Merge pull request Pyomo#3231 from jsiirola/ipopt_v2-disable-universa…

…l-newlines

Disable the use of universal newlines in the ipopt_v2 NL file

pyomo/contrib/solver/ipopt.py

@@ -307,7 +307,12 @@ def solve(self, model, **kwds):
                 raise RuntimeError(
                     f"NL file with the same name {basename + '.nl'} already exists!"
                 )
-            with open(basename + '.nl', 'w') as nl_file, open(
+            # Note: the ASL has an issue where string constants written
+            # to the NL file (e.g. arguments in external functions) MUST
+            # be terminated with '\n' regardless of platform.  We will
+            # disable universal newlines in the NL file to prevent
+            # Python from mapping those '\n' to '\r\n' on Windows.
+            with open(basename + '.nl', 'w', newline='\n') as nl_file, open(
                 basename + '.row', 'w'
             ) as row_file, open(basename + '.col', 'w') as col_file:
                 timer.start('write_nl_file')