20 files changed, 373 insertions, 41 deletions

diff --git a/src/api/burn/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h b/src/api/burn/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
index b507b167..0b81b35a 100644
--- a/src/api/burn/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
+++ b/src/api/burn/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
@@ -223,6 +223,7 @@ enum BOOTSTRAPPER_APPLICATION_MESSAGE
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANNEDCOMPATIBLEPACKAGE,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRESTORERELATEDBUNDLE,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRELATEDBUNDLETYPE,
+    BOOTSTRAPPER_APPLICATION_MESSAGE_ONAPPLYDOWNGRADE,
 };
 
 enum BOOTSTRAPPER_APPLYCOMPLETE_ACTION
@@ -354,6 +355,18 @@ struct BA_ONAPPLYCOMPLETE_RESULTS
     BOOTSTRAPPER_APPLYCOMPLETE_ACTION action;
 };
 
+struct BA_ONAPPLYDOWNGRADE_ARGS
+{
+    DWORD cbSize;
+    HRESULT hrRecommended;
+};
+
+struct BA_ONAPPLYDOWNGRADE_RESULTS
+{
+    DWORD cbSize;
+    HRESULT hrStatus;
+};
+
 struct BA_ONBEGINMSITRANSACTIONBEGIN_ARGS
 {
     DWORD cbSize;
diff --git a/src/api/burn/WixToolset.Mba.Core/BootstrapperApplication.cs b/src/api/burn/WixToolset.Mba.Core/BootstrapperApplication.cs
index fd36cf26..8a2e0e93 100644
--- a/src/api/burn/WixToolset.Mba.Core/BootstrapperApplication.cs
+++ b/src/api/burn/WixToolset.Mba.Core/BootstrapperApplication.cs
@@ -209,6 +209,9 @@ namespace WixToolset.Mba.Core
         public event EventHandler<ApplyCompleteEventArgs> ApplyComplete;
 
         /// <inheritdoc/>
+        public event EventHandler<ApplyDowngradeEventArgs> ApplyDowngrade;
+
+        /// <inheritdoc/>
         public event EventHandler<ExecuteProgressEventArgs> ExecuteProgress;
 
         /// <inheritdoc/>
@@ -1056,6 +1059,19 @@ namespace WixToolset.Mba.Core
         }
 
         /// <summary>
+        /// Called by the engine, raises the <see cref="ApplyDowngrade"/> event.
+        /// </summary>
+        /// <param name="args">Additional arguments for this event.</param>
+        protected virtual void OnApplyDowngrade(ApplyDowngradeEventArgs args)
+        {
+            EventHandler<ApplyDowngradeEventArgs> handler = this.ApplyDowngrade;
+            if (null != handler)
+            {
+                handler(this, args);
+            }
+        }
+
+        /// <summary>
         /// Called by the engine, raises the <see cref="ExecuteProgress"/> event.
         /// </summary>
         /// <param name="args">Additional arguments for this event.</param>
@@ -1907,6 +1923,15 @@ namespace WixToolset.Mba.Core
             return args.HResult;
         }
 
+        int IBootstrapperApplication.OnApplyDowngrade(int hrRecommendation, ref int hrStatus)
+        {
+            ApplyDowngradeEventArgs args = new ApplyDowngradeEventArgs(hrRecommendation, hrStatus);
+            this.OnApplyDowngrade(args);
+
+            hrStatus = args.Status;
+            return args.HResult;
+        }
+
         int IBootstrapperApplication.OnLaunchApprovedExeBegin(ref bool fCancel)
         {
             LaunchApprovedExeBeginEventArgs args = new LaunchApprovedExeBeginEventArgs(fCancel);
diff --git a/src/api/burn/WixToolset.Mba.Core/EventArgs.cs b/src/api/burn/WixToolset.Mba.Core/EventArgs.cs
index d8ec7998..c93c2885 100644
--- a/src/api/burn/WixToolset.Mba.Core/EventArgs.cs
+++ b/src/api/burn/WixToolset.Mba.Core/EventArgs.cs
@@ -1859,6 +1859,30 @@ namespace WixToolset.Mba.Core
     }
 
     /// <summary>
+    /// Event arguments for <see cref="IDefaultBootstrapperApplication.ApplyDowngrade"/>
+    /// </summary>
+    [Serializable]
+    public class ApplyDowngradeEventArgs : HResultEventArgs
+    {
+        /// <summary />
+        public ApplyDowngradeEventArgs(int hrRecommendation, int hrStatus)
+        {
+            this.Recommendation = hrRecommendation;
+            this.Status = hrStatus;
+        }
+
+        /// <summary>
+        /// Gets the recommended HRESULT.
+        /// </summary>
+        public int Recommendation { get; private set; }
+
+        /// <summary>
+        /// Gets or sets the HRESULT for Apply.
+        /// </summary>
+        public int Status { get; set; }
+    }
+
+    /// <summary>
     /// EventArgs for <see cref="IDefaultBootstrapperApplication.CacheAcquireResolving"/>.
     /// </summary>
     [Serializable]
diff --git a/src/api/burn/WixToolset.Mba.Core/IBootstrapperApplication.cs b/src/api/burn/WixToolset.Mba.Core/IBootstrapperApplication.cs
index 4ab0f8d9..d4fe8320 100644
--- a/src/api/burn/WixToolset.Mba.Core/IBootstrapperApplication.cs
+++ b/src/api/burn/WixToolset.Mba.Core/IBootstrapperApplication.cs
@@ -1160,6 +1160,16 @@ namespace WixToolset.Mba.Core
             [MarshalAs(UnmanagedType.U4)] ref RelatedBundlePlanType pRequestedType,
             [MarshalAs(UnmanagedType.Bool)] ref bool fCancel
             );
+
+        /// <summary>
+        /// See <see cref="IDefaultBootstrapperApplication.ApplyDowngrade"/>.
+        /// </summary>
+        [PreserveSig]
+        [return: MarshalAs(UnmanagedType.I4)]
+        int OnApplyDowngrade(
+            [MarshalAs(UnmanagedType.I4)] int hrRecommended,
+            [MarshalAs(UnmanagedType.I4)] ref int hrStatus
+            );
     }
 
     /// <summary>
diff --git a/src/api/burn/WixToolset.Mba.Core/IDefaultBootstrapperApplication.cs b/src/api/burn/WixToolset.Mba.Core/IDefaultBootstrapperApplication.cs
index ebd1580b..c9284b69 100644
--- a/src/api/burn/WixToolset.Mba.Core/IDefaultBootstrapperApplication.cs
+++ b/src/api/burn/WixToolset.Mba.Core/IDefaultBootstrapperApplication.cs
@@ -20,6 +20,11 @@ namespace WixToolset.Mba.Core
         event EventHandler<ApplyCompleteEventArgs> ApplyComplete;
 
         /// <summary>
+        /// Fired when the plan determined that nothing should happen to prevent downgrading.
+        /// </summary>
+        event EventHandler<ApplyDowngradeEventArgs> ApplyDowngrade;
+
+        /// <summary>
         /// Fired when the engine is about to begin an MSI transaction.
         /// </summary>
         event EventHandler<BeginMsiTransactionBeginEventArgs> BeginMsiTransactionBegin;
diff --git a/src/api/burn/balutil/inc/BAFunctions.h b/src/api/burn/balutil/inc/BAFunctions.h
index f772eb3f..58c26166 100644
--- a/src/api/burn/balutil/inc/BAFunctions.h
+++ b/src/api/burn/balutil/inc/BAFunctions.h
@@ -90,6 +90,7 @@ enum BA_FUNCTIONS_MESSAGE
     BA_FUNCTIONS_MESSAGE_ONPLANNEDCOMPATIBLEPACKAGE = BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANNEDCOMPATIBLEPACKAGE,
     BA_FUNCTIONS_MESSAGE_ONPLANRESTORERELATEDBUNDLE = BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRESTORERELATEDBUNDLE,
     BA_FUNCTIONS_MESSAGE_ONPLANRELATEDBUNDLETYPE = BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRELATEDBUNDLETYPE,
+    BA_FUNCTIONS_MESSAGE_ONAPPLYDOWNGRADE = BOOTSTRAPPER_APPLICATION_MESSAGE_ONAPPLYDOWNGRADE,
 
     BA_FUNCTIONS_MESSAGE_ONTHEMELOADED = 1024,
     BA_FUNCTIONS_MESSAGE_WNDPROC,
diff --git a/src/api/burn/balutil/inc/BalBaseBAFunctions.h b/src/api/burn/balutil/inc/BalBaseBAFunctions.h
index f558828f..fe5c99ba 100644
--- a/src/api/burn/balutil/inc/BalBaseBAFunctions.h
+++ b/src/api/burn/balutil/inc/BalBaseBAFunctions.h
@@ -869,6 +869,14 @@ public: // IBootstrapperApplication
         return S_OK;
     }
 
+    virtual STDMETHODIMP OnApplyDowngrade(
+        __in HRESULT /*hrRecommended*/,
+        __in HRESULT* /*phrStatus*/
+        )
+    {
+        return S_OK;
+    }
+
 public: // IBAFunctions
     virtual STDMETHODIMP OnPlan(
         )
diff --git a/src/api/burn/balutil/inc/BalBaseBAFunctionsProc.h b/src/api/burn/balutil/inc/BalBaseBAFunctionsProc.h
index ede00f28..100e5c30 100644
--- a/src/api/burn/balutil/inc/BalBaseBAFunctionsProc.h
+++ b/src/api/burn/balutil/inc/BalBaseBAFunctionsProc.h
@@ -161,6 +161,7 @@ static HRESULT WINAPI BalBaseBAFunctionsProc(
         case BA_FUNCTIONS_MESSAGE_ONPLANNEDCOMPATIBLEPACKAGE:
         case BA_FUNCTIONS_MESSAGE_ONPLANRESTORERELATEDBUNDLE:
         case BA_FUNCTIONS_MESSAGE_ONPLANRELATEDBUNDLETYPE:
+        case BA_FUNCTIONS_MESSAGE_ONAPPLYDOWNGRADE:
             hr = BalBaseBootstrapperApplicationProc((BOOTSTRAPPER_APPLICATION_MESSAGE)message, pvArgs, pvResults, pvContext);
             break;
         case BA_FUNCTIONS_MESSAGE_ONTHEMELOADED:
diff --git a/src/api/burn/balutil/inc/BalBaseBootstrapperApplication.h b/src/api/burn/balutil/inc/BalBaseBootstrapperApplication.h
index 49f4b7ca..fd06a83f 100644
--- a/src/api/burn/balutil/inc/BalBaseBootstrapperApplication.h
+++ b/src/api/burn/balutil/inc/BalBaseBootstrapperApplication.h
@@ -1069,6 +1069,14 @@ public: // IBootstrapperApplication
         return S_OK;
     }
 
+    virtual STDMETHODIMP OnApplyDowngrade(
+        __in HRESULT /*hrRecommended*/,
+        __in HRESULT* /*phrStatus*/
+        )
+    {
+        return S_OK;
+    }
+
 public: //CBalBaseBootstrapperApplication
     virtual STDMETHODIMP Initialize(
         __in const BOOTSTRAPPER_CREATE_ARGS* pCreateArgs
diff --git a/src/api/burn/balutil/inc/BalBaseBootstrapperApplicationProc.h b/src/api/burn/balutil/inc/BalBaseBootstrapperApplicationProc.h
index 698349f7..4e413e4e 100644
--- a/src/api/burn/balutil/inc/BalBaseBootstrapperApplicationProc.h
+++ b/src/api/burn/balutil/inc/BalBaseBootstrapperApplicationProc.h
@@ -738,6 +738,15 @@ static HRESULT BalBaseBAProcOnPlanRelatedBundleType(
     return pBA->OnPlanRelatedBundleType(pArgs->wzBundleId, pArgs->recommendedType, &pResults->requestedType, &pResults->fCancel);
 }
 
+static HRESULT BalBaseBAProcOnApplyDowngrade(
+    __in IBootstrapperApplication* pBA,
+    __in BA_ONAPPLYDOWNGRADE_ARGS* pArgs,
+    __inout BA_ONAPPLYDOWNGRADE_RESULTS* pResults
+    )
+{
+    return pBA->OnApplyDowngrade(pArgs->hrRecommended, &pResults->hrStatus);
+}
+
 /*******************************************************************
 BalBaseBootstrapperApplicationProc - requires pvContext to be of type IBootstrapperApplication.
                                      Provides a default mapping between the new message based BA interface and
@@ -1000,6 +1009,9 @@ static HRESULT WINAPI BalBaseBootstrapperApplicationProc(
         case BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRELATEDBUNDLETYPE:
             hr = BalBaseBAProcOnPlanRelatedBundleType(pBA, reinterpret_cast<BA_ONPLANRELATEDBUNDLETYPE_ARGS*>(pvArgs), reinterpret_cast<BA_ONPLANRELATEDBUNDLETYPE_RESULTS*>(pvResults));
             break;
+        case BOOTSTRAPPER_APPLICATION_MESSAGE_ONAPPLYDOWNGRADE:
+            hr = BalBaseBAProcOnApplyDowngrade(pBA, reinterpret_cast<BA_ONAPPLYDOWNGRADE_ARGS*>(pvArgs), reinterpret_cast<BA_ONAPPLYDOWNGRADE_RESULTS*>(pvResults));
+            break;
         }
     }
 
diff --git a/src/api/burn/balutil/inc/IBootstrapperApplication.h b/src/api/burn/balutil/inc/IBootstrapperApplication.h
index 462df0cc..c9cf3126 100644
--- a/src/api/burn/balutil/inc/IBootstrapperApplication.h
+++ b/src/api/burn/balutil/inc/IBootstrapperApplication.h
@@ -707,4 +707,11 @@ DECLARE_INTERFACE_IID_(IBootstrapperApplication, IUnknown, "53C31D56-49C0-426B-A
         __inout BOOTSTRAPPER_RELATED_BUNDLE_PLAN_TYPE* pRequestedType,
         __inout BOOL* pfCancel
         ) = 0;
+
+    // OnApplyDowngrade - called when the plan determined that nothing should happen to prevent downgrading.
+    //
+    STDMETHOD(OnApplyDowngrade)(
+        __in HRESULT hrRecommended,
+        __inout HRESULT* phrStatus
+        ) = 0;
 };
diff --git a/src/burn/engine/core.cpp b/src/burn/engine/core.cpp
index 9d4ea43e..37872e52 100644
--- a/src/burn/engine/core.cpp
+++ b/src/burn/engine/core.cpp
@@ -527,8 +527,15 @@ extern "C" HRESULT CorePlan(
             hr = PlanRelatedBundlesInitialize(&pEngineState->userExperience, &pEngineState->registration, pEngineState->command.relationType, &pEngineState->plan);
             ExitOnFailure(hr, "Failed to initialize related bundles for plan.");
 
-            hr = PlanRegistration(&pEngineState->plan, &pEngineState->registration, &pEngineState->dependencies, pEngineState->command.resumeType, pEngineState->command.relationType, &fContinuePlanning);
-            ExitOnFailure(hr, "Failed to plan registration.");
+            if (pEngineState->plan.fDowngrade)
+            {
+                fContinuePlanning = FALSE;
+            }
+            else
+            {
+                hr = PlanRegistration(&pEngineState->plan, &pEngineState->registration, &pEngineState->dependencies, pEngineState->command.resumeType, pEngineState->command.relationType, &fContinuePlanning);
+                ExitOnFailure(hr, "Failed to plan registration.");
+            }
 
             if (fContinuePlanning)
             {
@@ -615,6 +622,7 @@ extern "C" HRESULT CoreApply(
 {
     HRESULT hr = S_OK;
     HANDLE hLock = NULL;
+    BOOL fApplyBegan = FALSE;
     BOOL fApplyInitialize = FALSE;
     BOOL fElevated = FALSE;
     BOOL fRegistered = FALSE;
@@ -627,8 +635,6 @@ extern "C" HRESULT CoreApply(
     DWORD dwPhaseCount = 0;
     BOOTSTRAPPER_APPLYCOMPLETE_ACTION applyCompleteAction = BOOTSTRAPPER_APPLYCOMPLETE_ACTION_NONE;
 
-    LogId(REPORT_STANDARD, MSG_APPLY_BEGIN);
-
     if (!pEngineState->fPlanned)
     {
         ExitOnFailure(hr = E_INVALIDSTATE, "Apply cannot be done without a successful Plan.");
@@ -638,6 +644,10 @@ extern "C" HRESULT CoreApply(
         ExitOnFailure(hr = E_INVALIDSTATE, "Plans cannot be applied multiple times.");
     }
 
+    fApplyBegan = TRUE;
+
+    LogId(REPORT_STANDARD, MSG_APPLY_BEGIN);
+
     // Ensure any previous attempts to execute are reset.
     ApplyReset(&pEngineState->userExperience, &pEngineState->packages);
 
@@ -653,6 +663,14 @@ extern "C" HRESULT CoreApply(
     hr = UserExperienceOnApplyBegin(&pEngineState->userExperience, dwPhaseCount);
     ExitOnRootFailure(hr, "BA aborted apply begin.");
 
+    if (pEngineState->plan.fDowngrade)
+    {
+        hr = HRESULT_FROM_WIN32(ERROR_PRODUCT_VERSION);
+        UserExperienceOnApplyDowngrade(&pEngineState->userExperience, &hr);
+
+        ExitFunction();
+    }
+
     pEngineState->plan.fAffectedMachineState = pEngineState->plan.fCanAffectMachineState;
 
     hr = ApplyLock(FALSE, &hLock);
@@ -804,13 +822,16 @@ LExit:
         DeleteCriticalSection(&applyContext.csApply);
     }
 
-    UserExperienceOnApplyComplete(&pEngineState->userExperience, hr, restart, &applyCompleteAction);
-    if (BOOTSTRAPPER_APPLYCOMPLETE_ACTION_RESTART == applyCompleteAction)
+    if (fApplyBegan)
     {
-        pEngineState->fRestart = TRUE;
-    }
+        UserExperienceOnApplyComplete(&pEngineState->userExperience, hr, restart, &applyCompleteAction);
+        if (BOOTSTRAPPER_APPLYCOMPLETE_ACTION_RESTART == applyCompleteAction)
+        {
+            pEngineState->fRestart = TRUE;
+        }
 
-    LogId(REPORT_STANDARD, MSG_APPLY_COMPLETE, hr, LoggingRestartToString(restart), LoggingBoolToString(pEngineState->fRestart));
+        LogId(REPORT_STANDARD, MSG_APPLY_COMPLETE, hr, LoggingRestartToString(restart), LoggingBoolToString(pEngineState->fRestart));
+    }
 
     return hr;
 }
diff --git a/src/burn/engine/engine.mc b/src/burn/engine/engine.mc
index a5c4e2ba..53e6b256 100644
--- a/src/burn/engine/engine.mc
+++ b/src/burn/engine/engine.mc
@@ -499,6 +499,20 @@ Language=English
 Ignoring bundle dependents due to action UnsafeUninstall...
 .
 
+MessageId=224
+Severity=Warning
+SymbolicName=MSG_PLAN_SKIPPED_DUE_TO_DOWNGRADE
+Language=English
+Plan skipped due to related bundle of plan type Downgrade:
+.
+
+MessageId=225
+Severity=Warning
+SymbolicName=MSG_UPGRADE_BUNDLE_DOWNGRADE
+Language=English
+    id: %1!ls!, version: %2!ls!
+.
+
 MessageId=299
 Severity=Success
 SymbolicName=MSG_PLAN_COMPLETE
diff --git a/src/burn/engine/plan.cpp b/src/burn/engine/plan.cpp
index dcb919c7..46680636 100644
--- a/src/burn/engine/plan.cpp
+++ b/src/burn/engine/plan.cpp
@@ -1328,11 +1328,12 @@ LExit:
 extern "C" HRESULT PlanRelatedBundlesInitialize(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in BURN_REGISTRATION* pRegistration,
-    __in BOOTSTRAPPER_RELATION_TYPE /*relationType*/,
-    __in BURN_PLAN* /*pPlan*/
+    __in BOOTSTRAPPER_RELATION_TYPE relationType,
+    __in BURN_PLAN* pPlan
     )
 {
     HRESULT hr = S_OK;
+    BOOL fUninstalling = BOOTSTRAPPER_ACTION_UNINSTALL == pPlan->action || BOOTSTRAPPER_ACTION_UNSAFE_UNINSTALL == pPlan->action;
 
     for (DWORD i = 0; i < pRegistration->relatedBundles.cRelatedBundles; ++i)
     {
@@ -1356,6 +1357,19 @@ extern "C" HRESULT PlanRelatedBundlesInitialize(
 
         hr = UserExperienceOnPlanRelatedBundleType(pUserExperience, pRelatedBundle->package.sczId, &pRelatedBundle->planRelationType);
         ExitOnRootFailure(hr, "BA aborted plan related bundle type.");
+
+        if (BOOTSTRAPPER_RELATED_BUNDLE_PLAN_TYPE_DOWNGRADE == pRelatedBundle->planRelationType &&
+            pRelatedBundle->fPlannable && !fUninstalling && BOOTSTRAPPER_RELATION_UPGRADE != relationType)
+        {
+            if (!pPlan->fDowngrade)
+            {
+                pPlan->fDowngrade = TRUE;
+
+                LogId(REPORT_STANDARD, MSG_PLAN_SKIPPED_DUE_TO_DOWNGRADE);
+            }
+
+            LogId(REPORT_VERBOSE, MSG_UPGRADE_BUNDLE_DOWNGRADE, pRelatedBundle->package.sczId, pRelatedBundle->pVersion->sczVersion);
+        }
     }
 
     RelatedBundlesSortPlan(&pRegistration->relatedBundles);
@@ -3011,6 +3025,7 @@ extern "C" void PlanDump(
     LogStringLine(PlanDumpLevel, "     can affect machine state: %hs", LoggingTrueFalseToString(pPlan->fCanAffectMachineState));
     LogStringLine(PlanDumpLevel, "     disable-rollback: %hs", LoggingTrueFalseToString(pPlan->fDisableRollback));
     LogStringLine(PlanDumpLevel, "     disallow-removal: %hs", LoggingTrueFalseToString(pPlan->fDisallowRemoval));
+    LogStringLine(PlanDumpLevel, "     downgrade: %hs", LoggingTrueFalseToString(pPlan->fDowngrade));
     LogStringLine(PlanDumpLevel, "     registration options: %hs", LoggingRegistrationOptionsToString(pPlan->dwRegistrationOperations));
     LogStringLine(PlanDumpLevel, "     estimated size: %llu", pPlan->qwEstimatedSize);
     if (pPlan->sczLayoutDirectory)
diff --git a/src/burn/engine/plan.h b/src/burn/engine/plan.h
index 1f3fe07c..e73cbcfa 100644
--- a/src/burn/engine/plan.h
+++ b/src/burn/engine/plan.h
@@ -250,6 +250,7 @@ typedef struct _BURN_PLAN
     BOOL fAffectedMachineState;
     LPWSTR sczLayoutDirectory;
     BOOL fPlanPackageCacheRollback;
+    BOOL fDowngrade;
 
     DWORD64 qwCacheSizeTotal;
 
diff --git a/src/burn/engine/userexperience.cpp b/src/burn/engine/userexperience.cpp
index 8668cf6f..81ce8bb9 100644
--- a/src/burn/engine/userexperience.cpp
+++ b/src/burn/engine/userexperience.cpp
@@ -335,6 +335,30 @@ LExit:
     return hr;
 }
 
+EXTERN_C BAAPI UserExperienceOnApplyDowngrade(
+    __in BURN_USER_EXPERIENCE* pUserExperience,
+    __inout HRESULT* phrStatus
+    )
+{
+    HRESULT hr = S_OK;
+    BA_ONAPPLYDOWNGRADE_ARGS args = { };
+    BA_ONAPPLYDOWNGRADE_RESULTS results = { };
+
+    args.cbSize = sizeof(args);
+    args.hrRecommended = *phrStatus;
+
+    results.cbSize = sizeof(results);
+    results.hrStatus = *phrStatus;
+
+    hr = SendBAMessage(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONAPPLYDOWNGRADE, &args, &results);
+    ExitOnFailure(hr, "BA OnApplyDowngrade failed.");
+
+    *phrStatus = results.hrStatus;
+
+LExit:
+    return hr;
+}
+
 EXTERN_C BAAPI UserExperienceOnBeginMsiTransactionBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in LPCWSTR wzTransactionId
diff --git a/src/burn/engine/userexperience.h b/src/burn/engine/userexperience.h
index 11344365..2f18acdd 100644
--- a/src/burn/engine/userexperience.h
+++ b/src/burn/engine/userexperience.h
@@ -110,6 +110,10 @@ BAAPI UserExperienceOnApplyComplete(
     __in BOOTSTRAPPER_APPLY_RESTART restart,
     __inout BOOTSTRAPPER_APPLYCOMPLETE_ACTION* pAction
     );
+BAAPI UserExperienceOnApplyDowngrade(
+    __in BURN_USER_EXPERIENCE* pUserExperience,
+    __inout HRESULT* phrStatus
+    );
 BAAPI UserExperienceOnBeginMsiTransactionBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in LPCWSTR wzTransactionId
diff --git a/src/burn/test/BurnUnitTest/PlanTest.cpp b/src/burn/test/BurnUnitTest/PlanTest.cpp
index a3b58426..0a8ac369 100644
--- a/src/burn/test/BurnUnitTest/PlanTest.cpp
+++ b/src/burn/test/BurnUnitTest/PlanTest.cpp
@@ -67,6 +67,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -226,6 +227,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -358,6 +360,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -457,6 +460,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -575,6 +579,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -677,6 +682,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -742,6 +748,76 @@ namespace Bootstrapper
         }
 
         [Fact]
+        void SingleMsiDowngradeTest()
+        {
+            HRESULT hr = S_OK;
+            BURN_ENGINE_STATE engineState = { };
+            BURN_ENGINE_STATE* pEngineState = &engineState;
+            BURN_PLAN* pPlan = &engineState.plan;
+
+            InitializeEngineStateForCorePlan(wzSingleMsiManifestFileName, pEngineState);
+            DetectAttachedContainerAsAttached(pEngineState);
+            DetectPackagesAsAbsent(pEngineState);
+            DetectRelatedBundle(pEngineState, L"{AF8355C9-CCDD-4D61-BF5F-EA5F948D8F01}", L"1.1.0.0", BOOTSTRAPPER_RELATION_UPGRADE);
+
+            hr = CorePlan(pEngineState, BOOTSTRAPPER_ACTION_INSTALL);
+            NativeAssert::Succeeded(hr, "CorePlan failed");
+
+            Assert::Equal<DWORD>(BOOTSTRAPPER_ACTION_INSTALL, pPlan->action);
+            NativeAssert::StringEqual(L"{A6F0CBF7-1578-450C-B9D7-9CF2EEC40002}", pPlan->wzBundleId);
+            NativeAssert::StringEqual(L"{A6F0CBF7-1578-450C-B9D7-9CF2EEC40002}", pPlan->wzBundleProviderKey);
+            Assert::Equal<BOOL>(FALSE, pPlan->fEnabledForwardCompatibleBundle);
+            Assert::Equal<BOOL>(TRUE, pPlan->fPerMachine);
+            Assert::Equal<BOOL>(FALSE, pPlan->fCanAffectMachineState);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(TRUE, pPlan->fDowngrade);
+
+            BOOL fRollback = FALSE;
+            DWORD dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cRegistrationActions);
+
+            fRollback = TRUE;
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cRollbackRegistrationActions);
+
+            fRollback = FALSE;
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cCacheActions);
+
+            fRollback = TRUE;
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cRollbackCacheActions);
+
+            Assert::Equal(0ull, pPlan->qwEstimatedSize);
+            Assert::Equal(0ull, pPlan->qwCacheSizeTotal);
+
+            fRollback = FALSE;
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cExecuteActions);
+
+            fRollback = TRUE;
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cRollbackActions);
+
+            Assert::Equal(0ul, pPlan->cExecutePackagesTotal);
+            Assert::Equal(0ul, pPlan->cOverallProgressTicksTotal);
+
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cRestoreRelatedBundleActions);
+
+            dwIndex = 0;
+            Assert::Equal(dwIndex, pPlan->cCleanActions);
+
+            UINT uIndex = 0;
+            ValidatePlannedProvider(pPlan, uIndex++, L"{A6F0CBF7-1578-450C-B9D7-9CF2EEC40002}", NULL);
+            Assert::Equal(uIndex, pPlan->cPlannedProviders);
+
+            Assert::Equal(1ul, pEngineState->packages.cPackages);
+            ValidateNonPermanentPackageExpectedStates(&pEngineState->packages.rgPackages[0], L"PackageA", BURN_PACKAGE_REGISTRATION_STATE_UNKNOWN, BURN_PACKAGE_REGISTRATION_STATE_UNKNOWN);
+        }
+
+        [Fact]
         void SingleMsiForceAbsentTest()
         {
             HRESULT hr = S_OK;
@@ -770,6 +846,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -858,6 +935,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -948,6 +1026,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1053,6 +1132,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1131,6 +1211,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1225,6 +1306,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(TRUE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1294,6 +1376,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1377,6 +1460,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(TRUE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1471,6 +1555,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1601,6 +1686,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1716,6 +1802,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
@@ -1810,6 +1897,7 @@ namespace Bootstrapper
             Assert::Equal<BOOL>(TRUE, pPlan->fCanAffectMachineState);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisableRollback);
             Assert::Equal<BOOL>(FALSE, pPlan->fDisallowRemoval);
+            Assert::Equal<BOOL>(FALSE, pPlan->fDowngrade);
 
             BOOL fRollback = FALSE;
             DWORD dwIndex = 0;
diff --git a/src/ext/Bal/wixstdba/WixStandardBootstrapperApplication.cpp b/src/ext/Bal/wixstdba/WixStandardBootstrapperApplication.cpp
index 91033a26..2a5d839a 100644
--- a/src/ext/Bal/wixstdba/WixStandardBootstrapperApplication.cpp
+++ b/src/ext/Bal/wixstdba/WixStandardBootstrapperApplication.cpp
@@ -254,7 +254,6 @@ public: // IBootstrapperApplication
         )
     {
         BAL_INFO_PACKAGE* pPackage = NULL;
-        int nCompare = 0;
 
         if (!fMissingFromCache)
         {
@@ -262,14 +261,6 @@ public: // IBootstrapperApplication
             {
                 InitializePackageInfoForPackage(pPackage);
             }
-
-            // If we're not doing a prerequisite install, remember when our bundle would cause a downgrade.
-            if (!m_fPrereq && BOOTSTRAPPER_RELATION_UPGRADE == relationType &&
-                SUCCEEDED(m_pEngine->CompareVersions(m_sczBundleVersion, wzVersion, &nCompare)) && 0 > nCompare)
-            {
-                BalLog(BOOTSTRAPPER_LOG_LEVEL_STANDARD, "A newer version (v%ls) of this product is installed.", wzVersion);
-                m_fDowngrading = TRUE;
-            }
         }
 
         return CBalBaseBootstrapperApplication::OnDetectRelatedBundle(wzBundleId, relationType, wzBundleTag, fPerMachine, wzVersion, fMissingFromCache, pfCancel);
@@ -345,23 +336,6 @@ public: // IBootstrapperApplication
                     }
                 }
             }
-            else if (m_fDowngrading && BOOTSTRAPPER_ACTION_UNINSTALL < m_command.action)
-            {
-                if (m_fSuppressDowngradeFailure)
-                {
-                    BalLog(BOOTSTRAPPER_LOG_LEVEL_STANDARD, "Downgrade failure has been suppressed; exiting bundle.");
-
-                    hr = S_OK;
-                    SetState(WIXSTDBA_STATE_APPLIED, hr);
-                    ExitFunction();
-                }
-                else
-                {
-                    // If we are going to apply a downgrade, bail.
-                    hr = HRESULT_FROM_WIN32(ERROR_PRODUCT_VERSION);
-                    BalExitOnFailure(hr, "Cannot install a product when a newer version is installed.");
-                }
-            }
         }
 
         SetState(WIXSTDBA_STATE_DETECTED, hrStatus);
@@ -371,7 +345,6 @@ public: // IBootstrapperApplication
             ::PostMessageW(m_hWnd, WM_WIXSTDBA_PLAN_PACKAGES, 0, m_command.action);
         }
 
-    LExit:
         return hr;
     }
 
@@ -1092,6 +1065,20 @@ public: // IBootstrapperApplication
         return hr;
     }
 
+    virtual STDMETHODIMP OnApplyDowngrade(
+        __in HRESULT /*hrRecommendation*/,
+        __in HRESULT* phrStatus
+        )
+    {
+        HRESULT hr = S_OK;
+
+        if (m_fSuppressDowngradeFailure)
+        {
+            *phrStatus = S_OK;
+        }
+
+        return hr;
+    }
 
     virtual STDMETHODIMP OnApplyComplete(
         __in HRESULT hrStatus,
@@ -1445,6 +1432,9 @@ public: // IBootstrapperApplication
         case BOOTSTRAPPER_APPLICATION_MESSAGE_ONPLANRELATEDBUNDLETYPE:
             OnPlanRelatedBundleTypeFallback(reinterpret_cast<BA_ONPLANRELATEDBUNDLETYPE_ARGS*>(pvArgs), reinterpret_cast<BA_ONPLANRELATEDBUNDLETYPE_RESULTS*>(pvResults));
             break;
+        case BOOTSTRAPPER_APPLICATION_MESSAGE_ONAPPLYDOWNGRADE:
+            OnApplyDowngradeFallback(reinterpret_cast<BA_ONAPPLYDOWNGRADE_ARGS*>(pvArgs), reinterpret_cast<BA_ONAPPLYDOWNGRADE_RESULTS*>(pvResults));
+            break;
         default:
 #ifdef DEBUG
             BalLog(BOOTSTRAPPER_LOG_LEVEL_STANDARD, "WIXSTDBA: Forwarding unknown BA message: %d", message);
@@ -2118,6 +2108,14 @@ private: // privates
         BalLogId(BOOTSTRAPPER_LOG_LEVEL_STANDARD, MSG_WIXSTDBA_PLANNED_RESTORE_RELATED_BUNDLE, m_hModule, pArgs->wzBundleId, LoggingRequestStateToString(requestedState), LoggingRequestStateToString(pResults->requestedState));
     }
 
+    void OnApplyDowngradeFallback(
+        __in BA_ONAPPLYDOWNGRADE_ARGS* pArgs,
+        __inout BA_ONAPPLYDOWNGRADE_RESULTS* pResults
+        )
+    {
+        m_pfnBAFunctionsProc(BA_FUNCTIONS_MESSAGE_ONAPPLYDOWNGRADE, pArgs, pResults, m_pvBAFunctionsProcContext);
+    }
+
 
 public: //CBalBaseBootstrapperApplication
     virtual STDMETHODIMP Initialize(
@@ -4195,7 +4193,7 @@ public:
         __in BOOL fPrereq,
         __in HRESULT hrHostInitialization,
         __in IBootstrapperEngine* pEngine
-    ) : CBalBaseBootstrapperApplication(pEngine, 3, 3000)
+        ) : CBalBaseBootstrapperApplication(pEngine, 3, 3000)
     {
         THEME_ASSIGN_CONTROL_ID* pAssignControl = NULL;
 
@@ -4224,7 +4222,6 @@ public:
         m_state = WIXSTDBA_STATE_INITIALIZING;
         m_hrFinal = hrHostInitialization;
 
-        m_fDowngrading = FALSE;
         m_restartResult = BOOTSTRAPPER_APPLY_RESTART_NONE;
         m_fRestartRequired = FALSE;
         m_fShouldRestart = FALSE;
@@ -4529,7 +4526,6 @@ private:
     DWORD m_dwCalculatedCacheProgress;
     DWORD m_dwCalculatedExecuteProgress;
 
-    BOOL m_fDowngrading;
     BOOTSTRAPPER_APPLY_RESTART m_restartResult;
     BOOL m_fRestartRequired;
     BOOL m_fShouldRestart;
diff --git a/src/test/burn/WixToolsetTest.BurnE2E/WixStdBaTests.cs b/src/test/burn/WixToolsetTest.BurnE2E/WixStdBaTests.cs
new file mode 100644
index 00000000..e3418cc1
--- /dev/null
+++ b/src/test/burn/WixToolsetTest.BurnE2E/WixStdBaTests.cs
@@ -0,0 +1,55 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolsetTest.BurnE2E
+{
+    using WixTestTools;
+    using Xunit;
+    using Xunit.Abstractions;
+
+    public class WixStdBaTests : BurnE2ETests
+    {
+        public WixStdBaTests(ITestOutputHelper testOutputHelper) : base(testOutputHelper) { }
+
+        [Fact]
+        public void ExitsWithErrorWhenDowngradingWithoutSuppression()
+        {
+            var packageA = this.CreatePackageInstaller("PackageA");
+            var bundle1v10 = this.CreateBundleInstaller("WixStdBaTest1_v10");
+            var bundle1v11 = this.CreateBundleInstaller("WixStdBaTest1_v11");
+
+            packageA.VerifyInstalled(false);
+
+            bundle1v11.Install();
+            bundle1v11.VerifyRegisteredAndInPackageCache();
+
+            packageA.VerifyInstalled(true);
+
+            bundle1v10.Install((int)MSIExec.MSIExecReturnCode.ERROR_PRODUCT_VERSION);
+            bundle1v10.VerifyUnregisteredAndRemovedFromPackageCache();
+            bundle1v11.VerifyRegisteredAndInPackageCache();
+
+            packageA.VerifyInstalled(true);
+        }
+
+        [Fact]
+        public void ExitsWithoutErrorWhenDowngradingWithSuppression()
+        {
+            var packageA = this.CreatePackageInstaller("PackageA");
+            var bundle1v11 = this.CreateBundleInstaller("WixStdBaTest1_v11");
+            var bundle1v12 = this.CreateBundleInstaller("WixStdBaTest1_v12");
+
+            packageA.VerifyInstalled(false);
+
+            bundle1v12.Install();
+            bundle1v12.VerifyRegisteredAndInPackageCache();
+
+            packageA.VerifyInstalled(true);
+
+            bundle1v11.Install();
+            bundle1v11.VerifyUnregisteredAndRemovedFromPackageCache();
+            bundle1v12.VerifyRegisteredAndInPackageCache();
+
+            packageA.VerifyInstalled(true);
+        }
+    }
+}