Xcode local build failure: xcode-select : error : tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

[carlossanlop]

When building runtime in my local Macbook Pro with build.sh -rc Release today, I got this failure:

xcode-select : error : tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance [/Users/carlos/repos/runtime/src/coreclr/tools/aot/ILCompiler/ILCompiler.csproj]
/Users/carlos/repos/runtime/src/coreclr/tools/aot/ILCompiler/ILCompiler.csproj(79,24): error MSB4086: A numeric comparison was attempted on "$(_XcodeVersion)" that evaluates to "" instead of a number, in condition "'$(_XcodeVersion)' >= '15'".

It came from here:
https://github.com/dotnet/runtime/blob/main/src/coreclr/tools/aot/ILCompiler/ILCompiler.csproj#L79

Root cause was that the Xcode -> Preferences -> Location -> Command Line Tools dropdown was set to No Xcode selected. So I had to manually select the single only option in the dropdown and now the local build succeeded. It's explained here:
https://stackoverflow.com/a/72115137

The top error comes from Xcode itself, but that message wasn't helpful. But we could kind of address this from our side:

• We could add a new MSBuild message on our side when we detect such Xcode error message.
• We could document this as a manual configuration prerequisite step for building in https://github.com/dotnet/runtime/blob/main/docs/workflow/requirements/macos-requirements.md
• Or if this can be configured automatically for the user when building, even better.

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[jkotas]

Related to #100189

[carlossanlop]

Yes, it seems like the same failure, it just happened at different times. I'll close this and update that one with my findings and my suggestions.

[carlossanlop]

Oh I typed too soon - That one is already closed as fixed. Maybe it was a different root cause, as that one was merged 2 months ago.

Edit: Same root cause, different MSBuild script.

[jkotas]

You can try the change in #102473 to check that it fixes the build break for you.