Apply suggestions from code review

Co-authored-by: Ronnie Dutta <61982285+MetRonnie@users.noreply.github.com>

cylc/flow/graph_parser.py

@@ -463,9 +463,8 @@ def parse_graph(self, graph_string: str) -> None:
                 pairs.add((chain[i], chain[i + 1]))
 
         # Get a set of RH nodes which are not at the LH of another pair:
-        terminals = {
-            right for right in {right for _, right in pairs}
-            if right not in {left for left, _ in pairs}}
+        pairs_dict = dict(pairs)
+        terminals = set(pairs_dict.values()).difference(pairs_dict.keys())
 
         for pair in pairs:
             self._proc_dep_pair(pair, terminals)
@@ -514,7 +513,7 @@ def _proc_dep_pair(
                 'right' can be one or more node names joined by AND.
                 'right' can't be None or "".
             terminals:
-                Lits of nodes which are _only_ on the RH end of chains.
+                Nodes which are _only_ on the RH end of chains.
         """
         left, right = pair
         # Raise error for right-hand-side OR operators.
@@ -534,16 +533,15 @@ def _proc_dep_pair(
         if right.count("(") != right.count(")"):
             raise GraphParseError(mismatch_msg.format(right))
 
-        # Ignore/Error cycle point offsets on the right side:
-        # (Note we can only ban this for nodes at the end of chains)
+        # Raise error for cycle point offsets at the end of chains
         if '[' in right:
-            if left and right in terminals:
+            if left and (right in terminals):
                 # This right hand side is at the end of a chain:
                 raise GraphParseError(
                     'ERROR, illegal cycle point offset on the right:'
                     f' {left} => {right}')
             else:
-                # This right hand side is a left elsewhere:
+                # This RHS is also a LHS in a chain:
                 return
 
         # Split right side on AND.

tests/unit/test_graph_parser.py

@@ -139,27 +139,13 @@ def test_graph_syntax_errors_2(seq, graph, expected_err):
             'illegal cycle point offset on the right',
             id='no-cycle-point-RHS'
         ),
-        param(
-            "foo => bar[1649] => baz",
-            '!illegal cycle point offset on the right',
-            id='ignore-not-exclusively-RHS-cycle-point'
-        ),
-        param(
-            "foo => bar[1649]\nbar[1649] => baz",
-            '!illegal cycle point offset on the right',
-            id='ignore-not-exclusively-RHS-cycle-point2'
-        ),
     ]
 )
 def test_graph_syntax_errors(graph, expected_err):
     """Test various graph syntax errors."""
-    if expected_err[0] == '!':
-        # Assert method doesn't fail:
+    with pytest.raises(GraphParseError) as cm:
         GraphParser().parse_graph(graph)
-    else:
-        with pytest.raises(GraphParseError) as cm:
-            GraphParser().parse_graph(graph)
-        assert expected_err in str(cm.value)
+    assert expected_err in str(cm.value)
 
 
 def test_parse_graph_simple():
@@ -397,7 +383,16 @@ def test_line_continuation():
             foo => bar
             bar:succeed => baz
             """
-        ]
+        ],
+        [
+            """
+            foo => bar[1649] => baz
+            """,
+            """
+            foo => bar[1649]
+            bar[1649] => baz
+            """
+        ],
     ]
 )
 def test_trigger_equivalence(graph1, graph2):