Cannot overwrite pre-existing key/value in `preRender`

[dtothefp]

Demo repo here: https://github.com/dtothefp/assemble-yfm-nunj

"version": "0.8.0"
Essentially, overwritting pre-existing data on the file.data context does not seem to work in preRender hook

app.preRender(/\.(?:hbs|md|html)$/, (file, next) => {
  console.log('Append Pre-Render Data Before Merge', file.data);

  file.data = Object.assign({}, file.data, {
    title: 'From Pre-Render',
    custom_stuff: 'Custom stuff from Pre-Render'
  });

  console.log('Append Pre-Render Data After Merge', file.data);
  next();
});

if app.cache.data.title or file.data.title exists then the above doesn't work. I solve this by doing merge in onLoad

app.onLoad(/\.(?:hbs|md|html)$/, (file, next) => {
  matter.parse(file, (err, file) => {
    if (err) return next(err);

    _.assign(file.data, {title: 'blahhhh'});

    next(null, file);
  });
});

or by making a stream plugin

app.task('build', () => {
  return app.src('./templates/pages/**/*.html')
    .pipe(through.obj(function(file, enc, cb) {
      file.data = {title: 'blaahhhhh'}
      this.push(file);
      cb();
    }))
    .pipe(app.renderFile())
    .pipe(app.dest('dist'))
    .on('error', (err) => {
      console.error('Error [assemble]: build');
    })
    .on('data', (file) => {
      console.log('data', file.path);
    })
    .on('end', () => {
      console.log('ended');
    });
});

[assemblebot]

@dtothefp Thanks for the issue! If you're reporting a bug, please be sure to include:

• The version of assemble you are using.
• Your assemblefile.js (This can be in a gist)
• The commandline output. (Screenshot or gist is fine)
• What you expected to happen instead.

[jonschlinkert]

@dtothefp inside node_modules in assemble-render-file try commenting out the code that creates the ctx object, then just pass locals to render. See if that works. If so we can update that lib. (was just talking to @doowb, he mentioned this)

[dtothefp]

@jonschlinkert when I do that looks like locals is sometimes undefined which causes an error

        // create the context to pass to templates
        //var ctx = utils.merge({}, app.cache.data, locals, file.data);
        //ctx.engine = engine || ctx.engine;

        // render the file
        app.render(file, locals, function(err, res) { //...

/Users/davidfox-powell/dev/prerender-demo/node_modules/assemble-core/node_modules/templates/lib/utils/proto.js:105
  var engine = locals.engine || view.engine || opts.engine;
                     ^

TypeError: Cannot read property 'engine' of undefined

[jonschlinkert]

you probably need to do something like if (!locals) locals = {}