Expand read-only Mapping values as associative arrays

tests/test_readonly_mappings.py

@@ -0,0 +1,83 @@
+"""Associative values may implement Mapping without supporting mutation."""
+
+import collections.abc
+import types
+import typing as t
+
+import pytest
+
+from uritemplate import expand
+from uritemplate import variable
+
+
+class ReadOnlyMapping(t.Mapping[str, variable.ScalarVariableValue]):
+    def __init__(self, values: t.Mapping[str, variable.ScalarVariableValue]):
+        self._values = dict(values)
+
+    def __getitem__(self, key: str) -> variable.ScalarVariableValue:
+        return self._values[key]
+
+    def __iter__(self) -> t.Iterator[str]:
+        return iter(self._values)
+
+    def __len__(self) -> int:
+        return len(self._values)
+
+
+@pytest.mark.parametrize("factory", [types.MappingProxyType, ReadOnlyMapping])
+@pytest.mark.parametrize(
+    "operator,plain,exploded",
+    [
+        ("", "a,one,b,two", "a=one,b=two"),
+        ("+", "a,one,b,two", "a=one,b=two"),
+        ("#", "#a,one,b,two", "#a=one,b=two"),
+        (".", ".a,one,b,two", ".a=one.b=two"),
+        ("/", "/a,one,b,two", "/a=one/b=two"),
+        (";", ";v=a,one,b,two", ";a=one;b=two"),
+        ("?", "?v=a,one,b,two", "?a=one&b=two"),
+        ("&", "&v=a,one,b,two", "&a=one&b=two"),
+    ],
+)
+@pytest.mark.parametrize("explode", [False, True])
+def test_readonly_mapping_expands_as_associative_value(
+    factory: t.Callable[
+        [t.Dict[str, variable.ScalarVariableValue]],
+        t.Mapping[str, variable.ScalarVariableValue],
+    ],
+    operator: str,
+    plain: str,
+    exploded: str,
+    explode: bool,
+) -> None:
+    # Reverse insertion order also pins existing sorted-mapping behavior.
+    values: t.Dict[str, variable.ScalarVariableValue] = {
+        "b": "two",
+        "a": "one",
+    }
+    mapping = factory(values)
+    template = "{" + operator + "v" + ("*" if explode else "") + "}"
+    assert expand(template, v=mapping) == (exploded if explode else plain)
+    assert dict(mapping) == values
+    assert not isinstance(mapping, collections.abc.MutableMapping)
+
+
+@pytest.mark.parametrize("operator", ["", "+", "#", ".", "/", ";", "?", "&"])
+@pytest.mark.parametrize("explode", [False, True])
+def test_mapping_input_types_keep_identical_quoting(
+    operator: str, explode: bool
+) -> None:
+    values: t.Dict[str, variable.ScalarVariableValue] = {
+        "a b": "x/y",
+        "z": "0",
+    }
+    template = "{" + operator + "v" + ("*" if explode else "") + "}"
+    expected = expand(template, v=values)
+    assert expand(template, v=types.MappingProxyType(values)) == expected
+    assert expand(template, v=ReadOnlyMapping(values)) == expected
+
+
+@pytest.mark.parametrize("value", ["text", ["a", "b"], [("a", "b")], 0, None])
+def test_mapping_detection_does_not_reclassify_other_values(
+    value: t.Any,
+) -> None:
+    assert not variable.dict_test(value)

uritemplate/variable.py

@@ -549,7 +549,7 @@ def list_test(value: t.Any) -> bool:
 
 
 def dict_test(value: t.Any) -> bool:
-    return isinstance(value, (dict, collections.abc.MutableMapping))
+    return isinstance(value, collections.abc.Mapping)
 
 
 def _encode(value: t.AnyStr, encoding: str = "utf-8") -> bytes: