Add ENABLE_POLYGON_TO_CELLS_ASSERT to cmake options (#935)

* Add ENABLE_POLYGON_TO_CELLS_ASSERT

* typo

CMakeLists.txt

@@ -55,6 +55,9 @@ option(BUILD_GENERATORS "Build code generation applications." ON)
 # for afl++ is provided instead.
 option(ENABLE_LIBFUZZER "Build fuzzers with libFuzzer support." OFF)
 
+option(ENABLE_POLYGON_TO_CELLS_ASSERT "Build additional asserts into the polyfill algorithm for debugging." OFF)
+mark_as_advanced(ENABLE_POLYGON_TO_CELLS_ASSERT)
+
 # These options exist for integration with OSS-Fuzz, so that the fuzzer options
 # can be passed through only to the fuzzer executables but not the H3 library,
 # since passing those options to the library too may result in too many implementations
@@ -350,6 +353,9 @@ function(add_h3_library name h3_alloc_prefix_override)
     if(ENABLE_COVERAGE)
         target_compile_definitions(${name} PRIVATE H3_COVERAGE_TEST=1)
     endif()
+    if(ENABLE_POLYGON_TO_CELLS_ASSERT)
+        target_compile_definitions(${name} PRIVATE H3_POLYGON_TO_CELLS_ASSERT=1)
+    endif()
 
     target_compile_definitions(${name} PUBLIC H3_PREFIX=${H3_PREFIX})
     target_compile_definitions(${name} PRIVATE BUILDING_H3=1)

website/docs/core-library/compilation-options.md

@@ -89,6 +89,12 @@ Whether to enable using clang-tidy to lint source files when building. Only invo
 [Makefile or Ninja CMake generators](https://cmake.org/cmake/help/latest/prop_tgt/LANG_CLANG_TIDY.html)
 are used.
 
+## ENABLE_POLYGON_TO_CELLS_ASSERT
+
+Whether to enable additional debugging assertions in the `polygonToCells` functions. These are not compatible
+with all tests and are intended for debugging only. It is not recommended to build release versions with
+this flag because that configuration is not well tested.
+
 ## H3_ALLOC_PREFIX
 
 Used for directing the library to use a [different set of functions for memory management](./custom-alloc).