tsc includes previous output in result when allowJs is enabled and "exclude" is non-empty

[WasabiFan]

TypeScript Version: 2.7.0-dev.20171222

Code

For easy access, clone this gist: https://gist.github.com/WasabiFan/6922d6eb6224945ac809c216fdc37089

test.ts:

// Source code here

tsconfig.json:

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "outDir": "out",
    "allowJs": true
  },
  "exclude": [
    "node_modules"
  ]
}

Removing the exclude block or disabling allowJs avoids the issue.

Note that this is an easy state to get into: in my case, I generated a VSCode extension with their official templates and then enabled allowJs. I didn't realize what was going on until my PC ran out of RAM, as it automatically ran the watch task and the depth grew every time I saved.

Expected behavior:

I can compile the project with tsc as many times as I'd like.

Actual behavior:

PS D:\...> git clone https://gist.github.com/WasabiFan/6922d6eb6224945ac809c216fdc37089 tsc-recursion-demo-gist
Cloning into 'tsc-recursion-demo-gist'...
remote: Counting objects: 7, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 7 (delta 1), reused 0 (delta 0), pack-reused 0
Unpacking objects: 100% (7/7), done.
PS D:\...> cd .\tsc-recursion-demo-gist\
PS D:\...\tsc-recursion-demo-gist> tsc -p .
PS D:\...\tsc-recursion-demo-gist> tsc -p .
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/test.js' because it would overwrite input file.
PS D:\...\tsc-recursion-demo-gist> tsc -p .
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/test.js' because it would overwrite input file.
PS D:\...\tsc-recursion-demo-gist> tsc -p .
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/test.js' because it would overwrite input file.
PS D:\...\tsc-recursion-demo-gist> tsc -p .
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/test.js' because it would overwrite input file.
PS D:\...\tsc-recursion-demo-gist> tsc -p .
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/out/test.js' because it would overwrite input file.
error TS5055: Cannot write file 'D:/.../tsc-recursion-demo-gist/out/test.js' because it would overwrite input file.

The fix (and the best option) is to exclude the output directory. But given that existing templates don't do that, I think this is a significant issue. I don't understand why this doesn't happen when the exclude block is removed; I assume there's an internal safety to prevent this problem that's overridden.

[DanielRosenwasser]

We automatically exclude the outDir as well as node_modules, but given an explicit list of exclude files, I'm not sure what we can do to opt out of that behavior.

[WasabiFan]

Is there something that prevents you from always excluding the outDir (appending it to the exclude list)? I can't think of a scenario where including the output directory would be the "right" behavior, but I don't have visibility into the whole product so I could be missing something.

[DanielRosenwasser]

I'll need to chat with @mhegazy to recall the full context on this topic.

[mhegazy]

Is there something that prevents you from always excluding the outDir (appending it to the exclude list)? I can't think of a scenario where including the output directory would be the "right" behavior, but I don't have visibility into the whole product so I could be missing something.

consider the case where you have multiple project contribute to the same output directory, let's call it .\modules. all outputs will go there including .d.ts files. you can then set your baseUrl to be .\modules and now all your imports are resolved from the same root. This is common structure for AMD modules for instance.

[WasabiFan]

That seems reasonable to me. I have two questions/points of clarification:

• It seems to me that, in a project without any exclude configuration, that scenario is currently unsupported. To be able to do that you would need to override the exclude property -- apparently the exclude list implicitly contains outDir unless the former is modified in the config file. Is that right? I would think it odd that a supported use case relies on disabling that implicit behavior.
• The particular issue I had is perhaps more narrow than I imagined. My hope is to address the "infinitely recursed file structure" issue, which won't occur if baseDir == outDir as would be the case in the scenario you wanted to support. The problem I had is specific to when baseDir contains outDir, so that a new copy of the files is created rather than being overwritten (which would be benign).