revlog: fix index computation during inline->non-inline transition

The computation in 63edc384d3b7 failed to factor in the index entries
themselve as revlog.start() doesn't count them. Found by Valtenin
Gatienbaron with a more precise test case from me.

Differential Revision: https://phab.mercurial-scm.org/D10724

tests/helper-killhook.py

@@ -0,0 +1,5 b''
+import os
+
+
+def killme(ui, repo, hooktype, **wkargs):
+    os._exit(80)

tests/test-transaction-rollback-on-revlog-split.t

@@ -0,0 +1,35 b''
+Test correctness of revlog inline -> non-inline transition
+----------------------------------------------------------
+
+Test offset computation to correctly factor in the index entries themselve.
+Test repo has one small, one moderate and one big change. The clone has
+the small and moderate change and will transition to non-inline storage when
+adding the big change.
+
+  $ hg init troffset-computation --config format.revlog-compression=none
+  $ cd troffset-computation
+  $ printf '% 20d' '1' > file
+  $ hg commit -Aqm_
+  $ printf '% 1024d' '1' > file
+  $ hg commit -Aqm_
+  $ dd if=/dev/zero of=file bs=1k count=128 > /dev/null 2>&1
+  $ hg commit -Aqm_
+  $ cd ..
+
+  $ hg clone -r 1 troffset-computation troffset-computation-copy --config format.revlog-compression=none -q
+  $ cd troffset-computation-copy
+  $ cat > .hg/hgrc <<EOF
+  > [hooks]
+  > pretxnchangegroup = python:$TESTDIR/helper-killhook.py:killme
+  > EOF
+#if chg
+  $ hg pull ../troffset-computation
+  pulling from ../troffset-computation
+  [255]
+#else
+  $ hg pull ../troffset-computation
+  pulling from ../troffset-computation
+  [80]
+#endif
+  $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file | tail -1
+  data/file.i 128

mercurial/revlog.py

@@ -2174,7 +2174,7 b' class revlog(object):'
             with self._indexfp() as read_ifh:
                 for r in self:
                     new_dfh.write(self._getsegmentforrevs(r, r, df=read_ifh)[1])
-                    if troffset <= self.start(r):
+                    if troffset <= self.start(r) + r * self.index.entry_size:
                         trindex = r
                 new_dfh.flush()