BUG: Fix handling of f2py directives with --lower

Closes numpygh-2547, numpygh-27697, numpygh-26681

Author: HaoZeke

numpy/f2py/crackfortran.py

@@ -425,11 +425,14 @@ def readfortrancode(ffile, dowithline=show, istop=1):
             if l[-1] not in "\n\r\f":
                 break
             l = l[:-1]
+        # Do not lower for directives, gh-2547, gh-27697, gh-26681
+        is_f2py_directive = False
         # Unconditionally remove comments
         (l, rl) = split_by_unquoted(l, '!')
         l += ' '
         if rl[:5].lower() == '!f2py':  # f2py directive
             l, _ = split_by_unquoted(l + 4 * ' ' + rl[5:], '!')
+            is_f2py_directive = True
         if l.strip() == '':  # Skip empty line
             if sourcecodeform == 'free':
                 # In free form, a statement continues in the next line
@@ -449,6 +452,7 @@ def readfortrancode(ffile, dowithline=show, istop=1):
             if l[0] in ['*', 'c', '!', 'C', '#']:
                 if l[1:5].lower() == 'f2py':  # f2py directive
                     l = '     ' + l[5:]
+                    is_f2py_directive = True
                 else:  # Skip comment line
                     cont = False
                     continue
@@ -476,7 +480,7 @@ def readfortrancode(ffile, dowithline=show, istop=1):
                 else:
                     # clean up line beginning from possible digits.
                     l = '     ' + l[5:]
-                    if localdolowercase:
+                    if localdolowercase and not is_f2py_directive:
                         finalline = ll.lower()
                     else:
                         finalline = ll
@@ -504,7 +508,7 @@ def readfortrancode(ffile, dowithline=show, istop=1):
                 finalline = ''
                 origfinalline = ''
             else:
-                if localdolowercase:
+                if localdolowercase and not is_f2py_directive:
                     finalline = ll.lower()
                 else:
                     finalline = ll
@@ -537,7 +541,7 @@ def readfortrancode(ffile, dowithline=show, istop=1):
         else:
             dowithline(finalline)
         l1 = ll
-    if localdolowercase:
+    if localdolowercase and not is_f2py_directive:
         finalline = ll.lower()
     else:
         finalline = ll