test: clarify test-parseindex offsets

We will make this revlog non-inline, so we clarify the code to make sure it is
simple to adjust the test later.

tests/test-parseindex.t

@@ -1,220 +1,225 b''
 revlog.parseindex must be able to parse the index file even if
 an index entry is split between two 64k blocks.  The ideal test
 would be to create an index file with inline data where
 64k < size < 64k + 64 (64k is the size of the read buffer, 64 is
 the size of an index entry) and with an index entry starting right
 before the 64k block boundary, and try to read it.
 We approximate that by reducing the read buffer to 1 byte.
 
   $ hg init a
   $ cd a
   $ echo abc > foo
   $ hg add foo
   $ hg commit -m 'add foo'
   $ echo >> foo
   $ hg commit -m 'change foo'
   $ hg log -r 0:
   changeset:   0:7c31755bf9b5
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     add foo
   
   changeset:   1:26333235a41c
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     change foo
   
   $ cat >> test.py << EOF
   > from mercurial import changelog, node, pycompat, vfs
   > 
   > class singlebyteread(object):
   >     def __init__(self, real):
   >         self.real = real
   > 
   >     def read(self, size=-1):
   >         if size == 65536:
   >             size = 1
   >         return self.real.read(size)
   > 
   >     def __getattr__(self, key):
   >         return getattr(self.real, key)
   > 
   >     def __enter__(self):
   >         self.real.__enter__()
   >         return self
   > 
   >     def __exit__(self, *args, **kwargs):
   >         return self.real.__exit__(*args, **kwargs)
   > 
   > def opener(*args):
   >     o = vfs.vfs(*args)
   >     def wrapper(*a, **kwargs):
   >         f = o(*a, **kwargs)
   >         return singlebyteread(f)
   >     wrapper.options = o.options
   >     return wrapper
   > 
   > cl = changelog.changelog(opener(b'.hg/store'))
   > print(len(cl), 'revisions:')
   > for r in cl:
   >     print(pycompat.sysstr(node.short(cl.node(r))))
   > EOF
   $ "$PYTHON" test.py
   2 revisions:
   7c31755bf9b5
   26333235a41c
 
   $ cd ..
 
 #if no-pure
 
 Test SEGV caused by bad revision passed to reachableroots() (issue4775):
 
   $ cd a
 
   $ "$PYTHON" <<EOF
   > from mercurial import changelog, vfs
   > cl = changelog.changelog(vfs.vfs(b'.hg/store'))
   > print('good heads:')
   > for head in [0, len(cl) - 1, -1]:
   >     print('%s: %r' % (head, cl.reachableroots(0, [head], [0])))
   > print('bad heads:')
   > for head in [len(cl), 10000, -2, -10000, None]:
   >     print('%s:' % head, end=' ')
   >     try:
   >         cl.reachableroots(0, [head], [0])
   >         print('uncaught buffer overflow?')
   >     except (IndexError, TypeError) as inst:
   >         print(inst)
   > print('good roots:')
   > for root in [0, len(cl) - 1, -1]:
   >     print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root])))
   > print('out-of-range roots are ignored:')
   > for root in [len(cl), 10000, -2, -10000]:
   >     print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root])))
   > print('bad roots:')
   > for root in [None]:
   >     print('%s:' % root, end=' ')
   >     try:
   >         cl.reachableroots(root, [len(cl) - 1], [root])
   >         print('uncaught error?')
   >     except TypeError as inst:
   >         print(inst)
   > EOF
   good heads:
   0: [0]
   1: [0]
   -1: []
   bad heads:
   2: head out of range
   10000: head out of range
   -2: head out of range
   -10000: head out of range
   None: (an integer is required( .got type NoneType.)?|'NoneType' object cannot be interpreted as an integer) (re)
   good roots:
   0: [0]
   1: [1]
   -1: [-1]
   out-of-range roots are ignored:
   2: []
   10000: []
   -2: []
   -10000: []
   bad roots:
   None: (an integer is required( .got type NoneType.)?|'NoneType' object cannot be interpreted as an integer) (re)
 
   $ cd ..
 
 Test corrupted p1/p2 fields that could cause SEGV at parsers.c:
 
   $ mkdir invalidparent
   $ cd invalidparent
 
   $ hg clone --pull -q --config phases.publish=False ../a limit --config format.sparse-revlog=no
   $ hg clone --pull -q --config phases.publish=False ../a neglimit --config format.sparse-revlog=no
   $ hg clone --pull -q --config phases.publish=False ../a segv --config format.sparse-revlog=no
   $ rm -R limit/.hg/cache neglimit/.hg/cache segv/.hg/cache
 
   $ "$PYTHON" <<EOF
   > data = open("limit/.hg/store/00changelog.i", "rb").read()
   > poisons = [
   >     (b'limit', b'\0\0\0\x02'),
   >     (b'neglimit', b'\xff\xff\xff\xfe'),
   >     (b'segv', b'\0\x01\0\0'),
   > ]
   > for n, p in poisons:
   >     # corrupt p1 at rev0 and p2 at rev1
-  >     d = data[:24] + p + data[28:127 + 28] + p + data[127 + 32:]
-  >     open(n + b"/.hg/store/00changelog.i", "wb").write(d)
+  >     rev_0 = data[:64 + 63]
+  >     rev_1 = data[64 + 63:]
+  >     altered_rev_0 = rev_0[:24] + p + rev_0[24 + 4:]
+  >     altered_rev_1 = rev_1[:28] + p + rev_1[28 + 4:]
+  >     new_data = altered_rev_0 + altered_rev_1
+  >     with open(n + b"/.hg/store/00changelog.i", "wb") as f:
+  >         f.write(new_data)
   > EOF
 
   $ hg -R limit debugrevlogindex -f1 -c
      rev flag     size   link     p1     p2       nodeid
        0 0000       62      0      2     -1 7c31755bf9b5
        1 0000       65      1      0      2 26333235a41c
 
   $ hg -R limit debugdeltachain -c
       rev      p1      p2  chain# chainlen     prev   delta
         0       2      -1       1        1       -1    base
         1       0       2       2        1       -1    base
 
   $ hg -R neglimit debugrevlogindex -f1 -c
      rev flag     size   link     p1     p2       nodeid
        0 0000       62      0     -2     -1 7c31755bf9b5
        1 0000       65      1      0     -2 26333235a41c
 
   $ hg -R segv debugrevlogindex -f1 -c
      rev flag     size   link     p1     p2       nodeid
        0 0000       62      0  65536     -1 7c31755bf9b5
        1 0000       65      1      0  65536 26333235a41c
 
   $ hg -R segv debugdeltachain -c
       rev      p1      p2  chain# chainlen     prev   delta
         0   65536      -1       1        1       -1    base
         1       0   65536       2        1       -1    base
 
   $ cat <<EOF > test.py
   > import sys
   > from mercurial import changelog, pycompat, vfs
   > cl = changelog.changelog(vfs.vfs(pycompat.fsencode(sys.argv[1])))
   > n0, n1 = cl.node(0), cl.node(1)
   > ops = [
   >     ('reachableroots',
   >      lambda: cl.index.reachableroots2(0, [1], [0], False)),
   >     ('compute_phases_map_sets', lambda: cl.computephases({1: {cl.node(0)}})),
   >     ('index_headrevs', lambda: cl.headrevs()),
   >     ('find_gca_candidates', lambda: cl.commonancestorsheads(n0, n1)),
   >     ('find_deepest', lambda: cl.ancestor(n0, n1)),
   >     ]
   > for l, f in ops:
   >     print(l + ':', end=' ')
   >     try:
   >         f()
   >         print('uncaught buffer overflow?')
   >     except ValueError as inst:
   >         print(inst)
   > EOF
 
   $ "$PYTHON" test.py limit/.hg/store
   reachableroots: parent out of range
   compute_phases_map_sets: parent out of range
   index_headrevs: parent out of range
   find_gca_candidates: parent out of range
   find_deepest: parent out of range
   $ "$PYTHON" test.py neglimit/.hg/store
   reachableroots: parent out of range
   compute_phases_map_sets: parent out of range
   index_headrevs: parent out of range
   find_gca_candidates: parent out of range
   find_deepest: parent out of range
   $ "$PYTHON" test.py segv/.hg/store
   reachableroots: parent out of range
   compute_phases_map_sets: parent out of range
   index_headrevs: parent out of range
   find_gca_candidates: parent out of range
   find_deepest: parent out of range
 
   $ cd ..
 
 #endif