[PATCH] show-diff.c: -R option for reverse diff.

This adds -R option to obtain reverse diff.

It may be useful in the merge workflow.  After the base of the working
directory is merged and commited, in the working directory:

    $ read-tree <tree-id-of-merged-tree>
    $ show-diff -R

to re-validate if upstream changes make sense, and/or revert or
conflict with local changes you have in the working files.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/show-diff.c b/show-diff.c
index 4235933..4456230 100644 (file)
--- a/show-diff.c
+++ b/show-diff.c
@@ -7,6 +7,8 @@
 
 static char *diff_cmd = "diff -L 'a/%s' -L 'b/%s' ";
 static char *diff_opts = "-p -u";
+static char *diff_arg_forward  = " - '%s'";
+static char *diff_arg_reverse  = " '%s' -";
 
 static void prepare_diff_cmd(void)
 {
@@ -63,12 +65,12 @@ static char *sq_expand(char *src)
 }
 
 static void show_differences(char *name, char *label, void *old_contents,
-                            unsigned long long old_size)
+                            unsigned long long old_size, int reverse)
 {
-       static char *diff_arg = " - '%s'";
        FILE *f;
        char *name_sq = sq_expand(name);
        char *label_sq = (name != label) ? sq_expand(label) : name_sq;
+       char *diff_arg = reverse ? diff_arg_reverse : diff_arg_forward;
        int cmd_size = strlen(name_sq) + strlen(label_sq) * 2 +
                strlen(diff_cmd) + strlen(diff_opts) + strlen(diff_arg);
        char *cmd = malloc(cmd_size);
@@ -88,7 +90,7 @@ static void show_differences(char *name, char *label, void *old_contents,
        free(cmd);
 }
 
-static void show_diff_empty(struct cache_entry *ce)
+static void show_diff_empty(struct cache_entry *ce, int reverse)
 {
        char *old;
        unsigned long int size;
@@ -100,7 +102,7 @@ static void show_diff_empty(struct cache_entry *ce)
                      sha1_to_hex(ce->sha1));
                return;
        }
-       show_differences("/dev/null", ce->name, old, size);
+       show_differences("/dev/null", ce->name, old, size, reverse);
 }
 
 static const char *show_diff_usage = "show-diff [-q] [-s] [-z] [paths...]";
@@ -125,11 +127,14 @@ int main(int argc, char **argv)
        int silent = 0;
        int silent_on_nonexisting_files = 0;
        int machine_readable = 0;
+       int reverse = 0;
        int entries = read_cache();
        int i;
 
        while (1 < argc && argv[1][0] == '-') {
-               if (!strcmp(argv[1], "-s"))
+               if  (!strcmp(argv[1], "-R"))
+                       reverse = 1;
+               else if (!strcmp(argv[1], "-s"))
                        silent_on_nonexisting_files = silent = 1;
                else if (!strcmp(argv[1], "-q"))
                        silent_on_nonexisting_files = 1;
@@ -181,7 +186,7 @@ int main(int argc, char **argv)
                        else {
                                printf("%s: %s\n", ce->name, strerror(errno));
                                if (errno == ENOENT)
-                                       show_diff_empty(ce);
+                                       show_diff_empty(ce, reverse);
                        }
                        continue;
                }
@@ -202,7 +207,8 @@ int main(int argc, char **argv)
                        error("unable to read blob object for %s (%s)",
                              ce->name, sha1_to_hex(ce->sha1));
                else
-                       show_differences(ce->name, ce->name, old, size);
+                       show_differences(ce->name, ce->name, old, size,
+                                        reverse);
                free(old);
        }
        return 0;