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  TODO: .ci/Makefile is obsolete now, as well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.

4 files changed, 614 insertions, 0 deletions

diff --git a/.github/workflows/boost_clang_windows.yml b/.github/workflows/boost_clang_windows.yml
new file mode 100644
index 0000000..62c2cb5
--- /dev/null
+++ b/.github/workflows/boost_clang_windows.yml
@@ -0,0 +1,143 @@
+# This basically tests two things.
+#
+#   * If, instead of some kind of MinGW-born ar & ranlib, you only have
+#     upstream LLVM distribution on Windows, you wouldn't be able to use
+#     toolset=clang until 1.66.0.
+#   * toolset=clang-win is broken until 1.69.0.
+
+name: Boost & Clang on Windows
+
+on:
+  push:
+  pull_request:
+  schedule:
+    # Weekly, at 5:30 AM on Saturday (somewhat randomly chosen).
+    - cron: '30 5 * * 6'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: windows-2019
+
+    strategy:
+      fail-fast: false
+      matrix:
+        toolset: [clang, clang-cl]
+        boost-version: [1.63.0, 1.64.0, 1.65.1, 1.66.0, 1.67.0, 1.68.0, 1.69.0, 1.70.0, 1.71.0, 1.74.0]
+        include:
+          - {toolset: clang, b2_toolset: clang}
+          - {toolset: clang-cl, b2_toolset: clang-win}
+
+    name: '${{ matrix.toolset }} / ${{ matrix.boost-version }}'
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Clean up PATH
+        uses: egor-tensin/cleanup-path@v1
+        if: runner.os == 'Windows'
+
+      - name: Set common variables
+        uses: ./.github/actions/common-variables
+        with:
+          toolset: '${{ matrix.toolset }}'
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.x'
+
+      - name: Install Clang
+        uses: egor-tensin/setup-clang@v1
+
+      - name: Set up software environment
+        uses: ./.github/actions/software-environment
+        with:
+          toolset: ${{ matrix.toolset }}
+
+      - name: Download Boost
+        uses: ./.github/actions/download-boost
+        with:
+          boost-version: ${{ matrix.boost-version }}
+
+      - name: Bootstrap Boost
+        run: |
+          cd $env:BOOST_DIR
+          .\bootstrap.bat
+        continue-on-error: true
+
+      - name: Check that Boost was bootstrapped
+        uses: ./.github/actions/check-boost-bootstrapped
+
+      - name: Write toolset-config.jam (clang)
+        run: |
+          echo 'using ${{ matrix.b2_toolset }} : : clang++.exe : <archiver>llvm-ar <ranlib>llvm-ranlib ;' > "$env:BOOST_DIR\toolset-config.jam"
+        if: matrix.toolset == 'clang'
+      - name: Write toolset-config.jam (clang-cl)
+        run: |
+          echo 'using ${{ matrix.b2_toolset }} ;' > "$env:BOOST_DIR\toolset-config.jam"
+        if: matrix.toolset == 'clang-cl'
+
+      - name: Build Boost.Filesystem
+        run: |
+          cd $env:BOOST_DIR
+
+          $stagedir = "stage"
+          $librarydir = "$env:BOOST_DIR\$stagedir\lib"
+          echo "BOOST_LIBRARYDIR=$librarydir" >> $env:GITHUB_ENV
+
+          .\b2.exe                     `
+              "--stagedir=$stagedir"   `
+              --layout=system          `
+              --dump-configuration     `
+              address-model=64         `
+              "--user-config=$env:BOOST_DIR\toolset-config.jam" `
+              variant=debug            `
+              link=static              `
+              runtime-link=static      `
+              -d2 --dump-configuration `
+              --with-filesystem        `
+              --with-system
+        continue-on-error: true
+
+      - name: Boost.Filesystem failed to build
+        run: $(Test-Path "$env:BOOST_LIBRARYDIR\libboost_filesystem.lib" -Type Leaf) -and $(throw "libboost_filesystem.lib was build?!")
+        if: |
+          (matrix.toolset == 'clang' && matrix.boost-version < '1.66.0') || (matrix.toolset == 'clang-cl' && matrix.boost-version < '1.69.0')
+      - id: boost_filesystem_built
+        name: Boost.Filesystem was built
+        run: $(Test-Path "$env:BOOST_LIBRARYDIR\libboost_filesystem.lib" -Type Leaf) -or $(throw "libboost_filesystem.lib wasn't found")
+        if: |
+          !((matrix.toolset == 'clang' && matrix.boost-version < '1.66.0') || (matrix.toolset == 'clang-cl' && matrix.boost-version < '1.69.0'))
+
+      # Check that we can link to the built libraries.
+      - name: Build foo.exe using clang
+        run: |
+          clang++.exe                   `
+              "-I$env:BOOST_DIR"        `
+              -D BOOST_ALL_NO_LIB=1     `
+              "-L$env:BOOST_LIBRARYDIR" `
+              -llibboost_filesystem     `
+              -llibboost_system         `
+              -o foo.exe                `
+              examples/boost/foo.cpp
+        if: steps.boost_filesystem_built.conclusion == 'success' && matrix.toolset == 'clang'
+
+      - name: Build foo.exe using clang-cl
+        run: |
+          clang-cl.exe                `
+              /EHsc                   `
+              /MTd                    `
+              "/I$env:BOOST_DIR"      `
+              /D BOOST_ALL_NO_LIB=1   `
+              "/Fefoo.exe"            `
+              examples/boost/foo.cpp  `
+              libboost_filesystem.lib `
+              libboost_system.lib     `
+              /link "/LIBPATH:$env:BOOST_LIBRARYDIR"
+        if: steps.boost_filesystem_built.conclusion == 'success' && matrix.toolset == 'clang-cl'
+
+      - name: foo.exe
+        run: .\foo.exe
+        if: steps.boost_filesystem_built.conclusion == 'success'
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: '${{ steps.build_example.outputs.install-dir }}'
diff --git a/.github/workflows/cygwin_static_libstdc++.yml b/.github/workflows/cygwin_static_libstdc++.yml
new file mode 100644
index 0000000..156b111
--- /dev/null
+++ b/.github/workflows/cygwin_static_libstdc++.yml
@@ -0,0 +1,81 @@
+# -static-libstdc++ is broken on Cygwin for some reason, as this workflow tries
+# to demonstrate.  I don't know why exactly, but I'm not the only one with this
+# problem:
+#
+#   * https://stackoverflow.com/q/46854365/514684
+#   * https://sourceforge.net/p/stlplus/discussion/345536/thread/48c7fc9c17/?limit=25
+
+name: Cygwin & -static-libstdc++
+
+on:
+  push:
+  pull_request:
+  schedule:
+    # Weekly, at 5:30 AM on Saturday (somewhat randomly chosen).
+    - cron: '30 5 * * 6'
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: windows-2019
+
+    name: Test
+
+    defaults:
+      run:
+        shell: pwsh
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Clean up PATH
+        uses: egor-tensin/cleanup-path@v1
+        if: runner.os == 'Windows'
+
+      - name: Set common variables
+        uses: ./.github/actions/common-variables
+        with:
+          toolset: '${{ matrix.toolset }}'
+          cygwin: 1
+
+      - name: Install Cygwin
+        uses: egor-tensin/setup-cygwin@v3
+
+      - name: Install GCC
+        uses: egor-tensin/setup-gcc@v1
+        with:
+          cygwin: 1
+
+      - name: Set up software environment
+        uses: ./.github/actions/software-environment
+        with:
+          toolset: gcc
+
+      - name: test.cpp
+        run: |
+          $src = @"
+          #include <stdexcept>
+
+          int main() {
+              std::runtime_error x{"x"};
+              std::runtime_error y{x};
+              return 0;
+          }
+          "@
+
+          echo $src > test.cpp
+
+      - name: Build w/ -static-libstdc++
+        run: C:\tools\cygwin\bin\g++.exe -static-libstdc++ -o test test.cpp
+        continue-on-error: true
+
+      - name: Should fail
+        run: $(Test-Path test.exe -Type Leaf) -and $(throw "test.exe shouldn't have been built")
+
+      - name: Build w/ --allow-multiple-definition
+        run: C:\tools\cygwin\bin\g++.exe '-Wl,--allow-multiple-definition' -static-libstdc++ -o test test.cpp
+        continue-on-error: true
+
+      - name: Should succeed
+        run: $(Test-Path test.exe -Type Leaf) -or $(throw "test.exe should have been built")
diff --git a/.github/workflows/example_toolsets.yml b/.github/workflows/example_toolsets.yml
new file mode 100644
index 0000000..cb336aa
--- /dev/null
+++ b/.github/workflows/example_toolsets.yml
@@ -0,0 +1,168 @@
+name: Examples (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:
+        example: [simple, static, dynamic]
+        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.
+          - {example: simple, platform: x64}
+          - {example: static, platform: x86}
+          - {example: dynamic, platform: x64}
+          # Configuration.
+          - {example: simple, configuration: Release}
+          - {example: static, configuration: Debug}
+          - {example: dynamic, configuration: RelWithDebInfo}
+          # Expected symbols.
+          - example: simple
+            symbols:
+              - target: foo
+                type: exe
+                symbols: []
+          - example: static
+            symbols:
+              - target: foo
+                type: exe
+                symbols: [main, bar]
+          - example: dynamic
+            symbols:
+              - target: foo
+                type: exe
+                symbols: [main]
+              - target: baz
+                type: dll
+                symbols: [baz]
+        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}
+
+    runs-on: '${{ matrix.os }}'
+
+    name: '${{ matrix.example }} / ${{ matrix.toolset }} / ${{ matrix.name }}'
+
+    defaults:
+      run:
+        shell: pwsh
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Clean up PATH
+        uses: egor-tensin/cleanup-path@v1
+        if: runner.os == 'Windows'
+
+      - name: Set common variables
+        uses: ./.github/actions/common-variables
+        with:
+          toolset: '${{ 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_LINUX || env.CI_HOST_CYGWIN) && (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: '${{ matrix.platform }}'
+        if: matrix.toolset == 'clang-cl' && env.CI_HOST_WINDOWS
+
+      - name: Build example project
+        id: build
+        uses: ./.github/actions/build-example
+        with:
+          src-dir: 'examples/${{ matrix.example }}'
+          toolset: '${{ matrix.toolset }}'
+          platform: '${{ matrix.platform }}'
+          configuration: '${{ matrix.configuration }}'
+
+      - name: Verify runtime library linkage
+        uses: ./.github/actions/check-runtime-library
+        with:
+          path: '${{ steps.build.outputs.install-dir }}'
+
+      - name: Verify architecture
+        uses: ./.github/actions/check-arch
+        with:
+          path: '${{ steps.build.outputs.install-dir }}'
+          expected: '${{ matrix.platform }}'
+
+      - name: Run example project
+        uses: ./.github/actions/run-example
+        with:
+          path: '${{ steps.build.outputs.install-dir }}'
+
+      - name: Check symbols
+        uses: ./.github/actions/check-symbols
+        with:
+          path: '${{ steps.build.outputs.install-dir }}'
+          expected: '${{ toJson(matrix.symbols) }}'
+        if: env.CI_TARGET_ELF