[grpc] Fix protobuf compilation in isolated build environments (#16754)

python/setup.py

@@ -6,8 +6,7 @@ to automatically generate gRPC/protobuf Python files from .proto sources
 when building the wheel or doing editable installs.
 """
 
-import subprocess
-import sys
+import os
 from pathlib import Path
 
 from setuptools import setup
@@ -32,31 +31,44 @@ def compile_proto():
     output_dir = proto_path.parent
     proto_dir = proto_path.parent
 
-    # Build the protoc command
-    cmd = [
-        sys.executable,
-        "-m",
-        "grpc_tools.protoc",
+    # Import grpc_tools.protoc directly instead of running as subprocess.
+    # This ensures we use the grpcio-tools installed in the build environment,
+    # since sys.executable may point to the main Python interpreter in
+    # pip's isolated build environments.
+    try:
+        import grpc_tools
+        from grpc_tools import protoc
+    except ImportError as e:
+        raise SetupError(
+            f"Failed to import grpc_tools: {e}. "
+            "Ensure grpcio-tools is listed in build-system.requires in pyproject.toml"
+        )
+
+    # Get the path to well-known proto files bundled with grpcio-tools
+    # (e.g., google/protobuf/timestamp.proto, google/protobuf/struct.proto)
+    grpc_tools_proto_path = Path(grpc_tools.__file__).parent / "_proto"
+
+    # Build the protoc arguments (protoc.main expects argv-style list)
+    args = [
+        "protoc",  # argv[0] is the program name
         f"-I{proto_dir}",
+        f"-I{grpc_tools_proto_path}",  # Include path for well-known protos
         f"--python_out={output_dir}",
         f"--grpc_python_out={output_dir}",
         f"--pyi_out={output_dir}",
-        proto_path.name,
+        str(proto_dir / proto_path.name),
     ]
 
-    print(f"Running: {' '.join(cmd)}")
+    print(f"Running protoc with args: {args[1:]}")
 
+    # Save and restore cwd since protoc may change it
+    original_cwd = os.getcwd()
     try:
-        subprocess.run(
-            cmd,
-            capture_output=True,
-            text=True,
-            cwd=proto_dir,
-            check=True,
-        )
-    except subprocess.CalledProcessError as e:
-        error_msg = e.stderr or e.stdout or "Unknown error"
-        raise SetupError(f"protoc failed with exit code {e.returncode}: {error_msg}")
+        result = protoc.main(args)
+        if result != 0:
+            raise SetupError(f"protoc failed with exit code {result}")
+    finally:
+        os.chdir(original_cwd)
 
     # Fix imports in generated grpc file (change absolute to relative imports)
     _fix_imports(output_dir, proto_path.stem)