ci: Upload artifacts created by libc-test

This gives us something easier to inspect 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: ./ci/create-artifacts.py
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ${{ env.ARCHIVE_NAME }}-${{ matrix.target }}
+          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: ./ci/create-artifacts.py
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ${{ env.ARCHIVE_NAME }}-${{ matrix.target }}
+          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 +1,64 @@
+#!/usr/bin/env python3
+"""Create a tarball of intermediate output for inspection if tests fail.
+
+This is useful for seeing what exactly `ctest` is running.
+"""
+
+import os
+import subprocess as sp
+import sys
+
+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
+    print(f"Located build directory '{build_dir}'")
+
+    # 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__":
+    # FIXME(ci): remove after the bump to windoes-2025 GHA images
+    # Python <= 3.9 does not support the very helpful `root_dir` argument,
+    # and that is the version used by the Windows GHA images. Rather than
+    # using setup-python or doing something in the CI script, just find
+    # the newer version and relaunch if this happens to be run with an old
+    # version.
+    try:
+        glob("", root_dir="")
+    except TypeError:
+        if os.environ.get("CI") is None:
+            sys.exit(1)
+
+        # Find the next 3.1x Python version
+        dirs = sorted(list(Path(r"C:\hostedtoolcache\windows\Python").iterdir()))
+        usepy = next(x for x in dirs if r"\3.1" in str(x))
+        py = usepy.joinpath(r"x64\python.exe")
+        print(f"relaunching with {py}")
+        os.execvp(py, [__file__] + sys.argv)
+
+    main()