message & friends: make formattable

So we can easily debug-print them.

lib/message/mu-fields.hh

@@ -594,5 +594,20 @@ Option<Field> field_from_number(size_t id)
 }
 
 
+/**
+ * Get a fmt-printable representation of Field for fmt
+ *
+ * @param field a Field
+ *
+ * @return a printable representation
+ */
+static inline constexpr auto format_as(const Field& field) {
+	return field.name;
+}
+static inline constexpr auto format_as(const Field::Id id) {
+	return format_as(field_from_id(id));
+}
+
+
 } // namespace Mu
 #endif /* MU_FIELDS_HH__ */

lib/message/mu-flags.hh

@@ -387,6 +387,18 @@ flags_keep_unmutable(Flags old_flags, Flags new_flags, Flags unmutable_flag)
  */
 std::string to_string(Flags flags);
 
+
+/**
+ * Get a string representation of Flags for fmt
+ *
+ * @param flags flags
+ *
+ * @return string as a sequence of message-flag shortcuts
+ */
+static inline auto format_as(const Flags& flags) {
+	return to_string(flags);
+}
+
 } // namespace Mu
 
 #endif /* MU_FLAGS_HH__ */

lib/message/mu-message.hh

@@ -460,15 +460,10 @@ private:
 }; // Message
 MU_ENABLE_BITOPS(Message::Options);
 
-
-
-static inline std::ostream&
-operator<<(std::ostream& os, const Message& msg)
-{
-	os << msg.sexp();
-	return os;
+static inline auto
+format_as(const Message& msg) {
+	return msg.path();
 }
 
-
 } // Mu
 #endif /* MU_MESSAGE_HH__ */

lib/mu-query-results.hh

@@ -109,7 +109,7 @@ QueryMatch::has_flag(QueryMatch::Flags flag) const
 	return any_of(flags & flag);
 }
 
-inline std::ostream&
+static inline std::ostream&
 operator<<(std::ostream& os, QueryMatch::Flags mflags)
 {
 	if (mflags == QueryMatch::Flags::None) {
@@ -348,6 +348,13 @@ private:
 	QueryMatches&			query_matches_;
 };
 
+
+static inline auto
+format_as(const QueryResultsIterator& it)
+{
+	return it.path().value_or("<no path>");
+}
+
 constexpr auto MaxQueryResultsSize = std::numeric_limits<size_t>::max();
 
 class QueryResults {