setuptools: Fix passing empty include paths

RELEASE_NOTES.md

@@ -31,6 +31,10 @@ But you might still need to adapt your code:
 ## Bug Fixes
 
 - Fixed some typos in the docs.
+- `setuptools.grpc_tools`: Fix wrong passing of include paths when passed via:
+
+    * Command-line: Now extra white-spaces and empty strings are removed, before they were passed to `protoc -I`.
+    * `pyproject.toml`: Now an empty array/list can be passed to override the default paths, before this resulted in an empty string being passed to `protoc -I`.
 
 ### Cookiecutter template
 

src/frequenz/repo/config/setuptools/grpc_tools.py

@@ -13,7 +13,8 @@
 import pathlib as _pathlib
 import subprocess as _subprocess
 import sys as _sys
-from typing import cast
+from collections.abc import Iterable
+from typing import assert_never, cast
 
 import setuptools as _setuptools
 import setuptools.command.build as _build_command
@@ -30,8 +31,8 @@ class CompileProto(_setuptools.Command):
     proto_glob: str
     """The glob pattern to use to find the protobuf files."""
 
-    include_paths: str
-    """Comma-separated list of paths to include when compiling the protobuf files."""
+    include_paths: str | Iterable[str]
+    """Iterable or comma-separated list of paths to include when compiling the protobuf files."""
 
     py_path: str
     """The path of the root directory where the Python files will be generated."""
@@ -72,15 +73,25 @@ def initialize_options(self) -> None:
 
         self.proto_path = config.proto_path
         self.proto_glob = config.proto_glob
-        self.include_paths = ",".join(config.include_paths)
+        self.include_paths = config.include_paths
         self.py_path = config.py_path
 
     def finalize_options(self) -> None:
         """Finalize options."""
 
     def run(self) -> None:
         """Compile the Python protobuf files."""
-        include_paths = self.include_paths.split(",")
+        include_paths: Iterable[str]
+        match self.include_paths:
+            case str() as str_paths:
+                # If it comes as a comma-separated string, split it into a list,
+                # stripping whitespace and ignoring empty strings.
+                include_paths = filter(len, map(str.strip, str_paths.split(",")))
+            case Iterable() as paths_it:
+                include_paths = paths_it
+            case unexpected:
+                assert_never(unexpected)
+
         proto_files = [
             str(p) for p in _pathlib.Path(self.proto_path).rglob(self.proto_glob)
         ]