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

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]

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

[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).