* Fixed accumulating include dirs after compile

- fixes pypa/setuptools#3591

distutils/ccompiler.py

@@ -388,7 +388,7 @@ def _fix_compile_args(self, output_dir, macros, include_dirs):
             raise TypeError("'macros' (if supplied) must be a list of tuples")
 
         if include_dirs is None:
-            include_dirs = self.include_dirs
+            include_dirs = list(self.include_dirs)
         elif isinstance(include_dirs, (list, tuple)):
             include_dirs = list(include_dirs) + (self.include_dirs or [])
         else:

distutils/tests/test_ccompiler.py

@@ -53,3 +53,17 @@ def test_set_include_dirs(c_file):
     # do it again, setting include dirs after any initialization
     compiler.set_include_dirs([python])
     compiler.compile(_make_strs([c_file]))
+
+
+def test_include_dirs_after_multiple_compile_calls(c_file):
+    """
+    Calling compile multiple times should not change the include dirs
+    (regression test for setuptools issue #3591).
+    """
+    compiler = ccompiler.new_compiler()
+    python = sysconfig.get_paths()['include']
+    compiler.set_include_dirs([python])
+    compiler.compile(_make_strs([c_file]))
+    assert compiler.include_dirs == [python]
+    compiler.compile(_make_strs([c_file]))
+    assert compiler.include_dirs == [python]