Merge pull request #202 from davidhewitt/cache-cargo-metadata

perf: cache `cargo metadata` invocation to avoid multiple calls

Author: davidhewitt

setuptools_rust/build.py

@@ -670,19 +670,10 @@ def _base_cargo_target_dir(ext: RustExtension) -> str:
     If --target is passed to cargo in the command line, the target directory
     will have the target appended as a child.
     """
-    metadata_command = [
-        "cargo",
-        "metadata",
-        "--manifest-path",
-        ext.path,
-        "--format-version",
-        "1",
-    ]
-    metadata = json.loads(check_output(metadata_command))
-    target_directory = metadata["target_directory"]
+    target_directory = ext._metadata()["target_directory"]
     assert isinstance(
         target_directory, str
-    ), "expected cargo metadata to return a string target directory"
+    ), "expected cargo metadata to contain a string target directory"
     return target_directory
 
 

setuptools_rust/extension.py

@@ -4,7 +4,7 @@
 import subprocess
 from distutils.errors import DistutilsSetupError
 from enum import IntEnum, auto
-from typing import Dict, List, Optional, Union
+from typing import Any, Dict, List, NewType, Optional, Union
 
 from semantic_version import SimpleSpec
 from typing_extensions import Literal
@@ -145,22 +145,13 @@ def __init__(
         path = os.path.relpath(path)
         self.path = path
 
+        self._cargo_metadata: Optional[_CargoMetadata] = None
+
     def get_lib_name(self) -> str:
         """Parse Cargo.toml to get the name of the shared library."""
-        data = json.loads(
-            subprocess.check_output(
-                [
-                    "cargo",
-                    "metadata",
-                    "--manifest-path",
-                    self.path,
-                    "--format-version",
-                    "1",
-                ]
-            )
-        )
-        root_key = data["resolve"]["root"]
-        [pkg] = [p for p in data["packages"] if p["id"] == root_key]
+        metadata = self._metadata()
+        root_key = metadata["resolve"]["root"]
+        [pkg] = [p for p in metadata["packages"] if p["id"] == root_key]
         name = pkg["targets"][0]["name"]
         assert isinstance(name, str)
         return re.sub(r"[./\\-]", "_", name)
@@ -190,13 +181,33 @@ def install_script(self, module_name: str, exe_path: str) -> None:
             dirname, executable = os.path.split(exe_path)
             file = os.path.join(dirname, "_gen_%s.py" % module_name)
             with open(file, "w") as f:
-                f.write(TMPL.format(executable=repr(executable)))
+                f.write(_TMPL.format(executable=repr(executable)))
+
+    def _metadata(self) -> "_CargoMetadata":
+        """Returns cargo metedata for this extension package.
+
+        Cached - will only execute cargo on first invocation.
+        """
+        if self._cargo_metadata is None:
+            metadata_command = [
+                "cargo",
+                "metadata",
+                "--manifest-path",
+                self.path,
+                "--format-version",
+                "1",
+            ]
+            self._cargo_metadata = json.loads(subprocess.check_output(metadata_command))
+        return self._cargo_metadata
 
     def _uses_exec_binding(self) -> bool:
         return self.binding == Binding.Exec
 
 
-TMPL = """
+_CargoMetadata = NewType("_CargoMetadata", Dict[str, Any])
+
+
+_TMPL = """
 import os
 import sys