Illegal file system entry name character creates hidden file content on specific platforms inconsistently

[ghost]

• Version: 11.x
• Platform: Windows
• Subsystem: fs

We noticed that

fs.mkdirSync("a")
fs.writeFileSync("a/b:c", "123")

console.log(fs.readdirSync("a"))
console.log(fs.readFileSync("a/b:c"))
console.log(fs.readFileSync("a/b"))

• On Linux: Creates b:c in directory a and reads 123 as its content. Then fails on a/b as non-existing file.

• On Windows: Creates b in directory a and reads 123 as content of b:c, then also reads a/b as existing file with no content. Readdir displays b as the only file in directory a

We suppose this is some weird Windows quirk, but it's not documented and the behavior is not expected. We suggest adding additional check to writeFile to throw an error if file name contains colon, since it's illegal character in Windows file names.

[richardlau]

Colons on NTFS files systems on Windows denote file streams: https://docs.microsoft.com/en-us/windows/desktop/fileio/file-streams

[ghost]

Assuming this is working as intended then. Thanks.