ci: Upload artifacts created by libc-test

This gives us something that is easier to look at when the automatically
generated tests fail.

.github/workflows/ci.yaml

@@ -81,13 +81,23 @@ jobs:
       - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: ./ci/install-rust.sh
+
       - name: Run natively
         if: "!matrix.docker"
         run: ./ci/run.sh ${{ matrix.target }}
       - name: Run in Docker
         if: "matrix.docker"
         run: ./ci/run-docker.sh ${{ matrix.target }}
 
+      - name: Create CI artifacts
+        if: always()
+        run: ./ci/create-artifacts.sh
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ${{ env.ARCHIVE_NAME }}
+          path: ${{ env.ARCHIVE_PATH }}
+          retention-days: 5
+
   test_tier2:
     name: Test tier2
     needs: [test_tier1, style_check]
@@ -132,9 +142,19 @@ jobs:
       - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: ./ci/install-rust.sh
+
       - name: Execute run-docker.sh
         run: ./ci/run-docker.sh ${{ matrix.target }}
 
+      - name: Create CI artifacts
+        if: always()
+        run: ./ci/create-artifacts.sh
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ${{ env.ARCHIVE_NAME }}
+          path: ${{ env.ARCHIVE_PATH }}
+          retention-days: 5
+
   test_tier2_vm:
     name: Test tier2 VM
     needs: [test_tier1, style_check]

ci/create-artifacts.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+set -eux
+
+# Create a tarball of intermediate output for inspection if tests fail.
+
+# Find the most recently touched file named "main.c" in the target directory.
+# This will be libc-tests's `OUT_DIR`
+out_dir="$(
+    find target -name 'main.c' -exec ls -t {} + |
+        head -n1 |
+        xargs dirname
+)"
+
+out_name="archive-$(date -u -Iseconds | sed 's/://g')"
+(cd "$out_dir" && find -E . -regex '.*\.(rs|c)')") > file_list.txt
+
+tar -czvf "${out_name}.tar.gz" -C "$out_dir" -T file_list.txt
+
+if [ -n "$CI" ]; then
+    echo "ARCHIVE_NAME=${out_name}" >> "$GITHUB_ENV"
+    echo "ARCHIVE_PATH=${out_name}.tar.gz" >> "$GITHUB_ENV"
+fi