command/format: JSON value formatting heuristic not for primitive values

Since our own syntax for primitive values is similar to that of JSON, and
since we permit automatic conversions from number and bool to string, we
must do this special JSON value diff formatting only if the value is a
JSON array or object to avoid confusing results.

command/format/diff.go

@@ -424,10 +424,10 @@ func (p *blockBodyDiffPrinter) writeValue(val cty.Value, action plans.Action, in
 		switch ty {
 		case cty.String:
 			{
-				// Special behavior for JSON strings
+				// Special behavior for JSON strings containing array or object
 				src := []byte(val.AsString())
 				ty, err := ctyjson.ImpliedType(src)
-				if err == nil {
+				if err == nil && !ty.IsPrimitiveType() {
 					jv, err := ctyjson.Unmarshal(src, ty)
 					if err == nil {
 						p.buf.WriteString("jsonencode(")
@@ -548,12 +548,13 @@ func (p *blockBodyDiffPrinter) writeValueDiff(old, new cty.Value, indent int, pa
 			newS := new.AsString()
 
 			{
-				// Special behavior for JSON strings
+				// Special behavior for JSON strings containing object or
+				// list values.
 				oldBytes := []byte(oldS)
 				newBytes := []byte(newS)
 				oldType, oldErr := ctyjson.ImpliedType(oldBytes)
 				newType, newErr := ctyjson.ImpliedType(newBytes)
-				if oldErr == nil && newErr == nil {
+				if oldErr == nil && newErr == nil && !(oldType.IsPrimitiveType() && newType.IsPrimitiveType()) {
 					oldJV, oldErr := ctyjson.Unmarshal(oldBytes, oldType)
 					newJV, newErr := ctyjson.Unmarshal(newBytes, newType)
 					if oldErr == nil && newErr == nil {