Fix chrono formatting with invalid argument id (#1132)

include/fmt/chrono.h

@@ -585,18 +585,20 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
     }
   };
 
- public:
+  typedef typename basic_parse_context<Char>::iterator iterator;
-  formatter() : spec(), precision(-1) {}
+  struct parse_range {
+    iterator begin;
+    iterator end;
+  };
 
-  FMT_CONSTEXPR auto parse(basic_parse_context<Char>& ctx)
+  FMT_CONSTEXPR parse_range do_parse(basic_parse_context<Char>& ctx) {
-      -> decltype(ctx.begin()) {
     auto begin = ctx.begin(), end = ctx.end();
-    if (begin == end) return begin;
+    if (begin == end) return {begin, end};
     spec_handler handler{*this, ctx, format_str};
     begin = internal::parse_align(begin, end, handler);
-    if (begin == end) return begin;
+    if (begin == end) return {begin, end};
     begin = internal::parse_width(begin, end, handler);
-    if (begin == end) return begin;
+    if (begin == end) return {begin, end};
     if (*begin == '.') {
       if (std::is_floating_point<Rep>::value)
         begin = internal::parse_precision(begin, end, handler);
@@ -604,9 +606,18 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
         handler.on_error("precision not allowed for this argument type");
     }
     end = parse_chrono_format(begin, end, internal::chrono_format_checker());
-    format_str =
+    return {begin, end};
-        basic_string_view<Char>(&*begin, internal::to_unsigned(end - begin));
+  }
-    return end;
+
+ public:
+  formatter() : spec(), precision(-1) {}
+
+  FMT_CONSTEXPR auto parse(basic_parse_context<Char>& ctx)
+      -> decltype(ctx.begin()) {
+    auto range = do_parse(ctx);
+    format_str = basic_string_view<Char>(
+        &*range.begin, internal::to_unsigned(range.end - range.begin));
+    return range.end;
   }
 
   template <typename FormatContext>

test/chrono-test.cc

@@ -296,4 +296,9 @@ TEST(ChronoTest, FormatFullSpecsQq) {
   EXPECT_EQ("*1.2340 ms*", fmt::format("{:*^11.4%Q %q}", dms(1.234)));
 }
 
+TEST(ChronoTest, InvalidWidthId) {
+  EXPECT_THROW(fmt::format("{:{o}", std::chrono::seconds(0)),
+               fmt::format_error);
+}
+
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR