Don't try to validate length of strings without length (#118)

Single character appear like character array variables but with
no length.  The variable length array style rule should not apply
and this change adds an exemption for them.

source/stylist/fortran.py

@@ -601,7 +601,8 @@ class AutoCharArrayIntent(FortranRule):
     subroutine or function arguments have intent(in) to avoid writing
     outside the given array.
     """
-    def _message(self, name, intent):
+    @staticmethod
+    def __message(name, intent):
         return (f"Arguments of type character(*) must have intent IN, but "
                 f"{name} has intent {intent}.")
 
@@ -630,6 +631,9 @@ def examine_fortran(self, subject: FortranSource) -> List[Issue]:
             if not type_spec.items[0] == "CHARACTER":
                 continue
             param_value = type_spec.items[1]
+            # If no length is specified we don't care
+            if param_value is None:
+                continue
             # This might be a length selector, if so get the param value
             if isinstance(param_value, Fortran2003.Length_Selector):
                 param_value = param_value.items[1]
@@ -654,7 +658,7 @@ def examine_fortran(self, subject: FortranSource) -> List[Issue]:
             if intent_attr.items[1].string == "IN":
                 continue
             issues.append(Issue(
-                self._message(
+                self.__message(
                     declaration.items[2].string,
                     intent_attr.items[1]
                 ),

unit-tests/fortran_auto_char_array_intent_test.py

@@ -5,7 +5,7 @@
 import stylist.fortran
 from stylist.source import FortranSource, SourceStringReader
 
-TEST_CASE = """
+NORMAL_TEST_CASE = """
 program cases
     ! A char array outside a function or subroutine, no exception
     character (*) :: autochar_glob
@@ -30,28 +30,63 @@
 end program cases
 """
 
-TEST_EXPECTATION = [
+NORMAL_TEST_EXPECTATION = [
     ('12: Arguments of type character(*) must have intent IN, '
         'but autochar_inout has intent INOUT.'),
     ('14: Arguments of type character(*) must have intent IN, '
         'but autochar_out has intent OUT.')
 ]
 
+SINGLE_CHAR_CASE = """
+program single_char
+
+  implicit none
+
+  character :: single_program_character
+
+contains
+
+  subroutine single_character( char_in, char_inout, char_out, char_def )
+
+    implicit none
+
+    character, intent(in)    :: char_in
+    character, intent(inout) :: char_inout
+    character, intent(out)   :: char_out
+    character                :: char_def
+
+  end subroutine single_character
+
+end program single_char
+"""
+
 
 class TestAutoCharArrayIntent:
     """
     Tests the rule that variable length character arguments should
     have intent(in)
     """
 
-    def test(self):
+    def test_normal_behaviour(self):
         """
         Ensures the test case produces exactly the issues in expectation
         """
-        reader = SourceStringReader(TEST_CASE)
+        reader = SourceStringReader(NORMAL_TEST_CASE)
         source = FortranSource(reader)
         unit_under_test = stylist.fortran.AutoCharArrayIntent()
         issues = unit_under_test.examine(source)
         strings = [str(issue) for issue in issues]
 
-        assert strings == TEST_EXPECTATION
+        assert strings == NORMAL_TEST_EXPECTATION
+
+    def test_single_char(self):
+        """
+        Ensures the test can handle no length being specified.
+        """
+        reader = SourceStringReader(SINGLE_CHAR_CASE)
+        source = FortranSource(reader)
+        test_unit = stylist.fortran.AutoCharArrayIntent()
+        issues = test_unit.examine(source)
+
+        strings = [str(issue) for issue in issues]
+        assert strings == []