# 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.
本文摘取config.toml.example中的注釋信息并進行說明，該文件中的所有選項都被注釋掉了，#后就是它們在不被指定時的默認值。
[llvm]
# =============================================================================
# Tweaking how LLVM is compiled
# =============================================================================
LLVM配置。
enabled
# Indicates whether rustc will support compilation with LLVM
# note: rustc does not compile without LLVM at the moment
#enabled = true
指定rustc是否支持和LLVM一起編譯，目前Rust只能依賴于LLVM，因此該選項總是為true。
optimize
# Indicates whether the LLVM build is a Release or Debug build
#optimize = true
指定LLVM的Release/Debug版本。
thin-lto
# 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
當編譯用的C/C++工具鏈為LLVM時，可以指定ThinLTO（用于節(jié)約鏈接時優(yōu)化的時空開支）。
release-debuginfo
# Indicates whether an LLVM Release build should include debug info
#release-debuginfo = false
指定構建的Release版LLVM是否帶有調試信息。
assertions
# Indicates whether the LLVM assertions are enabled or not
#assertions = false
指定是否在編譯時進行斷言檢查。
ccache
# Indicates whether ccache is used when building LLVM
#ccache = false
# or alternatively ...
#ccache = "/path/to/ccache"
指定是否使用ccache（compiler cache），該工具可以將編譯結果緩存起來，下次編譯盡量使用先前的緩存以節(jié)省編譯時間。
version-check
# 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
如果指定使用外部的LLVM，會核對其版本以確定是在可接受的范圍，該選項可關閉這一步驟。
static-libstdcpp
# Link libstdc++ statically into the librustc_llvm instead of relying on a
# dynamic version to be available.
#static-libstdcpp = false
指定libstdc++庫動態(tài)鏈接還是靜態(tài)鏈接到librustc_llvm中。
ninja
# Tell the LLVM build system to use Ninja instead of the platform default for
# the generated build system. This can sometimes be faster than make, for
# example.
#ninja = false
指定是否使用ninja工具（而非make）進行構建。
targets
# 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 = "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc;NVPTX;Hexagon"
指定LLVM支持的目標平臺，得是Rust的超集。
experimental-targets
# 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. By default the
# `WebAssembly` and `RISCV` targets are enabled when compiling LLVM from scratch.
#experimental-targets = "WebAssembly;RISCV"
指定尚處在實驗階段的目標平臺。
link-jobs
# 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
指定鏈接線程數(shù)，為0時跟隨Rust構建的-j參數(shù)。
link-shared
# When invoking `llvm-config` this configures whether the `--shared` argument is
# passed to prefer linking to shared libraries.
#link-shared = false
如果使用了llvm-config工具，該選項用于指定靜態(tài)鏈接還是動態(tài)鏈接。
version-suffix
# When building llvm, this configures what is being appended to the version.
# If absent, we let the version as-is.
#version-suffix = "-rust"
指定所生成的LLVM版本的后綴。由于我們的目的是在Rust，通常把LLVM視為中間產(chǎn)物，該選項所謂不大。
clang-cl
# 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
#clang-cl = '/path/to/clang-cl.exe'
MSVC專用，指定使用clang-cl編譯LLVM。
cflags、cxxflags、ldflags
# Pass extra compiler and linker flags to the LLVM CMake build.
#cflags = "-fextra-flag"
#cxxflags = "-fextra-flag"
#ldflags = "-Wl,extra-flag"
構建LLVM時，傳給cmake的編譯和鏈接參數(shù)。
use-libcxx
# 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 = true
指定使用libc++（LLVM的C++標準庫，支持C++11）代替libstdc++（gcc的C++標準庫）。
use-linker
# The value specified here will be passed as `-DLLVM_USE_LINKER` to CMake.
#use-linker = "lld"
指定LLVM的連接器，作為-DLLVM_USE_LINKER參數(shù)傳給cmake。
[build]
# =============================================================================
# General build configuration options
# =============================================================================
構建配置。
build
# 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.
#build = "x86_64-unknown-linux-gnu" # defaults to your host platform
構建平臺。
host
# In addition to the build triple, other triples to produce full compiler
# toolchains for. Each of these triples will be bootstrapped from the build
# triple and then will continue to bootstrap themselves. This platform must
# currently be able to run all of the triples provided here.
#host = ["x86_64-unknown-linux-gnu"] # defaults to just the build triple
運行平臺。
target
# In addition to all host triples, other triples to produce the standard library
# for. Each host triple will be used to produce a copy of the standard library
# for each target triple.
#target = ["x86_64-unknown-linux-gnu"] # defaults to just the build triple
目標平臺。
cargo
# Instead of downloading the src/stage0.txt version of Cargo specified, use
# this Cargo binary instead to build all Rust code
#cargo = "/path/to/bin/cargo"
指定構建所用的cargo，構建Rust 1.34.2所用的是cargo 0.34.0，可預先安裝到指定路徑，缺省時boostrap會默認從官網(wǎng)下載并自動解壓到臨時目錄build/cache/2019-02-28中使用。
rustc
# Instead of downloading the src/stage0.txt version of the compiler
# specified, use this rustc binary instead as the stage0 snapshot compiler.
#rustc = "/path/to/bin/rustc"
指定構建所用的rustc，構建Rust 1.34.2所用的是rustc 1.33.0，可預先安裝到指定路徑，缺省時boostrap會默認從官網(wǎng)下載并自動解壓到臨時目錄build/cache/2019-02-28中使用。
docs
# 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
指定是否生成文檔，如否，可自行使用rustdoc工具按需生成。
compiler-docs
# Indicate whether the compiler should be documented in addition to the standard
# library and facade crates.
#compiler-docs = false
指定（除了庫之外）是否生成編譯器本身的文檔。
submodules
# Indicate whether submodules are managed and updated automatically.
#submodules = true
指定是否使用Git子模塊管理工具Submodules。當ignore-git = false時，如果項目中沒有使用Submodules，該選項需關閉。
fast-submodules
# Update submodules only when the checked out commit in the submodules differs
# from what is committed in the main rustc repo.
#fast-submodules = true
使用Submodules時，指定僅當子模塊有提交時才進行更新，提高效率。
gdb
# The path to (or name of) the GDB executable to use. This is only used for
# executing the debuginfo test suite.
#gdb = "gdb"
指定gdb路徑。
nodejs
# 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"
用于在構建emscripten版本時指定nodejs。
python
# Python interpreter to use for various tasks throughout the build, notably
# rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
# Note that Python 2 is currently required.
#python = "python2.7"
指定bootstrap所用的python。
locked-deps
# 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
指定cargo是否檢查Cargo.lock。
vendor
# Indicate whether the vendored sources are used for Rust dependencies or not
#vendor = false
指定是否使用源碼中攜帶的三方crate（位于vendor目錄），若否，bootstrap將從crates.io所需crate，速度比較慢，可在.cargo/config中配置鏡像站。
full-bootstrap
# 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
默認的bootstrap只進行到stage2，該選項指定是否進行stage3。
extended
# 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.
#extended = false
指定是否生成除rustc外的其他工具，包括cargo、clippy、miri、rls、rustdoc、rustfmt、rust-gdb、rust-gdbgui、rust-lldb等。雖然說明中特別指出可以生成combined installers（總安裝包），但實踐表明并不能。
tools
# Installs chosen set of extended tools if enables. By default builds all.
# If chosen tool failed to build the installation fails.
#tools = ["cargo", "rls", "clippy", "rustfmt", "analysis", "src"]
配合extended食用，指定要生成哪些工具，默認生成全部。
verbose
# Verbosity level: 0 == not verbose, 1 == verbose, 2 == very verbose
#verbose = 0
指定是否輸出詳細的構建命令。
sanitizers
# Build the sanitizer runtimes
#sanitizers = false
指定是否構建內存檢測工具集sanitizers。
profiler
# Build the profiler runtime
#profiler = false
指定是否構建優(yōu)化工具PGO。
cargo-native-static
# Indicates whether the native libraries linked into Cargo will be statically
# linked or not.
#cargo-native-static = false
指定cargo的依賴庫是否靜態(tài)鏈接到cargo。
low-priority
# 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
指定是否降低構建的優(yōu)先級，因為構建一次很占系統(tǒng)資源。
configure-args
# 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 = []
使用./configure自動生成config.toml時，這里存著該腳本收到的參數(shù)，手動配置config.toml時不用管該選項。
local-rebuild
# 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
指定是否為一次重新編譯，可以跳過stage0。
print-step-timings
# Print out how long each rustbuild step took (mostly intended for CI and
# tracking over time)
#print-step-timings = false
指定是否輸出構建過程中每一步的耗時。
[install]
# =============================================================================
# General install configuration options
# =============================================================================
安裝配置。
prefix、sysconfdir、docdir、bindir、libdir、mandir、datadir、infodir、localstatedir
# 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 (currently unused)
#datadir = "share"
# Where to install additional info in `prefix` above (currently unused)
#infodir = "share/info"
# Where to install local state (currently unused)
# If this is a relative path, it will get installed in `prefix` above
#localstatedir = "/var/lib"
指定安裝路徑。
[rust]
# =============================================================================
# Options for compiling Rust code itself
# =============================================================================
Rust編譯配置。
optimize
# Whether or not to optimize the compiler and standard library.
#
# Note: the slowness of the non optimized compiler compiling itself usually
# outweighs the time gains in not doing optimizations, therefore a
# full bootstrap takes much more time with `optimize` set to false.
#optimize = true
指定是否使用O2編譯。
debug
# 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
指定是否為debug版本。
codegen-units
# 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.
#codegen-units = 1
指定二進制代碼生成階段的LLVM工作線程數(shù)。按理說該選項能很大程度加快構建速度，但實測效果并不明顯。
codegen-units-std
# 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.
#codegen-units-std = 1
std庫可獨立指定二進制代碼生成階段的LLVM工作線程數(shù)，該選項不允許為0。
debug-assertions
# Whether or not debug assertions are enabled for the compiler and standard
# library.
#debug-assertions = false
指定是否啟用debug_assert!宏，在構建過程中進行一些斷言檢查。該宏在O0時默認啟用，詳見src/libcore/macros.rs中的注釋：
/// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
/// optimized builds by default. An optimized build will omit all
/// `debug_assert!` statements unless `-C debug-assertions` is passed to the
/// compiler. This makes `debug_assert!` useful for checks that are too
/// expensive to be present in a release build but may be helpful during
/// development.
debuginfo、debuginfo-lines、debuginfo-only-std、debuginfo-tools
# Whether or not debuginfo is emitted
#debuginfo = false
# Whether or not line number debug information is emitted
#debuginfo-lines = false
# Whether or not to only build debuginfo for the standard library if enabled.
# If enabled, this will not compile the compiler with debuginfo, just the
# standard library.
#debuginfo-only-std = false
# Enable debuginfo for the extended tools: cargo, rls, rustfmt
# Adding debuginfo makes them several times larger.
#debuginfo-tools = false
指定是否添加調試信息。
backtrace
# Whether or not `panic!`s generate backtraces (RUST_BACKTRACE)
#backtrace = true
指定程序panic時是否打印回溯信息。配合debuginfo-lines=true食用更佳，以下摘自src/doc/rustc-guide/src/compiler-debugging.md：
In the default configuration, you don't have line numbers enabled, so the
backtrace looks like this:stack backtrace: 0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace 1: std::sys_common::backtrace::_print 2: std::panicking::default_hook::{{closure}} 3: std::panicking::default_hook 4: std::panicking::rust_panic_with_hook 5: std::panicking::begin_panic (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) 32: rustc_typeck::check_crate 33: <std::thread::local::LocalKey<T>>::with 34: <std::thread::local::LocalKey<T>>::with 35: rustc::ty::context::TyCtxt::create_and_enter 36: rustc_driver::driver::compile_input 37: rustc_driver::run_compilerIf you want line numbers for the stack trace, you can enable
debuginfo-lines=trueordebuginfo=truein your config.toml and rebuild the
compiler. Then the backtrace will look like this:stack backtrace: (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) at /home/user/rust/src/librustc_typeck/check/cast.rs:110 7: rustc_typeck::check::cast::CastCheck::check at /home/user/rust/src/librustc_typeck/check/cast.rs:572 at /home/user/rust/src/librustc_typeck/check/cast.rs:460 at /home/user/rust/src/librustc_typeck/check/cast.rs:370 (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) 33: rustc_driver::driver::compile_input at /home/user/rust/src/librustc_driver/driver.rs:1010 at /home/user/rust/src/librustc_driver/driver.rs:212 34: rustc_driver::run_compiler at /home/user/rust/src/librustc_driver/lib.rs:253
incremental
# Whether to always use incremental compilation when building rustc
#incremental = false
指定是否采用增量編譯。
parallel-compiler
# Build a multi-threaded rustc
#parallel-compiler = false
指定是否生成多線程rustc。
default-linker
# The default linker that will be hard-coded into the generated compiler for
# targets that don't specify linker explicitly in their target specifications.
# Note that this is not the linker used to link said compiler.
#default-linker = "cc"
指定內嵌到編譯器中的默認鏈接器，在不指定-C linker時使用。注意不是構建編譯器本身時所用的鏈接器。
channel
# 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"
指定Rust的構建版本，dev、nightly或stable。由于源碼中許多特性需要nightly支持，一般只在發(fā)布時指定為stable。
rpath
# 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
該選項通過-C link-args=-Wl,-rpath,$ORIGIN/../lib告知編譯器共享庫的搜索路徑（連接器ld通過-rpath設置運行時共享庫的搜索路徑），使其可以直接在build目錄下運行。
verbose-tests
# Emits extraneous output from tests to ensure that failures of the test
# harness are debuggable just from logfiles.
#verbose-tests = false
指定使用測試框架進行測試時是否輸出詳細信息。
optimize-tests、debuginfo-tests
# Flag indicating whether tests are compiled with optimizations (the -O flag) or
# with debuginfo (the -g flag)
#optimize-tests = true
#debuginfo-tests = true
設置使用測試框架進行測試時的-O和-g選項。
codegen-tests
# 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
指定測試框架是否測試用于驗證LLVM的子集src/test/codegen。使用二進制LLVM時，如果該選項打開（默認就是打開），需要指定llvm-filecheck。
ignore-git
# 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 = true
指定是否忽略Git信息。使用Git管理源碼時，打開該選項可在rustc -V或rustc -vV添加Git提交本版的哈希碼和日期。
dist-src
# When creating source tarballs whether or not to create a source tarball.
#dist-src = false
指定是否生成源碼tar包，需要交付源碼時才打開。目前不清楚該選項在哪發(fā)揮作用，經(jīng)驗證./x.py dist受下面的src-tarball影響。
test-miri
# Whether to also run the Miri tests suite when running tests.
# As a side-effect also generates MIR for all libraries.
#test-miri = false
指定使用測試框架進行測試時是否測試miri（src/tools/miri/tests），也可以使用./x.py test src/tools/miri單獨進行測試。
save-toolstates
# After building or testing extended tools (e.g. clippy and rustfmt), append the
# result (broken, compiling, testing) into this JSON file.
#save-toolstates = "/path/to/toolstates.json"
指定工具集構建或測試結果的日志路徑。
codegen-backends
# 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,
# but you can also optionally enable the "emscripten" backend for asm.js or
# make this an empty array (but that probably won't get too far in the
# bootstrap)
#codegen-backends = ["llvm"]
指定編譯器后端，目前只能是LLVM。
codegen-backends-dir
# This is the name of the directory in which codegen backends will get installed
#codegen-backends-dir = "codegen-backends"
自定義后端目標碼生成庫坐在的目錄名稱，默認為codegen-backends（lib/rustlib/x86_64-unknown-linux-gnu/codegen-backends/librustc_codegen_llvm-llvm.so）。
wasm-syscall
# Flag indicating whether `libstd` calls an imported function to handle basic IO
# when targeting WebAssembly. Enable this to debug tests for the `wasm32-unknown-unknown`
# target, as without this option the test output will not be captured.
#wasm-syscall = false
WebAssembly專用。
lld
# Indicates whether LLD will be compiled and made available in the sysroot for
# rustc to execute.
#lld = false
指定是否構建LLD。
llvm-tools
# Indicates whether some LLVM tools, like llvm-objdump, will be made available in the
# sysroot.
#llvm-tools = false
指定是否將生成的LLVM工具集添加至Rust的可執(zhí)行路徑。
lldb
# Indicates whether LLDB will be made available in the sysroot.
# This is only built if LLVM is also being built.
#lldb = false
指定是否構建LLDB。
deny-warnings
# Whether to deny warnings in crates
#deny-warnings = true
指定是否禁用warning。
backtrace-on-ice
# Print backtrace on internal compiler errors during bootstrap
#backtrace-on-ice = false
指定bootstrap過程中遇到編譯器內部錯誤時是否打印回溯信息。
verify-llvm-ir
# Whether to verify generated LLVM IR
#verify-llvm-ir = false
指定生成LLVM IR后是否進行確認。
remap-debuginfo
# Map all debuginfo paths for libstd and crates to `/rust/$sha/$crate/...`,
# generally only set for releases
#remap-debuginfo = false
重定向調試信息？
jemalloc
# Link the compiler against `jemalloc`, where on Linux and OSX it should
# override the default allocator for rustc and LLVM.
#jemalloc = false
指定是否使用jemalloc代替默認的內存分配器。
test-compare-mode
# 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
指定測試框架測試模式（常規(guī)或NLL），針對src/test/ui子集，其部分用例有常規(guī)結果和NLL結果兩個stderr對比文件。
NLL是non-lexical lifetimes的意思，作為Rust編譯器的擴展特性（通過#![feature(nll)]開啟），意在優(yōu)化借用檢查。若無NLL，若某個變量被借用后又被更新會編譯不過，開啟NLL后，編譯器能識別借用與更新并不沖突的情況而允許通過。
? [譯] Rust - None Lexical Lifetimes (NLL) 使用指南
Rust防范「內存不安全」代碼的原則極其清晰明了。如果你對同一塊內存存在多個引用，就不要試圖對這塊內存做修改；如果你需要對一塊內存做修改，就不要同時保留多個引用。只要保證了這個原則，我們就可以保證內存安全。它在實踐中發(fā)揮了強大的作用，可以幫助我們盡早發(fā)現(xiàn)問題。這個原則是Rust的立身之本、生命之基、活力之源。
這個原則是沒問題的，但是，初始的實現(xiàn)版本有一個主要問題，那就是它讓借用指針的生命周期規(guī)則與普通對象的生命周期規(guī)則一樣，是按作用域來確定的。所有的變量、借用的生命周期就是從它的聲明開始，到當前整個語句塊結束。這個設計被稱為Lexical Lifetime，因為生命周期是嚴格和詞法中的作用域范圍綁定的。這個策略實現(xiàn)起來非常簡單，但它可能過于保守了，某些情況下借用的范圍被過度拉長了，以至于某些實質上是安全的代碼也被阻止了。在某些場景下，限制了程序員的發(fā)揮。
——《深入淺出Rust》
[target.x86_64-unknown-linux-gnu]
# =============================================================================
# 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.
# =============================================================================
目標平臺配置，可額外增加其他目標平臺的配置。
cc、cxx、ar、ranlib、linker
# C compiler to be used to compiler 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.
#cc = "cc"
# C++ compiler to be used to compiler C++ code (e.g. LLVM and our LLVM shims).
# This is only used for host targets.
#cxx = "c++"
# 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"
# 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"
# Linker to be used to link 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.
#linker = "cc"
編譯、鏈接工具。
llvm-config
# 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 = "../path/to/llvm/root/bin/llvm-config"
指定llvm-config工具的安裝路徑，該選項旨在使用現(xiàn)成的二進制LLVM，可省去編譯LLVM的時間。debug-assertions打開時需配合llvm-filecheck選項食用。
使用現(xiàn)成LLVM時，dist包中將不包含在src/bootstrap/lib.rs中指定的LLVM工具：
const LLVM_TOOLS: &[&str] = &[
"llvm-nm", // used to inspect binaries; it shows symbol names, their sizes and visibility
"llvm-objcopy", // used to transform ELFs into binary format which flashing tools consume
"llvm-objdump", // used to disassemble programs
"llvm-profdata", // used to inspect and merge files generated by profiles
"llvm-readobj", // used to get information from ELFs/objects that the other tools don't provide
"llvm-size", // used to prints the size of the linker sections of a program
"llvm-strip", // used to discard symbols from binary files to reduce their size
];
llvm-filecheck
# 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/FileCheck"
指定LLVM文件檢查工具FileCheck的路徑，與llvm-config位于同一目錄時無需指定。有趣的是，隨便給個叫FileCheck的文件就可以避免boostrap報找不到。
android-ndk
# 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.
#android-ndk = "/path/to/ndk"
指定安卓開發(fā)套件NDK（Native Development Kit）的路徑。
crt-static
# 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 = false
指定目標平臺的std庫是動態(tài)還是靜態(tài)鏈接。
musl-root
# 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 = "..."
MUSL專用。
qemu-rootfs
# Used in testing for configuring where the QEMU images are located, you
# probably don't want to use this.
#qemu-rootfs = "..."
QEMU專用。
[dist]
# =============================================================================
# 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
# =============================================================================
發(fā)布配置。
sign-folder
# 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 = "path/to/folder/to/sign"
指定需要gpg加密的目錄。
gpg-password-file
# This is a file which contains the password of the default gpg key. This will
# be passed to `gpg` down the road when signing all files in `sign-folder`
# above. This should be stored in plaintext.
#gpg-password-file = "path/to/gpg/password"
指定gpg密鑰文件。
upload-addr
# 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 = "https://example.com/folder"
指定線上發(fā)布的網(wǎng)址（上傳地址）。
src-tarball
# 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
指定是否生成源碼tar包，需要交付源碼時才打開。
missing-tools
# Whether to allow failures when building tools
#missing-tools = false
指定構建工具時是否允許出錯。
2020年8月7日、10～12日 無錫
