use relocatable again, add regression test

.travis/test.sh

@@ -13,4 +13,4 @@ py.test -n $NCPU \
     --cov --cov-config=$TOP/.coveragerc --cov-report='' \
     "$@" $TOP/tests $SITEPACKAGES/${PROJECT}.py
 coverage combine
-coverage report --rcfile=$TOP/.coveragerc --fail-under 95  # FIXME: should be 100
+coverage report --rcfile=$TOP/.coveragerc --fail-under 97  # FIXME: should be 100

tests/functional/relocation_test.py

@@ -0,0 +1,15 @@
+from py._path.local import LocalPath as Path
+
+from testing import get_scenario, run, venv_update
+
+
+def test_is_relocatable(tmpdir):
+    tmpdir.chdir()
+    get_scenario('trivial')
+    venv_update()
+
+    Path('virtualenv_run').rename('relocated')
+
+    pip = 'relocated/bin/pip'
+    assert Path(pip).exists()
+    run(pip, '--version')

venv_update.py

@@ -153,6 +153,7 @@ def pip(args):
         exit(result)
 
 
+@contextmanager
 def clean_venv(venv_path, venv_args):
     """Make a clean virtualenv."""
     from os.path import isdir
@@ -165,6 +166,11 @@ def clean_venv(venv_path, venv_args):
     virtualenv = ('virtualenv', venv_path)
     run(virtualenv + venv_args)
 
+    yield
+
+    # Postprocess: Make our venv relocatable, since we do plan to relocate it, sometimes.
+    run(virtualenv + ('--relocatable',))
+
 
 def do_install(reqs):
     from os import environ
@@ -241,11 +247,10 @@ def venv_update(stage, venv_path, reqs, venv_args):
     from os.path import join, abspath
     venv_python = abspath(join(venv_path, 'bin', 'python'))
     if stage == 1:
-        # we have a random python interpreter active, (possibly) outside the virtualenv we want
+        # we have a random python interpreter active, (possibly) outside the virtualenv we want.
         # make a fresh venv at the right spot, and use it to perform stage 2
-        clean_venv(venv_path, venv_args)
-
-        run((venv_python, dotpy(__file__), '--stage2', venv_path) + reqs + venv_args)
+        with clean_venv(venv_path, venv_args):
+            run((venv_python, dotpy(__file__), '--stage2', venv_path) + reqs + venv_args)
     elif stage == 2:
         import sys
         assert sys.executable == venv_python, "Executable not in venv: %s != %s" % (sys.executable, venv_python)