In the same vein, if there's a TARGET/ directory, it doesn't get excluded when packaging.

Caused by:
  Source directory was modified by build.rs during cargo publish. Build scripts should not modify anything outside of OUT_DIR.
  Added: /private/tmp/bla/target/package/testx-0.0.0/TARGET/.rustc_info.json
  	/private/tmp/bla/target/package/testx-0.0.0/TARGET/debug
  	/private/tmp/bla/target/package/testx-0.0.0/TARGET/debug/.cargo-lock
  	/private/tmp/bla/target/package/testx-0.0.0/TARGET/debug/.fingerprint

@rustbot label Command-package

so perhaps a simple case-insensitive comparison will suffice

While that sounds lovely, in what locale? For the languages I speak it is relatively straight forward, but my understanding is that case handling is lossy in some languages, such as German (ẞ is Ss in upper case I think?) and Turkish (I believe they have the letter "i" both with and without a dot, and the uppper/lower case there isn't straight forward, but don't ask me how exactly).

As a Swedish/English speaker this is all hearsay though, and I don't know how e.g. Windows or Mac OS handle these, though I think I heard that NTFS store a case normalisation table at file system creation time based on the locale set at that point?

On Windows, the NTFS up case table is initialized when the drive is first formatted. So it'll depend on the Windows version that did that. It is however language neutral and only acts on the Basic Multilingual Plane.

Also, depending on the configuration, NTFS can be case sensitive. In Windows this can even be set differently for each directory.

On Windows, the NTFS up case table is initialized when the drive is first formatted. So it'll depend on the Windows version that did that. It is however language neutral and only acts on the Basic Multilingual Plane.

Hm, maybe I'm thinking of FAT and Windows 9x then? Pretty sure things differed depending on code pages and such there. Not sure how modern OSes interacting with FAT32/exFAT works with that. Hopefully it is somewhat sane on any Windows version Rust still supports.

Ah yes FAT32 is indeed a mess. But then I'm also not sure how well Cargo and rustc support it as it lacks a lot of filesystem features that may be expected. Probably it does at least work if it's only read from (e.g. the target directory is on another drive).

While that sounds lovely, in what locale?

It is a messy problem, but fortunately the detection algorithm doesn't need to produce user-facing text, so it doesn't need to be perfect from linguistic perspective. It only needs to detect potential collisions between file names. Crates that work with only a specific combination of Windows locale and NTFS vintage are not generally useful, so the detection can also err on the side of over-normalizing (e.g. normalize all dotless ı's to i, forbid all control characters, check against both lower and upper case, treat codepoints with multiple transliterations/decompositions as a wildcard, etc.).

but for a start, even a simple .lowercase() will handle more than enough for the accidental variations of Readme.Md.