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How to: Modify a Project System So That Projects Load in Multiple Versions of Visual Studio

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In Visual Studio 2012, you can prevent a project that was created in your custom project system from loading in an earlier version of Visual Studio, or you can enable it to identify itself to a later version in case it requires repair, conversion, or deprecation.

Note

In this context, the term repair means modifying the project so that it can load automatically in Visual Studio 2010 with SP1 or in the later version. Conversion, or upgrade, means modifying a project so that it can no longer load in the version in which it was created.

Marking a Project as Incompatible

You can mark a project as incompatible with earlier versions of Visual Studio. For example, suppose you create in Visual Studio 2012 a project that uses a .NET Framework 5 feature. Because this project cannot be built in Visual Studio 2010 with SP1, you can mark it as incompatible with Visual Studio 2010 with SP1 to prevent that version from trying to load it.

The component that adds the incompatible feature is responsible for marking the project as incompatible. The component must have access to the IVsHierarchy interface that represents the projects of interest.

To mark a project as incompatible

  1. In the component, get an IVsAppCompat interface from the global service SVsSolution.

    For more information, see SVsSolution.

  2. In the component, call IVsAppCompat.AskForUserConsentToBreakAssetCompat, and pass it an array of IVsHierarchy interfaces that represent the projects of interest.

    This method has the following signature:

    HRESULT AskForUserConsentToBreakAssetCompat([in] SAFEARRAY(IVsHierarchy*) sarrProjectHierarchies)

    If you implement this code, a project compatibility dialog box will appear. The dialog box will asks the user for permission to mark all specified projects as incompatible. If the user agrees, AskForUserConsentToBreakAssetCompat returns S_OK; otherwise, AskForUserConsentToBreakAssetCompat returns OLE_E_PROMPTSAVECANCELLED.

    Warning

    In most common scenarios, the IVsHierarchy array will contain only one item.

  3. If AskForUserConsentToBreakAssetCompat returns S_OK, the component makes or accepts the changes that break compatibility.

  4. In your component, call the IVsAppCompat.BreakAssetCompatibility method for each project that you want to mark as incompatible. The component can set the value of the parameter lpszMinimumVersion to a specific minimum version instead of having Visual Studio look up the current version string in the registry. This approach minimizes the risk of the component inadvertently setting a higher value in the future, based on what is in the registry at that time.. If that higher value were set, Visual Studio 2012 couldn't open such a project.

    This method has the following signature:

    HRESULT BreakAssetCompatibility([in] IVsHierarchy * pProjHier), [in] LPCOLESTR lpszMinimumVersion);

    If the component sets lpszMinimumVersion to NULL, the BreakAssetCompatibility method calls the IVsAppCompat.GetCurrentDesignTimeCompatVersion method to obtain a string that represents the current version of Visual Studio.

    This method has the following signature:

    HRESULT GetCurrentDesignTimeCompatVersion([out] BSTR * pbstrCurrentDesignTimeCompatVersion)

    The BreakAssetCompatibility method then calls the IVsHierarchy.SetProperty method to set the root VSHPROPID_MinimumDesignTimeCompatVersion property to the value of the version string that you obtained in the previous step.

    For more information, see SetProperty.

Important

You must implement the VSHPROPID_MinimumDesignTimeCompatVersion property to mark a project as compatible or incompatible. For example, if the project system uses an MSBuild project file, add to the project file a <MinimumVisualStudioVersion> build property that has a value equal to the corresponding VSHPROPID_MinimumDesignTimeCompatVersion property value.

Detecting Whether a Project is Incompatible

Projects that are incompatible with the current version of Visual Studio must be kept from loading. Furthermore, a project that is incompatible cannot be upgraded or repaired. Therefore, a project must be checked for compatibility twice: first, when it is being considered for upgrade or repair, and second, before it is loaded.

To enable the detection of project incompatibility, you must implement the UpgradeProject_CheckOnly and CreateProject methods. If a project is incompatible, UpgradeProject_CheckOnly must return the success code VS_S_INCOMPATIBLEPROJECT, and CreateProject must return the error code VS_E_INCOMPATIBLEPROJECT. For flavored projects, you must implement IVsProjectFlavorUpgradeViaFactory2.UpgradeProjectFlavor_CheckOnly instead of IVsProjectUpgradeViaFactory4.UpgradeProject_CheckOnly.

A project system is referred to as flavored if it has a web, Office (VSTO), Silverlight, or other project type built on top of it. Older project systems that already implement IVsProjectUpgradeViaFactory.UpgradeProject_CheckOnly and flavored project systems that already implement IVsProjectFlavorUpgradeViaFactory.UpgradeProjectFlavor_CheckOnly continue to be supported. However those project systems can't specify in more detail the kind of migration that a project needs. Any migration that's detected in these methods is treated simply as “Minor Upgrade” and, more specifically, as though they had set an upgrade flag to the value VSPUVF_PROJECT_SAFEREPAIR as described later in this topic. For a better user experience, we recommend that existing project systems implement the new interfaces.

The new implementations in IVsProjectUpgradeViaFactory4 and IVsProjectFlavorUpgradeViaFactory2 enable specifying the migration type more precisely.

Note

You can cache the result of the compatibility check by the UpgradeProject_CheckOnly method so that it can also be used by the subsequent call to CreateProject.

For example, if the UpgradeProject_CheckOnly and CreateProject methods that are written for a Visual Studio 2010 with SP1 project system examine a project file and find that the <MinimumVisualStudioVersion> build property is "11.0", Visual Studio 2010 with SP1 would not load the project. In addition, Solution Navigator would indicate that the project is “incompatible” and would not load it.

Upgrading or Repairing a Project

By using Visual Studio 2012, you can modify most projects that were created in earlier versions of Visual Studio (for example Visual Studio 2008) to work in Visual Studio 2012 and in Visual Studio 2010 with SP1.

Before a project is loaded, Visual Studio calls the UpgradeProject_CheckOnly method to determine whether the project can be upgraded. If the project can be upgraded, the UpgradeProject_CheckOnly method sets a flag that causes a later call to the UpgradeProject method to upgrade the project. Because incompatible projects cannot be upgraded, UpgradeProject_CheckOnly must first check for project compatibility, as described in the earlier section.

In Visual Studio 2012, you, as the author of a project system, implement UpgradeProject_CheckOnly (from the IVsProjectUpgradeViaFactory4 interface) to provide users of your project system with an upgrade check. When users open a project, this method is called to determine whether a project must be repaired before it is loaded. The possible upgrade requirements are enumerated in VSPUVF_REPAIRFLAGS, and they include the following possibilities:

  1. SPUVF_PROJECT_NOREPAIR: Requires no repair.

  2. VSPUVF_PROJECT_SAFEREPAIR: Makes the project compatible with Visual Studio 2010 with SP1 without the issues that you might have encounter with the previous versions of the product.

  3. VSPUVF_PROJECT_UNSAFEREPAIR: Makes the project compatible with Visual Studio 2010 with SP1 but with some risk of the issues that you might have encountered with previous versions of the product. For example, the project would not be compatible if it depended on different SDK versions between Visual Studio 2012 and Visual Studio 2010 with SP1.

  4. VSPUVF_PROJECT_ONEWAYUPGRADE: Makes the project incompatible with Visual Studio 2010 with SP1.

  5. VSPUVF_PROJECT_INCOMPATIBLE: Indicates that Visual Studio 2012 does not support this project.

  6. VSPUVF_PROJECT_DEPRECATED: Indicates that this project is no longer supported.

Note

To avoid confusion, don’t combine upgrade flags when you set them. For example, don't create an ambiguous upgrade status such as VSPUVF_PROJECT_SAFEREPAIR | VSPUVF_PROJECT_DEPRECATED.

Project flavors may implement the function UpgradeProjectFlavor_CheckOnly from the IVsProjectFlavorUpgradeViaFactory2 interface. To make this function work, the IVsProjectUpgradeViaFactory4.UpgradeProject_CheckOnly implementation mentioned earlier must call it. This call is already implemented in the Visual Basic or C# base project system. The effect of this function enables project flavors to also determine the upgrade requirements of a project, in addition to what the base project system has determined. The compatibility dialog box shows the most severe of the two requirements.

When Visual Studio 2012 performs an upgrade check, it provides a logger instead of a NULL value as in previous versions of Visual Studio. The logger enables project systems and flavors to provide additional information that can help you understand the nature of the changes that are needed to make your older projects load properly. We recommend that you use the logger to provide more information instead of using dialog boxes. For more information, see The Upgrade Logger later in this topic.

For Managed implementations, the project upgrade interfaces are available in the [Microsoft.VisualStudio.Shell.Interop.11.0.dll] interop assembly.

The UpgradeProject method can determine whether the changes it makes would prevent the project from loading in an previous version of Visual Studio. If so, the method marks the project as incompatible. To understand how a project is marked as incompatible, see Marking a project as incompatible earlier in this topic. We recommend that, after this dialog box appears, you mark the project as incompatible by calling the method IVsAppCompat.BreakAssetCompatibility directly, instead of first calling the IVsAppCompat.AskForUserConsentToBreakAssetCompat method because the dialog box doesn’t need to appear twice.

Here is an example to help summarize the compatibility user experience. If a project was created in Visual Studio 2010 with SP1, that project is opened in Visual Studio 2012, and Visual Studio 2012 determines that an upgrade is required, Visual Studio displays a dialog box to ask the user for permission to make the changes. If the user agrees, the project is modified and then loaded. If the project was created using a much older version of Visual Studio (for example, Visual Studio 2008), the solution file will also be upgraded. If the solution is then closed and reopened in Visual Studio 2010 with SP1, the one-way-upgraded project will be incompatible and not loaded (but will load in Visual Studio 2012). If the project had only required a repair (instead of an upgrade), the repaired project will still open in both Visual Studio 2010 with SP1 and Visual Studio 2012.

The Upgrade Logger

The call to IVsProjectUpgradeViaFactory::UpgradeProject contains an IVsUpgradeLogger logger, which project systems and flavors should use to provide detailed upgrade tracing for troubleshooting. If a warning or an error is logged, Visual Studio shows the upgrade report.

When you write to the upgrade logger, consider the following guidelines:

  • Visual Studio will call Flush after all projects have finished upgrading. Don’t call it in your project system.

  • The LogMessage function has the following ErrorLevels:

    • 0 is for any information that you’d like to trace.

    • 1 is for a warning.

    • 2 is for an error

    • 3 is for the Report formatter. When your project is upgraded, log the word “Converted” once, and don’t localize the word.

  • If a project doesn’t require any repair or upgrade, Visual Studio will generate the log file only if the project system had logged a warning or an error during UpgradeProject_CheckOnly or UpgradeProjectFlavor_CheckOnly methods.