[PATCH v4 0/2] diff: add -I<regex> that ignores matching changes

This patch series adds a new diff option that enables ignoring changes whose all lines (changed, removed, and added) match a given regular expression. This is similar to the -I/--ignore-matching-lines option in standalone diff utilities and can be used e.g. to ignore changes which only affect code comments or to look for unrelated changes in commits containing a large number of automatically applied modifications (e.g. a tree-wide string replacement). The difference between -G/-S and the new -I option is that the latter filters output on a per-change basis.

Changes from v3:

  - Do not release the memory allocated in diff_opt_ignore_regex() after
    all as the free() calls added in v2 were triggering use-after-free
    errors when the diff machinery was invoked multiple times throughout
    the lifetime of a single Git command (e.g. by "git log -p").

  - Further test improvements: split various -I<regex> checks into
    multiple tests; add a check for "git log -p -I<regex>" to trigger
    the issue mentioned above; avoid using --no-index.

Changes from v2:

  - Add a long option for -I (--ignore-matching-lines) as it is
    commonplace in standalone diff utilities.  Update documentation and
    commit log messages accordingly.

  - Use xmalloc() instead of xcalloc() for allocating regex_t
    structures in diff_opt_ignore_regex().

  - Ensure the memory allocated in diff_opt_ignore_regex() gets
    released.

  - Use "return error(...)" instead of die() in the -I option callback.
    Make sure the error message is localizable.

  - Drastically reduce the number of -I<regex> tests due to excessive
    run time of t/t4069-diff-ignore-regex.sh from v1/v2 on some
    platforms (notably Windows).  Use a tweaked version of a test
    suggested by Johannes Schindelin (thanks!).  Squash patch 3 into
    patch 2.

  - Replace "see Documentation/diff-options.txt" with "-I<regex>" in the
    comments for the added structure fields, in order to make these
    comments more useful.

Changes from v1:

  - Add a new preliminary cleanup patch which ensures xpparam_t
    structures are always zero-initialized.  (This was a prerequisite
    for the next change below.)

  - Do not add a new 'xdl_opts' flag to check whether -I was used;
    instead, just check whether the array of regular expressions to
    match against is non-NULL.

  - Enable the -I option to be used multiple times.  As a consequence of
    this, regular expressions are now "pre-compiled" in the option's
    callback (and passed around as an array of regex_t structures)
    rather than deep down in xdiff code.  Add test cases exercising use
    of multiple -I options in the same git invocation.  Update
    documentation accordingly.

  - Rename xdl_mark_ignorable() to xdl_mark_ignorable_lines(), to
    indicate that it is logically a "sibling" of
    xdl_mark_ignorable_regex() rather than its "parent".

  - Optimize xdl_mark_ignorable_regex() by making it immediately skip
    changes already marked as ignored by xdl_mark_ignorable_lines().

  - Fix coding style issue in the prototype part of the definition of
    xdl_mark_ignorable_regex().

  - Add "/* see Documentation/diff-options.txt */" comments for the
    fields added to struct diff_options and xpparam_t, mimicking the
    comments used for 'anchors', 'anchors_nr', and 'anchors_alloc'.

  - Revise commit log messages to reflect all of the above.

Michał Kępień (2):
  merge-base, xdiff: zero out xpparam_t structures
  diff: add -I<regex> that ignores matching changes

 Documentation/diff-options.txt             |  5 ++
 builtin/merge-tree.c                       |  1 +
 diff.c                                     | 23 +++++
 diff.h                                     |  4 +
 t/t4013-diff-various.sh                    | 41 +++++++++
 t/t4013/diff.log_-IA_-IB_-I1_-I2_-p_master | 99 ++++++++++++++++++++++
 xdiff/xdiff.h                              |  4 +
 xdiff/xdiffi.c                             | 47 +++++++++-
 xdiff/xhistogram.c                         |  2 +
 xdiff/xpatience.c                          |  2 +
 10 files changed, 226 insertions(+), 2 deletions(-)
 create mode 100644 t/t4013/diff.log_-IA_-IB_-I1_-I2_-p_master