[PATCH v4 1/2] diff: add --line-prefix option for passing in a prefix

[Jacob Keller]

From: Jacob Keller <jacob.kel...@gmail.com>

This will be used by a future patch which implements a diff mode for
submodule display. Without this, the diff output would incorrectly
display when using both -p and --graph during a git-log.

Note that the --line-prefix will be displayed first prior to any other
output prefix.

Signed-off-by: Jacob Keller <jacob.kel...@gmail.com>
---
 Documentation/diff-options.txt |  3 +++
 diff.c                         | 13 ++++++++++++-
 diff.h                         |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 705a87394200..e7b729f3644f 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -569,5 +569,8 @@ endif::git-format-patch[]
 --no-prefix::
        Do not show any source or destination prefix.
 
+--line-prefix=<prefix>::
+       Prepend an additional prefix to every diff output line.
+
 For more detailed explanation on these common options, see also
 linkgit:gitdiffcore[7].
diff --git a/diff.c b/diff.c
index b43d3dd2ecb7..6fa9668b19e5 100644
--- a/diff.c
+++ b/diff.c
@@ -1167,10 +1167,17 @@ const char *diff_get_color(int diff_use_color, enum 
color_diff ix)
 const char *diff_line_prefix(struct diff_options *opt)
 {
        struct strbuf *msgbuf;
+
        if (!opt->output_prefix)
-               return "";
+               if (opt->line_prefix)
+                       return opt->line_prefix;
+               else
+                       return "";
 
        msgbuf = opt->output_prefix(opt, opt->output_prefix_data);
+       /* line prefix must be printed before the output_prefix() */
+       if (opt->line_prefix)
+               strbuf_insert(msgbuf, 0, opt->line_prefix, 
strlen(opt->line_prefix));
        return msgbuf->buf;
 }
 
@@ -3966,6 +3973,10 @@ int diff_opt_parse(struct diff_options *options,
                options->a_prefix = optarg;
                return argcount;
        }
+       else if ((argcount = parse_long_opt("line-prefix", av, &optarg))) {
+               options->line_prefix = optarg;
+               return argcount;
+       }
        else if ((argcount = parse_long_opt("dst-prefix", av, &optarg))) {
                options->b_prefix = optarg;
                return argcount;
diff --git a/diff.h b/diff.h
index 125447be09eb..6a91a1139686 100644
--- a/diff.h
+++ b/diff.h
@@ -115,6 +115,7 @@ struct diff_options {
        const char *pickaxe;
        const char *single_follow;
        const char *a_prefix, *b_prefix;
+       const char *line_prefix;
        unsigned flags;
        unsigned touched_flags;
 
-- 
2.9.2.872.g2dc3c84

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