update infrastructure.rst/compilers

src/maintainer/infrastructure.rst

@@ -281,35 +281,75 @@ Compilers and Runtimes
 
 Conda-forge builds and maintains its own set of compilers for various languages
 and/or systems (e.g., ``C``, ``FORTRAN``, ``C++``, ``CUDA``, etc.). These are used
-in all of our CI builds to build both core dependencies (e.g., ``Python``) and maintainer-contributed
-packages. While we do not have any formal policies or promises of support for these
-compilers, we have historically maintained them according to the following (non-binding)
-principles.
-
-* The authoritative source of the current compilers and versions for various languages
-  and platforms is the `conda_build_config.yaml <https://github.com/conda-forge/conda-forge-pinning-feedstock/blob/master/recipe/conda_build_config.yaml>`_
-  in the `conda-forge/conda-forge-pinning-feedstock <https://github.com/conda-forge/conda-forge-pinning-feedstock>`_
-  as described in :ref:`globally_pinned_packages`.
-* We provide no support of any kind in terms of the long-term stability of these pinnings.
-* We upgrade them in an ad-hoc manner on a periodic basis as we have the time and energy to do so.
-  Note that because of the way we enforce runtime constraints, these compiler upgrades will not break
-  existing packages. However, if you are using the compilers outside of ``conda``, then you may find issues.
-* We generally provide notice in the form of an announcement when a compiler is going to be upgraded.
-  Note that these changes take a bit of time to complete, so you will generally have time
-  to prepare should you need to.
-* Some of the criteria we think about when considering a compiler migration include
-  1) the degree of disruption to the ecosystem, 2) the amount of work for the ``core`` team,
-  and 3) the amount of time it will cost our (volunteer) feedstock maintainers.
-
-We do use some unofficial names for our compiler stack internally. Note however that
-the existence of these names does not imply any level of support or stability for the compilers
-that form the given stack.
-
-* Our current compiler stack is referred to internally as ``comp7``.
-* The previous compiler stack based in part on the various ``toolchain_*`` packages
-  was sometimes referred to as ``comp4``. On linux the ``toolchain_*`` compilers were
-  GCC 4.8.2 as packaged in the devtoolset-2 software collection. On osx, we use clang from
-  Apple's Xcode in the ``toolchain_*`` packages.
+in all of our CI builds to build essentially all artefacts published by conda-forge.
+
+In general, our compilers on Linux and OSX are using very recent compilers, whereas
+on windows, we generally use the last supported VS version.
+Note that we do not have any formal policies or promises of support for these
+compilers, they are primarily intended for use within conda-forge CI. Despite this,
+we try to keep them working and even provide an easy way to install them (through
+the `compilers<https://github.com/conda-forge/compilers-feedstock>`_ feedstock).
+
+The currently used compilers and versions for various languages and platforms 
+can be found in the `conda_build_config.yaml <https://github.com/conda-forge/conda-forge-pinning-feedstock/blob/master/recipe/conda_build_config.yaml>`_
+of the `conda-forge/conda-forge-pinning-feedstock <https://github.com/conda-forge/conda-forge-pinning-feedstock>`_
+as described in :ref:`globally_pinned_packages`.
+
+In more detail, our default compiler stack is made up very differently on each platform.
+More specifically, each compiler needs an _activation_ that makes the difference
+between it being merely present in a build environment, and it being used by default.
+These will be installed when using `{{ compiler('xyz') }}` in `meta.yaml`, where `'xyz'`
+is one of `'c', 'cxx', 'fortran', 'cuda', 'rust', 'go-cgo', 'go-nocgo'`.
+
+Linux:
+* [C, C++, Fortran] Activation: https://github.com/conda-forge/ctng-compiler-activation-feedstock/
+* [C, C++, Fortran] Implementation: https://github.com/conda-forge/ctng-compilers-feedstock
+* Note that when used in conjunction with CUDA, compiler versions are restricted by the
+  maximum GCC version supported by nvcc (which is also reflected in the global pinning).
+
+OSX:
+* [C, C++] Activation: https://github.com/conda-forge/clang-compiler-activation-feedstock/
+* [C, C++] Required feedstocks:
+  `llvmdev<https://github.com/conda-forge/llvmdev-feedstock>`_,
+  `clangdev<https://github.com/conda-forge/clangdev-feedstock>`_,
+  `compiler-rt<https://github.com/conda-forge/compiler-rt-feedstock>`_,
+  `libcxx<https://github.com/conda-forge/libcxx-feedstock>`_,
+  `openmp<https://github.com/conda-forge/openmp-feedstock>`_,
+  `lld<https://github.com/conda-forge/lld-feedstock>`_,
+  `cctools<https://github.com/conda-forge/cctools-and-ld64-feedstock>`_
+* [Fortran] Activation: https://github.com/conda-forge/gfortran_osx-64-feedstock/
+* [Fortran] Implementation: https://github.com/conda-forge/gfortran_impl_osx-64-feedstock/
+
+Windows:
+* [C, C++] Activation: https://github.com/conda-forge/vc-feedstock
+* [C, C++] We cannot redistribute the actual MSVC compilers due to licensing constraints
+* [Fortran] Activation & Implementation: https://github.com/conda-forge/flang-feedstock
+
+There exists an alternative, MinGW-based, compiler stack on windows, which is available
+with a `m2w64_` prefix (e.g. `{{ compiler('m2w64_c') }}`), which is however falling out
+of use now that most projects will natively support compilation also with MSVC, in addition
+to several complications arising from mixing compiler stacks.
+
+Additionally, there is a possibility to use clang as a compiler also on Linux & Windows:
+* Activation (Linux): https://github.com/conda-forge/clang-compiler-activation-feedstock/
+* Activation (Windows): https://github.com/conda-forge/clang-win-activation-feedstock/
+
+Aside from the main C/C++ compilers, these are the feedstocks for other compilers:
+* [CUDA] https://github.com/conda-forge/nvcc-feedstock (CUDA infra currently being overhauled)
+* [Rust] `Activation<https://github.com/conda-forge/rust-activation-feedstock>`_
+  and `Implementation<https://github.com/conda-forge/rust-feedstock>`_
+* [Go] https://github.com/conda-forge/go-feedstock
+
+To upgrade the compiler version of our default compilers in the global pinning for
+Linux or OSX, ensure that all the above feedstocks have been rebuilt for the respective
+new major version, that all interrelated versions are lifted at the same time,
+and obviously that the compilers work (e.g. by testing them on some feedstocks by
+specifying the new version through the feedstock-local `conda_build_config.yaml`).
+
+For Windows, we stay on older compilers for longer, because using a newer toolchain
+would force everyone wanting to locally develop with conda-forge artefacts to use
+a toolchain that's at least as new. A more in-depth explanation can be found
+`here<https://github.com/conda-forge/conda-forge.github.io/issues/1732>`_.
 
 CentOS ``sysroot`` for ``linux-*`` Platforms
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