GIANT CLUSTERFUCK OF A COMMIT

OK, this is epic.  I was basically just trying to a) support Clang and
b) add more test coverage.  _THREE MONTHS_ and a few hundred CI runs
later, this is what I came up with.  I don't know how it ended up being
what it is, but here we go.

Some highlights of the changes:

1) CI builds has been moved to GitHub Actions,
2) the entire notion of a toolchain has been reworked; it now supports
Clang on all platforms.

* .github: this directory contains the GitHub Actions workflow
scripts/actions.  In the process, I created like 6 external GitHub
actions, but it's still pretty massive.  An upside is that it covers
much more platform/toolchain combinations _and_ check a lot of the
expected post-conditions.  TODO: .ci/Makefile is obsolete now, as well
as .travis.yml and .appveyor.yml.

* common.cmake: added Clang support.  In the process, a great deal has
been learned about how CMake works; in particular, static runtime
support has been reworked to be more robust.

* project: the entire notion of a "toolchain" has been reworked.
Instead of a measly --mingw parameter, there's now a separate --toolset
parameter, which allows you to choose between GCC, Clang, MSVC, etc.
Both Boost and CMake build scripts were enhanced greatly to support
Clang and other toolchains in a more robust way.

1 files changed, 222 insertions, 0 deletions

diff --git a/.github/workflows/boost_toolsets.yml b/.github/workflows/boost_toolsets.yml
new file mode 100644
index 0000000..1319264
--- /dev/null
+++ b/.github/workflows/boost_toolsets.yml
@@ -0,0 +1,222 @@
+name: Boost (toolsets)
+
+on:
+  push:
+  pull_request:
+  schedule:
+    # Weekly, at 5:30 AM on Saturday (somewhat randomly chosen).
+    - cron: '30 5 * * 6'
+  workflow_dispatch:
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        boost-version: [1.58.0, 1.65.0, 1.72.0]
+        toolset: [auto, clang, clang-cl, gcc, mingw, msvc]
+        cygwin: [0, 1]
+        os: [ubuntu-18.04, windows-2016, windows-2019]
+
+        include:
+          # Prettier run names.
+          - {os: windows-2019, name: VS 2019}
+          - {os: windows-2016, name: VS 2017}
+          - {os: ubuntu-18.04, name: Ubuntu}
+          - {cygwin: 1, name: Cygwin}
+          # Target platform.
+          - {boost-version: 1.58.0, platform: x64}
+          - {boost-version: 1.65.0, platform: x86}
+          - {boost-version: 1.72.0, platform: x64}
+          # Configuration.
+          - {boost-version: 1.58.0, configuration: Debug}
+          - {boost-version: 1.65.0, configuration: MinSizeRel}
+          - {boost-version: 1.72.0, configuration: Release}
+
+          # Some Boost libraries commonly used by me.
+          - libraries: filesystem program_options regex system test
+          # On Windows, clang fails to build Boost.Test prior to version 1.61
+          # with the following error:
+          #
+          #     .\boost/test/impl/execution_monitor.ipp:1134:20: error: cannot compile this 'this' captured by SEH yet
+          #
+          # This was fixed for 1.61 in this commit:
+          # https://github.com/boostorg/test/commit/c94ef6982e2ebe77f9376579547c228f0d62e45f.
+          # On Linux/Cygwin, everything should be fine though.
+          - toolset: clang
+            boost-version: 1.58.0
+            os: windows-2019
+            libraries: filesystem program_options regex system
+          - toolset: clang
+            boost-version: 1.58.0
+            os: windows-2016
+            libraries: filesystem program_options regex system
+        exclude:
+          # Ubuntu: no MSVC/clang-cl/Cygwin.
+          - {os: ubuntu-18.04, toolset: msvc}
+          - {os: ubuntu-18.04, toolset: clang-cl}
+          - {os: ubuntu-18.04, cygwin: 1}
+          # Cygwin: no MSVC/clang-cl.
+          - {cygwin: 1, toolset: msvc}
+          - {cygwin: 1, toolset: clang-cl}
+          # Cygwin is the same on Windows Server 2016 & 2019.
+          - {os: windows-2016, cygwin: 1}
+          # clang-cl is only supported by Boost.Build since 1.69 (see the
+          # boost_clang_windows.yml workflow).
+          - {toolset: clang-cl, boost-version: 1.58.0}
+          - {toolset: clang-cl, boost-version: 1.65.0}
+
+    runs-on: '${{ matrix.os }}'
+
+    name: '${{ matrix.boost-version }} / ${{ matrix.toolset }} / ${{ matrix.name }}'
+
+    # 1) I have no idea why, but GCC 10.2 fails to build Boost.Filesystem with
+    #    the following errors:
+    #
+    #        libs\filesystem\src\path.cpp:36:11: fatal error: windows_file_codecvt.hpp: No such file or directory
+    #           36 | # include "windows_file_codecvt.hpp"
+    #              |           ^~~~~~~~~~~~~~~~~~~~~~~~~~
+    #        compilation terminated.
+    #        libs\filesystem\src\windows_file_codecvt.cpp:25:10: fatal error: windows_file_codecvt.hpp: No such file or directory
+    #           25 | #include "windows_file_codecvt.hpp"
+    #              |          ^~~~~~~~~~~~~~~~~~~~~~~~~~
+    #        compilation terminated.
+    #
+    #    This seems to be a compiler bug, since the file is _definitely_ there,
+    #    and Clang 8.0.1 builds it successfully.  This only applies to Boost
+    #    versions up to and including 1.60.0 for some reason.  I can easily
+    #    reproduce this locally.  TODO: remove when GCC on Cygwin is treated
+    #    with a bugfix to this?
+    #
+    # 2) 32-bit Cygwin fucking sucks.  In many ways actually, but the real
+    #    reason was the incomprehensible
+    #
+    #        undefined reference to `__chkstk_ms'
+    #
+    #    error when building with Clang.
+    continue-on-error: ${{
+            (matrix.cygwin == '1' && matrix.boost-version == '1.58.0'
+                && (matrix.toolset == 'auto'
+                    || matrix.toolset == 'gcc'
+                    || matrix.toolset == 'mingw'))
+            || (matrix.cygwin == '1' && matrix.platform == 'x86')
+        }}
+
+    defaults:
+      run:
+        shell: pwsh
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Clean up PATH
+        uses: egor-tensin/cleanup-path@v1
+        if: runner.os == 'Windows'
+
+      - name: Set common variables
+        uses: ./.github/actions/common-variables
+        with:
+          toolset: '${{ matrix.toolset }}'
+          cygwin: '${{ matrix.cygwin }}'
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.x'
+        if: '!env.CI_HOST_CYGWIN'
+
+      - name: Install Cygwin
+        uses: egor-tensin/setup-cygwin@v3
+        with:
+          platform: '${{ matrix.platform }}'
+          packages: cmake make python3
+          hardlinks: 1
+        if: env.CI_HOST_CYGWIN
+
+      - name: Install GCC
+        uses: egor-tensin/setup-gcc@v1
+        with:
+          cygwin: '${{ matrix.cygwin }}'
+          platform: '${{ matrix.platform }}'
+          hardlinks: 1
+        if: env.CI_HOST_CYGWIN || (env.CI_HOST_LINUX && (matrix.toolset == 'auto' || matrix.toolset == 'gcc'))
+
+      - name: Install Clang
+        uses: egor-tensin/setup-clang@v1
+        with:
+          cygwin: '${{ matrix.cygwin }}'
+          platform: '${{ matrix.platform }}'
+          hardlinks: 1
+        if: matrix.toolset == 'clang' || matrix.toolset == 'clang-cl'
+
+      - name: Install MinGW
+        uses: egor-tensin/setup-mingw@v2
+        with:
+          cygwin: '${{ matrix.cygwin }}'
+          platform: '${{ matrix.platform }}'
+          hardlinks: 1
+        # toolset == 'clang' needs some kind of make, e.g. mingw32-make:
+        if: env.CI_MINGW || (matrix.toolset == 'clang' && env.CI_HOST_WINDOWS)
+
+      - name: Set up software environment
+        uses: ./.github/actions/software-environment
+        with:
+          toolset: '${{ matrix.toolset }}'
+          platform: '${{ matrix.platform }}'
+
+      - name: Set up Visual Studio
+        uses: egor-tensin/vs-shell@v2
+        with:
+          arch: '${{ matrix.platform }}'
+        if: matrix.toolset == 'clang-cl' && env.CI_HOST_WINDOWS
+
+      - name: Download Boost
+        uses: ./.github/actions/download-boost
+        with:
+          boost-version: '${{ matrix.boost-version }}'
+
+      - name: Build Boost
+        uses: ./.github/actions/build-boost
+        with:
+          toolset: '${{ matrix.toolset }}'
+          libraries: '${{ matrix.libraries }}'
+          platform: '${{ matrix.platform }}'
+          configuration: '${{ matrix.configuration }}'
+        continue-on-error: true
+
+      - name: Check that Boost was bootstrapped
+        uses: ./.github/actions/check-boost-bootstrapped
+
+      - name: Check that Boost libraries were built
+        uses: ./.github/actions/check-boost-libraries
+        with:
+          libraries: '${{ matrix.libraries }}'
+          platform: '${{ matrix.platform }}'
+          configuration: '${{ matrix.configuration }}'
+
+      - name: Build examples/boost
+        id: build_example
+        uses: ./.github/actions/build-example
+        with:
+          src-dir: examples/boost
+          boost-dir: '${{ env.BOOST_DIR }}'
+          toolset: '${{ matrix.toolset }}'
+          platform: '${{ matrix.platform }}'
+          configuration: '${{ matrix.configuration }}'
+
+      - name: Verify runtime library linkage
+        uses: ./.github/actions/check-runtime-library
+        with:
+          path: '${{ steps.build_example.outputs.install-dir }}'
+
+      - name: Verify architecture
+        uses: ./.github/actions/check-arch
+        with:
+          path: '${{ steps.build_example.outputs.install-dir }}'
+          expected: '${{ matrix.platform }}'
+
+      - name: Run examples/boost
+        uses: ./.github/actions/run-example-boost
+        with:
+          path: '${{ steps.build_example.outputs.install-dir }}'