[Bug]: Packing a NUSPEC results in different behavior depending on the type of slash used

[jeffkl]

NuGet Product Used

NuGet.exe

Product Version

All

Worked before?

No response

Impact

No response

Repro Steps & Context

With the following directory structure:

foo\bar\file.txt

You will get different behavior with these two nuspecs:

Back slash

.nuspec

<files>
  <files src="foo\bar\**" target="tools" />
</files>

Result:

tools\file.txt

Forward slash

.nuspec

<files>
  <files src="foo/bar/**" target="tools" />
</files>

Result:

tools\foo\bar\file.txt

This was regressed here: https://github.com/NuGet/NuGet.Client/pull/3634/files#diff-c01d3caec0c8d4f43277fdc62db8f461cfa430fdadfd6f92d46804dfbe666c20R1107

And reported here: #11125

We'll revert the breaking behavior and figure out if there's a way to fix the behavior without it being a breaking change.

Verbose Logs

No response

[jeffkl]

Some more details here, the behavior changed on Windows between version 5.9 and 5.10:

version	content/*	/content/**	content\*	content\**
5.8.1	error	tools\content\file.txt	tools\file.txt	tools\file.txt
5.9.1	error	tools\content\file.txt	tools\file.txt	tools\file.txt
5.10.0	tools\file.txt	tools\file.txt	tools\file.txt	tools\file.txt
5.11.0	tools\file.txt	tools\file.txt	tools\file.txt	tools\file.txt
FUTURE	tools\content\file.txt	tools\content\file.txt	tools\content\file.txt	tools\content\file.txt
FUTURE		tools\content\sub\file.txt		tools\content\sub\file.txt

Add option to get old behavior back with something like flatten="true"

[rbleattler]

How on earth is this still an open issue... This was documented years ago by the community. It should at least have a footnote in the documentation...