PathVerifier fails on whitespace filename under Linux and .NET Core #1070
Description
Describe the bug
When using FileSystem and MockFileSystem I noticed there is different behavior when creating a new IFileInfo using only whitespaces.
The "error" trails down to the PathVerifier that the MockFileSystem uses
To Reproduce
// Both throw in Linux and windows
var mfs = new MockFileSystem();
mfs.FileInfo.New(" "); // ASCII space
mfs.FileInfo.New("\u00A0"); // Unicode char that's treated as whitespace
// Both pass in Linux
mfs.FileInfo.New("./ ") // Explicit relative path
mfs.FileInfo.New("/ ") // Explicit absolute path
// Passes in Linux
var fs = new FileSystem();
fs.FileInfo.New(" "); // ASCII space
// Passes in Linux and Windows (.NET Core); throws on NET4.8
fs.FileInfo.New("\u00A0"); // Unicode char that's treated as whitespaceExpected behavior
Both calls throw an exception when they should not.
For Linux (whitespace) is a valid file name
For Windows and Linux \u00A0 is a valid file name. However under .NET Framework it also fails
Additional context
In PathInternal.OS.cs .NET has a bool IsEffectivelyEmpty(string? path) method which behaves differently to linux and windows, just to cover those cases.
Currently PathVerifier uses the string.Trim() method, which causes the two explained scenarios
- valid unicode chars get trimmed (
\u00A0) - a whitespace-only relative path is considered to be illegal when it actually is not under linux.