scripts/build-nuitka.sh: generate single-file binary using nuitka, fixes #3227

Very experimental and little tested.

scripts/build-nuitka.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# Generate a single-file binary of borgbackup using Nuitka.
+
+set -euo pipefail
+
+OUTPUT_DIR="build"
+OUTPUT_FILENAME="borg-nuitka.exe"  # .exe does NOT mean windows here
+SRC_DIR="src/borg"
+
+echo "============================================"
+echo "Found Nuitka $(python -m nuitka --version | head -n 1)."
+echo "Building single-file binary of borgbackup..."
+echo "============================================"
+
+# Run Nuitka compilation
+# We use --assume-yes-for-downloads to avoid interactive prompts in automated runs.
+# We set PYTHONPATH=src to ensure the local version of borg is used.
+# We include cffi and _cffi_backend to avoid runtime ModuleNotFoundError in argon2-cffi.
+PYTHONPATH=src python -m nuitka \
+    --standalone \
+    --onefile \
+    --assume-yes-for-downloads \
+    --include-package=borg \
+    --include-package=borghash \
+    --include-package=borgstore \
+    --include-package=cffi \
+    --include-module=_cffi_backend \
+    --output-dir="$OUTPUT_DIR" \
+    --output-filename="$OUTPUT_FILENAME" \
+    "$SRC_DIR"
+
+echo "============================================="
+echo "Build completed successfully!"
+echo "Single-file binary generated at:"
+echo "  $OUTPUT_DIR/$OUTPUT_FILENAME"
+echo "============================================="