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OpenIDEA recognizes a folder as a Unity project when it has an Assets folder and ProjectSettings/ProjectVersion.txt. It opens scripts that Unity sends it, hides Unity’s caches, moves .meta files along with their assets, and uses the C# language server for code intelligence. No Unity package or editor plugin is needed.

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Set OpenIDEA as the external script editor

1

Open External Tools in Unity

In Unity, open Edit › Preferences › External Tools (on macOS, Unity › Settings or Unity › Preferences, then External Tools).
2

Choose OpenIDEA

Under External Script Editor, choose Browse and select the OpenIDEA executable (on macOS, OpenIDEA.app).
3

Set the arguments

Set External Script Editor Args to:
Unity quotes the expanded project and file paths itself, including paths with spaces. Do not add another pair of quotes around the placeholders.
Double-click a script in Unity’s Project window, or a source location in the Console. OpenIDEA opens the project, or focuses the window that already has it open, opens the file and puts the caret at the line and column. Other open tabs stay where they are.

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How the arguments work

These arguments belong to the application executable: --file=..., --line=... and --column=... also work. Invalid arguments or a missing file are reported as an error. Without a project folder, --file opens in an open project window that contains the file, or in LightEdit. If you call the executable yourself, quote paths as your shell requires. The separately installed openidea command has a different syntax (--line and --column come before the file, and there is no --file); see Command line.
On Windows, run Unity and OpenIDEA with the same permissions (both elevated or both not). If a running OpenIDEA does not react to a double-click, restart both with matching permissions and try again.

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The Unity project view

When a Unity project is open, the Project tool window switches to the Unity pane. Its root shows the editor version read from ProjectVersion.txt (for example Unity 6000.0.62f1). The Unity pane hides:
  • .meta files;
  • generated folders at the project root: Library, Temp, Obj, obj, Logs, Build, Builds, UserSettings, .vs, .idea, .vscode;
  • generated solution and project files at the root (.csproj, .sln, .slnx and similar).
To show them, open the pane’s options menu and turn on Show Meta Files or Show Generated Files under Appearance. The Project and Project Files panes always show everything. Assets and Packages are source folders and ProjectSettings is a resources folder. The generated folders listed above are excluded from indexing, search and file watching, even before Unity creates them, so Library/PackageCache does not slow the IDE down or show up in search results.

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Assets and .meta files

File operations on assets under Assets keep Unity’s metadata consistent:
  • Rename and move take the .meta file with the asset. This also applies to file moves caused by refactorings.
  • Delete removes the asset and its .meta file together; Local History keeps a copy of both.
  • Copy gives the copies new GUIDs and rewrites references between the copied files (in text-serialized YAML assets and in .asmdef / .asmref files), so the copy does not clash with the original. Binary-serialized assets (prefabs, scenes, materials and so on saved in binary mode) cannot be copied this way; switch Unity’s asset serialization to Force Text first.
  • The Assets folder itself cannot be moved, copied or deleted, and selecting only a .meta file whose asset exists is rejected: select the asset instead.
  • New file names are checked against existing .meta files too.
When Git asks whether to add a new file you created in the IDE, the .meta file Unity generates for it is added along with it.

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Code intelligence

C# in a Unity project uses the same language server as any other C# project, csharp-ls; see C# and .NET for installation. A Unity project is a workspace root for it even before a solution exists. csharp-ls reads the .sln and .csproj files that Unity generates. When they are missing, the Unity pane shows:
C# project files are missing. In Unity, select an external script editor in Preferences > External Tools, then regenerate project files.
The IDE notices when Unity writes those files and picks them up without reopening the project. Navigate › Declaration or Usages on a Unity type such as MonoBehaviour opens the decompiled source read-only. Decompiled files are not checked for errors, since they often use a different C# language version than your project.

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Limitations

  • OpenIDEA does not generate Unity’s C# project files; Unity has to.
  • There is no Unity debugger integration: you cannot attach to the Unity editor or a player from OpenIDEA.
  • There are no Unity-specific inspections, run configurations or ShaderLab support.
  • Opening files from Unity works for local projects only, not projects in WSL.