Bare-bone REAPER extension (prints Hello World! using the API)

reaper_barebone.cpp

// Bare-bone REAPER extension
//
// 1. Grab reaper_plugin.h from https://github.com/justinfrankel/reaper-sdk/raw/main/sdk/reaper_plugin.h
// 2. Grab reaper_plugin_functions.h by running the REAPER action "[developer] Write C++ API functions header"
// 3. Grab WDL: git clone https://github.com/justinfrankel/WDL.git
// 4. Build then copy or link the binary file into <REAPER resource directory>/UserPlugins
//
// Linux
// =====
//
// c++ -fPIC -O2 -std=c++14 -IWDL/WDL -shared reaper_barebone.cpp -o reaper_barebone.so
//
// macOS
// =====
//
// c++ -fPIC -O2 -std=c++14 -IWDL/WDL -dynamiclib reaper_barebone.cpp -o reaper_barebone.dylib
//
// Windows
// =======
//
// (Use the VS Command Prompt matching your REAPER architecture, eg. x64 to use the 64-bit compiler)
// cl /nologo /O2 /Z7 /Zo /DUNICODE reaper_barebone.cpp /link /DEBUG /OPT:REF /PDBALTPATH:%_PDB% /DLL /OUT:reaper_barebone.dll

#define REAPERAPI_IMPLEMENT
#include "reaper_plugin_functions.h"

#include <cstdio>

extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
  REAPER_PLUGIN_HINSTANCE instance, reaper_plugin_info_t *rec)
{
  if(!rec) {
    // cleanup code here

    return 0;
  }

  if(rec->caller_version != REAPER_PLUGIN_VERSION)
    return 0;
  
  // see also https://gist.github.com/cfillion/350356a62c61a1a2640024f8dc6c6770
  ShowConsoleMsg = (decltype(ShowConsoleMsg))rec->GetFunc("ShowConsoleMsg");
  
  if(!ShowConsoleMsg) {
    fprintf(stderr, "[reaper_barebone] Unable to import ShowConsoleMsg\n");
    return 0;
  }

  // initialization code here
  ShowConsoleMsg("Hello World!\n");

  return 1;
}

reaper_barebone.zig

// zig build-lib -dynamic -O ReleaseFast -femit-bin=reaper_barebone.so reaper_barebone.zig

const std = @import("std");
const reaper = struct { // @import("reaper");
  pub const PLUGIN_VERSION = 0x20E;

  pub const HINSTANCE = *opaque {};
  pub const HWND      = *opaque {};

  pub const plugin_info_t = extern struct {
    caller_version: c_int,
    hwnd_main: HWND,
    register: ?*fn(name: [*:0]const u8, infostruct: *anyopaque) callconv(.C) c_int,
    getFunc:  ?*fn(name: [*:0]const u8) callconv(.C) ?*anyopaque,
  };

  pub fn init(rec: *plugin_info_t) bool {
    if(rec.caller_version != PLUGIN_VERSION) {
      std.debug.print("expected REAPER API version {x}, got {x}\n",
        .{ PLUGIN_VERSION, rec.caller_version });
      return false;
    }

    const getFunc = rec.getFunc.?;
    inline for(@typeInfo(@This()).Struct.decls) |decl| {
      comptime var decl_type = @typeInfo(@TypeOf(@field(@This(), decl.name)));
      const is_optional = decl_type == .Optional;
      if(is_optional)
        decl_type = @typeInfo(decl_type.Optional.child);
      if(decl_type != .Pointer or @typeInfo(decl_type.Pointer.child) != .Fn)
        continue;
      if(getFunc(decl.name)) |func|
        @field(@This(), decl.name) = @ptrCast(func)
      else if(is_optional)
        @field(@This(), decl.name) = null
      else {
        std.debug.print("unable to import the API function '{s}'\n", .{ decl.name });
        return false;
      }
    }

    return true;
  }

  pub var ShowConsoleMsg: *fn(str: [*:0]const u8) callconv(.C) void = undefined;
};

export fn ReaperPluginEntry(instance: reaper.HINSTANCE, rec: ?*reaper.plugin_info_t) c_int {
  _ = instance;

  if(rec == null)
    return 0 // cleanup here
  else if(!reaper.init(rec.?))
    return 0;

  reaper.ShowConsoleMsg("Hello, Zig!\n");

  return 1;
}

Yes, thank you!