Incremental --build, then delete generated js file, then another incremental --build does not recreate js file

TypeScript Version: 3.4.0-dev.20190326

Search Terms:

incremental

Code

tsconfig.json:

{
  "compilerOptions": {
    "incremental": true
  }
}

x.ts:

console.log("hello");

Expected behavior:

• $ tsc --build
• x.js has been generated
• $ rm x.js
• $ tsc --build

Expected: x.js has been regenerated

Actual behavior:

x.js still does not exist

Related Issues:

Did not find any.

[irakliy81]

A separate, but possibly related issue: deleting source .ts files does not remove the related .js files. Right now, to address this, I clean the output directory before every compilation - but this makes it impossible for me to use the --incremental flag.

[simonbuchan]

Thanks for the clarification, @RyanCavanaugh. Here’s my thoughts:

Should --incremental assume that some files may have been deleted from disk?

In the general case, I’m fine with this, even if it breaks the cache transparency, I think. But it’s pretty common to delete the entire output directory, and it’s an unnecessary small cut to have to remember to delete the build cache too compared to other tools. Perhaps checking for just the output dir leads to false confidence?

Should a subsequent build delete files that were generated by a prior build but no longer have a source?

Scenarios where the enumerated set of files substantially matters

Substantially, perhaps, but the standard use case is the pack up everything in the out directory. For someone that’s not paying attention, this means they are bloating their package size.

as is deleting a source file in the first place.

Eh, depends on your style. moving source files is fairly common. The repo I’m in at the moment has 43 renames or deletes in the last 100 commits.

Incurring the cost of a clean or manual delete doesn’t seem like a very high burden compared to the amount of work and risk on our side to figure out what a “correct” delete is.

Not sure why there are scare quotes here: what’s wrong with lastBuildOutput.filter(f => !newBuildOutput.includes(f))?