Add helper for parsing the new reporter specs

The new reporter spec generalizes key-value options that can be
passed to the reporter, looking like this
`reporterName[::key=value]*`. A key can be either Catch2-recognized,
which currently means either `out` or `colour`, or reporter-specific
which is anything prefixed with `X`, e.g. `Xfoo`.

src/catch2/internal/catch_reporter_spec_parser.cpp

@@ -9,9 +9,28 @@
 #include <catch2/internal/catch_reporter_spec_parser.hpp>
 
 #include <catch2/interfaces/catch_interfaces_config.hpp>
+#include <catch2/internal/catch_move_and_forward.hpp>
+
+#include <algorithm>
+#include <ostream>
 
 namespace Catch {
 
+    namespace {
+        struct kvPair {
+            StringRef key, value;
+        };
+
+        kvPair splitKVPair(StringRef kvString) {
+            auto splitPos = static_cast<size_t>( std::distance(
+                kvString.begin(),
+                std::find( kvString.begin(), kvString.end(), '=' ) ) );
+
+            return { kvString.substr( 0, splitPos ),
+                     kvString.substr( splitPos + 1, kvString.size() ) };
+        }
+    }
+
     namespace Detail {
         std::vector<std::string> splitReporterSpec( StringRef reporterSpec ) {
             static constexpr auto separator = "::";
@@ -78,4 +97,78 @@ namespace Catch {
     } // namespace Detail
 
 
+    bool operator==( ReporterSpec const& lhs, ReporterSpec const& rhs ) {
+        return lhs.m_name == rhs.m_name &&
+               lhs.m_outputFileName == rhs.m_outputFileName &&
+               lhs.m_colourMode == rhs.m_colourMode &&
+               lhs.m_customOptions == rhs.m_customOptions;
+    }
+
+    Optional<ReporterSpec> parseReporterSpec( StringRef reporterSpec ) {
+        auto parts = Detail::splitReporterSpec( reporterSpec );
+
+        assert( parts.size() > 0 && "Split should never return empty vector" );
+
+        std::map<std::string, std::string> kvPairs;
+        Optional<std::string> outputFileName;
+        Optional<ColourMode> colourMode;
+
+        // First part is always reporter name, so we skip it
+        for ( size_t i = 1; i < parts.size(); ++i ) {
+            auto kv = splitKVPair( parts[i] );
+            auto key = kv.key, value = kv.value;
+
+            if ( key.empty() || value.empty() ) {
+                return {};
+            } else if ( key[0] == 'X' ) {
+                // This is a reporter-specific option, we don't check these
+                // apart from basic sanity checks
+                if ( key.size() == 1 ) {
+                    return {};
+                }
+
+                auto ret = kvPairs.emplace( kv.key, kv.value );
+                if ( !ret.second ) {
+                    // Duplicated key. We might want to handle this differently,
+                    // e.g. by overwriting the existing value?
+                    return {};
+                }
+            } else if ( key == "out" ) {
+                // Duplicated key
+                if ( outputFileName ) {
+                    return {};
+                }
+                outputFileName = static_cast<std::string>( value );
+            } else if ( key == "colour" ) {
+                // Duplicated key
+                if ( colourMode ) {
+                    return {};
+                }
+                colourMode = Detail::stringToColourMode( value );
+                // Parsing failed
+                if ( !colourMode ) {
+                    return {};
+                }
+            } else {
+                // Unrecognized option
+                return {};
+            }
+        }
+
+        return ReporterSpec{ CATCH_MOVE( parts[0] ),
+                             CATCH_MOVE( outputFileName ),
+                             CATCH_MOVE( colourMode ),
+                             CATCH_MOVE( kvPairs ) };
+    }
+
+ReporterSpec::ReporterSpec(
+        std::string name,
+        Optional<std::string> outputFileName,
+        Optional<ColourMode> colourMode,
+        std::map<std::string, std::string> customOptions ):
+        m_name( CATCH_MOVE( name ) ),
+        m_outputFileName( CATCH_MOVE( outputFileName ) ),
+        m_colourMode( CATCH_MOVE( colourMode ) ),
+        m_customOptions( CATCH_MOVE( customOptions ) ) {}
+
 } // namespace Catch