Wrong behavior if --outDir is a prefix of project dir

[njlr]

Description

A simple project layout like so:

./fable_src
├── fable.fsproj
└── Program.fs

When compiling like this:

dotnet fable fable_src/fable.fsproj --verbose --outDir fable --extension .fs.js --noRestore --noCache

The transpiled file Program.fs.js appears in fable_src instead of fable.

Repro code

Please see this repo: https://github.com/njlr/fable-out-dir-repro

The GitHub Action demonstrates the issue.

Expected and actual results

I would expect the transpiled file to be in the --outDir, so fable/Program.fs.js

Instead it appears under the source directory at fable_src/Program.fs.js

The _ in fable_src may be a significant factor.

Related information

• Fable version: 3.7.20
• Operating system: Ubuntu 22.04

[alfonsogarciacaro]

Oh, thanks a lot for providing the code, I can indeed reproduce. Still unsure why, but it seems the problem is using fable exactly as --outDir. If you pass something like fable_build or build/fable instead it will work.

I will try to find what's causing the problem exactly. I remember we had a similar issue in the past and had to "ban" some outDirs like "bin", maybe we need to add "fable" to the list 😅

[njlr]

I think it might be when the output directory is a prefix of the source directory - in this case "fable"

[alfonsogarciacaro]

You're right! 👀 The problem also happens when using fable_s as outDir. Probably this means we need to fix the algorithm to find the common base dir 👍