Add RPYBUILD_J2_DEBUG environment variable for debugging codegen

Author: virtuald

robotpy_build/autowrap/writer.py

@@ -1,6 +1,8 @@
 import json
+import os
 from os.path import join
 import pathlib
+import pprint
 import typing
 
 import jinja2
@@ -9,6 +11,8 @@
 
 templates_path = pathlib.Path(__file__).parent.absolute()
 
+_emit_j2_debug = os.getenv("RPYBUILD_J2_DEBUG") == "1"
+
 
 class WrapperWriter:
     def __init__(self) -> None:
@@ -50,6 +54,10 @@ def write_files(
         # Jinja requires input as a dictionary
         data = hctx.__dict__
 
+        if _emit_j2_debug:
+            with open(join(cxx_gen_dir, f"{name}.txt"), "w") as fp:
+                fp.write(pprint.pformat(hctx))
+
         # Write the cpp file first
         fname = join(cxx_gen_dir, f"{name}.cpp")
         generated_sources.append(fname)