Merge pull request #1753 from jwodder/feature/literal_attr

Support attr directive with static evaluation

changelog.d/1753.change.rst

+``attr:`` now extracts variables through rudimentary examination of the AST,
+thereby supporting modules with third-party imports. If examining the AST
+fails to find the variable, ``attr:`` falls back to the old behavior of
+importing the module. Works on Python 3 only.

docs/setuptools.txt

@@ -2193,7 +2193,7 @@ Metadata and options are set in the config sections of the same name.
 * In some cases, complex values can be provided in dedicated subsections for
   clarity.
 
-* Some keys allow ``file:``, ``attr:``, and ``find:`` and ``find_namespace:`` directives in
+* Some keys allow ``file:``, ``attr:``, ``find:``, and ``find_namespace:`` directives in
   order to cover common usecases.
 
 * Unknown keys are ignored.
@@ -2290,6 +2290,12 @@ Special directives:
 
 * ``attr:`` - Value is read from a module attribute.  ``attr:`` supports
   callables and iterables; unsupported types are cast using ``str()``.
+
+  In order to support the common case of a literal value assigned to a variable
+  in a module containing (directly or indirectly) third-party imports,
+  ``attr:`` first tries to read the value from the module by examining the
+  module's AST.  If that fails, ``attr:`` falls back to importing the module.
+
 * ``file:`` - Value is read from a list of files and then concatenated
 
 

setuptools/config.py

 from __future__ import absolute_import, unicode_literals
+import ast
 import io
 import os
 import sys
 
 import warnings
 import functools
+import importlib
 from collections import defaultdict
 from functools import partial
 from functools import wraps
-from importlib import import_module
+import contextlib
 
 from distutils.errors import DistutilsOptionError, DistutilsFileError
 from setuptools.extern.packaging.version import LegacyVersion, parse
@@ -19,6 +21,44 @@ from setuptools.extern.six import string_types, PY3
 __metaclass__ = type
 
 
+class StaticModule:
+    """
+    Attempt to load the module by the name
+    """
+    def __init__(self, name):
+        spec = importlib.util.find_spec(name)
+        with open(spec.origin) as strm:
+            src = strm.read()
+        module = ast.parse(src)
+        vars(self).update(locals())
+        del self.self
+
+    def __getattr__(self, attr):
+        try:
+            return next(
+                ast.literal_eval(statement.value)
+                for statement in self.module.body
+                if isinstance(statement, ast.Assign)
+                for target in statement.targets
+                if isinstance(target, ast.Name) and target.id == attr
+            )
+        except Exception:
+            raise AttributeError(
+                "{self.name} has no attribute {attr}".format(**locals()))
+
+
+@contextlib.contextmanager
+def patch_path(path):
+    """
+    Add path to front of sys.path for the duration of the context.
+    """
+    try:
+        sys.path.insert(0, path)
+        yield
+    finally:
+        sys.path.remove(path)
+
+
 def read_configuration(
         filepath, find_others=False, ignore_option_errors=False):
     """Read given configuration file and returns options from it as a dict.
@@ -344,15 +384,16 @@ class ConfigHandler:
             elif '' in package_dir:
                 # A custom parent directory was specified for all root modules
                 parent_path = os.path.join(os.getcwd(), package_dir[''])
-        sys.path.insert(0, parent_path)
-        try:
-            module = import_module(module_name)
-            value = getattr(module, attr_name)
 
-        finally:
-            sys.path = sys.path[1:]
+        with patch_path(parent_path):
+            try:
+                # attempt to load value statically
+                return getattr(StaticModule(module_name), attr_name)
+            except Exception:
+                # fallback to simple import
+                module = importlib.import_module(module_name)
 
-        return value
+        return getattr(module, attr_name)
 
     @classmethod
     def _get_parser_compound(cls, *parse_methods):

setuptools/tests/test_config.py

@@ -2,6 +2,7 @@
 from __future__ import unicode_literals
 
 import contextlib
+
 import pytest
 
 from distutils.errors import DistutilsOptionError, DistutilsFileError
@@ -9,6 +10,7 @@ from mock import patch
 from setuptools.dist import Distribution, _Distribution
 from setuptools.config import ConfigHandler, read_configuration
 from setuptools.extern.six.moves import configparser
+from setuptools.extern import six
 from . import py2_only, py3_only
 from .textwrap import DALS
 
@@ -53,6 +55,7 @@ def fake_env(
         '    return [3, 4, 5, "dev"]\n'
         '\n'
     )
+
     return package_dir, config
 
 
@@ -267,11 +270,23 @@ class TestMetadata:
 
     def test_version(self, tmpdir):
 
-        _, config = fake_env(
+        package_dir, config = fake_env(
             tmpdir,
             '[metadata]\n'
             'version = attr: fake_package.VERSION\n'
         )
+
+        sub_a = package_dir.mkdir('subpkg_a')
+        sub_a.join('__init__.py').write('')
+        sub_a.join('mod.py').write('VERSION = (2016, 11, 26)')
+
+        sub_b = package_dir.mkdir('subpkg_b')
+        sub_b.join('__init__.py').write('')
+        sub_b.join('mod.py').write(
+            'import third_party_module\n'
+            'VERSION = (2016, 11, 26)'
+        )
+
         with get_dist(tmpdir) as dist:
             assert dist.metadata.version == '1.2.3'
 
@@ -289,13 +304,20 @@ class TestMetadata:
         with get_dist(tmpdir) as dist:
             assert dist.metadata.version == '1'
 
-        subpack = tmpdir.join('fake_package').mkdir('subpackage')
-        subpack.join('__init__.py').write('')
-        subpack.join('submodule.py').write('VERSION = (2016, 11, 26)')
+        config.write(
+            '[metadata]\n'
+            'version = attr: fake_package.subpkg_a.mod.VERSION\n'
+        )
+        with get_dist(tmpdir) as dist:
+            assert dist.metadata.version == '2016.11.26'
+
+        if six.PY2:
+            # static version loading is unsupported on Python 2
+            return
 
         config.write(
             '[metadata]\n'
-            'version = attr: fake_package.subpackage.submodule.VERSION\n'
+            'version = attr: fake_package.subpkg_b.mod.VERSION\n'
         )
         with get_dist(tmpdir) as dist:
             assert dist.metadata.version == '2016.11.26'