<t>There is no auto-completion because the script says "Miscellaneous Files" instead of the of the name of the Project. Take a look at the image below that came from the video in your question:<br/>
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The "Miscellaneous Files" message can happen for many reasons:<br/>
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It can happen when you open your Unity C# file from another folder instead of opening it from Unity Editor.<br/>
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This can also happen because Unity crashed while Visual Studio is still open therefore corrupting some files.<br/>
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It can happen because Unity was closed then re-opened but is no longer connected to Visual Studio. When Visual Studio is opened you get "Miscellaneous Files" and no auto-completion.<br/>
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This can happen when Visual Studio Tools for unity is not installed.<br/>
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When you create a script from Unity then quickly open it before Unity finish processing it or before the round icon animation stuff finish animating.<br/>
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Most of the times, restarting Unity and Visual Studio should fix this.<br/>
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I can't tell which one is causing the problem but I will cover the most likely solution to fix this.<br/>
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Fix Part 1:<br/>
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Download and Install Visual Studio Tools for unity from this link. Do this while Unity and Visual Studio are both closed.<br/>
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From Unity Editor, go to Edit → Preferences... → External Tools. On the External Script Editor drop down menu, change that to Visual Studio 2015.<br/>
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Fix Part 2:<br/>
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If newly created C# files are coming up as Miscellaneous then follow the instruction below:<br/>
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From Visual Studio, go to Tools → Options... → Tools for Unity → Miscellaneous. Under Show connectivity icon, set it to true then restart Visual Studio.<br/>
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When you re-start, connection icon should now be available in Visual Studio. Click it then choose the Unity instance t<br/>
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(Réponse tronquée)</t>