Don't bail at preview when a protected resource needs replacement (#1…

…5969)

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# Description

Don't bail at preview when a protected resource needs replacement, just
error. This makes sure that users can see the actual diff that causes
the replacement.

Fixes #5027

Before:

```
$ pulumi preview
Type                                     Name                  Plan     Info
     pulumi:pulumi:Stack                      azure-native-ts-dev2           
     └─ azure-native:resources:ResourceGroup  rg                             1 error

Diagnostics:
  azure-native:resources:ResourceGroup (rg):
    error: unable to replace resource "urn:pulumi:dev2::azure-native-ts::azure-native:resources:ResourceGroup::rg"
    as it is currently marked for protection. To unprotect the resource, remove the `protect` flag from the resource in your Pulumi program and run `pulumi up`


$ pulumi preview --diff
pulumi:pulumi:Stack: (same)
    [urn=urn:pulumi:dev2::azure-native-ts::pulumi:pulumi:Stack::azure-native-ts-dev2]
error: unable to replace resource "urn:pulumi:dev2::azure-native-ts::azure-native:resources:ResourceGroup::rg"
as it is currently marked for protection. To unprotect the resource, remove the `protect` flag from the resource in your Pulumi program and run `pulumi up`
Resources:
    1 unchanged
```

After:

```
$ pulumi preview
Type                                     Name                  Plan        Info
     pulumi:pulumi:Stack                      azure-native-ts-dev2              1 error; 2 warnings
 +-  └─ azure-native:resources:ResourceGroup  rg                    replace     [diff: ~location]; 1 error

Diagnostics:
  azure-native:resources:ResourceGroup (rg):
    error: unable to replace resource "urn:pulumi:dev2::azure-native-ts::azure-native:resources:ResourceGroup::rg"
    as it is currently marked for protection. To unprotect the resource, remove the `protect` flag from the resource in your Pulumi program and run `pulumi up`

  pulumi:pulumi:Stack (azure-native-ts-dev2):
    error: preview failed


$ pulumi preview --diff
pulumi:pulumi:Stack: (same)
    [urn=urn:pulumi:dev2::azure-native-ts::pulumi:pulumi:Stack::azure-native-ts-dev2]
error: unable to replace resource "urn:pulumi:dev2::azure-native-ts::azure-native:resources:ResourceGroup::rg"
as it is currently marked for protection. To unprotect the resource, remove the `protect` flag from the resource in your Pulumi program and run `pulumi up`
    +-azure-native:resources:ResourceGroup: (replace) 🔒
        [id=/subscriptions/0282681f-7a9e-424b-80b2-96babd57a8a1/resourceGroups/rg5f8e30e4]
        [urn=urn:pulumi:dev2::azure-native-ts::azure-native:resources:ResourceGroup::rg]
        [provider=urn:pulumi:dev2::azure-native-ts::pulumi:providers:azure-native::default_2_30_0::3c957b2a-4852-439c-b211-22a115bbe89a]
      ~ location: "westeurope" => "westus2"
error: preview failed
Resources:
    +-1 to replace
    1 unchanged
```

## Checklist

- [ ] I have run `make tidy` to update any new dependencies
- [ ] I have run `make lint` to verify my code passes the lint check
  - [ ] I have formatted my code using `gofumpt`

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- [x] I have added tests that prove my fix is effective or that my
feature works
<!--- 
User-facing changes require a CHANGELOG entry.
-->
- [x] I have run `make changelog` and committed the
`changelog/pending/<file>` documenting my change
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then the service should honor older versions of the CLI where this
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changelog/pending/20240417--engine--dont-bail-at-preview-when-a-protected-resource-needs-replacement.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: fix
+  scope: engine
+  description: Display the entire preview with diff when a protected resource needs replacement

pkg/engine/lifecycletest/pulumi_test.go

@@ -3181,13 +3181,19 @@ func TestProtect(t *testing.T) {
 		return err
 	}
 
-	// Run a new update which will cause a replace, we should get an error
+	// Run a dry-run (preview) which will cause a replace, we should get an error.
+	// However, the preview doesn't bail, so we expect one "created" resource as a result of this operation.
 	expectedMessage = "<{%reset%}>unable to replace resource \"urn:pulumi:test::test::pkgA:m:typA::resA\"\n" +
 		"as it is currently marked for protection. To unprotect the resource, remove the `protect` flag from " +
 		"the resource in your Pulumi program and run `pulumi up`<{%reset%}>\n"
 	ins = resource.NewPropertyMapFromMap(map[string]interface{}{
 		"foo": "baz",
 	})
+	_, err = TestOp(Update).Run(project, p.GetTarget(t, snap), p.Options, true, p.BackendClient, validate)
+	assert.ErrorContains(t, err, "step generator errored")
+
+	// Run an update which will cause a replace, we should get an error.
+	// Contrary to the preview, the error is a bail, so no resources are created.
 	snap, err = TestOp(Update).Run(project, p.GetTarget(t, snap), p.Options, false, p.BackendClient, validate)
 	assert.Error(t, err)
 	assert.NotNil(t, snap)
@@ -3217,7 +3223,7 @@ func TestProtect(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, snap)
 	assert.Len(t, snap.Resources, 2)
-	assert.Equal(t, "created-id-1", snap.Resources[1].ID.String())
+	assert.Equal(t, "created-id-2", snap.Resources[1].ID.String())
 	assert.Equal(t, false, snap.Resources[1].Protect)
 	assert.Equal(t, 1, deleteCounter)
 
@@ -3227,7 +3233,7 @@ func TestProtect(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, snap)
 	assert.Len(t, snap.Resources, 2)
-	assert.Equal(t, "created-id-1", snap.Resources[1].ID.String())
+	assert.Equal(t, "created-id-2", snap.Resources[1].ID.String())
 	assert.Equal(t, true, snap.Resources[1].Protect)
 	assert.Equal(t, 1, deleteCounter)
 
@@ -3240,7 +3246,7 @@ func TestProtect(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, snap)
 	assert.Len(t, snap.Resources, 2)
-	assert.Equal(t, "created-id-2", snap.Resources[1].ID.String())
+	assert.Equal(t, "created-id-3", snap.Resources[1].ID.String())
 	assert.Equal(t, 2, deleteCounter)
 }
 

pkg/resource/deploy/step_generator.go

@@ -1034,7 +1034,14 @@ func (sg *stepGenerator) generateStepsFromDiff(
 					"program and run `pulumi up`", urn)
 				sg.deployment.ctx.Diag.Errorf(diag.StreamMessage(urn, message, 0))
 				sg.sawError = true
-				return nil, result.BailErrorf(message)
+				// In Preview, we mark the deployment as Error but continue to next steps,
+				// so that the preview is shown to the user and they can see the diff causing it.
+				// In Update mode, we bail to stop any further actions immediately. If we don't bail and
+				// we're doing a create before delete replacement we'll execute the create before getting
+				// to the delete error.
+				if !sg.deployment.preview {
+					return nil, result.BailErrorf(message)
+				}
 			}
 
 			// If the goal state specified an ID, issue an error: the replacement will change the ID, and is