tsc -b --watch emits unchanged js on each compilation round

[IIIristraM]

TypeScript Version: 3.7.2

Search Terms: project references

Code

tsc -b tsconfig.json --watch

Expected behavior: each recompilation write only changed js files to output

Actual behavior: each recompilation write all js files to output in all projects

As far as I understand, files should be written by writeFileIfUpdated, but it never invoked. Instead this function called

function writeFile(fileName, data, writeByteOrderMark) {
    ts.perfLogger.logEvent("WriteFile: " + fileName);
    if (writeByteOrderMark) {
        data = byteOrderMarkIndicator + data;
    }
    var fd;
    try {
        fd = _fs.openSync(fileName, "w");
        _fs.writeSync(fd, data, undefined, "utf8");
    }
    finally {
        if (fd !== undefined) {
            _fs.closeSync(fd);
        }
    }
}

Related Issues: probably regression of #29927

Steps to reproduce:

• clone https://github.com/IIIristraM/lerna-ts.git
• run npm run init
• in first terminal run npm run tsc:watch and wait till build will be completed
• in second terminal run npm start
• change here https://github.com/IIIristraM/lerna-ts/blob/master/packages/common/src/utils.ts#L1 number to any, which should not lead to changes in corresponding js file
• on each recompilation webpack build will print to stdout files that were changed, or you could just attach debugger to tsc process to see that all js files was emitted from scratch

[sheetalkamat]

This is working as intended.. We do not track if change in file will not result in its output js file or not. We emit it irrespectively.

[IIIristraM]

@sheetalkamat, It's may be OK for this particular file, but all other js files among all projects, which are linked up through project dependency graph, are also emitted despite whether they depends on changed file or not.

For example if I have project B which depends on project A, and I change one file in A, all files from A and all files from B will be emitted

How it supposed to be integrated to any dev-build pipeline which performance usually heavily depends on amount of changed files ?

By the way the problem appears only with -b flag, tsc --watch emits only one js file, so it looks like a bug, or at least inconsistent behaviour.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[IIIristraM]

Just for history, webpack was triggered by setting timestamps on all output files during project invalidation step, so there is nothing wrong with emit.