diff: add --word-diff option that generalizes --color-words

This teaches the --color-words engine a more general interface that
supports two new modes:

* --word-diff=plain, inspired by the 'wdiff' utility (most similar to
  'wdiff -n <old> <new>'): uses delimiters [-removed-] and {+added+}

* --word-diff=porcelain, which generates an ad-hoc machine readable
  format:
  - each diff unit is prefixed by [-+ ] and terminated by newline as
    in unified diff
  - newlines in the input are output as a line consisting only of a
    tilde '~'

Both of these formats still support color if it is enabled, using it
to highlight the differences.  --color-words becomes a synonym for
--word-diff=color, which is the color-only format.  Also adds some
compatibility/convenience options.

Thanks to Junio C Hamano and Miles Bader for good ideas.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/diff.h b/diff.h
index 6a71013dc6..9ace08cbae 100644
--- a/diff.h
+++ b/diff.h
@@ -54,7 +54,7 @@ typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
 #define DIFF_OPT_FIND_COPIES_HARDER  (1 <<  6)
 #define DIFF_OPT_FOLLOW_RENAMES      (1 <<  7)
 #define DIFF_OPT_COLOR_DIFF          (1 <<  8)
-#define DIFF_OPT_COLOR_DIFF_WORDS    (1 <<  9)
+/* (1 <<  9) unused */
 #define DIFF_OPT_HAS_CHANGES         (1 << 10)
 #define DIFF_OPT_QUICK               (1 << 11)
 #define DIFF_OPT_NO_INDEX            (1 << 12)
@@ -79,6 +79,13 @@ typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
 #define DIFF_XDL_SET(opts, flag)    ((opts)->xdl_opts |= XDF_##flag)
 #define DIFF_XDL_CLR(opts, flag)    ((opts)->xdl_opts &= ~XDF_##flag)
 
+enum diff_words_type {
+	DIFF_WORDS_NONE = 0,
+	DIFF_WORDS_PORCELAIN,
+	DIFF_WORDS_PLAIN,
+	DIFF_WORDS_COLOR
+};
+
 struct diff_options {
 	const char *filter;
 	const char *orderfile;
@@ -108,6 +115,7 @@ struct diff_options {
 	int stat_width;
 	int stat_name_width;
 	const char *word_regex;
+	enum diff_words_type word_diff;
 
 	/* this is set by diffcore for DIFF_FORMAT_PATCH */
 	int found_changes;