provision: Stop using shared var/ for caching apt state.

This didn't work at all when one did a `vagrant destroy` and then
`vagrant up`, because the cache state would be preserved even though
the machine is gone.

Fixes #5981.

scripts/lib/zulip_tools.py

@@ -12,6 +12,7 @@ import subprocess
 import sys
 import time
 import json
+import uuid
 
 if False:
     from typing import Sequence, Set, Text, Any
@@ -110,6 +111,27 @@ def mkdir_p(path):
         else:
             raise
 
+def get_dev_uuid_var_path(create_if_missing=False):
+    # type: (bool) -> str
+    zulip_path = os.path.realpath(os.path.dirname(os.path.dirname(os.path.dirname(os.path.realpath(__file__)))))
+    uuid_path = os.path.join(os.path.realpath(os.path.dirname(zulip_path)), ".zulip-dev-uuid")
+    if os.path.exists(uuid_path):
+        with open(uuid_path) as f:
+            zulip_uuid = f.read().strip()
+    else:
+        if create_if_missing:
+            zulip_uuid = str(uuid.uuid4())
+            # We need sudo here, since the path will be under /srv/ in the
+            # development environment.
+            subprocess.check_call(["sudo", "/bin/bash", "-c",
+                                   "echo %s > %s" % (zulip_uuid, uuid_path)])
+        else:
+            raise AssertionError("Missing UUID file; please run tools/provision!")
+
+    result_path = os.path.join(zulip_path, "var", zulip_uuid)
+    mkdir_p(result_path)
+    return result_path
+
 def get_deployment_lock(error_rerun_script):
     # type: (str) -> None
     start_time = time.time()

tools/lib/provision.py

@@ -13,7 +13,8 @@ os.environ["PYTHONUNBUFFERED"] = "y"
 ZULIP_PATH = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 sys.path.append(ZULIP_PATH)
-from scripts.lib.zulip_tools import run, subprocess_text_output, OKBLUE, ENDC, WARNING
+from scripts.lib.zulip_tools import run, subprocess_text_output, OKBLUE, ENDC, WARNING, \
+    get_dev_uuid_var_path
 from scripts.lib.setup_venv import VENV_DEPENDENCIES
 from scripts.lib.node_cache import setup_node_modules, NODE_MODULES_CACHE_PATH
 
@@ -67,7 +68,8 @@ if ram_gb < 1.5:
     sys.exit(1)
 
 try:
-    run(["mkdir", "-p", VAR_DIR_PATH])
+    UUID_VAR_PATH = get_dev_uuid_var_path(create_if_missing=True)
+    run(["mkdir", "-p", UUID_VAR_PATH])
     if os.path.exists(os.path.join(VAR_DIR_PATH, 'zulip-test-symlink')):
         os.remove(os.path.join(VAR_DIR_PATH, 'zulip-test-symlink'))
     os.symlink(
@@ -209,7 +211,7 @@ def main(options):
 
     new_apt_dependencies_hash = sha_sum.hexdigest()
     last_apt_dependencies_hash = None
-    apt_hash_file_path = 'var/apt_dependencies_hash'
+    apt_hash_file_path = os.path.join(UUID_VAR_PATH, "apt_dependencies_hash")
     try:
         hash_file = open(apt_hash_file_path, 'r+')
         last_apt_dependencies_hash = hash_file.read()