<SupportsSharedFolders> not included in schema definition for MailAppVersionOverridesV1_1 in Visual Studio 2017?

Question

When building a Office Add-in Manifest project in Visual Studio 2017, we're getting errors with the schema definition not including the SupportsSharedFolders element. However, documentation states that this element is supported in 1.8: https://learn.microsoft.com/en-us/office/dev/add-ins/reference/manifest/supportssharedfolders

error : The element 'DesktopFormFactor' in namespace 'http://schemas.microsoft.com/office/mailappversionoverrides/1.1' has invalid child element 'SupportsSharedFolders' in namespace 'http://schemas.microsoft.com/office/mailappversionoverrides/1.1'. List of possible elements expected: 'FunctionFile, ExtensionPoint' in namespace 'http://schemas.microsoft.com/office/mailappversionoverrides/1.1'.

Here is an example manifest that is able to be sideloaded into an Office 365 mailbox that includes the element:

<!--Published:70EDFC97-B41D-43C5-B751-7C00AD999804-->
<!--Created:cb85b80c-f585-40ff-8bfc-12ff4d0e34a9-->
<OfficeApp xmlns="http://schemas.microsoft.com/office/appforoffice/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0" xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0"
  xsi:type="MailApp">
  <Id>e6497c92-80b1-47c6-b983-28bb81fde0ca</Id>
  <Version>1.0.0</Version>
  <ProviderName>Example</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <DisplayName DefaultValue="Test Add-in" />
  <Description DefaultValue="An example add-in" />
  <IconUrl DefaultValue="https://localhost/icon.png" />
  <HighResolutionIconUrl DefaultValue="https://localhost/icon.png" />
  <SupportUrl DefaultValue="https://example.com" />
  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="MailBox" MinVersion="1.1" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="https://localhost/index.html" />
        <RequestedHeight>216</RequestedHeight>
      </DesktopSettings>
      <TabletSettings>
        <SourceLocation DefaultValue="https://localhost/index.html" />
        <RequestedHeight>216</RequestedHeight>
      </TabletSettings>
      <PhoneSettings>
        <SourceLocation DefaultValue="https://localhost/index.html" />
      </PhoneSettings>
    </Form>
  </FormSettings>
  <Permissions>ReadWriteMailbox</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read" />
  </Rule>
  <DisableEntityHighlighting>false</DisableEntityHighlighting>

  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <Requirements>
      <bt:Sets DefaultMinVersion="1.3">
        <bt:Set Name="Mailbox" />
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">
        <DesktopFormFactor>
          <!-- Message compose form -->
          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgComposeGroup">
                <Label resid="groupLabel" />
                <!-- Task pane button -->
                <Control xsi:type="Button" id="msgComposeOpenPaneButton">
                  <Label resid="paneComposeButtonLabel" />
                  <Supertip>
                    <Title resid="paneComposeSuperTipTitle" />
                    <Description resid="paneComposeSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="cmd-icon-16" />
                    <bt:Image size="32" resid="cmd-icon-32" />
                    <bt:Image size="80" resid="cmd-icon-80" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="composeTaskPaneUrl" />
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
        </DesktopFormFactor>
      </Host>
    </Hosts>

    <Resources>
      <bt:Images>
        <bt:Image id="cmd-icon-16" DefaultValue="https://localhost/icon.png" />
        <bt:Image id="cmd-icon-32" DefaultValue="https://localhost/icon.png" />
        <bt:Image id="cmd-icon-80" DefaultValue="https://localhost/icon.png" />
        <bt:Image id="cmd-icon-25" DefaultValue="https://localhost/icon.png" />
        <bt:Image id="cmd-icon-48" DefaultValue="https://localhost/icon.png" />
      </bt:Images>
      <bt:Urls>
        <bt:Url id="composeTaskPaneUrl" DefaultValue="https://localhost/index.html" />
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="groupLabel" DefaultValue="Example" />
        <bt:String id="paneComposeButtonLabel" DefaultValue="Test Add-in" />
        <bt:String id="paneComposeSuperTipTitle" DefaultValue="Test Add-in Super Tip" />
      </bt:ShortStrings>
      <bt:LongStrings>
        <bt:String id="paneComposeSuperTipDescription" DefaultValue="A test add-in" />
      </bt:LongStrings>
    </Resources>

    <!-- 1.1 overrides -->
    <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides/1.1" xsi:type="VersionOverridesV1_1">
      <Requirements>
        <bt:Sets DefaultMinVersion="1.3">
          <bt:Set Name="Mailbox" />
        </bt:Sets>
      </Requirements>

      <Hosts>
        <Host xsi:type="MailHost">
          <DesktopFormFactor>
          <SupportsSharedFolders>true</SupportsSharedFolders>
            <!-- Message compose form -->
            <ExtensionPoint xsi:type="MessageReadCommandSurface">
              <OfficeTab id="TabDefault">
                <Group id="msgComposeGroup">
                  <Label resid="groupLabel" />
                  <!-- Task pane button -->
                  <Control xsi:type="Button" id="msgComposeOpenPaneButton">
                    <Label resid="paneComposeButtonLabel" />
                    <Supertip>
                      <Title resid="paneComposeSuperTipTitle" />
                      <Description resid="paneComposeSuperTipDescription" />
                    </Supertip>
                    <Icon>
                      <bt:Image size="16" resid="cmd-icon-16" />
                      <bt:Image size="32" resid="cmd-icon-32" />
                      <bt:Image size="80" resid="cmd-icon-80" />
                    </Icon>
                    <Action xsi:type="ShowTaskpane">
                      <SourceLocation resid="composeTaskPaneUrl" />
                    </Action>
                  </Control>
                </Group>
              </OfficeTab>
            </ExtensionPoint>
          </DesktopFormFactor>
          <MobileFormFactor>
            <ExtensionPoint xsi:type="MobileMessageReadCommandSurface">
              <Group id="mobileGroupID">
                <Label resid="paneComposeButtonLabel" />
                <Control xsi:type="MobileButton" id="mobileButton1">
                  <Label resid="paneComposeButtonLabel" />
                  <Icon xsi:type="bt:MobileIconList">
                    <bt:Image size="25" scale="1" resid="cmd-icon-25" />
                    <bt:Image size="25" scale="2" resid="cmd-icon-25" />
                    <bt:Image size="25" scale="3" resid="cmd-icon-25" />

                    <bt:Image size="32" scale="1" resid="cmd-icon-32" />
                    <bt:Image size="32" scale="2" resid="cmd-icon-32" />
                    <bt:Image size="32" scale="3" resid="cmd-icon-32" />

                    <bt:Image size="48" scale="1" resid="cmd-icon-48" />
                    <bt:Image size="48" scale="2" resid="cmd-icon-48" />
                    <bt:Image size="48" scale="3" resid="cmd-icon-48" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="composeTaskPaneUrl" />
                  </Action>
                </Control>
              </Group>
            </ExtensionPoint>
          </MobileFormFactor>
        </Host>
      </Hosts>

      <Resources>
        <bt:Images>
          <bt:Image id="cmd-icon-16" DefaultValue="https://localhost/icon.png" />
          <bt:Image id="cmd-icon-32" DefaultValue="https://localhost/icon.png" />
          <bt:Image id="cmd-icon-80" DefaultValue="https://localhost/icon.png" />
          <bt:Image id="cmd-icon-25" DefaultValue="https://localhost/icon.png" />
          <bt:Image id="cmd-icon-48" DefaultValue="https://localhost/icon.png" />
        </bt:Images>
        <bt:Urls>
          <bt:Url id="composeTaskPaneUrl" DefaultValue="https://localhost/index.html" />
        </bt:Urls>
        <bt:ShortStrings>
          <bt:String id="groupLabel" DefaultValue="Example" />
          <bt:String id="paneComposeButtonLabel" DefaultValue="Test Add-in"/>
          <bt:String id="paneComposeSuperTipTitle" DefaultValue="Test Add-in Super Tip" />
        </bt:ShortStrings>
        <bt:LongStrings>
          <bt:String id="paneComposeSuperTipDescription" DefaultValue="An example add-in." />
        </bt:LongStrings>
      </Resources>
    </VersionOverrides>
  </VersionOverrides>
</OfficeApp>

Answer 1

It appears that this is due to the schema definition in Visual Studio 2017 being out of date and not including this new element. I was able to pull the MailAppVersionOverridesV1_1.xsd schema definitions file ("C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\Xml\Schemas\1033" depending on your install of VS) from a Visual Studio 2019 install to bypass this, but will there be any update to Visual Studio 2017 to support this?