How is error handling supposed to work?

[kyeotic]

When running yeoman environment errors in generators get swallowed. I've trying using env.on('error') to register a handler, but it does not get invoked when a generator throws an error. The error param in the run() callback isn't set either. What's going on? How do we catch errors?

[SBoudrias]

Hey @tyrsius, it is very hard to see what is the issue you're running into. Usually errors aren't swallowed and exposed properly to the user; so you're definitely not hitting the desired/default behavior .

As such, I can't help you find/fix the bug unless you provide a more complete example. Can you provide the exact code and steps to reproduce your issue?

[kyeotic]

Sure. Ive got a generator that composes other generators.

module.exports = class extends Generator {
    initializing() {
        // Make this available for all plugins to extend
        this.options.composer = new composer_1.default({
            projectName: this.options.projectName,
            namespace: this.options.namespace
        });
        this.destinationRoot(path.resolve(this.destinationRoot(), this.options.outputDir, outputSuffix));
        // Add all the plugins
        Object.keys(this.options.plugins).forEach(key => {
            console.log('handling', key, getPathForPlugin(key));
            let plugin = this.options.plugins[key];
            this.composeWith(getPathForPlugin(key), Object.assign({}, this.options, { inputs: plugin }));
        });
    }
};

And a runner that kicks it off

function runComposer(outputDir, options) {
    const yoEnv = yeoman.createEnv();
    yoEnv.registerStub(ComposerGenerator, 'ComposerGenerator');
    let zipFile = path.resolve(outputDir, zipName);
    let zipFolderPath = path.resolve(outputDir, outputSuffix);
    return new Promise((resolve, reject) => {
        yoEnv.run('ComposerGenerator', options, (err) => {
            if (err)
                return reject(err);
            zip_1.default(zipFolderPath, zipFile, (err) => {
                if (err)
                    return reject(err);
                console.log('composition complete');
                resolve(zipFile);
            });
        });
    }).catch(err => {
        console.error(err, err.stack);
        throw err;
    });
}

If any of the composed generators throws errors in their normal functions, like writing for example, those errors do not get returning to the err on the run() call. If I setup an error listenting with yoEnv.on('error') that is not invoked either.

[kyeotic]

@SBoudrias ☝️

[SBoudrias]

@tyrsius so if I understand this properly; only errors thrown inside composed generators are not being catch?

[kyeotic]

Yes.

[SBoudrias]

Okay, this looks like a valid bug. I don't think I'll have much time to dig into it in the next week. But let me know if I can help you prepare a PR to fix that!

[regevbr]

This should be an easy fix - just register the error event of created generators and emit error on the environment itself.
Temp fix:

    const generator = env.create(generatorName, { args: [], options: {} });
    if (generator instanceof Error) {
      return onError(generator);
    }
    generator.on('error', onError);
    generator.run((err) => {
      // error was handled already in the event handler above
      if (!err){
        console.log('Finished generating');
        resolve();
      }
    });

[SBoudrias]

@regevbr want to send a PR for this one? Looks like you got it figured out

[regevbr]

@SBoudrias sure ill give it a go