Don't require dependencies for foreign targets

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+### Fixed
+- Pass `--filter-platform` to `cargo metadata` so offline builds don't require dependencies exclusive to foreign targets. [#610](https://github.com/PyO3/setuptools-rust/pull/610)
+
 ## 1.13.0 (2026-06-27)
 ### Added
 - Add `generated-files` option to `RustExtension` to copy files from the build script output directory to the wheel. [#574](https://github.com/PyO3/setuptools-rust/pull/574)

setuptools_rust/build.py

@@ -32,6 +32,7 @@
 from .command import RustCommand
 from .extension import Binding, RustBin, RustExtension, Strip
 from .rustc_info import (
+    _is_custom_target,
     get_rust_host,
     get_rust_version,
     get_rustc_cfgs,
@@ -129,6 +130,17 @@ def run_for_extension(self, ext: RustExtension) -> None:
         dylib_paths, artifact_dir = self.build_extension(ext)
         self.install_extension(ext, dylib_paths, artifact_dir)
 
+    def _metadata_filter_platforms(self, ext: RustExtension) -> Tuple[str, ...]:
+        """Target triples of the platforms being built."""
+        target = self.target
+        if target is _Platform.CARGO_DEFAULT:
+            return (get_rust_host(ext.env),)
+        elif target is _Platform.UNIVERSAL2:
+            return _UNIVERSAL2_TARGETS
+        elif _is_custom_target(target):
+            return ()  # Custom target specs cannot be passed to --filter-platform
+        return target
+
     def build_extension(
         self, ext: RustExtension
     ) -> Tuple[List["_BuiltModule"], Optional[Path]]:
@@ -148,7 +160,10 @@ def build_extension(
         debug = self._is_debug_build(ext)
         use_cargo_crate_type = _check_cargo_supports_crate_type_option(ext.env)
 
-        package_id = ext.metadata(quiet=quiet)["resolve"]["root"]
+        package_id = ext.metadata(
+            quiet=quiet,
+            filter_platforms=self._metadata_filter_platforms(ext),
+        )["resolve"]["root"]
         if package_id is None:
             raise FileError(
                 f"manifest for Rust extention `{ext.name}` at path `{ext.path}` is a virtual manifest (a workspace root without a package).\n\n"

setuptools_rust/extension.py

@@ -256,16 +256,31 @@ def install_script(self, module_name: str, exe_path: str) -> None:
             with open(file, "w") as f:
                 f.write(_SCRIPT_TEMPLATE.format(executable=repr(executable)))
 
-    def metadata(self, *, quiet: bool) -> "CargoMetadata":
+    def metadata(
+        self,
+        *,
+        quiet: bool,
+        filter_platforms: Sequence[str] = (),
+    ) -> "CargoMetadata":
         """Returns cargo metadata for this extension package.
 
+        ``filter_platforms`` restricts the dependency resolution to the given
+        target triples (``cargo metadata --filter-platform``).
+
         Cached - will only execute cargo on first invocation.
         """
 
-        return self._metadata(os.environ.get("CARGO", "cargo"), quiet)
+        return self._metadata(
+            os.environ.get("CARGO", "cargo"), quiet, tuple(filter_platforms)
+        )
 
     @lru_cache()
-    def _metadata(self, cargo: str, quiet: bool) -> "CargoMetadata":
+    def _metadata(
+        self,
+        cargo: str,
+        quiet: bool,
+        filter_platforms: "tuple[str, ...]" = (),
+    ) -> "CargoMetadata":
         metadata_command = [
             cargo,
             "metadata",
@@ -274,6 +289,8 @@ def _metadata(self, cargo: str, quiet: bool) -> "CargoMetadata":
             "--format-version",
             "1",
         ]
+        for platform in filter_platforms:
+            metadata_command.append(f"--filter-platform={platform}")
         if self.cargo_manifest_args:
             metadata_command.extend(self.cargo_manifest_args)
 

tests/test_extension.py

@@ -4,6 +4,7 @@
 from pytest import CaptureFixture, MonkeyPatch
 
 from setuptools_rust.extension import RustBin, RustExtension
+from setuptools_rust.rustc_info import get_rust_host
 
 SETUPTOOLS_RUST_DIR = Path(__file__).parent.parent
 
@@ -33,6 +34,14 @@ def test_metadata_contents(hello_world_bin: RustBin) -> None:
     assert "target_directory" in metadata
 
 
+def test_metadata_filter_platforms(hello_world_bin: RustBin) -> None:
+    metadata = hello_world_bin.metadata(
+        quiet=False, filter_platforms=(get_rust_host(None),)
+    )
+    assert "target_directory" in metadata
+    assert metadata["resolve"]["root"] is not None
+
+
 def test_metadata_cargo_log(
     capfd: CaptureFixture, monkeypatch: MonkeyPatch, hello_world_bin: RustBin
 ) -> None: