bug: do not remove +subfolder with fast option

Otherwise, expected files are not present

doc/manual/source/running-dynare.rst

@@ -409,9 +409,11 @@ by the ``dynare`` command.
 
     .. option:: fast
 
-        Only useful with model option :opt:`use_dll`. Don’t recompile the
-        MEX files when running again the same model file and the lists
-        of variables and the equations haven’t changed. We use a 32
+        Don’t rewrite the output files otherwise written to the disk by the preprocessor 
+        when re-running the same model file while the lists of variables and the equations 
+        haven’t changed. Note that the whole model still needs to be preprocessed. This option 
+        is most useful with model option :opt:`use_dll`, because 
+        the time-consuming compilation of the MEX files will be skipped. We use a 32
         bit checksum, stored in ``<model filename>/checksum``. There
         is a very small probability that the preprocessor misses a
         change in the model. In case of doubt, re-run without the fast

matlab/dynare.m

@@ -184,6 +184,7 @@ preprocessoroutput = ~ismember('nopreprocessoroutput', varargin) && ...
 nolog = ismember('nolog', varargin) || ismember('nolog', file_opts);
 onlymacro = ismember('onlymacro', varargin) || ismember('onlymacro', file_opts);
 onlyjson = ismember('onlyjson', varargin) || ismember('onlyjson', file_opts);
+fast = ismember('fast', varargin) || ismember('fast', file_opts);
 
 % Start journal
 diary off
@@ -234,12 +235,14 @@ end
 % On MATLAB+Windows, the +folder may be locked by MATLAB, preventing its
 % removal by the preprocessor.
 % Trying to delete it here will actually fail, but surprisingly this allows
-% the preprocessor to actually remove the folder (see ModFile::writeOutputFiles())
+% the preprocessor to actually remove the folder (see ModFile::writeMOutput())
 % For an instance of this bug, see:
 % https://forum.dynare.org/t/issue-with-dynare-preprocessor-4-6-1/15448/1
+if ~fast
     if ispc && ~isoctave && exist(['+',fname(1:end-4)],'dir')
         [~,~]=rmdir(['+', fname(1:end-4)],'s');
     end
+end
 
 % Under Windows, make sure the MEX file is unloaded (in the use_dll case),
 % otherwise the preprocessor can't recompile it