command: don't show old values for create diffs in plan

New resources logically don't have "old values" for their attributes, so
showing them as updates from the empty string is misleading and confusing.

Instead, we'll skip showing the old value in a creation diff.

command/format_plan.go

@@ -87,6 +87,7 @@ func formatPlanModuleExpand(
 		// resource header.
 		color := "yellow"
 		symbol := "~"
+		oldValues := true
 		switch rdiff.ChangeType() {
 		case terraform.DiffDestroyCreate:
 			color = "green"
@@ -94,6 +95,7 @@ func formatPlanModuleExpand(
 		case terraform.DiffCreate:
 			color = "green"
 			symbol = "+"
+			oldValues = false
 		case terraform.DiffDestroy:
 			color = "red"
 			symbol = "-"
@@ -134,13 +136,22 @@ func formatPlanModuleExpand(
 				newResource = opts.Color.Color(" [red](forces new resource)")
 			}
 
-			buf.WriteString(fmt.Sprintf(
-				"    %s:%s %#v => %#v%s\n",
-				attrK,
-				strings.Repeat(" ", keyLen-len(attrK)),
-				attrDiff.Old,
-				v,
-				newResource))
+			if oldValues {
+				buf.WriteString(fmt.Sprintf(
+					"    %s:%s %#v => %#v%s\n",
+					attrK,
+					strings.Repeat(" ", keyLen-len(attrK)),
+					attrDiff.Old,
+					v,
+					newResource))
+			} else {
+				buf.WriteString(fmt.Sprintf(
+					"    %s:%s %#v%s\n",
+					attrK,
+					strings.Repeat(" ", keyLen-len(attrK)),
+					v,
+					newResource))
+			}
 		}
 
 		// Write the reset color so we don't overload the user's terminal