Add compile-time RustPython backend with centralized backend dispatch

.github/workflows/benches.yml

@@ -40,9 +40,14 @@ jobs:
         with:
           tool: cargo-codspeed
 
-      - name: Run the benchmarks
+      - name: Run the benchmarks with CodSpeed upload
+        if: ${{ github.repository == 'PyO3/pyo3' }}
         uses: CodSpeedHQ/action@v4
         with:
           run: uvx nox -s codspeed
           token: ${{ secrets.CODSPEED_TOKEN }}
           mode: simulation
+
+      - name: Run the benchmarks without upload
+        if: ${{ github.repository != 'PyO3/pyo3' }}
+        run: uvx nox -s codspeed

Cargo.toml

@@ -85,7 +85,7 @@ parking_lot = { version = "0.12.3", features = ["arc_lock"] }
 pyo3-build-config = { path = "pyo3-build-config", version = "=0.28.3", features = ["resolve-config"] }
 
 [features]
-default = ["macros"]
+default = ["macros", "runtime-cpython"]
 
 # Enables support for `async fn` for `#[pyfunction]` and `#[pymethods]`.
 experimental-async = ["macros", "pyo3-macros/experimental-async"]
@@ -97,6 +97,13 @@ experimental-inspect = ["pyo3-macros/experimental-inspect"]
 # Enables macros: #[pyclass], #[pymodule], #[pyfunction] etc.
 macros = ["pyo3-macros"]
 
+# Select the experimental RustPython runtime backend.
+runtime-rustpython = ["pyo3-ffi/runtime-rustpython", "pyo3-build-config/runtime-rustpython"]
+
+# Select the reference CPython-family runtime backend.
+# This path remains responsible for existing CPython, PyPy, and GraalPy support.
+runtime-cpython = []
+
 # Enables multiple #[pymethods] per #[pyclass]
 multiple-pymethods = ["inventory", "pyo3-macros/multiple-pymethods"]
 
@@ -175,6 +182,7 @@ full = [
 
 [workspace]
 members = [
+    "xtask",
     "pyo3-ffi",
     "pyo3-build-config",
     "pyo3-macros",

README.md

@@ -281,5 +281,3 @@ PyO3 is licensed under the [Apache-2.0 license](LICENSE-APACHE) or the [MIT lice
 Python is licensed under the [Python License](https://docs.python.org/3/license.html).
 
 Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in PyO3 by you, as defined in the Apache License, shall be dual-licensed as above, without any additional terms or conditions.
-
-[![Deploys by Netlify](https://www.netlify.com/assets/badges/netlify-badge-color-accent.svg)](https://www.netlify.com)

build.rs

@@ -51,6 +51,11 @@ fn configure_pyo3() -> Result<()> {
 
 fn main() {
     pyo3_build_config::print_expected_cfgs();
+    if cargo_env_var("CARGO_FEATURE_RUNTIME_RUSTPYTHON").is_some() {
+        println!("cargo:rustc-cfg=PyRustPython");
+        print_feature_cfgs();
+        return;
+    }
     if let Err(e) = configure_pyo3() {
         eprintln!("error: {}", e.report());
         std::process::exit(1)

newsfragments/5986.added.md

@@ -0,0 +1 @@
+Add a compile-time RustPython backend with centralized backend dispatch.

noxfile.py

@@ -472,6 +472,10 @@ def test_cross_compilation_windows(session: nox.Session):
     env = os.environ.copy()
     env["XWIN_ARCH"] = "x86_64"
 
+    # The GNU cross-compilation lane uses plain `cargo build`, so the Rust
+    # standard library for that target must be installed explicitly.
+    _run(session, "rustup", "target", "add", "x86_64-pc-windows-gnu")
+
     # abi3
     _run_cargo(
         session,
@@ -544,6 +548,8 @@ def docs(session: nox.Session, nightly: bool = False, internal: bool = False) ->
         rustdoc_flags.append("--cfg docsrs")
         toolchain_flags.append("+nightly")
         cargo_flags.extend(["-Z", "unstable-options", "-Z", "rustdoc-scrape-examples"])
+    else:
+        toolchain_flags.append("+stable")
 
     if internal:
         rustdoc_flags.append("--Z unstable-options")

proptest-regressions/conversions/std/num.txt

@@ -0,0 +1,7 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc 1faf170d32151a6cc954f574a6081472e069907c79f8f59b877fec806b993866 # shrinks to x = 9223372036854775808

pyo3-build-config/Cargo.toml

@@ -24,6 +24,9 @@ default = []
 # script. If this feature isn't enabled, the build script no-ops.
 resolve-config = []
 
+# Skip libpython/interpreter discovery and emit RustPython-specific cfgs.
+runtime-rustpython = []
+
 # deprecated
 extension-module = []
 

pyo3-build-config/build.rs

@@ -47,6 +47,13 @@ fn generate_build_configs() -> Result<()> {
 }
 
 fn main() {
+    if std::env::var("CARGO_FEATURE_RUNTIME_RUSTPYTHON").is_ok() {
+        let _ = configure(None, "pyo3-build-config-file.txt");
+        let _ = configure(None, "pyo3-build-config.txt");
+        println!("cargo:rustc-cfg=PyRustPython");
+        return;
+    }
+
     if std::env::var("CARGO_FEATURE_RESOLVE_CONFIG").is_ok() {
         if let Err(e) = generate_build_configs() {
             eprintln!("error: {}", e.report());

pyo3-build-config/src/lib.rs

@@ -39,6 +39,10 @@ use target_lexicon::OperatingSystem;
 /// | `#[cfg(PyPy)]` | This marks code which is run when compiling for PyPy. |
 /// | `#[cfg(GraalPy)]` | This marks code which is run when compiling for GraalPy. |
 ///
+/// These runtime distinctions remain part of the reference CPython-family backend in the
+/// frontend/backend split. They are existing compatibility constraints, not a separate first
+/// backend implementation.
+///
 /// For examples of how to use these attributes,
 #[doc = concat!("[see PyO3's guide](https://pyo3.rs/v", env!("CARGO_PKG_VERSION"), "/building-and-distribution/multiple_python_versions.html)")]
 /// .
@@ -261,6 +265,7 @@ pub fn print_expected_cfgs() {
     println!("cargo:rustc-check-cfg=cfg(Py_GIL_DISABLED)");
     println!("cargo:rustc-check-cfg=cfg(PyPy)");
     println!("cargo:rustc-check-cfg=cfg(GraalPy)");
+    println!("cargo:rustc-check-cfg=cfg(PyRustPython)");
     println!("cargo:rustc-check-cfg=cfg(py_sys_config, values(\"Py_DEBUG\", \"Py_REF_DEBUG\", \"Py_TRACE_REFS\", \"COUNT_ALLOCS\"))");
     println!("cargo:rustc-check-cfg=cfg(pyo3_disable_reference_pool)");
     println!("cargo:rustc-check-cfg=cfg(pyo3_leak_on_drop_without_reference_pool)");

pyo3-ffi/Cargo.toml

@@ -14,11 +14,20 @@ rust-version.workspace = true
 
 [dependencies]
 libc = "0.2.62"
+rustpython = { git = "https://github.com/RustPython/RustPython", rev = "b80c2bd5ecedacc23a04c28e5f6dcb82b5616e88", optional = true }
+rustpython-vm = { git = "https://github.com/RustPython/RustPython", rev = "b80c2bd5ecedacc23a04c28e5f6dcb82b5616e88", optional = true }
 
 [features]
 
 default = []
 
+# Build the ffi crate without libpython discovery/linking for the RustPython backend.
+runtime-rustpython = [
+    "dep:rustpython",
+    "dep:rustpython-vm",
+    "pyo3-build-config/runtime-rustpython",
+]
+
 # deprecated
 extension-module = ["pyo3-build-config/extension-module"]
 

pyo3-ffi/build.rs

@@ -264,6 +264,11 @@ fn print_config_and_exit(config: &InterpreterConfig) {
 
 fn main() {
     pyo3_build_config::print_expected_cfgs();
+    if std::env::var("CARGO_FEATURE_RUNTIME_RUSTPYTHON").is_ok() {
+        println!("cargo:rustc-cfg=PyRustPython");
+        print_feature_cfgs();
+        return;
+    }
     if let Err(e) = configure_pyo3() {
         eprintln!("error: {}", e.report());
         std::process::exit(1)