Thanks Tom, this worked for me!!!

close your project

make a backup of your current project by copy/pasting its folder or by relying on any source version system. (it shouldn't be useful, but who knows)

under your project folder, delete the Assets/VuforiaFolder

create a new empty Unity project using 2017.3

in the test scene, add any object under the Vuforia submenu; Unity will tell you that it needs to import Vuforia, accept.

navigate to your new project folder, then close Unity

in the new project folder, go in the Assets directory and cut the Vuforia folder

navigate to you project directory, go in Assets and paste the Vuforia folder there.

delete the  folder of the temporary project you created.

Reopen your project in Unity and voila, the errors mentioned below disappeared.

i already did auto migration with no backup.

my app use cloud recognition.

after auto migration, app doesn't work at all.

could i recover?

-----------------------------------------

it mean auto migration is below.

1.install UNITY 2017.3

2.open UNITY 2017.2 project

3.dialog box is shown.

4.push 'yes' button.

Updated question with a workaround; but this should be automated if possible.

-- Edited with workaround:

Here's workaround for the compiling issues described below:

1. close your project
2. make a backup of your current project by copy/pasting its folder or by relying on any source version system. (it shouldn't be useful, but who knows)
3. under your project folder, delete the Assets/VuforiaFolder
4. create a new empty Unity project using 2017.3
5. in the test scene, add any object under the Vuforia submenu; Unity will tell you that it needs to import Vuforia, accept.
6. navigate to your new project folder, then close Unity
7. in the new project folder, go in the Assets directory and cut the Vuforia folder
8. navigate to you project directory, go in Assets and paste the Vuforia folder there.
9. delete the  folder of the temporary project you created.
10. Reopen your project in Unity and voila, the errors mentioned below disappeared.

--

I updated to 2017.3 and open my 2017.2p4 project, reimported all the asset and i have 4 compiler errors:

Assets/Vuforia/Scripts/DefaultSmartTerrainEventHandler.cs(20,5): error CS0246: The type or namespace name `ReconstructionBehaviour' could not be found. Are you missing an assembly reference?

Assets/Vuforia/Scripts/DefaultSmartTerrainEventHandler.cs(26,12): error CS0246: The type or namespace name `PropBehaviour' could not be found. Are you missing an assembly reference?

Assets/Vuforia/Scripts/DefaultSmartTerrainEventHandler.cs(27,12): error CS0246: The type or namespace name `SurfaceBehaviour' could not be found. Are you missing an assembly reference?

Assets/Vuforia/Scripts/DefaultSmartTerrainEventHandler.cs(59,31): error CS0246: The type or namespace name `Prop' could not be found. Are you missing an assembly reference?

Assets/Vuforia/Scripts/DefaultSmartTerrainEventHandler.cs(68,34): error CS0246: The type or namespace name `Surface' could not be found. Are you missing an assembly reference?

What should I do?

Hello BennyOKC91,

There shouldn't be any major steps required to import from 2017.2 with 6.5 to 2017.3 with 7.0. If you encounter any issues while doing so, please let us know however.

Thanks,

Vuforia Support