scripts: Improve error importing Reg

docs/generated_code.md

@@ -7,6 +7,10 @@ values when the Vulkan Headers or SPIR-V Grammer is updated.
 - [Adding and Editing code generation](#adding-and-editing-code-generation)
 - [How it works](#how-it-works)
 
+# Dependency
+
+`pyparsing` is required so if no installed, you will need to call `pip install pyparsing`
+
 # How to generate the code
 
 - Linux:

scripts/generate_source.py

@@ -44,7 +44,13 @@ def RunGenerators(api: str, registry: str, grammar: str, directory: str, styleFi
     scripts_directory_path = os.path.dirname(os.path.abspath(__file__))
     registry_headers_path = os.path.join(scripts_directory_path, scripts)
     sys.path.insert(0, registry_headers_path)
-    from reg import Registry
+    try:
+        from reg import Registry
+    except:
+        print("ModuleNotFoundError: No module named 'reg'") # normal python error message
+        print(f'{registry_headers_path} is not pointing to the Vulkan-Headers registry directory.')
+        print("Inside Vulkan-Headers there is a registry/reg.py file that is used.")
+        sys.exit(1) # Return without call stack so easy to spot error
 
     from generators.base_generator import BaseGeneratorOptions
     from generators.thread_safety_generator import ThreadSafetyOutputGenerator

scripts/generators/extension_helper_generator.py

@@ -23,6 +23,7 @@
 from generators.base_generator import BaseGenerator
 from generators.generator_utils import PlatformGuardHelper
 
+# Need pyparsing because the Vulkan-Headers use it in dependencyBNF
 from pyparsing import ParseResults
 # From the Vulkan-Headers
 from parse_dependency import dependencyBNF