src/vs/workbench/contrib/files/browser/editors/fileEditorInput.ts/FileEditorInput/capabilities
class FileEditorInput:	override get capabilities(): EditorInputCapabilities {
		let capabilities = EditorInputCapabilities.CanSplitInGroup;

		if (this.model) {
			if (this.model.isReadonly()) {
				capabilities |= EditorInputCapabilities.Readonly;
			}
		} else {
			if (this.fileService.hasProvider(this.resource)) {
				if (this.fileService.hasCapability(this.resource, FileSystemProviderCapabilities.Readonly)) {
					capabilities |= EditorInputCapabilities.Readonly;
				}
			} else {
				capabilities |= EditorInputCapabilities.Untitled;
			}
		}

		return capabilities;
	}