Improve exception message for out of range numbers in format strings

2 files changed, 22 insertions, 12 deletions

diff --git a/include/cxxformat/core.hpp b/include/cxxformat/core.hpp
index 6eec0ef..2a78b26 100644
--- a/include/cxxformat/core.hpp
+++ b/include/cxxformat/core.hpp
@@ -224,6 +224,16 @@ namespace format {
 		return {val, p};
 	}
 
+	template<std::unsigned_integral T = unsigned int>
+	constexpr std::pair<std::optional<T>, std::size_t> parseNumberWithMessage(std::string_view s, std::size_t pos, std::string_view numberName)
+	{
+		try {
+			return parseNumber<T>(s, pos);
+		} catch(const std::out_of_range&) {
+			throw std::out_of_range{std::string{numberName} + " is too big; maximum is " + std::to_string(std::numeric_limits<T>::max())};
+		}
+	}
+
 	namespace exceptions {
 		struct incomplete_specifier : std::invalid_argument {
 			using std::invalid_argument::invalid_argument;
@@ -263,7 +273,7 @@ namespace format {
 		};
 
 		bool hasExplicitArgIndex = false;
-		const auto argIndex = parseNumber<ArgIndex>(fmt, pos);
+		const auto argIndex = parseNumberWithMessage<ArgIndex>(fmt, pos, "Argument index or field width");
 		if (argIndex.first)
 		{
 			checkEos(argIndex.second);
@@ -315,8 +325,8 @@ namespace format {
 		checkEos();
 
 		ArgIndex maxArg = 0;
-		const auto argIndexOrNextArg = [&pos, &nextArg, &maxArg, checkEos, fmt](decltype(*format_specifier::minWidth)& argIndex) {
-			const auto index = parseNumber<ArgIndex>(fmt, pos);
+		const auto argIndexOrNextArg = [&pos, &nextArg, &maxArg, checkEos, fmt](decltype(*format_specifier::minWidth)& argIndex, std::string_view numberName) {
+			const auto index = parseNumberWithMessage<ArgIndex>(fmt, pos, numberName);
 			checkEos(index.second);
 			if (index.first && fmt[index.second] == '$')
 			{
@@ -336,22 +346,22 @@ namespace format {
 			maxArg = std::max(maxArg, argIndex);
 		};
 
-		const auto handleWidthPrecision = [&pos, argIndexOrNextArg, fmt, checkEos](decltype(format_specifier::minWidth)& indexOrValue, bool allowEmpty = false){
+		const auto handleWidthPrecision = [&pos, argIndexOrNextArg, fmt, checkEos](decltype(format_specifier::minWidth)& indexOrValue, std::string_view numberName, bool allowEmpty = false){
 			bool asArg = false;
 			if (fmt[pos] == '*')
 			{
 				asArg = true;
 				++pos;
 				checkEos();
-				argIndexOrNextArg(indexOrValue.emplace());
+				argIndexOrNextArg(indexOrValue.emplace(), numberName);
 			}
 			else
 			{
-				const auto width = parseNumber<ArgIndex>(fmt, pos);
-				if (width.first)
+				const auto value = parseNumberWithMessage<ArgIndex>(fmt, pos, numberName);
+				if (value.first)
 				{
-					indexOrValue = *width.first;
-					pos = width.second;
+					indexOrValue = *value.first;
+					pos = value.second;
 				}
 				else if (allowEmpty)
 				{
@@ -360,14 +370,14 @@ namespace format {
 			}
 			return asArg;
 		};
-		spec.flags.widthAsArg = handleWidthPrecision(spec.minWidth);
+		spec.flags.widthAsArg = handleWidthPrecision(spec.minWidth, "Field width");
 
 
 		if (fmt[pos] == '.')
 		{
 			++pos;
 			checkEos();
-			spec.flags.precisionAsArg = handleWidthPrecision(spec.precision, true);
+			spec.flags.precisionAsArg = handleWidthPrecision(spec.precision, "Precision", true);
 		}
 
 		{
diff --git a/include/cxxformat/runtime.hpp b/include/cxxformat/runtime.hpp
index 85c6ecf..7659468 100644
--- a/include/cxxformat/runtime.hpp
+++ b/include/cxxformat/runtime.hpp
@@ -184,7 +184,7 @@ namespace format {
 						throw exceptions::incomplete_specifier{"Incomplete format specifier “%s” at end of format string"_format(fmt.substr(nextSpec))};
 					} catch(const std::exception& e) {
 						constexpr std::size_t showPartSize = 10;
-						throw std::invalid_argument{"%s when parsing format specifier “%s%s” at column %u"_format(e.what(), fmt.substr(nextSpec, showPartSize), nextSpec + showPartSize > fmt.size() ? "" : "…", nextSpec)};
+						throw std::invalid_argument{"%s; when parsing format specifier “%s%s” at column %u"_format(e.what(), fmt.substr(nextSpec, showPartSize), nextSpec + showPartSize > fmt.size() ? "" : "…", nextSpec)};
 					}
 				}
 			}