More sophisticated pre-processor error handling

src/ctypesgen/__main__.py

@@ -167,14 +167,42 @@ def _is_relative_to(path, other):
         return path == other or other in path.parents
 
 
+# -- Argument Parser (Backports) --
+
+if sys.version_info >= (3, 9):
+    from argparse import BooleanOptionalAction
+
+else:
+    # backport, adapted from argparse sources
+    class BooleanOptionalAction (argparse.Action):
+        def __init__(self, option_strings, dest, **kwargs):
+
+            _option_strings = []
+            for option_string in option_strings:
+                _option_strings.append(option_string)
+
+                if option_string.startswith('--'):
+                    option_string = '--no-' + option_string[2:]
+                    _option_strings.append(option_string)
+
+            super().__init__(option_strings=_option_strings, dest=dest, nargs=0, **kwargs)
+
+        def __call__(self, parser, namespace, values, option_string=None):
+            if option_string in self.option_strings:
+                setattr(namespace, self.dest, not option_string.startswith('--no-'))
+
+        def format_usage(self):
+            return ' | '.join(self.option_strings)
+
+
 # -- Argument Parser ---
 
 def generic_path_t(p):
     return Path(p).expanduser().resolve()
 
 def checked_path_t(p, check, exc):
     p = generic_path_t(p)
-    if not check(p): raise exc(f"{p}")
+    # if not check(p): raise exc(f"{p}")
     return p
 
 def input_file_t(p):
@@ -187,7 +215,7 @@ def input_dir_t(p):
 def get_parser():
 
     # FIXME argparse parameters are not ordered consistently...
-    # TODO consider BooleanOptionalAction (with compat backport)
+    # TODO expand use of BooleanOptionalAction
 
     parser = argparse.ArgumentParser(prog="ctypesgen")
 
@@ -340,6 +368,12 @@ def __call__(self, parser, namespace, values, option_string=None):
         metavar="FILENAME",
         help="Save preprocessor output to the specified FILENAME",
     )
+    parser.add_argument(
+        "--preproc-errcheck",
+        action=BooleanOptionalAction,
+        help="Whether to fail fast if the preprocessor returned a non-zero exit code. Defaults to True, unless on Windows.",
+        default=not sys.platform.startswith("win"),
+    )
     parser.add_argument(
         "--optimize-lexer",
         action="store_true",

src/ctypesgen/parser/preprocessor.py

@@ -15,7 +15,7 @@
 
 from ctypesgen.parser import pplexer, lex
 from ctypesgen.parser.lex import LexError
-from ctypesgen.messages import warning_message
+from ctypesgen.messages import warning_message, status_message
 
 
 IS_WINDOWS = sys.platform.startswith("win")
@@ -141,8 +141,14 @@ def parse(self, filename):
             cmd,
             universal_newlines=False,  # binary
             stdout=subprocess.PIPE,
-            check=not IS_WINDOWS,
         )
+        status_message(f"Pre-processor returned exit code {pp.returncode}")
+        if pp.returncode != 0:
+            msg = f"Pre-processor returned non-zero exit code {pp.returncode}"
+            if self.options.preproc_errcheck:
+                assert False, msg
+            else:
+                warning_message(msg)
 
         if IS_MAC:
             ppout = pp.stdout.decode("utf-8", errors="replace")