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

@@ -96,13 +96,23 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           key: ${{ matrix.target }}
+
       - 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: python3.12 ci/create-artifacts.py
+      - 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]
@@ -150,9 +160,19 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           key: ${{ matrix.target }}
+
       - name: Execute run-docker.sh
         run: ./ci/run-docker.sh ${{ matrix.target }}
 
+      - name: Create CI artifacts
+        if: always()
+        run: python3.12 ci/create-artifacts.py
+      - 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.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Create a tarball of intermediate output for inspection if tests fail."""
+
+import os
+import subprocess as sp
+
+from datetime import datetime, timezone
+from glob import glob
+from pathlib import Path
+
+
+def main():
+    # Find the most recently touched file named "main.c" in the target
+    # directory. This will be libc-tests's `OUT_DIR`
+    marker_files = [Path(p) for p in glob("target/**/main.c", recursive=True)]
+    marker_files.sort(key=lambda path: path.stat().st_mtime)
+    build_dir = marker_files[0].parent
+
+    # Collect all relevant Rust and C files
+    add_files = glob("**/*.rs", recursive=True, root_dir=build_dir)
+    add_files += glob("**/*.c", recursive=True, root_dir=build_dir)
+    file_list = "\n".join(add_files).encode()
+
+    now = datetime.now(timezone.utc).strftime("%Y-%m-%dT%H%MZ")
+    archive_name = f"archive-{now}"
+    archive_path = f"{archive_name}.tar.gz"
+
+    sp.run(["tar", "czvf", archive_path, "-C", build_dir, "-T-"], input=file_list)
+
+    # If we are in GHA, set these env vars for future use
+    gh_env = os.getenv("GITHUB_ENV")
+    if gh_env is not None:
+        print("Updating CI environment")
+        with open(gh_env, "w+") as f:
+            f.write(f"ARCHIVE_NAME={archive_name}\n")
+            f.write(f"ARCHIVE_PATH={archive_path}\n")
+
+
+if __name__ == "__main__":
+    main()