Vendor generated-files handling from setuptools-rust

We need PyO3/setuptools-rust#574 (or something
akin to it) to handle the movement of the generated files from the build
script to the output. This is not yet ready for merge, and is highly
unlikely to be ready in time for the Qiskit 2.4.0 release (or at least
2.4.0rc1), so to avoid blocking ourselves, we vendor in a
monkey-patching reimplementation of the code temporarily.

The allowed range of `setuptools-rust` is _probably_ larger than the
hard pin, but the monkey-patch is so invasive and v1.12.0 is
sufficiently old (August 2025) that it's not worth the risk.

There are no meaningful licensing concerns since the vendored code here
was entirely written by me both here and in the `setuptools-rust` patch;
there is no cross-contamination from that repository and no code
inclusion from it.

This commit should be reverted as soon as we can swap to a safe released
version of `setuptools-rust`.

Author: jakelishman

pyproject.toml

@@ -2,7 +2,7 @@
 # This is duplicated as `dependency-groups.build` for convenience.
 requires = [
     "setuptools>=77.0",
-    "setuptools-rust",
+    "setuptools-rust==1.12.0",
 ]
 build-backend = "setuptools.build_meta"
 
@@ -184,7 +184,7 @@ default = "qiskit.transpiler.preset_passmanagers.builtin_plugins:DefaultScheduli
 # process.  If you intended that, use `project.optional-dependencies` instead.
 [dependency-groups]
 # Sync with `build-system.requires`.
-build = ["setuptools>=77.0", "setuptools-rust"]
+build = ["setuptools>=77.0", "setuptools-rust==1.12.0"]
 # We use quite tight pins on pylint and astroid because they have a habit of adding new
 # on-by-default lints that are harder to deal with.
 lint = [

setup.py

@@ -17,6 +17,88 @@
 from setuptools import setup
 from setuptools_rust import Binding, RustExtension
 
+# ==================================================================================================
+# Warning: this section is a horrendous monkey-patching hack that re-implements a version of
+# https://github.com/PyO3/setuptools-rust/pull/574 on top of `setuptools-rust==1.12.0`, which
+# contains just enough functionality for our own use.
+
+from pathlib import Path
+import json
+import shutil
+import functools
+import setuptools_rust.build
+
+# This function is only called once in our build, to find the `cdylib` artifact.  It's passed the
+# `cargo` messages, which is what we need to locate the `OUT_DIR`; we use this as a hook point to
+# intercept them and leak them out for later use.
+find_cargo_artifacts_orig = setuptools_rust.build._find_cargo_artifacts
+install_extension_orig = setuptools_rust.build.build_rust.install_extension
+out_dir = None
+generated_files = {"include": "qiskit.capi"}
+
+
+@functools.wraps(find_cargo_artifacts_orig)
+def find_cargo_artifacts_patch(cargo_messages, *, package_id, kinds):
+    global out_dir  # noqa: PLW0603 (global) - we have to leak to get the monkeypatch to work.
+
+    # Chances are that the line we're looking for will be the third laste line in the
+    # messages.  The last is the completion report, the penultimate is generally the
+    # build of the final artifact.
+    for messsage in reversed(cargo_messages):
+        if "build-script-executed" not in messsage or package_id not in messsage:
+            continue
+        parsed = json.loads(messsage)
+        if parsed.get("package_id") == package_id:
+            out_dir = parsed.get("out_dir")
+            break
+
+    return find_cargo_artifacts_orig(cargo_messages, package_id=package_id, kinds=kinds)
+
+
+@functools.wraps(install_extension_orig)
+def install_extension_patch(self, ext, dylib_paths):
+    install_extension_orig(self, ext, dylib_paths)
+
+    # `out_dir` and `generated_files` are captured from the outer scope.
+    if out_dir is None:
+        raise RuntimeError("setup sanity check failed: the cargo `out_dir` is not set")
+    build_artifact_dirs = [Path(out_dir)]
+
+    # We'll delegate the finding of the package directories to Setuptools, so we
+    # can be sure we're handling editable installs and other complex situations
+    # correctly.
+    build_ext = self.get_finalized_command("build_ext")
+    build_py = self.get_finalized_command("build_py")
+
+    def get_package_dir(package: str) -> Path:
+        if self.inplace:
+            # If `inplace`, we have to ask `build_py` (like `build_ext` would).
+            return Path(build_py.get_package_dir(package))
+        # ... If not, `build_ext` knows where to put the package.
+        return Path(build_ext.build_lib) / Path(*package.split("."))
+
+    for source, package in generated_files.items():
+        dest = get_package_dir(package)
+        dest.mkdir(mode=0o755, parents=True, exist_ok=True)
+        for artifact_dir in build_artifact_dirs:
+            source_full = artifact_dir / source
+            dest_full = dest / source_full.name
+            if source_full.is_file():
+                # logger.info("Copying data file from %s to %s", source_full, dest_full)
+                shutil.copy2(source_full, dest_full)
+            elif source_full.is_dir():
+                # logger.info("Copying data directory from %s to %s", source_full, dest_full)
+                shutil.copytree(source_full, dest_full, dirs_exist_ok=True)
+            # This tacitly makes "no match" a silent non-error.
+
+
+setuptools_rust.build._find_cargo_artifacts = find_cargo_artifacts_patch
+setuptools_rust.build.build_rust.install_extension = install_extension_patch
+
+# Normal service resumes below here.
+# ==================================================================================================
+
+
 # Most of this configuration is managed by `pyproject.toml`.  This only includes the extra bits to
 # configure `setuptools-rust`, because we do a little dynamic trick with the debug setting, and we
 # also want an explicit `setup.py` file to exist so we can manually call
@@ -64,7 +146,6 @@
             binding=Binding.PyO3,
             debug=rust_debug,
             features=features,
-            data_files={"include": "qiskit.capi"},
         )
     ],
     options={"bdist_wheel": {"py_limited_api": "cp310"}},