error: constructor must explicitly initialize the base class Napi::ObjectWrap<>

[c4lliope]

Based on Automattic/node-canvas#1868 (comment),
I have forked the npm canvas library to https://github.com/assembleco/node-canvas,
and am replacing nan using node-addon-api.

I am going from nan @2.15.0 to node-addon-api @4.2.0.
I ran the conversion tool, and obeyed everything in the setup doc.

When I run yarn,

...
gyp info using [email protected]
gyp info using [email protected] | darwin | x64
gyp info spawn make
gyp info spawn args [ 'BUILDTYPE=Release', '-C', 'build' ]
  SOLINK_MODULE(target) Release/canvas-postbuild.node
  CXX(target) Release/obj.target/canvas/src/backend/Backend.o
../src/backend/Backend.cc:4:10: error: constructor for 'Backend' must explicitly initialize the base class
      'Napi::ObjectWrap<Backend>' which does not have a default constructor
Backend::Backend(std::string name, int width, int height)
         ^
../node_modules/node-addon-api/napi.h:2046:9: note: 'Napi::ObjectWrap<Backend>' declared here
  class ObjectWrap : public InstanceWrap<T>, public Reference<Object> {
        ^
../src/backend/Backend.cc:18:76: error: member reference base type 'uint32_t' (aka 'unsigned int') is not a
      structure or union
  if (info[0].IsNumber()) width  = info[0].As<Napi::Number>().Uint32Value().FromMaybe(0);
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
../src/backend/Backend.cc:19:76: error: member reference base type 'uint32_t' (aka 'unsigned int') is not a
      structure or union
  if (info[1].IsNumber()) height = info[1].As<Napi::Number>().Uint32Value().FromMaybe(0);
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
../src/backend/Backend.cc:23:12: error: no member named 'Wrap' in 'Backend'
  backend->Wrap(info.This());
  ~~~~~~~  ^
../src/backend/Backend.cc:24:3: error: void function 'init' should not return a value [-Wreturn-type]
  return info.This();
  ^      ~~~~~~~~~~~
In file included from ../src/backend/Backend.cc:1:
../src/backend/Backend.h:60:14: warning: private field 'backend' is not used [-Wunused-private-field]
    Backend* backend;
             ^
1 warning and 5 errors generated.
make: *** [Release/obj.target/canvas/src/backend/Backend.o] Error 1

gyp ERR! build error 
gyp ERR! stack Error: `make` failed with exit code: 2
gyp ERR! stack     at ChildProcess.onExit (/Users/grace/.nvm/versions/node/v12.22.1/lib/node_modules/npm/node_modules/node-gyp/lib/build.js:194:23)
gyp ERR! stack     at ChildProcess.emit (events.js:314:20)
gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:276:12)
gyp ERR! System Darwin 19.6.0
gyp ERR! command "/Users/grace/.nvm/versions/node/v12.22.1/bin/node" "/Users/grace/.nvm/versions/node/v12.22.1/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "build" "--fallback-to-build" "--module=/Users/grace/place/assemble/node-canvas/build/Release/canvas.node" "--module_name=canvas" "--module_path=/Users/grace/place/assemble/node-canvas/build/Release" "--napi_version=8" "--node_abi_napi=napi" "--napi_build_version=0" "--node_napi_label=node-v72"
gyp ERR! cwd /Users/grace/place/assemble/node-canvas
gyp ERR! node -v v12.22.1
gyp ERR! node-gyp -v v5.1.0
gyp ERR! not ok

node-pre-gyp ERR! build error 
node-pre-gyp ERR! stack Error: Failed to execute '/Users/grace/.nvm/versions/node/v12.22.1/bin/node /Users/grace/.nvm/versions/node/v12.22.1/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js build --fallback-to-build --module=/Users/grace/place/assemble/node-canvas/build/Release/canvas.node --module_name=canvas --module_path=/Users/grace/place/assemble/node-canvas/build/Release --napi_version=8 --node_abi_napi=napi --napi_build_version=0 --node_napi_label=node-v72' (1)
node-pre-gyp ERR! stack     at ChildProcess.<anonymous> (/Users/grace/place/assemble/node-canvas/node_modules/@mapbox/node-pre-gyp/lib/util/compile.js:89:23)
node-pre-gyp ERR! stack     at ChildProcess.emit (events.js:314:20)
node-pre-gyp ERR! stack     at maybeClose (internal/child_process.js:1022:16)
node-pre-gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:287:5)
node-pre-gyp ERR! System Darwin 19.6.0
node-pre-gyp ERR! command "/Users/grace/.nvm/versions/node/v12.22.1/bin/node" "/Users/grace/place/assemble/node-canvas/node_modules/.bin/node-pre-gyp" "install" "--fallback-to-build"
node-pre-gyp ERR! cwd /Users/grace/place/assemble/node-canvas
node-pre-gyp ERR! node -v v12.22.1
node-pre-gyp ERR! node-pre-gyp -v v1.0.8
node-pre-gyp ERR! not ok 

This is a bunch, but I hope it's clear where the problem is coming from;
seems like the Backend constructor
is missing some setup code.

I can't quite figure out what code should go in this constructor, because it doesn't share the same structure as other constructors in the codebase, like Canvas,
which uses an ::Initialize function instead of a constructor.

I'm out of my depth here; though I do need a running copy of canvas using the node-addon-api.
If anyone has experience with this error, please recommend an approach.

I'm much obliged.
G

[KevinEady]

Hi @c4lliope ,

If you look at the ObjectWrap example, you need to pass the CallbackInfo argument to the ObjectWrap constructor.

Does this help?

[mhdawson]

@c4lliope are you still looking at this? If so did @KevinEady suggestion help?

[github-actions]

This issue is stale because it has been open many days with no activity. It will be closed soon unless the stale label is removed or a comment is made.

[mhdawson]

I'm going to close this since there was no response after Kevin's suggestions. Please let us know if that was not the right thing to do.