From e7917bbdfbdcccdf5516910709f60f245830c59c Mon Sep 17 00:00:00 2001
From: Markus Mittendrein <maxmitti@maxmitti.tk>
Date: Tue, 22 Mar 2022 21:29:06 +0100
Subject: Fix compile time formatters for use with 0 arguments

---
 include/cxxformat/core.hpp | 53 ++++++++++++++++++++++++----------------------
 main.cpp                   |  2 ++
 2 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/include/cxxformat/core.hpp b/include/cxxformat/core.hpp
index 662f4f8..43b3c41 100644
--- a/include/cxxformat/core.hpp
+++ b/include/cxxformat/core.hpp
@@ -486,33 +486,36 @@ namespace format {
 				const auto out = make_output(std::forward<Output>(output));
 				const auto format_arg = [&args..., &out]<format_specifier spec>(holder<spec>) -> decltype(auto)
 				{
-					optional_int<std::size_t> minWidth = spec.minWidth;
-					if constexpr (spec.flags.widthAsArg)
+					if constexpr (sizeof...(Args) > 0)
 					{
-						using Arg = std::decay_t<nth_type<*spec.minWidth, Args...>>;
-						static_assert(std::unsigned_integral<Arg>, "Width argument must be an unsigned integral");
-						static_assert(sizeof(Arg) <= sizeof(std::size_t), "Width argument type must be at most as big as std::size_t");
-						minWidth = nth_argument<*spec.minWidth>(std::forward<Args>(args)...);
+						optional_int<std::size_t> minWidth = spec.minWidth;
+						if constexpr (spec.flags.widthAsArg)
+						{
+							using Arg = std::decay_t<nth_type<*spec.minWidth, Args...>>;
+							static_assert(std::unsigned_integral<Arg>, "Width argument must be an unsigned integral");
+							static_assert(sizeof(Arg) <= sizeof(std::size_t), "Width argument type must be at most as big as std::size_t");
+							minWidth = nth_argument<*spec.minWidth>(std::forward<Args>(args)...);
+						}
+						optional_int<std::size_t> precision = spec.precision;
+						if constexpr (spec.flags.precisionAsArg)
+						{
+							using Arg = std::decay_t<nth_type<*spec.precision, Args...>>;
+							static_assert(std::unsigned_integral<Arg>, "Precision argument must be an unsigned integral");
+							static_assert(sizeof(Arg) <= sizeof(std::size_t), "Precision argument type must be at most as big as std::size_t");
+							precision = nth_argument<*spec.precision>(std::forward<Args>(args)...);
+						}
+
+						using Arg = nth_type<spec.argIndex, Args...>;
+						Arg&& arg = nth_argument<spec.argIndex>(std::forward<Args>(args)...);
+						using formatter = formatter_with_fallback<std::decay_t<Arg>>;
+
+						[]() consteval {
+							// throws on error
+							formatter::conversionSupported(spec);
+						}();
+
+						return formatter::format(out, std::forward<Arg>(arg), spec, minWidth, precision);
 					}
-					optional_int<std::size_t> precision = spec.precision;
-					if constexpr (spec.flags.precisionAsArg)
-					{
-						using Arg = std::decay_t<nth_type<*spec.precision, Args...>>;
-						static_assert(std::unsigned_integral<Arg>, "Precision argument must be an unsigned integral");
-						static_assert(sizeof(Arg) <= sizeof(std::size_t), "Precision argument type must be at most as big as std::size_t");
-						precision = nth_argument<*spec.precision>(std::forward<Args>(args)...);
-					}
-
-					using Arg = nth_type<spec.argIndex, Args...>;
-					Arg&& arg = nth_argument<spec.argIndex>(std::forward<Args>(args)...);
-					using formatter = formatter_with_fallback<std::decay_t<Arg>>;
-
-					[]() consteval {
-						// throws on error
-						formatter::conversionSupported(spec);
-					}();
-
-					return formatter::format(out, std::forward<Arg>(arg), spec, minWidth, precision);
 				};
 
 				(([&]{
diff --git a/main.cpp b/main.cpp
index 849face..17a1f64 100644
--- a/main.cpp
+++ b/main.cpp
@@ -30,6 +30,8 @@ int main(int argc, char* argv[])
 	format_to("Hallo %%du %1$s %s%c %s %u = %4$#x = %4$#X = %4$#o %f!\n", std::cout, "Knirp", 's', argv[0], 42u, 1.337);
 	assert(format("Hallo %%du %1$s %s%c %s %u = %4$#x = %4$#X = %4$#o %f!\n", "Knirp", 's', argv[0], 42u, 1.337) == "Hallo %%du %1$s %s%c %s %u = %4$#x = %4$#X = %4$#o %f!\n"_format("Knirp", 's', argv[0], 42u, 1.337));
 
+	"Hallo\n"_format_to(stdout);
+	format_to("Hallo\n", stdout);
 	"-%20s-\n"_format_to(stdout, "Hallo");
 	"-%'20s-\n"_format_to(stdout, R"(H\"all"o)");
 	"-%'-20s-\n"_format_to(stdout, R"(H\"all"o)");
-- 
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