Clear unscoped messages lazily

This improves the fast path performance for successful assertions
by about 7%, at the cost of potentially keeping around the message
allocation longer.

Author: horenmar

src/catch2/internal/catch_run_context.cpp

@@ -296,6 +296,10 @@ namespace Catch {
         }
 
         {
+            if ( m_clearMessageScopes ) {
+                m_messageScopes.clear();
+                m_clearMessageScopes = false;
+            }
             auto _ = scopedDeactivate( *m_outputRedirect );
             m_reporter->assertionEnded( AssertionStats( result, m_messages, m_totals ) );
         }
@@ -524,9 +528,9 @@ namespace Catch {
 
     void RunContext::assertionPassedFastPath(SourceLineInfo lineInfo) {
         m_lastKnownLineInfo = lineInfo;
-        m_lastAssertionPassed = true;
         ++m_totals.assertions.passed;
-        m_messageScopes.clear();
+        m_lastAssertionPassed = true;
+        m_clearMessageScopes = true;
     }
 
     bool RunContext::aborting() const {

src/catch2/internal/catch_run_context.hpp

@@ -148,7 +148,8 @@ namespace Catch {
         Totals m_totals;
         IEventListenerPtr m_reporter;
         std::vector<MessageInfo> m_messages;
-        std::vector<ScopedMessage> m_messageScopes; /* Keeps owners of so-called unscoped messages. */
+        // Owners for the UNSCOPED_X information macro
+        std::vector<ScopedMessage> m_messageScopes;
         SourceLineInfo m_lastKnownLineInfo;
         std::vector<SectionEndInfo> m_unfinishedSections;
         std::vector<ITracker*> m_activeSections;
@@ -158,6 +159,9 @@ namespace Catch {
         // Caches m_config->abortAfter() to avoid vptr calls/allow inlining
         size_t m_abortAfterXFailedAssertions;
         bool m_lastAssertionPassed = false;
+        // Should we clear message scopes before sending off the messages to reporter?
+        // Set in `assertionPassedFastPath` to avoid doing the full clear there.
+        bool m_clearMessageScopes = false;
         bool m_shouldReportUnexpected = true;
         // Caches whether `assertionStarting` events should be sent to the reporter.
         bool m_reportAssertionStarting;