rbc: fix invalid rbc-revs entries caused by missing cache growth

rbc: fix invalid rbc-revs entries caused by missing cache growth

It was in some cases possible to end up writing to the cache file without
growing it first. The range assignment in _setcachedata would append instead of
writing at the requested position and thus write the new record in the wrong
place.

To fix this, we avoid looking up in too small caches, and when growing the
cache, do it right before writing the new record to it so we know it has been
done correctly.

--- a/mercurial/branchmap.py	Mon Jul 18 22:21:42 2016 +0200
+++ b/mercurial/branchmap.py	Mon Jul 18 22:22:38 2016 +0200
@@ -402,10 +402,9 @@
         if rev == nullrev:
             return changelog.branchinfo(rev)
 
-        # if requested rev is missing, add and populate all missing revs
+        # if requested rev isn't allocated, grow and cache the rev info
         if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
-            self._rbcrevs.extend('\0' * (len(changelog) * _rbcrecsize -
-                                         len(self._rbcrevs)))
+            return self._branchinfo(rev)
 
         # fast path: extract data from cache, use it if node is matching
         reponode = changelog.node(rev)[:_rbcnodelen]
@@ -452,6 +451,10 @@
         rbcrevidx = rev * _rbcrecsize
         rec = array('c')
         rec.fromstring(pack(_rbcrecfmt, node, branchidx))
+        if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
+            self._rbcrevs.extend('\0' *
+                                 (len(self._repo.changelog) * _rbcrecsize -
+                                  len(self._rbcrevs)))
         self._rbcrevs[rbcrevidx:rbcrevidx + _rbcrecsize] = rec
         self._rbcrevslen = min(self._rbcrevslen, rev)
 

--- a/tests/test-branches.t	Mon Jul 18 22:21:42 2016 +0200
+++ b/tests/test-branches.t	Mon Jul 18 22:22:38 2016 +0200
@@ -655,12 +655,16 @@
   $ rm .hg/cache/rbc*
   $ hg log -r "5 & branch(5)" -T "{rev}\n"
   5
-BUG: rbc-revs should have an entry as 5th record but has it misplaced as the
-first:
   $ f --size --hexdump .hg/cache/rbc-*
   .hg/cache/rbc-names-v1: size=1
   0000: 61                                              |a|
-  .hg/cache/rbc-revs-v1: size=8
-  0000: d8 cb c6 1d 00 00 00 00                         |........|
+  .hg/cache/rbc-revs-v1: size=112
+  0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
+  0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
+  0020: 00 00 00 00 00 00 00 00 d8 cb c6 1d 00 00 00 00 |................|
+  0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
+  0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
+  0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
+  0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
 
   $ cd ..