[PATCH STABLE] debugrevlog: improve handling of empty manifests/changelogs

[timeless]

> Why checking numerator?

If it's 0, then I'm happy saying the value is 0. If it's not zero,
then I don't want to decide how to handle it. I.e. from my perspective
0/x should be treated as 0, people can understand that. 1/0 otoh
should be Inf, and that's too hard to reason through. If we manage to
hit that case, I'd like someone else to solve it.

diff -r 8b7958075035 tests/test-debugcommands.t
--- a/tests/test-debugcommands.t    Mon Jan 25 20:40:38 2016 +0000
+++ b/tests/test-debugcommands.t    Fri Jan 29 16:24:05 2016 +0000
@@ -1,5 +1,3 @@
-#require test-repo
-
   $ cat << EOF >> $HGRCPATH
   > [format]
   > usegeneraldelta=yes

Removing the require is correct (and I'll do it if I can resend
something useful).

> You can make an empty commit by "--config ui.allowemptycommit=True" or
> "hg branch foo && hg ci".


@@ -13,48 +11,23 @@
   $ hg debugrevlog -m
   abort: repository manifest is empty
   [255]
-  $ hg pull "$TESTDIR/bundles/issue5062.hg" -r 0
-  pulling from *issue5062.hg (glob)
-  adding changesets
-  adding manifests
-  adding file changes
-  added 1 changesets with 0 changes to 0 files
-  (run 'hg update' to get a working copy)
+  $ hg commit --config ui.allowemptycommit=True -m 'empty'
+  $ hg debugrevlog -m
+  abort: repository manifest is empty
+  [255]
+
+  $ echo a > a
+  $ hg ci -Am adda
+  adding a
   $ hg debugrevlog -m
   format : 1
   flags  : inline, generaldelta

-  revisions     : 1
-      merges    : 0 ( 0.00%)
-      normal    : 1 (100.00%)
-  revisions     : 1
-      full      : 1 (100.00%)
-      deltas    : 0 ( 0.00%)
-  revision size : 0
-      full      : 0 (100.00%)
-      deltas    : 0 (100.00%)
-
-  avg chain length  : 0
-  max chain length  : 0
-  compression ratio : 1
-
-  uncompressed data size (min/max/avg) : 0 / 0 / 0
-  full revision size (min/max/avg)     : 0 / 0 / 0
-  delta size (min/max/avg)             : 0 / 0 / 0
-
-  $ echo a > a
-  $ hg ci -Am adda
-  adding a
-  created new head
-  $ hg debugrevlog -m
-  format : 1
-  flags  : inline, generaldelta
-
-  revisions     :  2
+  revisions     :  1
       merges    :  0 ( 0.00%)
-      normal    :  2 (100.00%)
-  revisions     :  2
-      full      :  2 (100.00%)
+      normal    :  1 (100.00%)
+  revisions     :  1
+      full      :  1 (100.00%)
       deltas    :  0 ( 0.00%)
   revision size : 44
       full      : 44 (100.00%)

This doesn't seem to match what I was expecting at all. Apparently an
empty commit isn't considered a revision (?!).

@@ -64,8 +37,8 @@
   max chain length  : 0
   compression ratio : 0

-  uncompressed data size (min/max/avg) : 0 / 43 / 21
-  full revision size (min/max/avg)     : 0 / 44 / 22
+  uncompressed data size (min/max/avg) : 43 / 43 / 43
+  full revision size (min/max/avg)     : 44 / 44 / 44
   delta size (min/max/avg)             : 0 / 0 / 0

 Test debugindex, with and without the --debug flag
@@ -86,32 +59,16 @@

   $ hg debugdeltachain -m
       rev  chain# chainlen     prev   delta       size    rawsize
chainsize     ratio   lindist extradist extraratio
-        0       1        1       -1    base          0          0
     0   0.00000         0         0    0.00000
-        1       2        1       -1    base         44         43
    44   1.02326        44         0    0.00000
+        0       1        1       -1    base         44         43
    44   1.02326        44         0    0.00000

   $ hg debugdeltachain -m -T '{rev} {chainid} {chainlen}\n'
   0 1 1
-  1 2 1

   $ hg debugdeltachain -m -Tjson
   [
    {
     "chainid": 1,
     "chainlen": 1,
-    "chainratio": 0.0,
-    "chainsize": 0,
-    "compsize": 0,
-    "deltatype": "base",
-    "extradist": 0,
-    "extraratio": 0.0,
-    "lindist": 0,
-    "prevrev": -1,
-    "rev": 0,
-    "uncompsize": 0
-   },
-   {
-    "chainid": 2,
-    "chainlen": 1,
     "chainratio": 1.02325581395,
     "chainsize": 44,
     "compsize": 44,
@@ -120,7 +77,7 @@
     "extraratio": 0.0,
     "lindist": 44,
     "prevrev": -1,
-    "rev": 1,
+    "rev": 0,
     "uncompsize": 43
    }
   ]