What is gcc-config?
-------------------

gcc-config allows Gentoo users to switch active gcc safely
and allows querying facts about installed toolchains.

To switch active gcc while system runs:
    $ gcc-config x86_64-pc-linux-gnu-8.1.0
    $ gcc-config x86_64-pc-linux-gnu-7.2.0

    Ideally changes should be visible instantly and atomically
    without shell restart.

To query where real gcc binaries are hiding:
    $ gcc-config -B $(gcc-config -c)

To parse a profile into TARGET and toolchain version:
    $ gcc-config -S sparc64-unknown-linux-gnu-9.2.0

Files, variables, things.
-------------------------

- Wrappers (symlinks to compiler binary like /usr/${CTARGET}/gcc-bin/${GCC_VERSION}/gcc)
    /usr/bin/gcc (native)
    /usr/bin/g++ (native)
    /usr/bin/${CTARGET}-gcc (native and cross)
    ...
    (all files from /usr/${CTARGET}/gcc-bin/$GCC_VERSION/*)

      See `gcc-config` script for wrapping details.

- private gcc configs (provided by `toolchain.eclass`, gcc ebuilds)

    /etc/env.d/gcc/x86_64-pc-linux-gnu-8.1.0

      Contains variables that describe toolchain layout:

          LDPATH="/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0"
          MANPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/8.1.0/man"
          INFOPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/8.1.0/info"
          STDCXX_INCDIR="g++-v8"
          CTARGET="x86_64-pc-linux-gnu"
          GCC_SPECS=""
          MULTIOSDIRS="../lib64"
          GCC_PATH="/usr/x86_64-pc-linux-gnu/gcc-bin/8.1.0"

      Used by gcc-config to generate wrappers and 05gcc- env.d files.

- gcc env.d compiler entries (provided by gcc-config)

    /etc/env.d/04gcc-${CTARGET} (native)

      Populates paths for native-compilers

        GCC_SPECS=""
        MANPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/8.2.0/man"
        INFOPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/8.2.0/info"

      Used by env-update to populate PATH and more (TODO: remove PATH population).

TODOs
-----

- Write proper `gcc-config` manpage off this readme to be more discoverable.

- Figure out symlink ownership story. Today symlinks don't belong to any package.

  See https://bugs.gentoo.org/626606