add unit build support [ci build]

Author: nmwsharp

CMakeLists.txt

@@ -1,6 +1,7 @@
 cmake_minimum_required(VERSION 3.15.0) # minimum imposed by scikit-build-core
 project(polyscope LANGUAGES CXX)
 
+option(POLYSCOPE_PY_UNITY_BUILD "Enable Unity builds" OFF)
 
 ## Gather dependencies
 
@@ -37,7 +38,25 @@ set_target_properties(polyscope_bindings PROPERTIES CXX_VISIBILITY_PRESET "defau
 target_include_directories(polyscope_bindings PUBLIC "${EIGEN3_INCLUDE_DIR}")
 target_link_libraries(polyscope_bindings PRIVATE polyscope)
 
-# make the resulting target actually be called polyscope, without the py
-# set_target_properties(polyscope_py PROPERTIES OUTPUT_NAME polyscope)
+if(POLYSCOPE_PY_UNITY_BUILD)
+
+  # NOTE: these are not perfect, sometimes the explicit template 
+  # instantiations get messed up and cause compile errors. The current
+  # batch sizes were chosen because they happen to work around that.
+  # 
+  # However, this does give a nearly 50% speedup, so it can be worth using 
+  # for long-running CI builds.
+
+  set_target_properties(polyscope PROPERTIES
+      UNITY_BUILD ON
+      UNITY_BUILD_BATCH_SIZE 5
+  )
+
+  set_target_properties(polyscope_bindings PROPERTIES
+      UNITY_BUILD ON
+      UNITY_BUILD_BATCH_SIZE 4
+  )
+
+endif()
 
 install(TARGETS polyscope_bindings LIBRARY DESTINATION .)

pyproject.toml

@@ -33,4 +33,8 @@ build-backend = "scikit_build_core.build"
 
 [tool.scikit-build]
 build.verbose = true
-logging.level = "INFO"
+logging.level = "INFO"
+
+[tool.cibuildwheel]
+# for cibuildwheel only, use unity builds by default
+environment = {POLYSCOPE_PY_UNITY_BUILD="ON"}