Improve format parsing exception messages

2 files changed, 39 insertions, 24 deletions

diff --git a/include/cxxformat/core.hpp b/include/cxxformat/core.hpp
index 4e9858b..6eec0ef 100644
--- a/include/cxxformat/core.hpp
+++ b/include/cxxformat/core.hpp
@@ -224,6 +224,14 @@ namespace format {
 		return {val, p};
 	}
 
+	namespace exceptions {
+		struct incomplete_specifier : std::invalid_argument {
+			using std::invalid_argument::invalid_argument;
+
+			incomplete_specifier() : std::invalid_argument{"Incomplete format specifier at end of format string"} {}
+		};
+	};
+
 	constexpr auto parseSpec(std::string_view fmt, std::size_t pos, ArgIndex nextArg)
 	{
 		struct Result {
@@ -236,7 +244,7 @@ namespace format {
 		const auto checkEos = [&pos, fmt](std::optional<std::size_t> p = std::nullopt) {
 			if (p.value_or(pos) >= fmt.size())
 			{
-				throw std::invalid_argument{"Incomplete format specifier at end of format string"};
+				throw exceptions::incomplete_specifier{};
 			}
 		};
 
diff --git a/include/cxxformat/runtime.hpp b/include/cxxformat/runtime.hpp
index 1c881cc..7e25ee2 100644
--- a/include/cxxformat/runtime.hpp
+++ b/include/cxxformat/runtime.hpp
@@ -122,11 +122,11 @@ namespace format {
 			{
 				if (args > argCount)
 				{
-					throw std::invalid_argument{"Too many arguments passed!"};
+					throw std::invalid_argument{"Too many arguments passed! Expected %u."_format(argCount)};
 				}
 				else if (args < argCount)
 				{
-					throw std::invalid_argument{"Not enough arguments passed!"};
+					throw std::invalid_argument{"Not enough arguments passed! Expected %u."_format(argCount)};
 				}
 			}
 		};
@@ -159,33 +159,40 @@ namespace format {
 					break;
 				}
 
-				if (nextSpec + 1 >= fmt.size())
-				{
-					throw std::invalid_argument{"Incomplete format specifier at end of format string"};
-				}
+				try {
+					if (nextSpec + 1 >= fmt.size())
+					{
+						throw exceptions::incomplete_specifier{};
+					}
 
-				const auto specStart = fmt[nextSpec + 1];
-				if (specStart == '%')
-				{
-					// + 1 to include the first %
-					addString(fmt.substr(pos, nextSpec - pos + 1));
-					pos = nextSpec + 2;
-				}
-				else
-				{
-					const auto [newPos, spec, newNextArg, specMaxArg] = parseSpec(fmt, nextSpec + 1, nextArg);
-					if (!checkValidConversion(spec.conversion))
+					const auto specStart = fmt[nextSpec + 1];
+					if (specStart == '%')
 					{
-						throw std::invalid_argument{"Invalid conversion specifier ‘%c’ in format specifier “%s”"_format(spec.conversion, fmt.substr(nextSpec, newPos - nextSpec))};
+						// + 1 to include the first %
+						addString(fmt.substr(pos, nextSpec - pos + 1));
+						pos = nextSpec + 2;
 					}
+					else
+					{
+						const auto [newPos, spec, newNextArg, specMaxArg] = parseSpec(fmt, nextSpec + 1, nextArg);
+						if (!checkValidConversion(spec.conversion))
+						{
+							throw std::invalid_argument{"Invalid conversion specifier ‘%c’"_format(spec.conversion)};
+						}
 
-					addString(fmt.substr(pos, nextSpec - pos));
+						addString(fmt.substr(pos, nextSpec - pos));
 
-					nextArg = newNextArg;
-					maxArg = std::max(maxArg, specMaxArg);
-					pos = newPos;
+						nextArg = newNextArg;
+						maxArg = std::max(maxArg, specMaxArg);
+						pos = newPos;
 
-					parts.emplace_back(spec);
+						parts.emplace_back(spec);
+					}
+				} catch(const exceptions::incomplete_specifier&) {
+					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)};
 				}
 			}