Developer Notes

The behavior, in general, is correct - you can't do a full rebuild while the editor is still open. I've added a better error message to that effect.


Performing a Rebuild with a hot reload on a brand new code project will fail unless both the Editor and Visual Studio have first been closed and then re-opened. The same result occurs if a Clean is attempted.

This was only tested in a binary build of the Engine, since rebuilds of a source-built Engine rebuild the entire Engine.

Yes. This behavior did not occur in 4.17.2

Steps to Reproduce
  1. Create a new code project using the Third Person template.
  2. Once both the Editor and Visual Studio have opened, right-click the project in the Solution Explorer window in Visual Studio and select Rebuild.

The rebuild fails with an error similar to the following: error : Unable to delete D:\Unreal Projects\Current Issues\TestRebuild\Binaries\Win64\UE4Editor-TestRebuild.dll (Access to the path 'D:\Unreal Projects\Current Issues\TestRebuild\Binaries\Win64\UE4Editor-TestRebuild.dll' is denied.)

The rebuild completes successfully.

Close and then re-open both the Editor and Visual Studio. A rebuild with a hot reload will now complete successfully.

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ComponentCore - Hot Reload
Affects Versions4.18.3
Target Fix4.19
Fix Commit3870013
Main Commit3990065
Release Commit3870013
CreatedJan 18, 2018
ResolvedFeb 2, 2018
UpdatedApr 27, 2018