only validate package_data when it might be used

closes #5046

setup.py

@@ -58,6 +58,7 @@ from setupbase import (
     setup_args,
     find_packages,
     find_package_data,
+    check_package_data,
     find_entry_points,
     build_scripts_entrypt,
     find_data_files,
@@ -191,12 +192,22 @@ if len(sys.argv) >= 2 and sys.argv[1] in ('sdist','bdist_rpm'):
 
 packages = find_packages()
 package_data = find_package_data()
+
 data_files = find_data_files()
 
 setup_args['packages'] = packages
 setup_args['package_data'] = package_data
 setup_args['data_files'] = data_files
 
+def maybe_check_package_data():
+    for should_check in ('bdist', 'sdist', 'build', 'install'):
+        for arg in sys.argv:
+            if arg.startswith(should_check):
+                check_package_data(package_data)
+                return
+
+maybe_check_package_data()
+
 #---------------------------------------------------------------------------
 # custom distutils commands
 #---------------------------------------------------------------------------

setupbase.py

@@ -188,7 +188,11 @@ def find_package_data():
         'IPython.nbformat' : ['tests/*.ipynb']
     }
     
-    # verify that package_data makes sense
+    return package_data
+
+def check_package_data(package_data):
+    """verify that package_data globs make sense"""
+    print("checking package data")
     for pkg, data in package_data.items():
         pkg_root = pjoin(*pkg.split('.'))
         for d in data:
@@ -198,8 +202,6 @@ def find_package_data():
             else:
                 assert os.path.exists(path), "Missing package data: %s" % path
 
-    return package_data
-
 
 #---------------------------------------------------------------------------
 # Find data files