Constant USAGE 

pub const USAGE: &str = "\
rucc, an optimizing C compiler

usage: rucc [options] file...

options:
  -c                     compile and assemble, do not link
  -S                     compile only, emit assembly
  -E                     preprocess only
  -o <file>              write output to <file>, or to standard output for -
  -D <name>[=<value>], -U <name>      define a macro, or undefine one after every -D
  -I <dir>               add <dir> to the include search path
  -iquote -isystem -idirafter <dir>   the other chains, -nostdinc drops ours
  -I-, -iprefix <p>, -iwithprefix[before] <dir>   the older spellings of those
  -include <file>, -imacros <file>    read <file> first, the second for its macros only
  --sysroot=<dir>        look for the library's headers under <dir>, -isysroot too
  -P, -dM                with -E: leave out the markers, or dump the macros
  -M -MM -MD -MMD        write a make rule for the source, the last two compile as well
  -MF <file> -MT <t> -MQ <t> -MP   where the rule goes, what it builds, targets with no recipe
  -std=<dialect>         c89 through c23, and the gnu spellings
  -fgnuc-version=<v>     the GCC release to claim, default 7.0.0
  -x <lang>              treat later inputs as <lang>, or none to stop
  -O<level>              optimize: 0, 1, 2, 3, s, z
  -fsafety=<tier>        check memory safety: off, detect, enforce, kernel
  -f[no-]sanitize=<what>   the negative is taken, the positive is refused by name
  -f[no-]safety-subobject   a write has to stay inside the member it names
  -f[no-]safety-restrict    two restrict pointers of one block may not meet
  -f<pass> -fno-<pass> -fdump-ir=<what> -fopt-info[-<kind>][=FILE]
  -fpass-fuel=<pass>=<n>, -fpass-fuel-global=<n>   stop a pass, or all of them, after n
  -fdisable-<pass>[=<funcs>], -fenable-<pass>[=<funcs>]   run a pass on some functions only
  -g -g0 -gdwarf-5, -fno-omit-frame-pointer, -mno-red-zone   debug info, frame pointer, red zone
  -gz[=none|zlib|zlib-gnu|zstd] -gno-split-dwarf   compress debug sections, one file not two
  -flto[=auto|jobserver|<n>] -fno-lto -ffat-lto-objects   read, and not done yet
  -fprofile-use[=<path>] -fprofile-dir=<dir>   read too, where -fprofile-generate is refused
  -f[no-]stack-protector[-strong|-all], -f[no-]stack-clash-protection, -fcf-protection=<edges>
  -ffunction-sections -fdata-sections   a section per function or variable, for --gc-sections
  -fvisibility=<what>    default, hidden, internal or protected, when nothing in the source said
  -l<name>, -L <dir>, -B <dir>   link a library, where to look for one, where our own tools are
  -fPIC -fpic -fPIE -fpie, -fno-common, -pipe   what it does anyway
  -f[no-]strict-aliasing, -f[no-]delete-null-pointer-checks   what it assumes anyway
  -static -shared -pie -no-pie -nostdlib -nostartfiles -nodefaultlibs -rdynamic -s   how to link
  -Wl,<arg>, -Xlinker <arg>, -fuse-ld=<name>   hand an argument to the linker, or pick one
  -Werror -pedantic -pedantic-errors -w -W[no-]system-headers   how much to say, and how fatal
  -m64 -march= -mtune= -mcpu= -mabi= -mcmodel=   what machine to generate for
  -pg -p, -mfentry -mno-fentry   call a profiler on the way in, and where that call goes
  -fpatchable-function-entry=<n>[,<m>]   room at the top of every function to patch later
  -fwrapv, -fwrapv-pointer, -fno-strict-overflow   signed or pointer overflow wraps
  -ftrapv                signed overflow stops the program instead
  -f[no-]signed-char, -f[no-]unsigned-char, -f[no-]short-enums   change the ABI
  -ffp-contract=<how>    fuse a multiply and an addition: fast, on or off
  -fexcess-precision=<how>, -f[no-]rounding-math, -f[no-]trapping-math   what may be folded
  -ffile-prefix-map=<old>=<new>   rewrite that front of every path we put in the output
  -fmacro-prefix-map= -fdebug-prefix-map= -fprofile-prefix-map=   the same, one output each
  -pthread               build for more than one thread, and link the library for it
  -dumpmachine -dumpversion -print-multiarch -print-search-dirs   what this compiler is
  -print-file-name=<name> -print-prog-name=<name>   where a file or a program is
  -print-sysroot         the root the headers and the libraries are read under
  -print-sysroot-provenance   every input under it, where it came from and its licence
  -print-sysroot-digest   the sha256 of that record, which names the whole sysroot in one line
  --fetch <tuple>        get the sysroot this release pins for <tuple> and install it in the cache
  --offline              never download anything, which a compilation never does anyway
  -j[n]                  compile n translation units at once, default all
  -v, -###               print each phase as it runs, or without running any
  -save-temps[=cwd|obj], -time   keep the .i and the .s, say how long each step took
  --target=<triple>      generate code for <triple>
  --emit=<kind>          exe, obj, archive, asm, preprocessed, tast, ir, mir-final,
                         safety-summary, type-granules
  --print-config, --print-pipeline    print the configuration or the pipeline, and exit
  --version              print the version and exit
  -h, --help             print this message and exit

See spec/04-driver-and-cli.md for the full flag reference.
";

Usage text.

Deliberately short. spec/04-driver-and-cli.md puts the full flag reference in the manual page, because a --help nobody can read in one screen is a --help nobody reads.