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  TODO: .ci/Makefile is obsolete now, as well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, 143 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'