view tests/test-import-context.t @ 35810:113a30b87716 stable

lazymanifest: avoid reading uninitialized memory

I got errors running tests with clang UBSAN [1] enabled. One of them is:

```
--- test-dirstate.t
+++ test-dirstate.t.err
@@ -85,9 +85,115 @@
   $ echo "[extensions]" >> .hg/hgrc
   $ echo "dirstateex=../dirstateexception.py" >> .hg/hgrc
   $ hg up 0
-  abort: simulated error while recording dirstateupdates
-  [255]
+  mercurial/cext/manifest.c:781:13: runtime error: load of value 190, which is not a valid value for type 'bool'
+      #0 0x7f668a8cf748 in lazymanifest_diff mercurial/cext/manifest.c:781
+      #1 0x7f6692fc1dc4 in call_function Python-2.7.11/Python/ceval.c:4350
+      .......
+  SUMMARY: UndefinedBehaviorSanitizer: invalid-bool-load mercurial/cext/manifest.c:781:13 in
+  [1]
   $ hg log -r . -T '{rev}\n'
   1
   $ hg status
-  ? a
```

While the code is not technically wrong, but switching the condition would
make clang UBSAN happy. So let's do it.

The uninitialized memory could come from, for example, `lazymanifest_copy`
allocates `self->maxlines` items but only writes the first `self->lines`
items.

[1]: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

Test Plan:
Run `test-dirstate.t` with UBSAN and it no longer reports the issue.

Differential Revision: https://phab.mercurial-scm.org/D1948

Test applying context diffs

  $ cat > writepatterns.py <<EOF
  > import sys
  > 
  > path = sys.argv[1]
  > lasteol = sys.argv[2] == '1'
  > patterns = sys.argv[3:]
  > 
  > fp = file(path, 'wb')
  > for i, pattern in enumerate(patterns):
  >     count = int(pattern[0:-1])
  >     char = pattern[-1] + '\n'
  >     if not lasteol and i == len(patterns) - 1:
  >         fp.write((char*count)[:-1])
  >     else:
  >         fp.write(char*count)
  > fp.close()
  > EOF
  $ cat > cat.py <<EOF
  > import sys
  > sys.stdout.write(repr(file(sys.argv[1], 'rb').read()) + '\n')
  > EOF

Initialize the test repository

  $ hg init repo
  $ cd repo
  $ $PYTHON ../writepatterns.py a 0 5A 1B 5C 1D
  $ $PYTHON ../writepatterns.py b 1 1A 1B
  $ $PYTHON ../writepatterns.py c 1 5A
  $ $PYTHON ../writepatterns.py d 1 5A 1B
  $ hg add
  adding a
  adding b
  adding c
  adding d
  $ hg ci -m addfiles

Add file, missing a last end of line

  $ hg import --no-commit - <<EOF
  > *** /dev/null	2010-10-16 18:05:49.000000000 +0200
  > --- b/newnoeol	2010-10-16 18:23:26.000000000 +0200
  > ***************
  > *** 0 ****
  > --- 1,2 ----
  > + a
  > + b
  > \ No newline at end of file
  > *** a/a	Sat Oct 16 16:35:51 2010
  > --- b/a	Sat Oct 16 16:35:51 2010
  > ***************
  > *** 3,12 ****
  >   A
  >   A
  >   A
  > ! B
  >   C
  >   C
  >   C
  >   C
  >   C
  > ! D
  > \ No newline at end of file
  > --- 3,13 ----
  >   A
  >   A
  >   A
  > ! E
  >   C
  >   C
  >   C
  >   C
  >   C
  > ! F
  > ! F
  > 
  > *** a/b	2010-10-16 18:40:38.000000000 +0200
  > --- /dev/null	2010-10-16 18:05:49.000000000 +0200
  > ***************
  > *** 1,2 ****
  > - A
  > - B
  > --- 0 ----
  > *** a/c	Sat Oct 16 21:34:26 2010
  > --- b/c	Sat Oct 16 21:34:27 2010
  > ***************
  > *** 3,5 ****
  > --- 3,7 ----
  >   A
  >   A
  >   A
  > + B
  > + B
  > *** a/d	Sat Oct 16 21:47:20 2010
  > --- b/d	Sat Oct 16 21:47:22 2010
  > ***************
  > *** 2,6 ****
  >   A
  >   A
  >   A
  > - A
  > - B
  > --- 2,4 ----
  > EOF
  applying patch from stdin
  $ hg st
  M a
  M c
  M d
  A newnoeol
  R b

What's in a

  $ $PYTHON ../cat.py a
  'A\nA\nA\nA\nA\nE\nC\nC\nC\nC\nC\nF\nF\n'
  $ $PYTHON ../cat.py newnoeol
  'a\nb'
  $ $PYTHON ../cat.py c
  'A\nA\nA\nA\nA\nB\nB\n'
  $ $PYTHON ../cat.py d
  'A\nA\nA\nA\n'

  $ cd ..