My issue with constant rebuilds seems to be from my project switching back and forth from the VS 2015 toolchain to the 2017 toolchain. I turned on -verbose on UBT and I see this when it happens:
2>UnrealBuildTool: VERBOSE: Module.Core.2_of_9.cpp: Produced item "Module.Core.2_of_9.cpp.obj" was produced by outdated command-line.
2> Old command-line: F:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\cl.exe @"E:\git\UnrealEngine\Engine\Intermediate\Build\Win64\UE4Editor\Development\Core\Module.Core.2_of_9.cpp.obj.response"
2> New command-line: E:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.13.26128\bin\HostX64\x64\cl.exe
@"E:\git\UnrealEngine\Engine\Intermediate\Build\Win64\UE4Editor\Development\Core\Module.Core.2_of_9.cpp.obj.response"
I generated the engine files with:
GenerateProjectFiles.bat -2017
And my game project has:
[/Script/SourceCodeAccess.SourceCodeAccessSettings]
PreferredAccessor=VisualStudio2017
in DefaultEditorPerProjectUserSettings.ini
Any ideas on what could be going wrong?