Don't take ownership of SECTION's name for inactive sections

This eliminates 1945 (432709 -> 430764) allocations from running
`./tests/SelfTest -o /dev/null`. In general terms, this saves
an allocation every time an unvisited `SECTION` is passed, which
means that the saved allocations are quadratic in number of sibling
(same level) `SECTION`s in a test case.

src/catch2/interfaces/catch_interfaces_capture.hpp

@@ -44,7 +44,8 @@ namespace Catch {
     public:
         virtual ~IResultCapture();
 
-        virtual bool sectionStarted(    SectionInfo const& sectionInfo,
+        virtual bool sectionStarted( StringRef sectionName,
+                                     SourceLineInfo const& sectionLineInfo,
                                      Counts& assertions ) = 0;
         virtual void sectionEnded( SectionEndInfo&& endInfo ) = 0;
         virtual void sectionEndedEarly( SectionEndInfo&& endInfo ) = 0;

src/catch2/internal/catch_run_context.cpp

@@ -297,13 +297,17 @@ namespace Catch {
         m_lastAssertionInfo.capturedExpression = "{Unknown expression after the reported line}"_sr;
     }
 
-    bool RunContext::sectionStarted(SectionInfo const & sectionInfo, Counts & assertions) {
+    bool RunContext::sectionStarted(StringRef sectionName, SourceLineInfo const& sectionLineInfo, Counts & assertions) {
-        ITracker& sectionTracker = SectionTracker::acquire(m_trackerContext, TestCaseTracking::NameAndLocationRef(sectionInfo.name, sectionInfo.lineInfo));
+        ITracker& sectionTracker =
+            SectionTracker::acquire( m_trackerContext,
+                                     TestCaseTracking::NameAndLocationRef(
+                                         sectionName, sectionLineInfo ) );
 
         if (!sectionTracker.isOpen())
             return false;
         m_activeSections.push_back(&sectionTracker);
 
+        SectionInfo sectionInfo( sectionLineInfo, static_cast<std::string>(sectionName) );
         m_lastAssertionInfo.lineInfo = sectionInfo.lineInfo;
 
         m_reporter->sectionStarting(sectionInfo);

src/catch2/internal/catch_run_context.hpp

@@ -68,7 +68,9 @@ namespace Catch {
                     ResultWas::OfType resultType,
                     AssertionReaction &reaction ) override;
 
-        bool sectionStarted( SectionInfo const& sectionInfo, Counts& assertions ) override;
+        bool sectionStarted( StringRef sectionName,
+                             SourceLineInfo const& sectionLineInfo,
+                             Counts& assertions ) override;
 
         void sectionEnded( SectionEndInfo&& endInfo ) override;
         void sectionEndedEarly( SectionEndInfo&& endInfo ) override;

src/catch2/internal/catch_section.cpp

@@ -15,7 +15,7 @@ namespace Catch {
     Section::Section( SectionInfo&& info ):
         m_info( CATCH_MOVE( info ) ),
         m_sectionIncluded(
-            getResultCapture().sectionStarted( m_info, m_assertions ) ) {
+            getResultCapture().sectionStarted( m_info.name, m_info.lineInfo, m_assertions ) ) {
         // Non-"included" sections will not use the timing information
         // anyway, so don't bother with the potential syscall.
         if (m_sectionIncluded) {
@@ -23,6 +23,23 @@ namespace Catch {
         }
     }
 
+    Section::Section( SourceLineInfo const& _lineInfo,
+                      StringRef _name,
+                      const char* const ):
+        m_info( { "invalid", static_cast<std::size_t>(-1) }, "" ),
+        m_sectionIncluded(
+            getResultCapture().sectionStarted( _name, _lineInfo, m_assertions ) ) {
+        // We delay initialization the SectionInfo member until we know
+        // this section needs it, so we avoid allocating std::string for name.
+        // We also delay timer start to avoid the potential syscall unless we
+        // will actually use the result.
+        if ( m_sectionIncluded ) {
+            m_info.name = static_cast<std::string>( _name );
+            m_info.lineInfo = _lineInfo;
+            m_timer.start();
+        }
+    }
+
     Section::~Section() {
         if( m_sectionIncluded ) {
             SectionEndInfo endInfo{ CATCH_MOVE(m_info), m_assertions, m_timer.getElapsedSeconds() };

src/catch2/internal/catch_section.hpp

@@ -20,6 +20,9 @@ namespace Catch {
     class Section : Detail::NonCopyable {
     public:
         Section( SectionInfo&& info );
+        Section( SourceLineInfo const& _lineInfo,
+                 StringRef _name,
+                 const char* const = nullptr );
         ~Section();
 
         // This indicates whether the section should be executed or not
@@ -38,7 +41,7 @@ namespace Catch {
 #define INTERNAL_CATCH_SECTION( ... ) \
     CATCH_INTERNAL_START_WARNINGS_SUPPRESSION \
     CATCH_INTERNAL_SUPPRESS_UNUSED_VARIABLE_WARNINGS \
-    if( Catch::Section const& INTERNAL_CATCH_UNIQUE_NAME( catch_internal_Section ) = Catch::SectionInfo( CATCH_INTERNAL_LINEINFO, __VA_ARGS__ ) ) \
+    if( Catch::Section const& INTERNAL_CATCH_UNIQUE_NAME( catch_internal_Section ) = Catch::Section( CATCH_INTERNAL_LINEINFO, __VA_ARGS__ ) ) \
     CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION
 
 #define INTERNAL_CATCH_DYNAMIC_SECTION( ... ) \