Core functionality for fx variables handling in volume and area statistics in light of PR 439 (PR 439 child 2)

esmvalcore/_data_finder.py

@@ -240,7 +240,7 @@ def get_input_filelist(variable, rootpath, drs):
     return (files, dirnames, filenames)
 
 
-def get_output_file(variable, preproc_dir):
+def get_output_file(variable, preproc_dir, fx_var_alias=None):
     """Return the full path to the output (preprocessed) file."""
     cfg = get_project_config(variable['project'])
 
@@ -249,11 +249,12 @@ def get_output_file(variable, preproc_dir):
         variable = dict(variable)
         variable['exp'] = '-'.join(variable['exp'])
 
+    tag_source = variable if fx_var_alias is None else fx_var_alias
     outfile = os.path.join(
         preproc_dir,
         variable['diagnostic'],
         variable['variable_group'],
-        _replace_tags(cfg['output_file'], variable)[0],
+        _replace_tags(cfg['output_file'], tag_source)[0],
     )
     if variable['frequency'] != 'fx':
         outfile += '_{start_year}-{end_year}'.format(**variable)