Error, warn, or fix behavior when specifying output path when building a solution

[dsplaisted]

Specifying the output path (commonly by using the -o command line option to dotnet build or dotnet publish) when building or publishing a solution can lead to issues, as multiple projects building to the same path may override each other's files.

We should either block specifying the output path for a solution, or do something to fix the behavior (for example by appending the project name to the specified output path for each project).

Related:

• Warn on publishing solutions / path forward for publishing solutions #3650
• BUG: SDK-3.1.300 dotnet publish .sln now chooses the older DLL in version conflict #11953
• Prevent --output command-line option for multi-targeted projects #13369
• Error on runtime identifier specified at solution level #12126

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ericstj]

@dsplaisted @marcpopMSFT this should be prioritized. In the past month I've observed multiple teams hit this issue and spend a tremendous amount of time chasing down the source of the binclash / wrong binaries in the output.

[dsplaisted]

@ericstj Can you link the examples of where people have hit this if you have them?

Related: dotnet/msbuild#3497

[ericstj]

One case is linked above: dotnet/runtime#75086. The other was an internal request which I just forwarded. I'm pretty sure this has also come up on the .NET discussion alias a few times.

[dsplaisted]

This will be fixed in 7.0.200 (by erroring when you use the --output parameter for solution files).