Workaround crash in msvc when raising a GEOS exception

nyalldawson · nyalldawson · commit ad1fef9f7c55 · 2018-05-29T20:26:44.000+10:00
In some circumstances MSVC tries to raise it's own internal exception when we try to raise a GEOSException. This results in a hard crash of QGIS. To workaround this, we cautiously try to raise a GEOSException on msvc builds, catching all other raised exceptions if throwing the GEOSException triggers them. This at least allows us to gracefully handle the geos error without crashing QGIS (although the detailed GEOS error message is not available when this situation occurs... but that's still better than a crash!). If you want to try to find a better fix for this, the testqgsexpression.cpp test suite will demonstrate the issue. Without this fix the test will crash on the "line_interpolate_point point" test. Refs #14752
diff --git a/src/core/geometry/qgsgeos.cpp b/src/core/geometry/qgsgeos.cpp
@@ -58,10 +58,29 @@ static void throwGEOSException( const char *fmt, ... )
   va_end( ap );
 
   qWarning( "GEOS exception: %s", buffer );
-
-  throw GEOSException( QString::fromUtf8( buffer ) );
+  QString message = QString::fromUtf8( buffer );
+
+#ifdef _MSC_VER
+  // stupid stupid MSVC, *SOMETIMES* raises it's own exception if we throw GEOSException, resulting in a crash!
+  // see https://issues.qgis.org/issues/14752
+  // if you want to test alternative fixes for this, run the testqgsexpression.cpp test suite - that will crash
+  // and burn on the "line_interpolate_point point" test if a GEOSException is thrown.
+  // TODO - find a real fix for the underlying issue
+  try
+  {
+    throw GEOSException( message );
+  }
+  catch ( ... )
+  {
+    // oops, msvc threw an exception when we tried to throw the exception!
+    // just throw nothing instead (except your mouse at your monitor)
+  }
+#else
+  throw GEOSException( message );
+#endif
 }
 
+
 static void printGEOSNotice( const char *fmt, ... )
 {
 #if defined(QGISDEBUG)
