Speed up Docker container preparation (#107)

* Use a Dockerfile so CentOS configuration is cachable

* Use docker/build-push-action for caching

Author: jameysharp

.github/actions/binary-compatible-builds/action.yml

@@ -2,5 +2,54 @@ name: 'Set up a CentOS 6 container to build releases in'
 description: 'Set up a CentOS 6 container to build releases in'
 
 runs:
-  using: node12
-  main: 'main.js'
+  using: "composite"
+  steps:
+    # On OSX all we need to do is configure our deployment target as old as
+    # possible. For now 10.9 is the limit.
+    - if: runner.os == 'macOS'
+      shell: bash
+      run: |
+        cat >> $GITHUB_ENV <<EOF
+        MACOSX_DEPLOYMENT_TARGET=10.9
+        python=python3
+        EOF
+
+    # On Windows we build against the static CRT to reduce dll dependencies
+    - if: runner.os == 'Windows'
+      shell: bash
+      run: |
+        cat >> $GITHUB_ENV <<EOF
+        RUSTFLAGS=-Ctarget-feature=+crt-static
+        python=python
+        EOF
+
+    # ... and on Linux we do fancy things with containers. We'll spawn an old
+    # CentOS container in the background with a super old glibc, and then we'll run
+    # commands in there with the `$CENTOS` env var.
+    - name: Set up Docker Buildx
+      if: runner.os == 'Linux'
+      uses: docker/setup-buildx-action@v2
+
+    - name: Build old Linux container
+      if: runner.os == 'Linux'
+      uses: docker/build-push-action@v3
+      with:
+        context: ${{ github.action_path }}/docker
+        load: true
+        tags: binary-compatible-builds
+        cache-from: type=gha
+        cache-to: type=gha,mode=max
+
+    - if: runner.os == 'Linux'
+      shell: bash
+      run: |
+        # FIXME(rust-lang/rust#80703) LD_LIBRARY_PATH shouldn't be necessary
+        docker run -di --name centos -v $PWD:$PWD -v $(rustc --print sysroot):/rust:ro \
+          --env LD_LIBRARY_PATH=/rust/lib \
+          --env PATH="/opt/rh/devtoolset-8/root/usr/bin:$PATH:/rust/bin" \
+          binary-compatible-builds
+
+        cat >> $GITHUB_ENV <<EOF
+        CENTOS=$GITHUB_ACTION_PATH/run-linux
+        python=python3
+        EOF

.github/actions/binary-compatible-builds/docker/Dockerfile

@@ -0,0 +1,10 @@
+FROM centos:7
+
+# See https://edwards.sdsu.edu/research/c11-on-centos-6/ for where these
+RUN yum install -y centos-release-scl cmake xz epel-release python3 unzip git
+RUN yum install -y patchelf devtoolset-8-gcc devtoolset-8-binutils devtoolset-8-gcc-c++
+
+# Delete `libstdc++.so` to force gcc to link against `libstdc++.a` instead.
+# This is a hack and not the right way to do this, but it ends up doing the
+# right thing for now.
+RUN rm -f /opt/rh/devtoolset-8/root/usr/lib/gcc/x86_64-redhat-linux/8/libstdc++.so

.github/actions/binary-compatible-builds/main.js

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec docker exec --env PREBUILT_ENGINE=${PREBUILT_ENGINE:-} -w $PWD -i centos "$@"