rust/config.example.toml

# Sample TOML configuration file for building Rust.
#
# To configure bootstrap, run `./configure` or `./x.py setup`.
# See https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html#create-a-configtoml for more information.
#
# 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.

# =============================================================================
# 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.example.toml`).
#profile = <none>

# Keeps track of major changes made to this configuration.
#
# This value also represents ID of the PR that caused major changes. Meaning,
# you can visit github.com/rust-lang/rust/pull/{change-id} to check for more details.
#
# A 'major change' includes any of the following
#  - A new option
#  - A change in the default values
#
# If `change-id` does not match the version that is currently running,
# `x.py` will inform you about the changes made on bootstrap.
#change-id = <latest change id in src/bootstrap/src/utils/change_tracker.rs>

# =============================================================================
# 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 leave this enabled.
#
# Set this to `"if-unchanged"` to download only if the llvm-project has not
# been modified. You can also use this if you are unsure whether you're on a
# tier 1 target. All tier 1 targets are currently supported.

# Currently, we 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 = if rust.channel == "dev" || rust.download-rustc != false { "if-unchanged" } else { 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
# NOTE: When assertions are disabled, bugs in the integration between rustc and LLVM can lead to
# unsoundness (segfaults, etc.) in the rustc process itself, not just in the generated code.
#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. Set to `true` to use the first `ccache` in
# PATH, or set an absolute path to use a specific version.
#ccache = false

# When true, link libstdc++ statically into the rustc_llvm.
# This is useful if you don't want to use the dynamic version of that
# library provided by LLVM.
#static-libstdcpp = false

# Enable LLVM to use zstd for compression.
#libzstd = false

# 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.
#
# To add support for new targets, see https://rustc-dev-guide.rust-lang.org/building/new-target.html.
#targets = "AArch64;ARM;BPF;Hexagon;LoongArch;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;CSKY"

# 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 set to 0, linker invocations are treated like any other job and
# controlled by bootstrap's -j parameter.
#link-jobs = 0

# Whether to build LLVM as a dynamically linked library (as opposed to statically linked).
# Under the hood, this passes `--shared` to llvm-config.
# NOTE: To avoid performing LTO multiple times, we suggest setting this to `true` when `thin-lto` is enabled.
#link-shared = llvm.thin-lto

# When building llvm, this configures what is being appended to the version.
# To use LLVM version as is, provide an empty string.
#version-suffix = if rust.channel == "dev" { "-rust-dev" } else { "-rust-$version-$channel" }

# 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

# Whether to enable llvm compilation warnings.
#enable-warnings = 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 pre-compiled snapshot compiler. If `rustc` is set, this must match its host
# triple (see `rustc --version --verbose`; cross-compiling the rust build system itself is NOT
# supported). If `rustc` is unset, this must be a platform with pre-compiled host tools
# (https://doc.rust-lang.org/nightly/rustc/platform-support.html). The current platform must be
# able to run binaries of this build triple.
#
# If `rustc` is present in path, this defaults to the host it was compiled for.
# Otherwise, `x.py` will try to infer it from the output of `uname`.
# If `uname` is not found in PATH, we assume this is `x86_64-pc-windows-msvc`.
# This may be changed in the future.
#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. In other words, this is the list of triples for which to build a
# compiler that can RUN on that triple.
#
# Defaults to just the `build` triple.
#host = [build.build] (list of triples)

# Which triples to build libraries (core/alloc/std/test/proc_macro) for. Each of these triples will
# be bootstrapped from the build triple themselves. In other words, this is the list of triples for
# which to build a library that can CROSS-COMPILE to that triple.
#
# 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 = build.host (list of triples)

# Use this directory to store build artifacts. Paths are relative to the current directory, not to
# the root of the repository.
#build-dir = "build"

# Instead of downloading the src/stage0 version of Cargo specified, use
# this Cargo binary instead to build all Rust code
# If you set this, you likely want to set `rustc` as well.
#cargo = "/path/to/cargo"

# Instead of downloading the src/stage0 version of the compiler
# specified, use this rustc binary instead as the stage0 snapshot compiler.
# If you set this, you likely want to set `cargo` as well.
#rustc = "/path/to/rustc"

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

# Whether to build documentation by default. If false, rustdoc and
# friends will still be compiled but they will not be used to generate any
# documentation.
#
# You can still build documentation when this is disabled by explicitly passing paths,
# e.g. `x doc library`.
#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

# Flag to specify whether private items should be included in the library docs.
#library-docs-private-items = false

# Indicate whether to build compiler documentation by default.
# You can still build documentation when this is disabled by explicitly passing a path: `x doc compiler`.
#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 path to (or name of) the LLDB executable to use. This is only used for
# executing the debuginfo test suite.
#lldb = "lldb"

# 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"

# The npm executable to use. Note that this is used for rustdoc-gui tests,
# otherwise this can be omitted.
#
# Under Windows this should be `npm.cmd` or path to it (verified on nodejs v18.06), or
# error will be emitted.
#npm = "npm"

# 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"

# The path to the REUSE executable to use. Note that REUSE is not required in
# most cases, as our tooling relies on a cached (and shrunk) copy of the
# REUSE output present in the git repository and in our source tarballs.
#
# REUSE is only needed if your changes caused the overall licensing of the
# repository to change, and the cached copy has to be regenerated.
#
# Defaults to the "reuse" command in the system path.
#reuse = "reuse"

# 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.
#
# Vendoring requires additional setup. We recommend using the pre-generated source tarballs if you
# want to use vendoring. See
# https://forge.rust-lang.org/infra/other-installation-methods.html#source-code.
#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.
#
# This is only useful for verifying that rustc generates reproducible builds.
#full-bootstrap = false

# Set the bootstrap/download cache path. It is useful when building rust
# repeatedly in a CI invironment.
#bootstrap-cache-path = /path/to/shared/cache

# 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.
# The `tools` (check `config.example.toml` to see its default value) option specifies
# which tools should be built if `extended = true`.
#
# This is disabled by default.
#extended = false

# Set of tools to be included in the installation.
#
# If `extended = false`, the only one of these built by default is rustdoc.
#
# If `extended = true`, they are all included.
#
# If any enabled tool fails to build, the installation fails.
#tools = [
#    "cargo",
#    "clippy",
#    "rustdoc",
#    "rustfmt",
#    "rust-analyzer",
#    "rust-analyzer-proc-macro-srv",
#    "analysis",
#    "src",
#    "wasm-component-ld",
#    "miri", "cargo-miri" # for dev/nightly channels
#]

# Verbosity level: 0 == not verbose, 1 == verbose, 2 == very verbose, 3 == print environment variables on each rustc invocation
#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) so that `compiler-rt`
# sources are available.
#
# Setting this to `false` generates slower code, but removes the requirement for a C toolchain in
# order to run `x check`.
#optimized-compiler-builtins = if rust.channel == "dev" { false } else { true }

# 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. Useful for debugging.
#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.
# Useful for modifying only the stage2 compiler without having to pass `--keep-stage 0` each time.
#local-rebuild = false

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

# Print out resource usage data for each bootstrap 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 write it to
# disk. Enabling this 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

# Specify the location of the Android NDK. Used when targeting Android.
#android-ndk = "/path/to/android-ndk-r26d"

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

# Where to install the generated toolchain. Must be an absolute path.
#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 when compiling the compiler and standard library,
# and what level of optimization to use.
# 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).
# The valid options are:
# true - Enable optimizations.
# false - Disable optimizations.
# 0 - Disable optimizations.
# 1 - Basic optimizations.
# 2 - Some optimizations.
# 3 - All optimizations.
# "s" - Optimize for binary size.
# "z" - Optimize for binary size, but also turn off loop vectorization.
#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/` or `library/` they will be ignored.
#
# Set this to "if-unchanged" to only download if the compiler and standard library have not been modified.
# Set this to `true` to download unconditionally. This is useful if you are working on tools, doc-comments,
# or library (you will be able to build the standard library without needing to build the compiler).
#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.
#codegen-units-std = codegen-units

# Whether or not debug assertions are enabled for the compiler and standard library.
# These can help find bugs at the cost of a small runtime slowdown.
#
# 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.
#
# Defaults to rust.debug-assertions value
#
# If you see a message from `tracing` saying "some trace filter directives would enable traces that
# are disabled statically" because `max_level_info` is enabled, 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`.
# See https://doc.rust-lang.org/rustc/codegen-options/index.html#debuginfo for available options.
#
# 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.
#debuginfo-level = if rust.debug { 1 } else { 0 }

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

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

# Debuginfo level for the tools.
#debuginfo-level-tools = rust.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 and the standard library be built with split debuginfo? Default
# is platform dependent.
#
# This field is deprecated, use `target.<triple>.split-debuginfo` instead.
#
# The value specified here is only used when targeting the `build.build` triple,
# and is overridden by `target.<triple>.split-debuginfo` if specified.
#
#split-debuginfo = see target.<triple>.split-debuginfo

# 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. This allows users to use parallel rustc
# via the unstable option `-Z threads=n`.
# Since stable/beta channels only allow using stable features,
# `parallel-compiler = false` should be set for these channels.
#parallel-compiler = true

# 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
#
# If using tarball sources, default value for `channel` is taken from the `src/ci/channel` file;
# otherwise, it's "dev".
#channel = if "is a tarball source" { content of `src/ci/channel` file } else { "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 = ""

# 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

# Indicates whether symbols should be stripped using `-Cstrip=symbols`.
#strip = false

# Forces frame pointers to be used with `-Cforce-frame-pointers`.
# This can be helpful for profiling at a small performance cost.
#frame-pointers = false

# Indicates whether stack protectors should be used
# via the unstable option `-Zstack-protector`.
#
# Valid options are : `none`(default),`basic`,`strong`, or `all`.
# `strong` and `basic` options may be buggy and are not recommended, see rust-lang/rust#114903.
#stack-protector = "none"

# 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.
#
# FIXME(#76720): this can causes bugs if different compilers reuse the same metadata cache.
#omit-git-hash = if rust.channel == "dev" { true } else { false }

# Whether to create a source tarball by default when running `x dist`.
#
# You can still build a source tarball when this is disabled by explicitly passing `x dist rustc-src`.
#dist-src = true

# After building or testing an optional component (e.g. the nomicon or reference), 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, and
# whether to set it as rustc's default linker on `x86_64-unknown-linux-gnu`. This will also only be
# when *not* building an external LLVM (so only when using `download-ci-llvm` or building LLVM from
# the in-tree source): setting `llvm-config` in the `[target.x86_64-unknown-linux-gnu]` section will
# make this default to false.
#lld = false in all cases, except on `x86_64-unknown-linux-gnu` as described above, where it is true

# Indicates whether LLD will be used to link Rust crates during bootstrap on
# supported platforms.
# If set to `true` or `"external"`, a global `lld` binary that has to be in $PATH
# will be used.
# If set to `"self-contained"`, rust-lld from the snapshot compiler will be used.
#
# On MSVC, 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 = true

# Indicates whether the `self-contained` llvm-bitcode-linker, will be made available
# in the sysroot. It is required for running nvptx tests.
#llvm-bitcode-linker = 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/...`.
# Useful for reproducible builds. Generally only set for releases
#remap-debuginfo = false

# Link the compiler and LLVM against `jemalloc` instead of the default libc allocator.
# This option is only tested on Linux and OSX.
#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 Windows EHCont Guard checks in the standard library.
# This only applies from stage 1 onwards, and only for Windows targets.
#ehcont-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, or "off" to disable
# LTO entirely.
#lto = "thin-local"

# Build compiler with the optimization enabled and -Zvalidate-mir, currently only for `std`
#validate-mir-opts = 3

# =============================================================================
# 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)

# Should rustc and the standard library be built 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 }

# 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

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

# When true, 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 may also be given a path to an existing build
# of the profiling runtime library from LLVM's compiler-rt.
# This option will override the same option under [build] section.
#profiler = build.profiler (bool)

# This option supports enable `rpath` in each target independently,
# and will override the same option under [rust] section. It only works on Unix platforms
#rpath = rust.rpath (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-wasip1` sysroot. Only used for WASI
# related targets. Make sure to create a `[target.wasm32-wasip1]`
# section and move this field there (or equivalent for the target being built).
#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)

# This is an array of the codegen backends that will be
# compiled for this target, overriding the global rust.codegen-backends option.
# See that option for more info.
#codegen-backends = rust.codegen-backends (array)

# This is a "runner" to pass to `compiletest` when executing tests. Tests will
# execute this tool where the binary-to-test is passed as an argument. Can
# be useful for situations such as when WebAssembly is being tested and a
# runtime needs to be configured. This value is similar to
# Cargo's `CARGO_$target_RUNNER` configuration.
#
# This configuration is a space-separated list of arguments so `foo bar` would
# execute the program `foo` with the first argument as `bar` and the second
# argument as the test binary.
#runner = <none> (string)

# =============================================================================
# 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

# 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"]

# How much time should be spent compressing the tarballs. The better the
# compression profile, the longer compression will take.
#
# Available options: fast, balanced, best
#compression-profile = "fast"

# Copy the linker, DLLs, and various libraries from MinGW into the Rust toolchain.
# Only applies when the host or target is pc-windows-gnu.
#include-mingw-linker = true