[Feature] .NET Core 2.1 System.IO API changes

[JeremyKuhne]

.NET Core 2.1 System.IO API changes

There are a number of behavior changes to System.IO APIs in .NET Core 2.1 and new APIs. This issue summarizes the high level changes and links to relevant documents.

Still Needed:

• Content Types
• Table of Contents
• Prioritization

General

APIs have been modified to better support cross platform code writing and substantially improve performance. Here is a summary of the API changes:

1. Path validation has been simplified
2. Span overloads have been added for a number of System.IO.Path APIs
3. There is a new overload for Path.GetFullPath() that allows specifying a base path for resolving the path
4. Directory enumeration results are more consistent cross-plat
5. New enumeration options have been added
6. A new extensible enumeration API has been added

Initial details are below. I'll be adding more links and details shortly.

Path Validation

To facilitate writing cross platform code, System.IO.Path APIs have had their preemptive error checking simplified. Notably:

• Path.GetFullPath() only checks for embedded nulls, null strings, and empty strings
• No IO APIs check for invalid characters
• Path.GetDirectoryName() returns null for empty strings, instead of throwing
• Search patterns are no longer validated beyond null check and rooting (they cannot return true from Path.IsPathRooted())

Span overloads

https://github.com/dotnet/corefx/issues/25539

Path.GetFullPath overload

https://github.com/dotnet/corefx/issues/25539

Enumeration API changes

https://github.com/dotnet/corefx/issues/25873

[mairaw]

Thank you @JeremyKuhne! I'll be adding this to our .NET Core 2.1 project.

[JeremyKuhne]

I put together some blog posts covering the details that can be used as a starting point:

https://blogs.msdn.microsoft.com/jeremykuhne/2018/03/08/system-io-in-net-core-2-1-sneak-peek/
https://blogs.msdn.microsoft.com/jeremykuhne/2018/03/09/custom-directory-enumeration-in-net-core-2-1/

[JeremyKuhne]

When we do these updates we should clarify legacy behavior. https://github.com/dotnet/corefx/issues/26008 brought up the fact that we didn't do whitespace trimming on Unix platforms. Please sync with me to ensure that you've got accurate details across the platforms/versions. :)

[mairaw]

Thanks @JeremyKuhne. We'll do and also ping you for reviews. 😄

[mairaw]

Moving this to the backlog until we're actually ready to start working on this