Fix parsing of build_ext --libraries option (#1326113)

command/build_ext.py

@@ -165,8 +165,7 @@ class build_ext(Command):
         if plat_py_include != py_include:
             self.include_dirs.append(plat_py_include)
 
-        if isinstance(self.libraries, str):
-            self.libraries = [self.libraries]
+        self.ensure_string_list('libraries')
 
         # Life is easier if we're not forever checking for None, so
         # simplify these options to empty lists if unset

tests/test_build_ext.py

@@ -178,21 +178,21 @@ class BuildExtTestCase(TempdirManager,
         # make sure cmd.libraries is turned into a list
         # if it's a string
         cmd = build_ext(dist)
-        cmd.libraries = 'my_lib'
+        cmd.libraries = 'my_lib, other_lib lastlib'
         cmd.finalize_options()
-        self.assertEqual(cmd.libraries, ['my_lib'])
+        self.assertEqual(cmd.libraries, ['my_lib', 'other_lib', 'lastlib'])
 
         # make sure cmd.library_dirs is turned into a list
         # if it's a string
         cmd = build_ext(dist)
-        cmd.library_dirs = 'my_lib_dir'
+        cmd.library_dirs = 'my_lib_dir%sother_lib_dir' % os.pathsep
         cmd.finalize_options()
-        self.assertTrue('my_lib_dir' in cmd.library_dirs)
+        self.assertEqual(cmd.library_dirs, ['my_lib_dir', 'other_lib_dir'])
 
         # make sure rpath is turned into a list
-        # if it's a list of os.pathsep's paths
+        # if it's a string
         cmd = build_ext(dist)
-        cmd.rpath = os.pathsep.join(['one', 'two'])
+        cmd.rpath = 'one%stwo' % os.pathsep
         cmd.finalize_options()
         self.assertEqual(cmd.rpath, ['one', 'two'])