Fix disable cache (Bug: #260) (#261).

Fixes a bug introduced with --pex-root that raised an exception on when --disable-cache was used.

pex/bin/pex.py

@@ -68,7 +68,7 @@ def increment_verbosity(option, opt_str, _, parser):
 
 
 def process_disable_cache(option, option_str, option_value, parser):
-  setattr(parser.values, option.dest, [])
+  setattr(parser.values, option.dest, None)
 
 
 def process_pypi_option(option, option_str, option_value, parser, builder):
@@ -530,7 +530,9 @@ def main(args=None):
   else:
     options.pex_root = ENV.PEX_ROOT  # If option not specified fallback to env variable.
 
-  options.cache_dir = make_relative_to_root(options.cache_dir)
+  # Don't alter cache if it is disabled.
+  if options.cache_dir:
+    options.cache_dir = make_relative_to_root(options.cache_dir)
   options.interpreter_cache_dir = make_relative_to_root(options.interpreter_cache_dir)
 
   with ENV.patch(PEX_VERBOSE=str(options.verbosity)):

tests/test_integration.py

@@ -40,6 +40,28 @@ def test_pex_root():
           assert 'build' in os.listdir(td), 'Expected build directory in tmp pex root.'
 
 
+def test_cache_disable():
+  with temporary_dir() as tmp_home:
+    with environment_as(HOME=tmp_home):
+      with temporary_dir() as td:
+        with temporary_dir() as output_dir:
+          env = os.environ.copy()
+          env['PEX_INTERPRETER'] = '1'
+
+          output_path = os.path.join(output_dir, 'pex.pex')
+          args = [
+            'pex',
+            '-o', output_path,
+            '--not-zip-safe',
+            '--disable-cache',
+            '--pex-root={0}'.format(td),
+          ]
+          results = run_pex_command(args=args, env=env)
+          results.assert_success()
+          assert ['pex.pex'] == os.listdir(output_dir), 'Expected built pex file.'
+          assert [] == os.listdir(tmp_home), 'Expected empty temp home dir.'
+
+
 def test_pex_interpreter():
   with named_temporary_file() as fp:
     fp.write(b"print('Hello world')")