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Empty files break sourcemap

See original GitHub issue

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.