diff mercurial/revlogutils/nodemap.py @ 47310:9a3aa54774ff

persistent-nodemap: add a way to make the picked uid predictable

This will make the test less volatile and therefore easier to maintain. I am
setting this is for the persistent nodemap docket first, but my target is to use
similar logic for the revlogv2 (and co) test.

For persisent nodemap, they are too many different in how each test variants (with rust, without rust, etc) needs new uid for this be really useful (right now). However it will be directly useful for the revlogv2 logic.

Differential Revision: https://phab.mercurial-scm.org/D10753

--- a/mercurial/revlogutils/nodemap.py	Thu May 06 19:39:19 2021 -0400
+++ b/mercurial/revlogutils/nodemap.py	Wed May 19 17:19:46 2021 +0200
@@ -10,13 +10,16 @@
 
 import errno
 import os
+import random
 import re
 import struct
 
 from ..node import hex
 
 from .. import (
+    encoding,
     error,
+    pycompat,
     util,
 )
 
@@ -288,6 +291,45 @@
     return hex(os.urandom(ID_SIZE))
 
 
+# some special test logic to avoid anoying random output in the test
+stable_docket_file = encoding.environ.get(b'HGTEST_DOCKETIDFILE')
+
+if stable_docket_file:
+
+    def _make_uid():
+        try:
+            with open(stable_docket_file, mode='rb') as f:
+                seed = f.read().strip()
+        except IOError as inst:
+            if inst.errno != errno.ENOENT:
+                raise
+            seed = b'4'  # chosen by a fair dice roll. garanteed to be random
+        if pycompat.ispy3:
+            iter_seed = iter(seed)
+        else:
+            iter_seed = (ord(c) for c in seed)
+        # some basic circular sum hashing on 64 bits
+        int_seed = 0
+        low_mask = int('1' * 35, 2)
+        for i in iter_seed:
+            high_part = int_seed >> 35
+            low_part = (int_seed & low_mask) << 28
+            int_seed = high_part + low_part + i
+        r = random.Random()
+        if pycompat.ispy3:
+            r.seed(int_seed, version=1)
+        else:
+            r.seed(int_seed)
+        # once we drop python 3.8 support we can simply use r.randbytes
+        raw = r.getrandbits(ID_SIZE * 8)
+        assert ID_SIZE == 8
+        p = struct.pack('>Q', raw)
+        new = hex(p)
+        with open(stable_docket_file, 'wb') as f:
+            f.write(new)
+        return new
+
+
 class NodeMapDocket(object):
     """metadata associated with persistent nodemap data