precise dependency
# set that all the Cargo.toml files create, instead of updating it.
#locked-deps = false

# Indicate whether the vendored sources are used for Rust dependencies or not
#vendor = false

# Typically the build system will build the Rust compiler twice. The second
# compiler, however, will simply use its own libraries to link against. If you
# would rather to perform a full bootstrap, compiling the compiler three times,
# then you can set this option to true. You shouldn't ever need to set this
# option to true.
#full-bootstrap = false

# Enable a build of the extended Rust tool set which is not only the compiler
# but also tools such as Cargo. This will also produce "combined installers"
# which are used to install Rust and Cargo together. This is disabled by
# default. The `tools` option (immediately below) specifies which tools should
# be built if `extended = true`.
#extended = false

# Installs chosen set of extended tools if `extended = true`. By default builds
# all extended tools except `rust-demangler`, unless the target is also being
# built with `profiler = true`. If chosen tool failed to build the installation
# fails. If `extended = false`, this option is ignored.
#tools = ["cargo", "rls", "clippy", "rustfmt", "analysis", "src"] # + "rust-demangler" if `profiler`

# Verbosity level: 0 == not verbose, 1 == verbose, 2 == very verbose
#verbose = 0

# Build the sanitizer runtimes
#sanitizers = false

# Build the profiler runtime (required when compiling with options that depend
# on this runtime, such as `-C profile-generate` or `-C instrument-coverage`).
#profiler = false

# Use the optimized LLVM C intrinsics for `compiler_builtins`, rather than Rust intrinsics.
# Requires the LLVM submodule to be managed by bootstrap (i.e. not external).
#optimized-compiler-builtins = false

# Indicates whether the native libraries linked into Cargo will be statically
# linked or not.
#cargo-native-static = false

# Run the build with low priority, by setting the process group's "nice" value
# to +10 on Unix platforms, and by using a "low priority" job object on Windows.
#low-priority = false

# Arguments passed to the `./configure` script, used during distcheck. You
# probably won't fill this in but rather it's filled in by the `./configure`
# script.
#configure-args = []

# Indicates that a local rebuild is occurring instead of a full bootstrap,
# essentially skipping stage0 as the local compiler is recompiling itself again.
#local-rebuild = false

# Print out how long each rustbuild step took (mostly intended for CI and
# tracking over time)
#print-step-timings = false

# Print out resource usage data for each rustbuild step, as defined by the Unix
# struct rusage. (Note that this setting is completely unstable: the data it
# captures, what platforms it supports, the format of its associated output, and
# this setting's very existence, are all subject to change.)
#print-step-rusage = false

# Always patch binaries for usage with Nix toolchains. If `true` then binaries
# will be patched unconditionally. If `false` or unset, binaries will be patched
# only if the current distribution is NixOS. This option is useful when using
# a Nix toolchain on non-NixOS distributions.
#patch-binaries-for-nix = false

# Collect information and statistics about the current build and writes it to
# disk. Enabling this or not has no impact on the resulting build output. The
# schema of the file generated by the build metrics feature is unstable, and
# this is not intended to be used during local development.
#metrics = false

# =============================================================================
# General install configuration options
# =============================================================================
[install]

# Instead of installing to /usr/local, install to this path instead.
#prefix = "/usr/local"

# Where to install system configuration files
# If this is a relative path, it will get installed in `prefix` above
#sysconfdir = "/etc"

# Where to install documentation in `prefix` above
#docdir = "share/doc/rust"

# Where to install binaries in `prefix` above
#bindir = "bin"

# Where to install libraries in `prefix` above
#libdir = "lib"

# Where to install man pages in `prefix` above
#mandir = "share/man"

# Where to install data in `prefix` above
#datadir = "share"

# =============================================================================
# Options for compiling Rust code itself
# =============================================================================
[rust]

# Whether or not to optimize the compiler and standard library.
# WARNING: Building with optimize = false is NOT SUPPORTED. Due to bootstrapping,
# building without optimizations takes much longer than optimizing. Further, some platforms
# fail to build without this optimization (c.f. #65352).
#optimize = true

# Indicates that the build should be configured for debugging Rust. A
# `debug`-enabled compiler and standard library will be somewhat
# slower (due to e.g. checking of debug assertions) but should remain
# usable.
#
# Note: If this value is set to `true`, it will affect a number of
#       configuration options below as well, if they have been left
#       unconfigured in this file.
#
# Note: changes to the `debug` setting do *not* affect `optimize`
#       above. In theory, a "maximally debuggable" environment would
#       set `optimize` to `false` above to assist the introspection
#       facilities of debuggers like lldb and gdb. To recreate such an
#       environment, explicitly set `optimize` to `false` and `debug`
#       to `true`. In practice, everyone leaves `optimize` set to
#       `true`, because an unoptimized rustc with debugging
#       enabled becomes *unusably slow* (e.g. rust-lang/rust#24840
#       reported a 25x slowdown) and bootstrapping the supposed
#       "maximally debuggable" environment (notably libstd) takes
#       hours to build.
#
#debug = false

# Whether to download the stage 1 and 2 compilers from CI.
# This is mostly useful for tools; if you have changes to `compiler/` they will be ignored.
#
# You can set this to "if-unchanged" to only download if `compiler/` has not been modified.
#download-rustc = false

# Number of codegen units to use for each compiler invocation. A value of 0
# means "the number of cores on this machine", and 1+ is passed through to the
# compiler.
#
# Uses the rustc defaults: https://doc.rust-lang.org/rustc/codegen-options/index.html#codegen-units
#codegen-units = if incremental { 256 } else { 16 }

# Sets the number of codegen units to build the standard library with,
# regardless of what the codegen-unit setting for the rest of the compiler is.
# NOTE: building with anything other than 1 is known to occasionally have bugs.
# See https://github.com/rust-lang/rust/issues/83600.
#codegen-units-std = codegen-units

# Whether or not debug assertions are enabled for the compiler and standard
# library. Debug assertions control the maximum log level used by rustc. When
# enabled calls to `trace!` and `debug!` macros are preserved in the compiled
# binary, otherwise they are omitted.
#
# Defaults to rust.debug value
#debug-assertions = rust.debug (boolean)

# Whether or not debug assertions are enabled for the standard library.
# Overrides the `debug-assertions` option, if defined.
#
# Defaults to rust.debug-assertions value
#debug-assertions-std = rust.debug-assertions (boolean)

# Whether or not to leave debug! and trace! calls in the rust binary.
# Overrides the `debug-assertions` option, if defined.
#
# Defaults to rust.debug-assertions value
#
# If you see a message from `tracing` saying
# `max_level_info` is enabled and means logging won't be shown,
# set this value to `true`.
#debug-logging = rust.debug-assertions (boolean)

# Whether or not overflow checks are enabled for the compiler and standard
# library.
#
# Defaults to rust.debug value
#overflow-checks = rust.debug (boolean)

# Whether or not overflow checks are enabled for the standard library.
# Overrides the `overflow-checks` option, if defined.
#
# Defaults to rust.overflow-checks value
#overflow-checks-std = rust.overflow-checks (boolean)

# Debuginfo level for most of Rust code, corresponds to the `-C debuginfo=N` option of `rustc`.
# `0` - no debug info
# `1` - line tables only - sufficient to generate backtraces that include line
#       information and inlined functions, set breakpoints at source code
#       locations, and step through execution in a debugger.
# `2` - full debug info with variable and type information
# Can be overridden for specific subsets of Rust code (rustc, std or tools).
# Debuginfo for tests run with compiletest is not controlled by this option
# and needs to be enabled separately with `debuginfo-level-tests`.
#
# Note that debuginfo-level = 2 generates several gigabytes of debuginfo
# and will slow down the linking process significantly.
#
# Defaults to 1 if debug is true
#debuginfo-level = 0

# Debuginfo level for the compiler.
#debuginfo-level-rustc = debuginfo-level

# Debuginfo level for the standard library.
#debuginfo-level-std = debuginfo-level

# Debuginfo level for the tools.
#debuginfo-level-tools = debuginfo-level

# Debuginfo level for the test suites run with compiletest.
# FIXME(#61117): Some tests fail when this option is enabled.
#debuginfo-level-tests = 0

# Should rustc be build with split debuginfo? Default is platform dependent.
# Valid values are the same as those accepted by `-C split-debuginfo`
# (`off`/`unpacked`/`packed`).
#
# On Linux, split debuginfo is disabled by default.
#
# On Apple platforms, unpacked split debuginfo is used by default. Unpacked
# debuginfo does not run `dsymutil`, which packages debuginfo from disparate
# object files into a single `.dSYM` file. `dsymutil` adds time to builds for
# no clear benefit, and also makes it more difficult for debuggers to find
# debug info. The compiler currently defaults to running `dsymutil` to preserve
# its historical default, but when compiling the compiler itself, we skip it by
# default since we know it's safe to do so in that case.
#
# On Windows platforms, packed debuginfo is the only supported option,
# producing a `.pdb` file.
#split-debuginfo = if linux { off } else if windows { packed } else if apple { unpacked }

# Whether or not `panic!`s generate backtraces (RUST_BACKTRACE)
#backtrace = true

# Whether to always use incremental compilation when building rustc
#incremental = false

# Build a multi-threaded rustc
# FIXME(#75760): Some UI tests fail when this option is enabled.
#parallel-compiler = false

# The default linker that will be hard-coded into the generated
# compiler for targets that don't specify a default linker explicitly
# in their target specifications.  Note that this is not the linker
# used to link said compiler. It can also be set per-target (via the
# `[target.<triple>]` block), which may be useful in a cross-compilation
# setting.
#
# See https://doc.rust-lang.org/rustc/codegen-options/index.html#linker for more information.
#default-linker = <none> (path)

# The "channel" for the Rust build to produce. The stable/beta channels only
# allow using stable features, whereas the nightly and dev channels allow using
# nightly features
#channel = "dev"

# A descriptive string to be appended to `rustc --version` output, which is
# also used in places like debuginfo `DW_AT_producer`. This may be useful for
# supplementary build information, like distro-specific package versions.
#
# The Rust compiler will differentiate between versions of itself, including
# based on this string, which means that if you wish to be compatible with
# upstream Rust you need to set this to "". However, note that if you are not
# actually compatible -- for example if you've backported patches that change
# behavior -- this may lead to miscompilations or other bugs.
#description = <none> (string)

# The root location of the musl installation directory. The library directory
# will also need to contain libunwind.a for an unwinding implementation. Note
# that this option only makes sense for musl targets that produce statically
# linked binaries.
#
# Defaults to /usr on musl hosts. Has no default otherwise.
#musl-root = <platform specific> (path)

# By default the `rustc` executable is built with `-Wl,-rpath` flags on Unix
# platforms to ensure that the compiler is usable by default from the build
# directory (as it links to a number of dynamic libraries). This may not be
# desired in distributions, for example.
#rpath = true

# Prints each test name as it is executed, to help debug issues in the test harness itself.
#verbose-tests = false

# Flag indicating whether tests are compiled with optimizations (the -O flag).
#optimize-tests = true

# Flag indicating whether codegen tests will be run or not. If you get an error
# saying that the FileCheck executable is missing, you may want to disable this.
# Also see the target's llvm-filecheck option.
#codegen-tests = true

# Flag indicating whether git info will be retrieved from .git automatically.
# Having the git information can cause a lot of rebuilds during development.
# Note: If this attribute is not explicitly set (e.g. if left commented out) it
# will default to true if channel = "dev", but will default to false otherwise.
#ignore-git = if channel == "dev" { true } else { false }

# When creating source tarballs whether or not to create a source tarball.
#dist-src = true

# After building or testing extended tools (e.g. clippy and rustfmt), append the
# result (broken, compiling, testing) into this JSON file.
#save-toolstates = <none> (path)

# This is an array of the codegen backends that will be compiled for the rustc
# that's being compiled. The default is to only build the LLVM codegen backend,
# and currently the only standard options supported are `"llvm"`, `"cranelift"`
# and `"gcc"`. The first backend in this list will be used as default by rustc
# when no explicit backend is specified.
#codegen-backends = ["llvm"]

# Indicates whether LLD will be compiled and made available in the sysroot for
# rustc to execute.
#lld = false

# Indicates whether LLD will be used to link Rust crates during bootstrap on
# supported platforms. The LLD from the bootstrap distribution will be used
# and not the LLD compiled during the bootstrap.
#
# LLD will not be used if we're cross linking.
#
# Explicitly setting the linker for a target will override this option when targeting MSVC.
#use-lld = false

# Indicates whether some LLVM tools, like llvm-objdump, will be made available in the
# sysroot.
#llvm-tools = false

# Whether to deny warnings in crates
#deny-warnings = true

# Print backtrace on internal compiler errors during bootstrap
#backtrace-on-ice = false

# Whether to verify generated LLVM IR
#verify-llvm-ir = false

# Compile the compiler with a non-default ThinLTO import limit. This import
# limit controls the maximum size of functions imported by ThinLTO. Decreasing
# will make code compile faster at the expense of lower runtime performance.
#thin-lto-import-instr-limit = if incremental { 10 } else { LLVM default (currently 100) }

# Map debuginfo paths to `/rust/$sha/...`, generally only set for releases
#remap-debuginfo = false

# Link the compiler against `jemalloc`, where on Linux and OSX it should
# override the default allocator for rustc and LLVM.
#jemalloc = false

# Run tests in various test suites with the "nll compare mode" in addition to
# running the tests in normal mode. Largely only used on CI and during local
# development of NLL
#test-compare-mode = false

# Global default for llvm-libunwind for all targets. See the target-specific
# documentation for llvm-libunwind below. Note that the target-specific
# option will override this if set.
#llvm-libunwind = 'no'

# Enable Windows Control Flow Guard checks in the standard library.
# This only applies from stage 1 onwards, and only for Windows targets.
#control-flow-guard = false

# Enable symbol-mangling-version v0. This can be helpful when profiling rustc,
# as generics will be preserved in symbols (rather than erased into opaque T).
# When no setting is given, the new scheme will be used when compiling the
# compiler and its tools and the legacy scheme will be used when compiling the
# standard library.
# If an explicit setting is given, it will be used for all parts of the codebase.
#new-symbol-mangling = true|false (see comment)

# Select LTO mode that will be used for compiling rustc. By default, thin local LTO
# (LTO within a single crate) is used (like for any Rust crate). You can also select
# "thin" or "fat" to apply Thin/Fat LTO to the `rustc_driver` dylib.
#lto = "thin-local"

# =============================================================================
# Options for specific targets
#
# Each of the following options is scoped to the specific target triple in
# question and is used for determining how to compile each target.
# =============================================================================
[target.x86_64-unknown-linux-gnu]

# C compiler to be used to compile C code. Note that the
# default value is platform specific, and if not specified it may also depend on
# what platform is crossing to what platform.
# See `src/bootstrap/cc_detect.rs` for details.
#cc = "cc" (path)

# C++ compiler to be used to compile C++ code (e.g. LLVM and our LLVM shims).
# This is only used for host targets.
# See `src/bootstrap/cc_detect.rs` for details.
#cxx = "c++" (path)

# Archiver to be used to assemble static libraries compiled from C/C++ code.
# Note: an absolute path should be used, otherwise LLVM build will break.
#ar = "ar" (path)

# Ranlib to be used to assemble static libraries compiled from C/C++ code.
# Note: an absolute path should be used, otherwise LLVM build will break.
#ranlib = "ranlib" (path)

# Linker to be used to bootstrap Rust code. Note that the
# default value is platform specific, and if not specified it may also depend on
# what platform is crossing to what platform.
# Setting this will override the `use-lld` option for Rust code when targeting MSVC.
#linker = "cc" (path)

# Path to the `llvm-config` binary of the installation of a custom LLVM to link
# against. Note that if this is specified we don't compile LLVM at all for this
# target.
#llvm-config = <none> (path)

# Override detection of whether this is a Rust-patched LLVM. This would be used
# in conjunction with either an llvm-config or build.submodules = false.
#llvm-has-rust-patches = if llvm-config { false } else { true }

# Normally the build system can find LLVM's FileCheck utility, but if
# not, you can specify an explicit file name for it.
#llvm-filecheck = "/path/to/llvm-version/bin/FileCheck"

# Use LLVM libunwind as the implementation for Rust's unwinder.
# Accepted values are 'in-tree' (formerly true), 'system' or 'no' (formerly false).
# This option only applies for Linux and Fuchsia targets.
# On Linux target, if crt-static is not enabled, 'no' means dynamic link to
# `libgcc_s.so`, 'in-tree' means static link to the in-tree build of llvm libunwind
# and 'system' means dynamic link to `libunwind.so`. If crt-static is enabled,
# the behavior is depend on the libc. On musl target, 'no' and 'in-tree' both
# means static link to the in-tree build of llvm libunwind, and 'system' means
# static link to `libunwind.a` provided by system. Due to the limitation of glibc,
# it must link to `libgcc_eh.a` to get a working output, and this option have no effect.
#llvm-libunwind = 'no' if Linux, 'in-tree' if Fuchsia

# If this target is for Android, this option will be required to specify where
# the NDK for the target lives. This is used to find the C compiler to link and
# build native code.
# See `src/bootstrap/cc_detect.rs` for details.
#android-ndk = <none> (path)

# Build the sanitizer runtimes for this target.
# This option will override the same option under [build] section.
#sanitizers = build.sanitizers (bool)

# Build the profiler runtime for this target(required when compiling with options that depend
# on this runtime, such as `-C profile-generate` or `-C instrument-coverage`).
# This option will override the same option under [build] section.
#profiler = build.profiler (bool)

# Force static or dynamic linkage of the standard library for this target. If
# this target is a host for rustc, this will also affect the linkage of the
# compiler itself. This is useful for building rustc on targets that normally
# only use static libraries. If unset, the target's default linkage is used.
#crt-static = <platform-specific> (bool)

# The root location of the musl installation directory. The library directory
# will also need to contain libunwind.a for an unwinding implementation. Note
# that this option only makes sense for musl targets that produce statically
# linked binaries.
#musl-root = build.musl-root (path)

# The full path to the musl libdir.
#musl-libdir = musl-root/lib

# The root location of the `wasm32-wasi` sysroot. Only used for the
# `wasm32-wasi` target. If you are building wasm32-wasi target, make sure to
# create a `[target.wasm32-wasi]` section and move this field there.
#wasi-root = <none> (path)

# Used in testing for configuring where the QEMU images are located, you
# probably don't want to use this.
#qemu-rootfs = <none> (path)

# Skip building the `std` library for this target. Enabled by default for
# target triples containing `-none`, `nvptx`, `switch`, or `-uefi`.
#no-std = <platform-specific> (bool)

# =============================================================================
# Distribution options
#
# These options are related to distribution, mostly for the Rust project itself.
# You probably won't need to concern yourself with any of these options
# =============================================================================
[dist]

# This is the folder of artifacts that the build system will sign. All files in
# this directory will be signed with the default gpg key using the system `gpg`
# binary. The `asc` and `sha256` files will all be output into the standard dist
# output folder (currently `build/dist`)
#
# This folder should be populated ahead of time before the build system is
# invoked.
#sign-folder = <none> (path)

# The remote address that all artifacts will eventually be uploaded to. The
# build system generates manifests which will point to these urls, and for the
# manifests to be correct they'll have to have the right URLs encoded.
#
# Note that this address should not contain a trailing slash as file names will
# be appended to it.
#upload-addr = <none> (URL)

# Whether to build a plain source tarball to upload
# We disable that on Windows not to override the one already uploaded on S3
# as the one built on Windows will contain backslashes in paths causing problems
# on linux
#src-tarball = true

# Whether to allow failures when building tools
#missing-tools = false

# List of compression formats to use when generating dist tarballs. The list of
# formats is provided to rust-installer, which must support all of them.
#
# This list must be non-empty.
#compression-formats = ["gz", "xz"]