Why didn't you just add that steamapps folder as a new installation folder in the settings?
This is nearly what I usually did before Proton was released. Wine + Steam for Windows + soft-linked 'steamapps' folder.
But with Steam for Linux + Proton I can't link whole 'steamapps' from Windows, because I have some native games installed, nor I can't pick any of existing steam folders to install to, because Steam/Proton demands empty(!) folder when selecting custom.
So (in OP) I tried to link installed game folder to default '~/.steam/steam/steamapps/common/' folder, but without luck.
Just now I also tried to create empty folder and soft-link installed game there. Same result, it just re-downloads everything, ruining existing files in process.
Is there any way to make Steam believe that particular game is alreay installed, and theres's no need to download it, maybe ini-file or something?
Is there any way to make Steam believe that particular game is alreay installed, and theres's no need to download it, maybe ini-file or something?
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Answering myself: Yes! Seems all we need is to copy 'appmanifest_%appid%.acf' to '~/.steam/steam/steamapps/' (one level above 'common' folder). For example to run Wreckfest with Proton we need soft-link 'Bugbear Entertainment' folder into '~/.steam/steam/steamapps/common/' and copy 'appmanifest_228380.acf' file to '~/.steam/steam/steamapps/'
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Considering problem solved, though in a somewhat unnatural way.
Closing per the last comment. In general, sharing a Steam library between Windows and Linux is not supported and this is a rather odd way to mingle two Steam installs.
Issue transferred from https://github.com/ValveSoftware/Proton/issues/780.
@ssv-170379 posted on 2018-08-27T21:26:39:
(Sorry for bad English) The Evil Within 2. Created a soft-link to a folder with pre-downloaded game (from another Steam installation) in ~/.steam/steam/steamapps/common/ . When installing via Proton it checks for existing files for a moment but immediately starts to re-download the whole game, and finally fails to extract files to that linked folder (in passing ruining existing there installation). And only after removing soft link game files are deploying normally. But when installation is finished you may to move TheEvilWithin2 folder to other partition, create soft-link and play the game. i.e. soft-linking works correctly except the installation process.