From: Junio C Hamano <>

The diff_opt infrastructure sets flags based on defaults and command
line options. Currently, it is impossible to detect whether a flag has
been set as a default or on explicit request.

Amend the structure so that this detection is possible:

 * There is an extra "opt->touched_flags" that keeps track of all
   the fields that have been touched by DIFF_OPT_SET and

 * You may continue setting the default values to the flags, like
   commands in the "log" family do in cmd_log_init_defaults(), but
   after you finished setting the defaults, you clear the
   touched_flags field;

 * And then you let the usual callchain call diff_opt_parse(),
   allowing the opt->flags be set or unset, while keeping track of
   which bits the user touched;

 * There is an optional callback "opt->set_default" that is called
   at the very beginning to lets you inspect touched_flags and
   update opt->flags appropriately, before the remainder of the
   diffcore machinery is set up, taking the opt->flags value into

Signed-off-by: Michael J Gruber <>
 Documentation/technical/api-diff.txt | 10 +++++++++-
 builtin/log.c                        |  1 +
 diff.c                               |  3 +++
 diff.h                               |  8 ++++++--
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/Documentation/technical/api-diff.txt 
index 2d2ebc0..8b001de 100644
--- a/Documentation/technical/api-diff.txt
+++ b/Documentation/technical/api-diff.txt
@@ -28,7 +28,8 @@ Calling sequence
 * Call `diff_setup_done()`; this inspects the options set up so far for
   internal consistency and make necessary tweaking to it (e.g. if
-  textual patch output was asked, recursive behaviour is turned on).
+  textual patch output was asked, recursive behaviour is turned on);
+  the callback set_default in diff_options can be used to tweak this more.
 * As you find different pairs of files, call `diff_change()` to feed
   modified files, `diff_addremove()` to feed created or deleted files,
@@ -115,6 +116,13 @@ Notable members are:
        operation, but some do not have anything to do with the diffcore
+       Records whether a flag has been changed due to user request
+       (rather than just set/unset by default).
+       Callback which allows tweaking the options in diff_setup_done().
        Affects the way how a file that is seemingly binary is treated.
diff --git a/builtin/log.c b/builtin/log.c
index 9e21232..f19d779 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -111,6 +111,7 @@ static void cmd_log_init_defaults(struct rev_info *rev)
        if (default_date_mode)
                rev->date_mode = parse_date_format(default_date_mode);
+       rev->diffopt.touched_flags = 0;
 static void cmd_log_init_finish(int argc, const char **argv, const char 
diff --git a/diff.c b/diff.c
index f0b3e7c..7c24872 100644
--- a/diff.c
+++ b/diff.c
@@ -3213,6 +3213,9 @@ void diff_setup_done(struct diff_options *options)
        int count = 0;
+       if (options->set_default)
+               options->set_default(options);
        if (options->output_format & DIFF_FORMAT_NAME)
        if (options->output_format & DIFF_FORMAT_NAME_STATUS)
diff --git a/diff.h b/diff.h
index 78b4091..e995ae1 100644
--- a/diff.h
+++ b/diff.h
@@ -87,8 +87,9 @@ typedef struct strbuf *(*diff_prefix_fn_t)(struct 
diff_options *opt, void *data)
 #define DIFF_OPT_TST(opts, flag)    ((opts)->flags & DIFF_OPT_##flag)
-#define DIFF_OPT_SET(opts, flag)    ((opts)->flags |= DIFF_OPT_##flag)
-#define DIFF_OPT_CLR(opts, flag)    ((opts)->flags &= ~DIFF_OPT_##flag)
+#define DIFF_OPT_TOUCHED(opts, flag)    ((opts)->touched_flags & 
+#define DIFF_OPT_SET(opts, flag)    (((opts)->flags |= 
DIFF_OPT_##flag),((opts)->touched_flags |= DIFF_OPT_##flag))
+#define DIFF_OPT_CLR(opts, flag)    (((opts)->flags &= 
~DIFF_OPT_##flag),((opts)->touched_flags |= DIFF_OPT_##flag))
 #define DIFF_XDL_TST(opts, flag)    ((opts)->xdl_opts & XDF_##flag)
 #define DIFF_XDL_SET(opts, flag)    ((opts)->xdl_opts |= XDF_##flag)
 #define DIFF_XDL_CLR(opts, flag)    ((opts)->xdl_opts &= ~XDF_##flag)
@@ -109,6 +110,7 @@ struct diff_options {
        const char *single_follow;
        const char *a_prefix, *b_prefix;
        unsigned flags;
+       unsigned touched_flags;
        int use_color;
        int context;
        int interhunkcontext;
@@ -145,6 +147,8 @@ struct diff_options {
        /* to support internal diff recursion by --follow hack*/
        int found_follow;
+       void (*set_default)(struct diff_options *);
        FILE *file;
        int close_file;

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