Fix parameter passing of describe patterns

When ffi.new() is used to build a new pointer object, the returned
pointer object has ownership on the allocated memory. When it is
garbage-collected, then the memory is freed. Thus, we need to make sure
the original object survives its use, otherwise the casted pointer will
point to garbage.

This fixes one test which was failing with the latest CFFI version, see
issue #694. Thus, this commit also reverts 803b1cb (cffi 1.10 not yet
supported, 2017-03-22) where the latest CFFI version was marked as
unsupported.

Signed-off-by: Lukas Fleischer <lfleischer@lfos.de>

.travis.yml

@@ -14,7 +14,7 @@ env: LIBGIT2=~/libgit2/_install/ LD_LIBRARY_PATH=~/libgit2/_install/lib
 
 before_install:
   - sudo apt-get install cmake
-  - pip install cffi==1.9.1
+  - pip install cffi
   - "./.travis.sh"
 
 script:

pygit2/repository.py

@@ -692,7 +692,11 @@ class BaseRepository(_Repository):
         if describe_strategy is not None:
             options.describe_strategy = describe_strategy
         if pattern:
-            options.pattern = ffi.new('char[]', to_bytes(pattern))
+            # The returned pointer object has ownership on the allocated
+            # memory. Make sure it is kept alive until git_describe_commit() or
+            # git_describe_workdir() are called below.
+            pattern_char = ffi.new('char[]', to_bytes(pattern))
+            options.pattern = pattern_char
         if only_follow_first_parent is not None:
             options.only_follow_first_parent = only_follow_first_parent
         if show_commit_oid_as_fallback is not None:

setup.py

@@ -203,8 +203,8 @@ setup(name='pygit2',
       long_description=long_description,
       packages=['pygit2'],
       package_data={'pygit2': ['decl.h']},
-      setup_requires=['cffi<1.10'],
-      install_requires=['cffi<1.10', 'six'],
+      setup_requires=['cffi'],
+      install_requires=['cffi', 'six'],
       zip_safe=False,
       cmdclass=cmdclass,
       **extra_args)