utils: replace time_to_string with fmt-based formatting

It's faster; make "mu find" ~5-10% faster, and removes some code we no
longer need.

lib/utils/mu-utils.cc

@@ -334,33 +334,7 @@ Mu::vformat(const char* frm, va_list args)
 	return str;
 }
 
-std::string
+static Option<::time_t>
-Mu::time_to_string(const char *frm, time_t t, bool utc)
-{
-	g_return_val_if_fail(frm, "");
-
-	GDateTime* dt = std::invoke([&] {
-		if (utc)
-			return g_date_time_new_from_unix_utc(t);
-		else
-			return g_date_time_new_from_unix_local(t);
-	});
-
-	if (!dt) {
-		mu_warning("time_t out of range: <{}>", t);
-		return {};
-	}
-
-	frm = frm ? frm : "%c";
-	auto datestr{to_string_opt_gchar(g_date_time_format(dt, frm))};
-	g_date_time_unref(dt);
-	if (!datestr)
-		mu_warning("failed to format time with format '{}'", frm);
-
-	return datestr.value_or("");
-}
-
-static Option<int64_t>
 delta_ymwdhMs(const std::string& expr)
 {
 	char* endptr;
@@ -390,7 +364,7 @@ delta_ymwdhMs(const std::string& expr)
 		then =
 		    g_date_time_add_full(now, -years, -months, -days, -hours, -minutes, -seconds);
 
-	auto  t = std::max<int64_t>(0, g_date_time_to_unix(then));
+	auto  t = std::max<::time_t>(0, g_date_time_to_unix(then));
 
 	g_date_time_unref(then);
 	g_date_time_unref(now);
@@ -398,7 +372,7 @@ delta_ymwdhMs(const std::string& expr)
 	return t;
 }
 
-static Option<int64_t>
+static Option<::time_t>
 special_date_time(const std::string& d, bool is_first)
 {
 	if (d == "now")
@@ -467,12 +441,12 @@ fixup_month(struct tm* tbuf)
  }
 
 
-Option<int64_t>
+Option<::time_t>
 Mu::parse_date_time(const std::string& dstr, bool is_first)
 {
 	struct tm tbuf{};
 	GDateTime *dtime{};
-	int64_t t;
+	::time_t t;
 
 	/* one-sided dates */
 	if (dstr.empty())
@@ -506,7 +480,7 @@ Mu::parse_date_time(const std::string& dstr, bool is_first)
 	t = g_date_time_to_unix(dtime);
 	g_date_time_unref(dtime);
 
-	return std::max<int64_t>(t, 0);
+	return std::max<::time_t>(t, 0);
 }
 
 

lib/utils/mu-utils.hh

@@ -43,6 +43,7 @@
 #endif /*FMT_HEADER_ONLY*/
 #include <fmt/format.h>
 #include <fmt/core.h>
+#include <fmt/chrono.h>
 
 namespace Mu {
 
@@ -133,6 +134,11 @@ auto mu_join(Range&& range, std::string_view sepa) {
 	return fmt::join(std::forward<Range>(range), sepa);
 }
 
+template <typename T>
+auto mu_time(T t, bool use_utc=false) {
+	::time_t tt{static_cast<::time_t>(t)};
+	return use_utc ? fmt::gmtime(tt) : fmt::localtime(tt);
+}
 
 using StringVec = std::vector<std::string>;
 
@@ -145,8 +151,7 @@ using StringVec = std::vector<std::string>;
  */
 std::string utf8_flatten(const char* str);
 inline std::string
-utf8_flatten(const std::string& s)
+utf8_flatten(const std::string& s) {
-{
 	return utf8_flatten(s.c_str());
 }
 
@@ -240,30 +245,7 @@ static inline bool mu_print_encoded(fmt::format_string<T...> frm, T&&... args) n
  *
  * @return the corresponding time_t or Nothing if parsing failed.
  */
-Option<int64_t> parse_date_time(const std::string& date, bool first);
+Option<::time_t> parse_date_time(const std::string& date, bool first);
-
-/**
- * 64-bit incarnation of time_t expressed as a 10-digit string. Uses 64-bit for the time-value,
- *  regardless of the size of time_t.
- *
- * @param t some time value
- *
- * @return
- */
-std::string date_to_time_t_string(int64_t t);
-
-/**
- * Get a string for a given time_t and format
- * memory that must be freed after use.
- *
- * @param frm the format of the string (in strftime(3) format)
- * @param t the time as time_t
- * @param utc whether to display as UTC(if true) or local time
- *
- * @return a string representation of the time in UTF8-format, or empty in case
- * of error.
- */
-std::string time_to_string(const char *frm, time_t t, bool utc = false) G_GNUC_CONST;
 
 /**
  * Crudely convert HTML to plain text. This attempts to scrape the