Disabled SA1649 code fix for linked files

[vweijsters]

Changed the behavior of the SA1649 code fix to no longer offer a code fix when a document has linked documents. This was done to protect the user from getting unexpected copied or moved source code files.

This prevents #1693 and #1665 from happening. Proper fixing can only be done when dotnet/roslyn#6261 is resolved.

[codecov-io]

Current coverage is 79.48%

Merging #1714 into master will decrease coverage by -0.01% as of 7d2bb59

@@            master   #1714   diff @@
======================================
  Files          545     545       
  Stmts        32585   32583     -2
  Branches      9005    9006     +1
  Methods                          
======================================
- Hit          25902   25900     -2
- Partial       5232    5234     +2
+ Missed        1451    1449     -2

Review entire Coverage Diff as of 7d2bb59

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[sharwell]

The frustrating thing here is the add/remove document functionality actually does work when you have multiple project files in the same folder. This is a layout that many projects I work on use.

Also, the implementation here is disabling the code fix for files that appear in more than one project, whether or not the file is a linked file or simply included as a normal file in more than one project. The code fix will still behave incorrectly for the following cases:

• A file is included as a link into only one project in the solution
• A file is part of a shared project, and that shared project is only referenced by one project in the solution

💭 Perhaps it's better to go with a configuration approach where users can disable a code fix if it's known to be problematic in their solution.

[pdelvo]

Do we still want this PR?

[vweijsters]

I'm still undecided on this, as the issues are still valid. There is no progress on the roslyn issue yet.

It will probably be possible to create a workaround where we use either VisualStudioWorkspace or EnvDTE to make the code fix work properly for Visual Studio only. This will improve the usability for the majority of users, but it will render (part of) the codefix useless outside of Visual Studio.

@sharwell what is your opinion?

[sharwell]

Such a frustrating case. In some projects, the code fix works wonderfully, while in others it fails completely. 😟

[vweijsters]

Its not really relevant anymore