Cylc Message Help Contains two patterns of use

cylc/flow/option_parsers.py

@@ -369,6 +369,8 @@ class CylcOptionParser(OptionParser):
         )
     ]
 
+    LINEBREAK = ('\n', '')
+
     def __init__(
         self,
         usage: str,
@@ -407,7 +409,6 @@ def __init__(
         if multitask:
             usage += self.MULTITASK_USAGE
 
-        args = ""
         self.n_compulsory_args = 0
         self.n_optional_args = 0
         self.unlimited_args = False
@@ -419,21 +420,7 @@ def __init__(
         self.segregated_log = segregated_log
 
         if argdoc:
-            maxlen = max(len(arg) for arg, _ in argdoc)
-            usage += "\n\nArguments:"
-            for arg, descr in argdoc:
-                if arg.startswith('['):
-                    self.n_optional_args += 1
-                else:
-                    self.n_compulsory_args += 1
-                if arg.rstrip(']').endswith('...'):
-                    self.unlimited_args = True
-
-                args += arg + " "
-
-                pad = (maxlen - len(arg)) * ' ' + '               '
-                usage += "\n   " + arg + pad + descr
-            usage = usage.replace('ARGS', args)
+            usage = self.argdoc_parser(argdoc, usage)
 
         OptionParser.__init__(
             self,
@@ -442,6 +429,43 @@ def __init__(
             formatter=CylcHelpFormatter()
         )
 
+    def argdoc_parser(self, argdoc, usage) -> str:
+        """Convert argdoc list into a string to be passed to
+        OptionParser.__init__ as usage argument.
+        """
+        args = ""
+        maxlen = max(len(arg) for arg, _ in argdoc)
+        usage += "\n\nArguments:"
+        if 'ARGS' in usage:
+            script_name, usage = usage.split('ARGS', 1)
+        else:
+            return usage
+        used_args = [self.LINEBREAK]
+        if self.LINEBREAK in argdoc:
+            args += ' One of:\n'
+        args += script_name
+        for arg, descr in argdoc:
+            if arg.startswith('['):
+                self.n_optional_args += 1
+            else:
+                self.n_compulsory_args += 1
+            if arg.rstrip(']').endswith('...'):
+                self.unlimited_args = True
+
+            if arg == '\n':
+                args += arg
+                args += script_name
+            else:
+                args += arg + " "
+
+            if (arg, descr) not in used_args:
+                pad = (maxlen - len(arg)) * ' ' + '               '
+                usage += "\n   " + arg + pad + descr
+                used_args.append((arg, descr))
+
+        usage = args + usage
+        return usage
+
     def get_std_options(self):
         """Get a data-structure of standard options"""
         opts = []

cylc/flow/scripts/message.py

@@ -117,13 +117,14 @@ def get_option_parser() -> COP:
         __doc__,
         comms=True,
         argdoc=[
-            COP.optional(WORKFLOW_ID_ARG_DOC),
+            WORKFLOW_ID_ARG_DOC,
+            ('JOB', 'Job ID - CYCLE/TASK_NAME/SUBMIT_NUM'),
             COP.optional(
-                ('JOB', 'Job ID - CYCLE/TASK_NAME/SUBMIT_NUM')
+                ('[SEVERITY:]MESSAGE ...', 'Severity Level:Message')
             ),
-            COP.optional(
-                ('[SEVERITY:]MESSAGE ...', 'Messages')
-            )
+            COP.LINEBREAK,
+            COP.optional(('[SEVERITY:]MESSAGE', 'Severity Level:Message')),
+            COP.optional(('[SEVERITY:]MESSAGE', 'Severity Level:Message')),
         ]
     )
 

tests/unit/test_option_parsers.py

@@ -30,13 +30,20 @@
 )
 
 
-USAGE_WITH_COMMENT = "usage \n # comment"
+USAGE_WITH_COMMENT = "ARGS usage \n # comment"
 ARGS = 'args'
 KWARGS = 'kwargs'
 SOURCES = 'sources'
 USEIF = 'useif'
 
 
+class MockCylcOptionParser(COP):
+    """A stub subclass to allow unit-like testing of methods."""
+    def __init__(self, **kwargs):
+        for key, value in kwargs.items():
+            self.__dict__[key] = value
+
+
 @pytest.fixture(scope='module')
 def parser():
     return COP(
@@ -94,7 +101,9 @@ def test_help_nocolor(monkeypatch: pytest.MonkeyPatch, parser: COP):
     f = io.StringIO()
     with redirect_stdout(f):
         parser.print_help()
-    assert (f.getvalue()).startswith("Usage: " + USAGE_WITH_COMMENT)
+    str_ = f.getvalue()
+    assert str_.startswith(
+        "Usage: " + USAGE_WITH_COMMENT.replace('ARGS', 'SOME_ARG '))
 
 
 def test_Options_std_opts():
@@ -580,3 +589,61 @@ def test__in_list():
         second = OptionSettings(['--foo'])
         third = OptionSettings(['--bar'])
         assert first._in_list([second, third]) is True
+
+    @pytest.mark.parametrize(
+        'argdoc, usage, expect',
+        (
+            param(
+                [('WORKFLOW', 'Workflow ID')],
+                'cylc play [OPTIONS] ARGS\n\nStart, resume...',
+                enumerate(('cylc play [OPTIONS] WORKFLOW',)),
+                id='basic'
+            ),
+            param(
+                [
+                    ('WORKFLOW', 'Workflow ID'),
+                    COP.LINEBREAK,
+                    ('[TASK]', 'Task ID'),
+                ],
+                'cylc total-perspective [OPTIONS] ARGS\n\nThe most savage...',
+                enumerate([
+                    'One of:',
+                    'cylc total-perspective [OPTIONS] WORKFLOW',
+                    'cylc total-perspective [OPTIONS] [TASK]'
+                ]),
+                id='has-line-break'
+            ),
+            param(
+                [('[TASK]', 'Task ID')],
+                'cylc infinite-improbability [OPTIONS] ARGS\n\nEvery point...',
+                enumerate(['cylc infinite-improbability [OPTIONS] [TASK]',]),
+                id='startswith-sq-bracket',
+            ),
+            param(
+                [
+                    ('WORKFLOW', 'Workflow ID'),
+                    COP.LINEBREAK,
+                    ('WORKFLOW', 'Workflow ID'),
+                ],
+                'cylc skin-cat [OPTIONS] ARGS\n\nThere are many ways.',
+                {
+                    -2: 'Arguments:',
+                    -1: 'WORKFLOW               Workflow ID'
+                }.items(),
+                id='no-repeated-arg-descriptions'
+            )
+        )
+    )
+    def test_argdoc_parser(self, argdoc, usage, expect):
+        """Tests for standalone argdoc_parser method when argdoc
+        offers multiple ways to call a command.
+        """
+        parser = MockCylcOptionParser(
+            n_compulsory_args=0,
+            n_optional_args=0,
+            unlimited_args=False)
+
+        result = parser.argdoc_parser(argdoc, usage)
+        results = [r for r in result.split('\n') if r]
+        for i, line in expect:
+            assert results[i].strip() == line