There should be a way to generate warnings when reject is called after resolve

I have lost many hours investigating a problem that arrived due to a promise being resolved and rejected afterward. Here is an example to illustrate the problem I had:

var Promise = require('bluebird')

new Promise(function (resolve, reject) {
    console.log('resolving')
    resolve()

    setTimeout(function () {
        console.log('rejecting')
        reject(new Error())
    }, 0)
}).then(function () {
    console.log('resolved')
}).catch(function (err) {
    console.log('rejected', err)
})

I tried to activate warnings but I din’t get any:

root@874aba35616a:/tmp# BLUEBIRD_WARNINGS=1 node example.js 
resolving
rejecting
resolved
root@874aba35616a:/tmp# 

When I don’t supply an error to reject, I get a warning so I’m confident that the warning mechanism gets activated using the environment variable.

Is there a way to have these warnings? If not can you add this feature? I bet it would save a lot of debugging time.

[aalexgabi]

Here is the code I was debugging:

return new Promise(function (resolve, reject) {
        var csvStream = csv.parse({ delimiter: self.request.separator || ',', columns: true, relax_column_count: true });
        csvStream.on('pipe', function (src) {
            src.on('data', function (data) { self.progressSize += data.length; });
        });
        self.sftpConnection.readAndPipeFile(file.filename, csvStream).catch(function(err){
            err.context = err.context || {};
            err.context.filename = file.filename
            reject(err);
        });
       // BulkPromiseStream is a transformer that waits for promise returned by the mapper to fulfill before acknowledging the fake "write" and emits error on rejection
        csvStream.pipe(new streamTools.BulkPromiseStream(function(slice) {
            return self.processSomeRows(slice).then(function (sliceReport) {
                addReports(report, sliceReport);
                lines += slice.length;
            }).then(function () {
                return self.updateProgress({
                    totalFiles: totalFiles,
                    processedFiles: fileNumber,
                    totalSize: self.totalSize,
                    processedSize: self.progressSize,
                    currentProcessedLines: lines,
                    currentReport: JSON.stringify(report),
                });
            });
        }))
            // we need to add a data consumer in order to finish the stream
            // if we don't, the end event is never called :(
            // it's because BulkPromiseStream is based on Transform
            .on('data', function() {})
            .on('end', resolve)
            .on('error', reject);
        csvStream.on('error', reject);
    })

The bug was in self.processSomeRows that returned too quickly for the last chunk. That resolved the promise but the previous chunk was generating an error later on. This error was totally invisible.

[benjamingr]

I actually use this fact as a feature (resolving after rejecting)