improve `package_data` check

Ensure the dictionary values are lists/tuples of strings.

Fix #1459.

changelog.d/1769.change.rst

+Improve ``package_data`` check: ensure the dictionary values are lists/tuples of strings.

setuptools/dist.py

@@ -215,6 +215,10 @@ def check_importable(dist, attr, value):
 def assert_string_list(dist, attr, value):
     """Verify that value is a string list"""
     try:
+        # verify that value is a list or tuple to exclude unordered
+        # or single-use iterables
+        assert isinstance(value, (list, tuple))
+        # verify that elements of value are strings
         assert ''.join(value) != value
     except (TypeError, ValueError, AttributeError, AssertionError):
         raise DistutilsSetupError(
@@ -307,20 +311,17 @@ def check_test_suite(dist, attr, value):
 
 def check_package_data(dist, attr, value):
     """Verify that value is a dictionary of package names to glob lists"""
-    if isinstance(value, dict):
-        for k, v in value.items():
-            if not isinstance(k, str):
-                break
-            try:
-                iter(v)
-            except TypeError:
-                break
-        else:
-            return
-    raise DistutilsSetupError(
-        attr + " must be a dictionary mapping package names to lists of "
-        "wildcard patterns"
-    )
+    if not isinstance(value, dict):
+        raise DistutilsSetupError(
+            "{!r} must be a dictionary mapping package names to lists of "
+            "string wildcard patterns".format(attr))
+    for k, v in value.items():
+        if not isinstance(k, six.string_types):
+            raise DistutilsSetupError(
+                "keys of {!r} dict must be strings (got {!r})"
+                .format(attr, k)
+            )
+        assert_string_list(dist, 'values of {!r} dict'.format(attr), v)
 
 
 def check_packages(dist, attr, value):

setuptools/tests/test_dist.py

@@ -3,7 +3,13 @@
 from __future__ import unicode_literals
 
 import io
-from setuptools.dist import DistDeprecationWarning, _get_unpatched
+import re
+from distutils.errors import DistutilsSetupError
+from setuptools.dist import (
+    _get_unpatched,
+    check_package_data,
+    DistDeprecationWarning,
+)
 from setuptools import Distribution
 from setuptools.extern.six.moves.urllib.request import pathname2url
 from setuptools.extern.six.moves.urllib_parse import urljoin
@@ -263,3 +269,48 @@ def test_maintainer_author(name, attrs, tmpdir):
         else:
             line = '%s: %s' % (fkey, val)
             assert line in pkg_lines_set
+
+
+CHECK_PACKAGE_DATA_TESTS = (
+    # Valid.
+    ({
+        '': ['*.txt', '*.rst'],
+        'hello': ['*.msg'],
+    }, None),
+    # Not a dictionary.
+    ((
+        ('', ['*.txt', '*.rst']),
+        ('hello', ['*.msg']),
+    ), (
+        "'package_data' must be a dictionary mapping package"
+        " names to lists of string wildcard patterns"
+    )),
+    # Invalid key type.
+    ({
+        400: ['*.txt', '*.rst'],
+    }, (
+        "keys of 'package_data' dict must be strings (got 400)"
+    )),
+    # Invalid value type.
+    ({
+        'hello': str('*.msg'),
+    }, (
+        "\"values of 'package_data' dict\" must be a list of strings (got '*.msg')"
+    )),
+    # Invalid value type (generators are single use)
+    ({
+        'hello': (x for x in "generator"),
+    }, (
+        "\"values of 'package_data' dict\" must be a list of strings "
+        "(got <generator object"
+    )),
+)
+
+
+@pytest.mark.parametrize('package_data, expected_message', CHECK_PACKAGE_DATA_TESTS)
+def test_check_package_data(package_data, expected_message):
+    if expected_message is None:
+        assert check_package_data(None, 'package_data', package_data) is None
+    else:
+        with pytest.raises(DistutilsSetupError, match=re.escape(expected_message)):
+            check_package_data(None, str('package_data'), package_data)