Empty files break sourcemap

[xealot]

Occasionally you have a step (in my case, typescript compilation) that generates an empty file. This causes concat to fail.

<root>/applications/gulp-tools/node_modules/gulp-concat/node_modules/concat-with-sourcemaps/node_modules/source-map/lib/source-map/source-map-generator.js:273
        throw new Error('Invalid mapping: ' + JSON.stringify({
              ^
Error: Invalid mapping: {"generated":{"line":1,"column":0},"original":{"line":1,"column":0},"name":null}
    at SourceMapGenerator_validateMapping [as _validateMapping] (<root>/applications/gulp-tools/node_modules/gulp-concat/node_modules/concat-with-sourcemaps/node_modules/source-map/lib/source-map/source-map-generator.js:273:15)
    at SourceMapGenerator_addMapping [as addMapping] (<root>/applications/gulp-tools/node_modules/gulp-concat/node_modules/concat-with-sourcemaps/node_modules/source-map/lib/source-map/source-map-generator.js:102:12)
    at Concat.add (<root>/applications/gulp-tools/node_modules/gulp-concat/node_modules/concat-with-sourcemaps/index.js:75:25)
    at Stream.bufferContents (<root>/applications/gulp-tools/node_modules/gulp-concat/index.js:35:12)
    at Stream.stream.write (<root>/applications/gulp-tools/node_modules/gulp-concat/node_modules/through/index.js:26:11)
    at write (_stream_readable.js:583:24)
    at flow (_stream_readable.js:592:7)
    at CompileStream.pipeOnReadable (_stream_readable.js:624:5)
    at CompileStream.EventEmitter.emit (events.js:92:17)
    at emitReadable_ (_stream_readable.js:408:10)
    at emitReadable (_stream_readable.js:404:5)
    at readableAddChunk (_stream_readable.js:165:9)
    at CompileStream.Readable.push (_stream_readable.js:127:10)
    at emit (<root>/applications/gulp-tools/node_modules/gulp-typescript/release/project.js:245:22)
    at sortedEmit (<root>/applications/gulp-tools/node_modules/gulp-typescript/release/project.js:267:17)
    at Project.compile (<root>/applications/gulp-tools/node_modules/gulp-typescript/release/project.js:273:17)
    at CompileStream.compile (<root>/applications/gulp-tools/node_modules/gulp-typescript/release/main.js:53:23)
    at CompileStream.end (<root>/applications/gulp-tools/node_modules/gulp-typescript/release/main.js:63:14)
    at DestroyableTransform.onend (<root>/applications/gulp-tools/node_modules/gulp-sourcemaps/node_modules/through2/node_modules/readable-stream/lib/_stream_readable.js:523:10)
    at DestroyableTransform.g (events.js:180:16)
    at DestroyableTransform.EventEmitter.emit (events.js:117:20)
    at <root>/applications/gulp-tools/node_modules/gulp-sourcemaps/node_modules/through2/node_modules/readable-stream/lib/_stream_readable.js:965:16
    at process._tickDomainCallback (node.js:459:13)

Here is an example of the task that causes this failure.

var ts = require('gulp-typescript');
var concat = require('gulp-concat');
var sourcemaps = require('gulp-sourcemaps');

gulp.task('compile-ts', function () {
    var compile = gulp.src(conf.tscSources)
        .pipe(sourcemaps.init())
        .pipe(ts({
            declarationFiles: true,
            noExternalResolve: true,
            sortOutput: true,
            target: 'ES5'
        }));

    return compile.js
        .pipe(concat('app.js'))
        .pipe(sourcemaps.write('./maps'))
        .pipe(gulp.dest(conf.distDir));
});

While it's relatively trivial to filter empty files from a stream I believe not doing so shouldn't cause concat to tank.

[ivogabe]

Actually, empty files aren't the problem but files with empty source maps (source maps whose property mappings is "") are.

A bit shorter gulp file that reproduces the problem:

var gulp = require('gulp');
var ts = require('gulp-typescript');
var concat = require('gulp-concat');
var sourcemaps = require('gulp-sourcemaps');

gulp.task('default', function () {
    return gulp.src('empty.ts')
        .pipe(sourcemaps.init())
        .pipe(ts())
        .pipe(concat('app.js'))
        .pipe(sourcemaps.write('./maps'))
        .pipe(gulp.dest('release'));
});

The source map is:

{ version: 3,
  file: 'empty.ts',
  sourceRoot: '...',
  sources: [ 'source.ts' ],
  names: [],
  mappings: '' }

[yocontra]

cc @floridoo

[karlvr]

I get this fault too with an input file that is empty, with a source map. It sounds like exactly the same case as above.

I had a subsequent interest situation where the gulp-newer plugin swallowed the error, so the pipe just stopped. I've raised an issue there. It then occurred that the error out of gulp-concat isn't very useful. It doesn't tell you which file triggered the fault, for example.

Would it be cool to catch these errors and augment them with the filename? I'm not sure the best practice for doing something like that. I tried a simple try {} catch {} around concat.add(file.relative, file.contents.toString(), file.sourceMap); in bufferContents(file), and added the following in the catch:

return this.emit('error', new PluginError('gulp-concat', 'Failed to concat file: ' + file.relative + ', Caused by: ' + e.message));

Would this be a useful addition?

[bsr203]

Having the same issue. any update?

[yocontra]

This error is actually coming from a module that gulp-concat uses, not gulp-concat. Can you open this issue there? https://github.com/floridoo/concat-with-sourcemaps

Include the stacktrace from the original post and link back to this issue so people here can track it there once it is created

[floridoo]

I could not reproduce the error. Nor with plain concat-with-sourcemaps, nor with the example by @ivogabe.

[MartinJohns]

@floridoo I am having the same issue. I prepared a gist for you.

Just do the following:

git clone https://gist.github.com/MartinJohns/7bca27eddd9fc85f421f
cd 7bca27eddd9fc85f421f
npm install
gulp watch

Then, while the watch task is running, open the test.ts and save it. The watcher should notice it, restart the script-task and the error will occur.

[ivogabe]

I re-tested my gulpfile, and it does throw an error here. I used the latest releases of everything on npm. Did empty.ts exists and was it empty when you tested it? I've tested it on windows & mac and both failed.

[floridoo]

Thanks @MartinJohns! Found the issue and fixed it. It was the combination of an empty mappings property and an empty sources array that produced the error.

[MartinJohns]

Can confirm, it does not crash anymore after one npm update. :-)

[yocontra]

Thanks @floridoo

[hupad]

@floridoo could you elaborate on this fix you made please. I am running into the issue and not sure what exactly went wrong.