refactor(godbolt): rewrite wrapper as a stand-alone rust binary with integration test

Author: g-ampo

contrib/godbolt/README.md

@@ -9,8 +9,8 @@ Rust GPU kernel code and see the resulting PTX assembly.
 Compiler Explorer expects a single "compiler" binary that reads source on
 stdin or from a file and writes assembly to stdout.  Since rust-cuda has no
 standalone compiler (the pipeline is `rustc` with a custom codegen backend
-plus `cargo` for dependency resolution), the integration uses a wrapper
-script that:
+plus `cargo` for dependency resolution), the integration uses a small Rust
+wrapper binary that:
 
 1. Accepts a `.rs` file containing `#[kernel]` functions.
 2. Creates a temporary Cargo project that depends on `cuda_std`.
@@ -25,10 +25,10 @@ script that:
 
 | File | Purpose |
 |------|---------|
-| `rust-cuda-wrapper.sh` | The wrapper script CE invokes as the "compiler" |
+| `rust-cuda-wrapper/` | Rust crate for the wrapper binary CE invokes as the "compiler" |
 | `rust-cuda.defaults.properties` | CE configuration (compiler type, flags, defaults) |
 | `rust-cuda.amazon.properties` | CE instance-specific overrides for the AWS fleet |
-| `install.sh` | Installs the pinned nightly, builds the codegen backend, and lays out the prefix |
+| `install.sh` | Installs the pinned nightly, builds the codegen backend and the wrapper, and lays out the prefix |
 | `test-kernel.rs` | Sample kernel with shared memory and thread indexing |
 
 ## Supported flags
@@ -61,7 +61,7 @@ export CUDA_PATH=/usr/local/cuda
 ./contrib/godbolt/install.sh
 
 # Then test:
-./contrib/godbolt/rust-cuda-wrapper.sh contrib/godbolt/test-kernel.rs
+$RUST_CUDA_ROOT/bin/rust-cuda-wrapper contrib/godbolt/test-kernel.rs
 ```
 
 You should see PTX assembly printed to stdout.
@@ -73,8 +73,21 @@ point the wrapper at the repo tree directly:
 
 ```bash
 export RUST_CUDA_ROOT=/path/to/rust-cuda
-# Ensure lib/librustc_codegen_nvvm.so exists at that path, or adjust
-# CODEGEN_SO in the script.
+# Ensure $RUST_CUDA_ROOT/lib/librustc_codegen_nvvm.so exists.
+
+cd contrib/godbolt/rust-cuda-wrapper
+cargo run --release -- ../test-kernel.rs
+```
+
+### Running the integration test
+
+The wrapper crate ships a smoke test that compiles `test-kernel.rs`
+end-to-end and asserts the output looks like PTX:
+
+```bash
+cd contrib/godbolt/rust-cuda-wrapper
+cargo test                                       # skips without RUST_CUDA_ROOT
+RUST_CUDA_ROOT=/path/to/rust-cuda cargo test     # runs the real build
 ```
 
 ## Submitting to Compiler Explorer

contrib/godbolt/install.sh

@@ -104,9 +104,14 @@ done
 # important so dependency resolution is reproducible).
 cp "${REPO_DIR}/Cargo.lock" "${INSTALL_PREFIX}/" 2>/dev/null || true
 
-# The wrapper script.
-cp "${REPO_DIR}/contrib/godbolt/rust-cuda-wrapper.sh" "${INSTALL_PREFIX}/bin/"
-chmod +x "${INSTALL_PREFIX}/bin/rust-cuda-wrapper.sh"
+# Build and install the wrapper binary.
+(
+    cd "${REPO_DIR}/contrib/godbolt/rust-cuda-wrapper"
+    cargo build --release
+)
+cp "${REPO_DIR}/contrib/godbolt/rust-cuda-wrapper/target/release/rust-cuda-wrapper" \
+    "${INSTALL_PREFIX}/bin/"
+chmod +x "${INSTALL_PREFIX}/bin/rust-cuda-wrapper"
 
 # Version marker.
 echo "${NIGHTLY}" > "${INSTALL_PREFIX}/rust-toolchain-version"
@@ -121,4 +126,4 @@ echo "==> Installation complete."
 echo ""
 echo "Test with:"
 echo "  RUST_CUDA_ROOT=${INSTALL_PREFIX} CUDA_PATH=${CUDA_PATH} \\"
-echo "    ${INSTALL_PREFIX}/bin/rust-cuda-wrapper.sh contrib/godbolt/test-kernel.rs"
+echo "    ${INSTALL_PREFIX}/bin/rust-cuda-wrapper contrib/godbolt/test-kernel.rs"

contrib/godbolt/rust-cuda-wrapper.sh

@@ -0,0 +1 @@
+/target