Allow eval substitutions with spaced expressions

launch/launch/substitutions/python_expression.py

@@ -68,9 +68,22 @@ def __init__(self, expression: SomeSubstitutionsType,
     def parse(cls, data: Sequence[SomeSubstitutionsType]
               ) -> Tuple[Type['PythonExpression'], Dict[str, Any]]:
         """Parse `PythonExpression` substitution."""
-        if len(data) < 1 or len(data) > 2:
-            raise TypeError('eval substitution expects 1 or 2 arguments')
-        kwargs = {'expression': data[0]}
+        if len(data) < 1:
+            raise TypeError('eval substitution expects at least 1 argument')
+        kwargs: Dict[str, Any] = {}
+        if len(data) <= 2:
+            kwargs['expression'] = data[0]
+        else:
+            # The expression is split into multiple arguments when it contains
+            # spaces, e.g. `$(eval 1 == 1)`.
+            # Join the arguments back with spaces to recover the expression.
+            from ..utilities import normalize_to_list_of_substitutions
+            expression: List[Substitution] = []
+            for i, sub_expression in enumerate(data):
+                if i > 0:
+                    expression += normalize_to_list_of_substitutions(' ')
+                expression += normalize_to_list_of_substitutions(sub_expression)
+            kwargs['expression'] = expression
         if len(data) == 2:
             # We get a text substitution from XML,
             # whose contents are comma-separated module names

launch/test/launch/substitutions/test_python_expression.py

@@ -137,3 +137,20 @@ def test_python_substitution_submodule():
 
     # The expression should evaluate to True
     assert result
+
+
+def test_python_substitution_parse_multiple_arguments():
+    """Check that parse() joins an expression split across multiple arguments."""
+    lc = LaunchContext()
+
+    # The frontend splits an expression containing spaces, e.g. `$(eval 1 == 1)`
+    cls, kwargs = PythonExpression.parse(['1', '==', '1'])
+    subst = cls(**kwargs)
+    result = subst.perform(lc)
+
+    assert result == 'True'
+
+    # Test the describe() method
+    assert subst.describe() == (
+        "PythonExpr('1' + ' ' + '==' + ' ' + '1', ['math'])"
+    )