Update skip logic when using an exception context record for unwinding

Author: jeremy-rifkin

src/from_current.cpp

@@ -58,9 +58,8 @@ namespace detail {
      CPPTRACE_FORCE_NO_INLINE void collect_current_trace(std::size_t skip, EXCEPTION_POINTERS* exception_ptrs) {
          try {
              #if defined(_M_IX86) || defined(__i386__)
-              // skip one frame, first is CxxThrowException
-              (void)skip;
-              auto trace = raw_trace{detail::capture_frames(1, SIZE_MAX, exception_ptrs)};
+              (void)skip; // don't skip any frames, the context record is at the throw point
+              auto trace = raw_trace{detail::capture_frames(0, SIZE_MAX, exception_ptrs)};
              #else
               (void)exception_ptrs;
               auto trace = raw_trace{detail::capture_frames(skip + 1, SIZE_MAX)};
@@ -615,9 +614,9 @@ CPPTRACE_BEGIN_NAMESPACE
         int maybe_collect_trace(EXCEPTION_POINTERS* exception_ptrs, int filter_result) {
             if(filter_result == EXCEPTION_EXECUTE_HANDLER) {
                 #ifdef CPPTRACE_UNWIND_WITH_DBGHELP
-                 collect_current_trace(2, exception_ptrs);
+                 collect_current_trace(1, exception_ptrs);
                 #else
-                 collect_current_trace(2);
+                 collect_current_trace(1);
                  (void)exception_ptrs;
                 #endif
             }

src/unwind/unwind_with_dbghelp.cpp

@@ -29,7 +29,6 @@ namespace detail {
         std::size_t max_depth,
         EXCEPTION_POINTERS* exception_pointers
     ) {
-        skip++;
         // https://jpassing.com/2008/03/12/walking-the-stack-of-the-current-thread/
 
         // Get current thread context
@@ -40,6 +39,7 @@ namespace detail {
         if(exception_pointers) {
             context = *exception_pointers->ContextRecord;
         } else {
+            skip++; // we're unwinding from the capture_frames frame, skip it
             #if defined(_M_IX86) || defined(__i386__)
              context.ContextFlags = CONTEXT_CONTROL;
              #if IS_MSVC

test/unit/tracing/from_current.cpp

@@ -211,15 +211,14 @@ TEST(FromCurrent, SEHBasic) {
                 does_enter_catch = true;
                 EXPECT_FALSE(cpptrace::current_exception_was_rethrown());
                 const auto& trace = cpptrace::from_current_exception();
-                ASSERT_GE(trace.frames.size(), 4);
                 auto it = std::find_if(
                     trace.frames.begin(),
                     trace.frames.end(),
                     [](const cpptrace::stacktrace_frame& frame) {
                         return frame.symbol.find("my_div_function") != std::string::npos;
                     }
                 );
-                EXPECT_NE(it, trace.frames.end()) << trace;
+                ASSERT_NE(it, trace.frames.end()) << trace;
                 size_t i = static_cast<size_t>(it - trace.frames.begin());
                 EXPECT_FILE(trace.frames[i].filename, "from_current.cpp");
             } ();