potential fix for 5932

[dsyme]

Possible fix for perf problem #5932

[dsyme]

seems to work on my local machine

[TIHan]

So, CI passes on your local machine?

[dsyme]

Some test is being very picky about exactly which exceptions are raised when for badly formed file paths. Trying again.

[dsyme]

OK, this is now ready. I included some cleanup and some notes about the somewhat odd use of path normalization in that code (which I couldn't remove easily but I left some notes about how we might go about removing it)

[cartermp]

I recommend changing the normalization function to use an explicit parameter annotation. Should we ever move to .NET Core or .NET Standard 2.1 in the future, this code will break due to the ReadOnlySpan<char> overload: https://docs.microsoft.com/en-us/dotnet/api/system.io.path.ispathrooted?view=netcore-2.2#System_IO_Path_IsPathRooted_System_ReadOnlySpan_System_Char__

[dsyme]

@cartermp Done, thanks

[cartermp]

Great, LGTM. Should alleviate #5932 to the point where any further work would require a redesign, which is exactly where we want to be w.r.t. perf problems