From 071a1d73459cbe4ba1991c6047befbe551107ba0 Mon Sep 17 00:00:00 2001
From: Matthew Jeffryes <mjeffryes@pulumi.com>
Date: Fri, 20 Jun 2025 13:32:07 -0700
Subject: [PATCH 1/2] WIP: try to bubble up resource replacements to module
 replacements

---
 pkg/modprovider/module.go | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/pkg/modprovider/module.go b/pkg/modprovider/module.go
index 71cc529c..bf67cb3a 100644
--- a/pkg/modprovider/module.go
+++ b/pkg/modprovider/module.go
@@ -127,9 +127,9 @@ func (h *moduleHandler) Diff(
 		return nil, err
 	}
 
+	inputsChanged := false
 	if !oldInputs.DeepEquals(newInputs) {
-		// Inputs have changed, so we need tell the engine that an update is needed.
-		return &pulumirpc.DiffResponse{Changes: pulumirpc.DiffResponse_DIFF_SOME}, nil
+		inputsChanged = true
 	}
 
 	// Here, inputs have not changes but the underlying module might have changed
@@ -142,7 +142,7 @@ func (h *moduleHandler) Diff(
 	tf, err := h.prepSandbox(
 		ctx,
 		urn,
-		oldInputs,
+		newInputs,
 		oldOutputs,
 		inferredModule,
 		moduleSource,
@@ -159,12 +159,19 @@ func (h *moduleHandler) Diff(
 		return nil, fmt.Errorf("error performing plan during Diff(...) %w", err)
 	}
 
+	replaceKeys := []string{}
 	resourcesChanged := false
-	plan.VisitResourcePlans(func(resource *tfsandbox.ResourcePlan) {
-		if resource.ChangeKind() != tfsandbox.NoOp {
+	plan.VisitResourcePlans(func(res *tfsandbox.ResourcePlan) {
+		println("Visiting resource plan for", res.Address())
+		println("Change kind is", res.ChangeKind())
+		if res.ChangeKind() != tfsandbox.NoOp {
 			// if there is any resource change that is not a no-op, we need to update.
 			resourcesChanged = true
 		}
+		// Add any resources that are replacing to the replaceKeys list.
+		if res.ChangeKind() == tfsandbox.Replace || res.ChangeKind() == tfsandbox.ReplaceDestroyBeforeCreate {
+			replaceKeys = append(replaceKeys, string(res.Address()))
+		}
 	})
 
 	outputsChanged := false
@@ -175,8 +182,16 @@ func (h *moduleHandler) Diff(
 		}
 	}
 
-	if resourcesChanged || outputsChanged {
-		return &pulumirpc.DiffResponse{Changes: pulumirpc.DiffResponse_DIFF_SOME}, nil
+	println("Is it DIFF_SOME?", inputsChanged || resourcesChanged || outputsChanged)
+	println("inputsChanged?", inputsChanged)
+	println("resourcesChanged?", resourcesChanged)
+	println("outputsChanged?", outputsChanged)
+
+	if inputsChanged || resourcesChanged || outputsChanged {
+		return &pulumirpc.DiffResponse{
+			Changes:  pulumirpc.DiffResponse_DIFF_SOME,
+			Replaces: replaceKeys,
+		}, nil
 	}
 
 	// the module has not changed, return DIFF_NONE.

From 056eb0c4a0b45ca585eaee2b3287afb8c3d92677 Mon Sep 17 00:00:00 2001
From: Anton Tayanovskyy <anton@pulumi.com>
Date: Fri, 27 Jun 2025 11:00:28 -0400
Subject: [PATCH 2/2] Use a delete-before-replace variation

---
 pkg/modprovider/module.go | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/pkg/modprovider/module.go b/pkg/modprovider/module.go
index bf67cb3a..47a0064a 100644
--- a/pkg/modprovider/module.go
+++ b/pkg/modprovider/module.go
@@ -188,10 +188,14 @@ func (h *moduleHandler) Diff(
 	println("outputsChanged?", outputsChanged)
 
 	if inputsChanged || resourcesChanged || outputsChanged {
-		return &pulumirpc.DiffResponse{
-			Changes:  pulumirpc.DiffResponse_DIFF_SOME,
-			Replaces: replaceKeys,
-		}, nil
+		resp := &pulumirpc.DiffResponse{
+			Changes: pulumirpc.DiffResponse_DIFF_SOME,
+		}
+		if len(replaceKeys) > 0 {
+			resp.Replaces = replaceKeys
+			resp.DeleteBeforeReplace = true
+		}
+		return resp, nil
 	}
 
 	// the module has not changed, return DIFF_NONE.