feat(hugr-py): Allow linking packages and modules from Python

hugr-core/src/hugr.rs

@@ -166,6 +166,24 @@ impl Hugr {
         }
     }
 
+    /// Read a HUGR from an Envelope, and return the enclosed extensions.
+    ///
+    /// To load a HUGR, all the extensions used in its definition must be
+    /// available. The Envelope may include some of the extensions, but any
+    /// additional extensions must be provided in the `extensions` parameter. If
+    /// `extensions` is `None`, the default [`crate::std_extensions::STD_REG`]
+    /// is used.
+    pub fn load_with_exts(
+        reader: impl io::BufRead,
+        extensions: Option<&ExtensionRegistry>,
+    ) -> Result<(Self, ExtensionRegistry), ReadError> {
+        let pkg = Package::load(reader, extensions)?;
+        match pkg.modules.into_iter().exactly_one() {
+            Ok(hugr) => Ok((hugr, pkg.extensions)),
+            Err(e) => Err(ReadError::ExpectedSingleHugr { count: e.count() }),
+        }
+    }
+
     /// Read a HUGR from an Envelope encoded in a string.
     ///
     /// Note that not all Envelopes are valid strings. In the general case,

hugr-py/rust/lib.rs

@@ -1,5 +1,6 @@
 //! Supporting Rust library for the hugr Python bindings.
 
+mod linking;
 mod metadata;
 mod model;
 mod zstd_util;
@@ -8,6 +9,8 @@ use pyo3::pymodule;
 
 #[pymodule]
 mod _hugr {
+    #[pymodule_export]
+    use super::linking::linking;
     #[pymodule_export]
     use super::metadata::metadata;
     #[pymodule_export]

hugr-py/rust/linking.rs

@@ -0,0 +1,76 @@
+//! Bindings for linking utilities defined in the hugr-core crate
+
+use pyo3::exceptions::PyException;
+use pyo3::{create_exception, pymodule};
+
+#[pymodule(submodule)]
+#[pyo3(module = "hugr._hugr.linking")]
+pub mod linking {
+    use hugr_core::envelope::EnvelopeConfig;
+    use hugr_core::hugr::hugrmut::HugrMut;
+    use hugr_core::hugr::linking::{HugrLinking, NameLinkingPolicy};
+    use hugr_core::{Hugr, HugrView};
+    use pyo3::exceptions::PyValueError;
+    use pyo3::types::{PyAnyMethods, PyModule};
+    use pyo3::{Bound, PyResult, Python, pyfunction};
+
+    /// Hack: workaround for <https://github.com/PyO3/pyo3/issues/759>
+    #[pymodule_init]
+    fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
+        Python::attach(|py| {
+            py.import("sys")?
+                .getattr("modules")?
+                .set_item("hugr._hugr.linking", m)
+        })
+    }
+
+    #[pyfunction]
+    fn link_modules(module_into: &[u8], module_from: &[u8]) -> PyResult<Vec<u8>> {
+        let (mut hugr_into, mut exts_into) =
+            Hugr::load_with_exts(module_into, None).map_err(|err| {
+                PyValueError::new_err(format!("Loading of first envelope failed: {}", err))
+            })?;
+        let (hugr_from, exts_from) = Hugr::load_with_exts(module_from, None).map_err(|err| {
+            PyValueError::new_err(format!("Loading of second envelope failed: {}", err))
+        })?;
+        let into_executable = hugr_into.entrypoint() != hugr_into.module_root();
+        let from_executable = hugr_from.entrypoint() != hugr_from.module_root();
+        let replacement_entrypoint = if into_executable && from_executable {
+            return Err(PyValueError::new_err(
+                "Cannot link two executable modules together.",
+            ));
+        } else if !into_executable && from_executable {
+            Some(hugr_from.entrypoint())
+        } else {
+            None
+        };
+
+        let forest = hugr_into
+            .link_module(hugr_from, &NameLinkingPolicy::default())
+            .map_err(|err| super::HugrLinkingError::new_err(err.to_string()))?;
+        if let Some(new_entrypoint) = replacement_entrypoint {
+            let Some(node) = forest.node_map.get(&new_entrypoint) else {
+                panic!("Entrypoint is to be replaced but was not found after linking");
+            };
+            hugr_into.set_entrypoint(*node);
+        }
+        exts_into.extend(exts_from);
+
+        let mut result = Vec::new();
+        hugr_into
+            .store_with_exts(&mut result, EnvelopeConfig::binary(), &exts_into)
+            .unwrap();
+
+        hugr_core::package::Package::load(&result[..], None)
+            .map_err(|err| PyValueError::new_err(format!("Roundtrip failed: {:?}", err)))?;
+
+        Ok(result)
+    }
+}
+
+create_exception!(
+    _hugr.linking,
+    HugrLinkingError,
+    PyException,
+    "Base exception for HUGR linking errors."
+);

hugr-py/src/hugr/_hugr/linking.pyi

@@ -0,0 +1,3 @@
+class HugrLinkingError(Exception): ...
+
+def link_modules(module_into: bytes, module_from: bytes) -> bytes: ...

hugr-py/src/hugr/package.py

@@ -10,6 +10,7 @@
 import hugr._serialization.extension as ext_s
 import hugr.model as model
 from hugr import ext
+from hugr._hugr.linking import link_modules
 from hugr.envelope import (
     EnvelopeConfig,
     _make_envelope,
@@ -188,6 +189,34 @@ def used_extensions(
 
         return result
 
+    def link(self, *other: Package):
+        """Link this package with other packages, returning a new package containing the
+        extensions of all packages, as well as a single module created from linking the
+        modules from all packages.
+
+        Args:
+            *other: Other packages to link with.
+
+        Returns:
+            A new package containing the modules and extensions of all packages.
+        """
+        modules = self.modules[:]
+        extensions = self.extensions[:]
+        for pkg in other:
+            modules.extend(pkg.modules)
+            for new_ext in pkg.extensions:
+                if new_ext not in extensions:
+                    extensions.append(new_ext)
+
+        if len(modules) == 0:
+            return Package([], extensions)
+
+        result_module_bytes = modules[0].to_bytes()
+        for module in modules[1:]:
+            result_module_bytes = link_modules(result_module_bytes, module.to_bytes())
+
+        return Package([Hugr.from_bytes(result_module_bytes)], extensions)
+
 
 @dataclass(frozen=True)
 class PackagePointer:

hugr-py/tests/test_linking.py

@@ -0,0 +1,103 @@
+import pytest
+
+from hugr import Hugr, tys
+from hugr._hugr.linking import link_modules
+from hugr.build import Module
+from hugr.ops import FuncDefn
+from hugr.package import Package
+from hugr.std import float, int, logic, ptr
+
+
+def build_module(*, entrypoint: bool) -> Hugr:
+    builder = Module()
+    if entrypoint:
+        main = builder.define_function(
+            "main", input_types=[tys.Bool], output_types=[tys.Bool], visibility="Public"
+        )
+        main.set_outputs(*main.inputs())
+        builder.hugr.entrypoint = main.parent_node
+
+    return builder.hugr
+
+
+def test_link_modules_no_entrypoints():
+    hugr1 = build_module(entrypoint=False)
+    hugr2 = build_module(entrypoint=False)
+
+    linked = Hugr.from_bytes(link_modules(hugr1.to_bytes(), hugr2.to_bytes()))
+    assert linked.entrypoint == linked.module_root
+
+
+def test_link_modules_entrypoint_lhs():
+    hugr1 = build_module(entrypoint=True)
+    hugr2 = build_module(entrypoint=False)
+
+    linked = Hugr.from_bytes(link_modules(hugr1.to_bytes(), hugr2.to_bytes()))
+    assert linked.entrypoint != linked.module_root
+    entrypoint = linked.entrypoint_op()
+    assert isinstance(entrypoint, FuncDefn)
+    assert entrypoint.f_name == "main"
+
+
+def test_link_modules_entrypoint_rhs():
+    hugr1 = build_module(entrypoint=False)
+    hugr2 = build_module(entrypoint=True)
+
+    linked = Hugr.from_bytes(link_modules(hugr1.to_bytes(), hugr2.to_bytes()))
+    assert linked.entrypoint != linked.module_root
+    entrypoint = linked.entrypoint_op()
+    assert isinstance(entrypoint, FuncDefn)
+    assert entrypoint.f_name == "main"
+
+
+def test_link_modules_multiple_entrypoints():
+    hugr1 = build_module(entrypoint=True)
+    hugr2 = build_module(entrypoint=True)
+
+    with pytest.raises(ValueError, match="Cannot link two executable modules together"):
+        link_modules(hugr1.to_bytes(), hugr2.to_bytes())
+
+
+def test_link_packages_no_modules():
+    pkg1 = Package(modules=[])
+    pkg2 = Package(modules=[])
+
+    result_pkg = pkg1.link(pkg2)
+
+    assert result_pkg.modules == []
+
+
+def test_link_packages_extensions():
+    pkg1 = Package(
+        modules=[build_module(entrypoint=False)],
+        extensions=[
+            int.CONVERSIONS_EXTENSION,
+            int.INT_TYPES_EXTENSION,
+            int.INT_OPS_EXTENSION,
+            # Shared
+            logic.EXTENSION,
+            ptr.EXTENSION,
+        ],
+    )
+    pkg2 = Package(
+        modules=[build_module(entrypoint=False)],
+        extensions=[
+            float.FLOAT_OPS_EXTENSION,
+            float.FLOAT_TYPES_EXTENSION,
+            # Shared
+            logic.EXTENSION,
+            ptr.EXTENSION,
+        ],
+    )
+
+    result_pkg = pkg1.link(pkg2)
+
+    assert result_pkg.extensions == [
+        int.CONVERSIONS_EXTENSION,
+        int.INT_TYPES_EXTENSION,
+        int.INT_OPS_EXTENSION,
+        logic.EXTENSION,
+        ptr.EXTENSION,
+        float.FLOAT_OPS_EXTENSION,
+        float.FLOAT_TYPES_EXTENSION,
+    ]