revlog: make sure we never use sparserevlog without general delta (issue6056) stable

revlog: make sure we never use sparserevlog without general delta (issue6056)

We are getting user report where the delta code tries to use `sparse-revlog`
logic on repository where `generaldelta` is disabled. This can't work so we
ensure the two booleans have a consistent value.

Creating this kind of repository is not expected to be possible the current bug
report point at a clonebundle related bug that is still to be properly isolated
(Yuya Nishihara seems to a have done it).

Corrupting a repository to reproduce the issue is possible. A test using this
method is included in this fix.

--- a/mercurial/revlog.py	Wed Jan 30 18:15:38 2019 +0100
+++ b/mercurial/revlog.py	Thu Jan 24 18:22:47 2019 -0500
@@ -497,6 +497,9 @@
         else:
             raise error.RevlogError(_('unknown version (%d) in revlog %s') %
                                     (fmt, self.indexfile))
+        # sparse-revlog can't be on without general-delta (issue6056)
+        if not self._generaldelta:
+            self._sparserevlog = False
 
         self._storedeltachains = True
 

--- a/mercurial/revlogutils/deltas.py	Wed Jan 30 18:15:38 2019 +0100
+++ b/mercurial/revlogutils/deltas.py	Thu Jan 24 18:22:47 2019 -0500
@@ -755,7 +755,8 @@
     The group order aims at providing fast or small candidates first.
     """
     gdelta = revlog._generaldelta
-    sparse = revlog._sparserevlog
+    # gate sparse behind general-delta because of issue6056
+    sparse = gdelta and revlog._sparserevlog
     curr = len(revlog)
     prev = curr - 1
     deltachain = lambda rev: revlog._deltachain(rev)[0]

--- a/tests/test-init.t	Wed Jan 30 18:15:38 2019 +0100
+++ b/tests/test-init.t	Thu Jan 24 18:22:47 2019 -0500
@@ -268,3 +268,25 @@
   exporting bookmark test
   $ hg -R remote-bookmarks bookmarks
      test                      0:08b9e9f63b32
+
+Check format constraint
+-----------------------
+
+  $ hg init issue6056 --config format.usegeneraldelta=0 --config format.sparse-revlog=0
+  $ cd issue6056
+  $ echo foo > 1
+  $ echo foo > 2
+  $ echo foo > 3
+  $ echo foo > 4
+  $ echo foo > 5
+  $ hg add *
+
+Build a bogus repository (sparserevlog without general delta)
+
+  $ hg commit -m 'initial changesets'
+  $ echo 'sparserevlog' >> .hg/requires
+  $ for x in `$TESTDIR/seq.py 100`; do
+  >     echo $x >> `expr $x % 5 + 1`
+  >     hg commit -m $x
+  > done
+  $ cd ..