How to idiomatically set up code generation?

[pcewing]

I'm trying to understand the idiomatic way in premake to handle build commands
for code generation in a project. As a simple example, consider the
following directory structure:

myapp/
|_ build/
|  |_ generated/
|_ src/
|  |_ generator/
|  |  |_ main.cpp
|  |_ myapp/
|  |  |_ main.cpp
|  |_ data/
|     |_ error_codes.json
|_ premake5.lua

In this example, the high level build steps for myapp would be:

• Build the generator application which will be used for code generation
• Run the generator application built in the previous step, reading the
  myapp/src/data/error_codes.json file as input and writing
  error_codes.{h,cpp} files as output to the build/generated directory
• Build build/generated/error_codes.{h,cpp} as a library project
  called error_codes
• Compile the myapp executable which includes build/generated/error_codes.h
  and links the error_codes library project

Omitting all but the important bits for brevity, I imagine the premake5.lua
for this would something like:

workspace "myapp"
    location "build"

project "generator"
    kind "ConsoleApp"
    files { "src/generator/main.cpp" }

project "error_codes"
    kind "StaticLib"
    includedirs { "build/generated" }
    files { "build/generated/error_codes.cpp" }
    prebuildcommands { "build/generator --input=src/data/error_codes.json --output_dir=build/generated" }

project "myapp"
    kind "ConsoleApp"
    includedirs { "build/generated" }
    files { "src/myapp/main.cpp" }
    links { "error_codes" }

There are a few problems with the above:

• Building the error_codes project no-ops due to a chicken/egg problem
  • I believe this is because the build/generated/error_codes.cpp file
    doesn't exist yet because the pre-build command hasn't run
  • Because the file doesn't exist, the pre-build command doesn't run because
    there's nothing to build
  • I'm not 100% certain this is the reason and still need to confirm
• Moving the pre-build command to be a post-build command of the generator
  project sort of works as a hacky workaround but isn't ideal
  • Modifying error_codes.json will not result in error_codes project
    rebuilding
  • The only thing that will trigger code to be regenerated is updating the
    generator application

Ideally, I'd want the following criteria to be met:

• If generator is rebuilt, rebuild the error_codes project
  • Not sure how to declare a dependency like this where a StaticLib
    project depends on an ConsoleApp project
• If src/data/error_codes.json is modified, rebuild the error_codes project
  • I thought maybe adding src/data/*.json to the files { ... } directive
    would accomplish this but it doesn't seem like it

I feel like the easiest way to accomplish the above would be to leave the
generation step as a pre-build command and make sure it always runs but I
don't think there's an option for that.

I feel like code generation is a pretty common build step so I'd be surprised
if I'm the first person to encounter this but I'm struggling to find a
solution.

My only other thought process is to premake the generator separately and do
code generation completely outside premake. Like:

• Premake the generator app
• Run the generator app
• Premake and build myapp

But it would be a lot more convenient to just premake the whole thing at once.

Edit: And after writing this whole thing up it seems like pre-build steps are running consistently for me now. Pretty sure all I did was update to latest version of premake and move the prebuildcommands to the end of my project definition so maybe this was a bug that was fixed. Closing this out

[KyrietS]

I had a number of situations like this when I found a solution to my problem in the process of writing a question on StackOverflow 😄