add (forces new resource) to provider test diffs

Add the (forces new resource) annotation to the diff output for provider
tests failures when we can. This helps providers narrow down what might
be triggering changes when encountering test failures with the new SDK.

config/hcl2shim/paths.go

@@ -251,3 +251,26 @@ func pathFromFlatmapKeySet(key string, ty cty.Type) (cty.Path, error) {
 	// set as a whole changed.
 	return nil, nil
 }
+
+// FlatmapKeyFromPath returns the flatmap equivalent of the given cty.Path for
+// use in generating legacy style diffs.
+func FlatmapKeyFromPath(path cty.Path) string {
+	var parts []string
+
+	for _, step := range path {
+		switch step := step.(type) {
+		case cty.GetAttrStep:
+			parts = append(parts, step.Name)
+		case cty.IndexStep:
+			switch ty := step.Key.Type(); {
+			case ty == cty.String:
+				parts = append(parts, step.Key.AsString())
+			case ty == cty.Number:
+				i, _ := step.Key.AsBigFloat().Int64()
+				parts = append(parts, strconv.Itoa(int(i)))
+			}
+		}
+	}
+
+	return strings.Join(parts, ".")
+}

config/hcl2shim/paths_test.go

@@ -3,6 +3,7 @@ package hcl2shim
 import (
 	"fmt"
 	"reflect"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -365,5 +366,43 @@ func TestRequiresReplace(t *testing.T) {
 		})
 
 	}
+}
 
+func TestFlatmapKeyFromPath(t *testing.T) {
+	for i, tc := range []struct {
+		path cty.Path
+		attr string
+	}{
+		{
+			path: cty.Path{
+				cty.GetAttrStep{Name: "force_new"},
+			},
+			attr: "force_new",
+		},
+		{
+			path: cty.Path{
+				cty.GetAttrStep{Name: "attr"},
+				cty.IndexStep{Key: cty.NumberIntVal(0)},
+				cty.GetAttrStep{Name: "force_new"},
+			},
+			attr: "attr.0.force_new",
+		},
+		{
+			path: cty.Path{
+				cty.GetAttrStep{Name: "attr"},
+				cty.IndexStep{Key: cty.StringVal("key")},
+				cty.GetAttrStep{Name: "obj_attr"},
+				cty.IndexStep{Key: cty.NumberIntVal(0)},
+				cty.GetAttrStep{Name: "force_new"},
+			},
+			attr: "attr.key.obj_attr.0.force_new",
+		},
+	} {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			attr := FlatmapKeyFromPath(tc.path)
+			if attr != tc.attr {
+				t.Fatalf("expected:%q got:%q", tc.attr, attr)
+			}
+		})
+	}
 }

helper/resource/testing_config.go

@@ -214,6 +214,7 @@ func legacyDiffComparisonString(changes *plans.Changes) string {
 	}
 	byModule := map[string]map[string]*ResourceChanges{}
 	resourceKeys := map[string][]string{}
+	requiresReplace := map[string][]string{}
 	var moduleKeys []string
 	for _, rc := range changes.Resources {
 		if rc.Action == plans.NoOp {
@@ -239,6 +240,12 @@ func legacyDiffComparisonString(changes *plans.Changes) string {
 		} else {
 			byModule[moduleKey][resourceKey].Deposed[rc.DeposedKey] = rc
 		}
+
+		rr := []string{}
+		for _, p := range rc.RequiredReplace.List() {
+			rr = append(rr, hcl2shim.FlatmapKeyFromPath(p))
+		}
+		requiresReplace[resourceKey] = rr
 	}
 	sort.Strings(moduleKeys)
 	for _, ks := range resourceKeys {
@@ -254,6 +261,8 @@ func legacyDiffComparisonString(changes *plans.Changes) string {
 		for _, resourceKey := range resourceKeys[moduleKey] {
 			rc := rcs[resourceKey]
 
+			forceNewAttrs := requiresReplace[resourceKey]
+
 			crud := "UPDATE"
 			if rc.Current != nil {
 				switch rc.Current.Action {
@@ -341,7 +350,17 @@ func legacyDiffComparisonString(changes *plans.Changes) string {
 				// at the core layer.
 
 				updateMsg := ""
-				// TODO: Mark " (forces new resource)" in updateMsg when appropriate.
+
+				// This may not be as precise as in the old diff, as it matches
+				// everything under the attribute that was originally marked as
+				// ForceNew, but should help make it easier to determine what
+				// caused replacement here.
+				for _, k := range forceNewAttrs {
+					if strings.HasPrefix(attrK, k) {
+						updateMsg = " (forces new resource)"
+						break
+					}
+				}
 
 				fmt.Fprintf(
 					&mBuf, "  %s:%s %#v => %#v%s\n",