Compile with clang by default

This should speed up template compilation times and improve
#275.

This also ensures that clang is used on all platforms. Before this PR,
our CI servers were building with gcc.

.bazelrc

@@ -6,21 +6,20 @@ build --enable_platform_specific_config
 # Verbose failure logs when something goes wrong.
 build --verbose_failures
 
+# Build with clang (rather than the default of gcc) since clang compiles
+# templates faster and produces better error messages.
+build --repo_env=CC=clang
+
 # Use Clang as a default compiler on Windows.
-# TODO: use Clang as a default compiler on every platform.
+# TODO(xander): Does repo_env above cover the windows case?
 build:windows --compiler="clang-cl"
 
-# Compiler options.
-build:gcc --action_env=CC=gcc
-build:clang --action_env=CC=clang
+# Make it easy to use gcc.
+build:gcc --repo_env=CC=gcc
 
 # Build eventuals in C++17 mode.
-build:linux --cxxopt=-std=c++17
-build:linux --host_cxxopt=-std=c++17
-build:macos --cxxopt=-std=c++17
-build:macos --host_cxxopt=-std=c++17
-build:windows --cxxopt=/std:c++17
-build:windows --host_cxxopt=/std:c++17
+build --cxxopt=-std=c++17
+build --host_cxxopt=-std=c++17
 
 # On Windows, `__cplusplus` is wrongly defined without this switch.
 # See https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/

.github/workflows/build_and_test.yml

@@ -90,6 +90,28 @@ jobs:
         if: ${{ matrix.bazel-command == 'dazel' }}
         run: ${{ matrix.sudo-command }} pip3 install dazel
 
+      # Stop any running Dazel instances, so that any volume mounts for the
+      # caches removed above don't stick around. Volume mounts for nonexistent
+      # directories cause build failures.
+      #
+      # Note that after a clean reboot this may print an error saying that
+      # `docker stop` was given no arguments, as there were no containers running
+      # at the time: that's ok, so pipe errors to /dev/null.
+      - name: Stop Dazel instances
+        if: ${{ matrix.bazel-command == 'dazel' }}
+        run: |
+          docker ps --filter name="dazel/*" --filter status=running -aq \
+            | xargs docker stop 2> /dev/null \
+            || true
+
+      # Clean up any artifacts from previous builds to ensure that we aren't
+      # mixing state across novel and old builds. This is especially important
+      # if new builds use different compiler settings than old builds.
+      - name: Remove Dazel cache
+        if: ${{ matrix.bazel-command == 'dazel' }}
+        run: |
+          sudo rm -rf ~/.cache/dazel
+
       # Invoke 'dazel version' in order to build the Docker container
       # as a separate step so we can track how long it takes and
       # optimize as necessary.
@@ -108,6 +130,13 @@ jobs:
            --google_credentials=${{ env.GOOGLE_APPLICATION_CREDENTIALS }}" \
            >> $GITHUB_ENV
 
+      # Clean up any artifacts from previous builds to ensure that we aren't
+      # mixing state across novel and old builds. This is especially important
+      # if new builds use different compiler settings than old builds.
+      - name: Clean
+        run: |
+          bazelisk clean --expunge
+
       - name: Build
         run: |
           ${{ matrix.bazel-command }} \
@@ -116,7 +145,6 @@ jobs:
             ${{ matrix.bazel-config }} \
             ${{ env.BAZEL_REMOTE_CACHE }} \
             --verbose_failures \
-            --spawn_strategy=local \
             -c dbg \
             --strip="never" \
             ...
@@ -130,7 +158,6 @@ jobs:
             --experimental_ui_max_stdouterr_bytes=-1 \
             ${{ env.BAZEL_REMOTE_CACHE }} \
             --verbose_failures \
-            --spawn_strategy=local \
             -c dbg \
             --strip="never" \
             --test_output=errors \

eventuals/just.h

@@ -2,6 +2,11 @@
 
 #include "eventuals/eventual.h"
 
+// DO NOT SUBMIT !
+#ifndef __clang__
+#error "Should be compiled using clang!"
+#endif
+
 ////////////////////////////////////////////////////////////////////////
 
 namespace eventuals {