git-blame: refactor code to emit "porcelain format" output
[gitweb.git] / diff-lib.c
index d85d8f34ba055ad7e02bf5d61ae4a675ce0be1d3..ae96c64ca209f4df9008198e8a04b160bed618c7 100644 (file)
 #include "diffcore.h"
 #include "revision.h"
 #include "cache-tree.h"
-#include "path-list.h"
+#include "unpack-trees.h"
+#include "refs.h"
 
 /*
  * diff-files
  */
 
-static int read_directory(const char *path, struct path_list *list)
-{
-       DIR *dir;
-       struct dirent *e;
-
-       if (!(dir = opendir(path)))
-               return error("Could not open directory %s", path);
-
-       while ((e = readdir(dir)))
-               if (strcmp(".", e->d_name) && strcmp("..", e->d_name))
-                       path_list_insert(e->d_name, list);
-
-       closedir(dir);
-       return 0;
-}
-
-static int get_mode(const char *path, int *mode)
-{
-       struct stat st;
-
-       if (!path || !strcmp(path, "/dev/null"))
-               *mode = 0;
-       else if (!strcmp(path, "-"))
-               *mode = ntohl(create_ce_mode(0666));
-       else if (stat(path, &st))
-               return error("Could not access '%s'", path);
-       else
-               *mode = st.st_mode;
-       return 0;
-}
-
-static int queue_diff(struct diff_options *o,
-               const char *name1, const char *name2)
-{
-       int mode1 = 0, mode2 = 0;
-
-       if (get_mode(name1, &mode1) || get_mode(name2, &mode2))
-               return -1;
-
-       if (mode1 && mode2 && S_ISDIR(mode1) != S_ISDIR(mode2))
-               return error("file/directory conflict: %s, %s", name1, name2);
-
-       if (S_ISDIR(mode1) || S_ISDIR(mode2)) {
-               char buffer1[PATH_MAX], buffer2[PATH_MAX];
-               struct path_list p1 = {NULL, 0, 0, 1}, p2 = {NULL, 0, 0, 1};
-               int len1 = 0, len2 = 0, i1, i2, ret = 0;
-
-               if (name1 && read_directory(name1, &p1))
-                       return -1;
-               if (name2 && read_directory(name2, &p2)) {
-                       path_list_clear(&p1, 0);
-                       return -1;
-               }
-
-               if (name1) {
-                       len1 = strlen(name1);
-                       if (len1 > 0 && name1[len1 - 1] == '/')
-                               len1--;
-                       memcpy(buffer1, name1, len1);
-                       buffer1[len1++] = '/';
-               }
-
-               if (name2) {
-                       len2 = strlen(name2);
-                       if (len2 > 0 && name2[len2 - 1] == '/')
-                               len2--;
-                       memcpy(buffer2, name2, len2);
-                       buffer2[len2++] = '/';
-               }
-
-               for (i1 = i2 = 0; !ret && (i1 < p1.nr || i2 < p2.nr); ) {
-                       const char *n1, *n2;
-                       int comp;
-
-                       if (i1 == p1.nr)
-                               comp = 1;
-                       else if (i2 == p2.nr)
-                               comp = -1;
-                       else
-                               comp = strcmp(p1.items[i1].path,
-                                       p2.items[i2].path);
-
-                       if (comp > 0)
-                               n1 = NULL;
-                       else {
-                               n1 = buffer1;
-                               strncpy(buffer1 + len1, p1.items[i1++].path,
-                                               PATH_MAX - len1);
-                       }
-
-                       if (comp < 0)
-                               n2 = NULL;
-                       else {
-                               n2 = buffer2;
-                               strncpy(buffer2 + len2, p2.items[i2++].path,
-                                               PATH_MAX - len2);
-                       }
-
-                       ret = queue_diff(o, n1, n2);
-               }
-               path_list_clear(&p1, 0);
-               path_list_clear(&p2, 0);
-
-               return ret;
-       } else {
-               struct diff_filespec *d1, *d2;
-
-               if (DIFF_OPT_TST(o, REVERSE_DIFF)) {
-                       unsigned tmp;
-                       const char *tmp_c;
-                       tmp = mode1; mode1 = mode2; mode2 = tmp;
-                       tmp_c = name1; name1 = name2; name2 = tmp_c;
-               }
-
-               if (!name1)
-                       name1 = "/dev/null";
-               if (!name2)
-                       name2 = "/dev/null";
-               d1 = alloc_filespec(name1);
-               d2 = alloc_filespec(name2);
-               fill_filespec(d1, null_sha1, mode1);
-               fill_filespec(d2, null_sha1, mode2);
-
-               diff_queue(&diff_queued_diff, d1, d2);
-               return 0;
-       }
-}
-
 /*
- * Does the path name a blob in the working tree, or a directory
- * in the working tree?
+ * Has the work tree entity been removed?
+ *
+ * Return 1 if it was removed from the work tree, 0 if an entity to be
+ * compared with the cache entry ce still exists (the latter includes
+ * the case where a directory that is not a submodule repository
+ * exists for ce that is a submodule -- it is a submodule that is not
+ * checked out).  Return negative for an error.
  */
-static int is_in_index(const char *path)
+static int check_removed(const struct cache_entry *ce, struct stat *st)
 {
-       int len, pos;
-       struct cache_entry *ce;
-
-       len = strlen(path);
-       while (path[len-1] == '/')
-               len--;
-       if (!len)
-               return 1; /* "." */
-       pos = cache_name_pos(path, len);
-       if (0 <= pos)
+       if (lstat(ce->name, st) < 0) {
+               if (errno != ENOENT && errno != ENOTDIR)
+                       return -1;
                return 1;
-       pos = -1 - pos;
-       while (pos < active_nr) {
-               ce = active_cache[pos++];
-               if (ce_namelen(ce) <= len ||
-                   strncmp(ce->name, path, len) ||
-                   (ce->name[len] > '/'))
-                       break; /* path cannot be a prefix */
-               if (ce->name[len] == '/')
-                       return 1;
-       }
-       return 0;
-}
-
-static int handle_diff_files_args(struct rev_info *revs,
-                                 int argc, const char **argv,
-                                 unsigned int *options)
-{
-       *options = 0;
-
-       /* revs->max_count == -2 means --no-index */
-       while (1 < argc && argv[1][0] == '-') {
-               if (!strcmp(argv[1], "--base"))
-                       revs->max_count = 1;
-               else if (!strcmp(argv[1], "--ours"))
-                       revs->max_count = 2;
-               else if (!strcmp(argv[1], "--theirs"))
-                       revs->max_count = 3;
-               else if (!strcmp(argv[1], "-n") ||
-                               !strcmp(argv[1], "--no-index")) {
-                       revs->max_count = -2;
-                       DIFF_OPT_SET(&revs->diffopt, EXIT_WITH_STATUS);
-                       DIFF_OPT_SET(&revs->diffopt, NO_INDEX);
-               }
-               else if (!strcmp(argv[1], "-q"))
-                       *options |= DIFF_SILENT_ON_REMOVED;
-               else
-                       return error("invalid option: %s", argv[1]);
-               argv++; argc--;
        }
+       if (has_symlink_leading_path(ce_namelen(ce), ce->name))
+               return 1;
+       if (S_ISDIR(st->st_mode)) {
+               unsigned char sub[20];
 
-       if (revs->max_count == -1 && revs->diffopt.nr_paths == 2) {
                /*
-                * If two files are specified, and at least one is untracked,
-                * default to no-index.
+                * If ce is already a gitlink, we can have a plain
+                * directory (i.e. the submodule is not checked out),
+                * or a checked out submodule.  Either case this is not
+                * a case where something was removed from the work tree,
+                * so we will return 0.
+                *
+                * Otherwise, if the directory is not a submodule
+                * repository, that means ce which was a blob turned into
+                * a directory --- the blob was removed!
                 */
-               read_cache();
-               if (!is_in_index(revs->diffopt.paths[0]) ||
-                                       !is_in_index(revs->diffopt.paths[1])) {
-                       revs->max_count = -2;
-                       DIFF_OPT_SET(&revs->diffopt, NO_INDEX);
-               }
-       }
-
-       /*
-        * Make sure there are NO revision (i.e. pending object) parameter,
-        * rev.max_count is reasonable (0 <= n <= 3),
-        * there is no other revision filtering parameters.
-        */
-       if (revs->pending.nr || revs->max_count > 3 ||
-           revs->min_age != -1 || revs->max_age != -1)
-               return error("no revision allowed with diff-files");
-
-       if (revs->max_count == -1 &&
-           (revs->diffopt.output_format & DIFF_FORMAT_PATCH))
-               revs->combine_merges = revs->dense_combined_merges = 1;
-
-       return 0;
-}
-
-static int is_outside_repo(const char *path, int nongit, const char *prefix)
-{
-       int i;
-       if (nongit || !strcmp(path, "-") || is_absolute_path(path))
-               return 1;
-       if (prefixcmp(path, "../"))
-               return 0;
-       if (!prefix)
-               return 1;
-       for (i = strlen(prefix); !prefixcmp(path, "../"); ) {
-               while (i > 0 && prefix[i - 1] != '/')
-                       i--;
-               if (--i < 0)
+               if (!S_ISGITLINK(ce->ce_mode) &&
+                   resolve_gitlink_ref(ce->name, "HEAD", sub))
                        return 1;
-               path += 3;
-       }
-       return 0;
-}
-
-int setup_diff_no_index(struct rev_info *revs,
-               int argc, const char ** argv, int nongit, const char *prefix)
-{
-       int i;
-       for (i = 1; i < argc; i++)
-               if (argv[i][0] != '-' || argv[i][1] == '\0')
-                       break;
-               else if (!strcmp(argv[i], "--")) {
-                       i++;
-                       break;
-               } else if (i < argc - 3 && !strcmp(argv[i], "--no-index")) {
-                       i = argc - 3;
-                       DIFF_OPT_SET(&revs->diffopt, EXIT_WITH_STATUS);
-                       break;
-               }
-       if (argc != i + 2 || (!is_outside_repo(argv[i + 1], nongit, prefix) &&
-                               !is_outside_repo(argv[i], nongit, prefix)))
-               return -1;
-
-       diff_setup(&revs->diffopt);
-       for (i = 1; i < argc - 2; )
-               if (!strcmp(argv[i], "--no-index"))
-                       i++;
-               else {
-                       int j = diff_opt_parse(&revs->diffopt,
-                                       argv + i, argc - i);
-                       if (!j)
-                               die("invalid diff option/value: %s", argv[i]);
-                       i += j;
-               }
-
-       if (prefix) {
-               int len = strlen(prefix);
-
-               revs->diffopt.paths = xcalloc(2, sizeof(char*));
-               for (i = 0; i < 2; i++) {
-                       const char *p = argv[argc - 2 + i];
-                       /*
-                        * stdin should be spelled as '-'; if you have
-                        * path that is '-', spell it as ./-.
-                        */
-                       p = (strcmp(p, "-")
-                            ? xstrdup(prefix_filename(prefix, len, p))
-                            : p);
-                       revs->diffopt.paths[i] = p;
-               }
        }
-       else
-               revs->diffopt.paths = argv + argc - 2;
-       revs->diffopt.nr_paths = 2;
-       DIFF_OPT_SET(&revs->diffopt, NO_INDEX);
-       revs->max_count = -2;
-       if (diff_setup_done(&revs->diffopt) < 0)
-               die("diff_setup_done failed");
        return 0;
 }
 
-int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv)
-{
-       unsigned int options;
-
-       if (handle_diff_files_args(revs, argc, argv, &options))
-               return -1;
-
-       if (DIFF_OPT_TST(&revs->diffopt, NO_INDEX)) {
-               if (revs->diffopt.nr_paths != 2)
-                       return error("need two files/directories with --no-index");
-               if (queue_diff(&revs->diffopt, revs->diffopt.paths[0],
-                               revs->diffopt.paths[1]))
-                       return -1;
-               diffcore_std(&revs->diffopt);
-               diff_flush(&revs->diffopt);
-               /*
-                * The return code for --no-index imitates diff(1):
-                * 0 = no changes, 1 = changes, else error
-                */
-               return revs->diffopt.found_changes;
-       }
-
-       if (read_cache() < 0) {
-               perror("read_cache");
-               return -1;
-       }
-       return run_diff_files(revs, options);
-}
-
 int run_diff_files(struct rev_info *revs, unsigned int option)
 {
        int entries, i;
@@ -340,10 +61,14 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
        int silent_on_removed = option & DIFF_SILENT_ON_REMOVED;
        unsigned ce_option = ((option & DIFF_RACY_IS_MODIFIED)
                              ? CE_MATCH_RACY_IS_DIRTY : 0);
+       char symcache[PATH_MAX];
+
+       diff_set_mnemonic_prefix(&revs->diffopt, "i/", "w/");
 
        if (diff_unmerged_stage < 0)
                diff_unmerged_stage = 2;
        entries = active_nr;
+       symcache[0] = '\0';
        for (i = 0; i < entries; i++) {
                struct stat st;
                unsigned int oldmode, newmode;
@@ -375,16 +100,17 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
                        memset(&(dpath->parent[0]), 0,
                               sizeof(struct combine_diff_parent)*5);
 
-                       if (lstat(ce->name, &st) < 0) {
-                               if (errno != ENOENT && errno != ENOTDIR) {
+                       changed = check_removed(ce, &st);
+                       if (!changed)
+                               dpath->mode = ce_mode_from_stat(ce, st.st_mode);
+                       else {
+                               if (changed < 0) {
                                        perror(ce->name);
                                        continue;
                                }
                                if (silent_on_removed)
                                        continue;
                        }
-                       else
-                               dpath->mode = ntohl(ce_mode_from_stat(ce, st.st_mode));
 
                        while (i < entries) {
                                struct cache_entry *nce = active_cache[i];
@@ -398,10 +124,10 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
                                 */
                                stage = ce_stage(nce);
                                if (2 <= stage) {
-                                       int mode = ntohl(nce->ce_mode);
+                                       int mode = nce->ce_mode;
                                        num_compare_stages++;
                                        hashcpy(dpath->parent[stage-2].sha1, nce->sha1);
-                                       dpath->parent[stage-2].mode = ntohl(ce_mode_from_stat(nce, mode));
+                                       dpath->parent[stage-2].mode = ce_mode_from_stat(nce, mode);
                                        dpath->parent[stage-2].status =
                                                DIFF_STATUS_MODIFIED;
                                }
@@ -435,25 +161,32 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
                                continue;
                }
 
-               if (lstat(ce->name, &st) < 0) {
-                       if (errno != ENOENT && errno != ENOTDIR) {
+               if (ce_uptodate(ce))
+                       continue;
+
+               changed = check_removed(ce, &st);
+               if (changed) {
+                       if (changed < 0) {
                                perror(ce->name);
                                continue;
                        }
                        if (silent_on_removed)
                                continue;
-                       diff_addremove(&revs->diffopt, '-', ntohl(ce->ce_mode),
-                                      ce->sha1, ce->name, NULL);
+                       diff_addremove(&revs->diffopt, '-', ce->ce_mode,
+                                      ce->sha1, ce->name);
                        continue;
                }
                changed = ce_match_stat(ce, &st, ce_option);
-               if (!changed && !DIFF_OPT_TST(&revs->diffopt, FIND_COPIES_HARDER))
-                       continue;
-               oldmode = ntohl(ce->ce_mode);
-               newmode = ntohl(ce_mode_from_stat(ce, st.st_mode));
+               if (!changed) {
+                       ce_mark_uptodate(ce);
+                       if (!DIFF_OPT_TST(&revs->diffopt, FIND_COPIES_HARDER))
+                               continue;
+               }
+               oldmode = ce->ce_mode;
+               newmode = ce_mode_from_stat(ce, st.st_mode);
                diff_change(&revs->diffopt, oldmode, newmode,
                            ce->sha1, (changed ? null_sha1 : ce->sha1),
-                           ce->name, NULL);
+                           ce->name);
 
        }
        diffcore_std(&revs->diffopt);
@@ -465,30 +198,38 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
  * diff-index
  */
 
+struct oneway_unpack_data {
+       struct rev_info *revs;
+       char symcache[PATH_MAX];
+};
+
 /* A file entry went away or appeared */
 static void diff_index_show_file(struct rev_info *revs,
                                 const char *prefix,
                                 struct cache_entry *ce,
-                                unsigned char *sha1, unsigned int mode)
+                                const unsigned char *sha1, unsigned int mode)
 {
-       diff_addremove(&revs->diffopt, prefix[0], ntohl(mode),
-                      sha1, ce->name, NULL);
+       diff_addremove(&revs->diffopt, prefix[0], mode,
+                      sha1, ce->name);
 }
 
 static int get_stat_data(struct cache_entry *ce,
-                        unsigned char **sha1p,
+                        const unsigned char **sha1p,
                         unsigned int *modep,
-                        int cached, int match_missing)
+                        int cached, int match_missing,
+                        struct oneway_unpack_data *cbdata)
 {
-       unsigned char *sha1 = ce->sha1;
+       const unsigned char *sha1 = ce->sha1;
        unsigned int mode = ce->ce_mode;
 
        if (!cached) {
-               static unsigned char no_sha1[20];
                int changed;
                struct stat st;
-               if (lstat(ce->name, &st) < 0) {
-                       if (errno == ENOENT && match_missing) {
+               changed = check_removed(ce, &st);
+               if (changed < 0)
+                       return -1;
+               else if (changed) {
+                       if (match_missing) {
                                *sha1p = sha1;
                                *modep = mode;
                                return 0;
@@ -498,7 +239,7 @@ static int get_stat_data(struct cache_entry *ce,
                changed = ce_match_stat(ce, &st, 0);
                if (changed) {
                        mode = ce_mode_from_stat(ce, st.st_mode);
-                       sha1 = no_sha1;
+                       sha1 = null_sha1;
                }
        }
 
@@ -507,32 +248,35 @@ static int get_stat_data(struct cache_entry *ce,
        return 0;
 }
 
-static void show_new_file(struct rev_info *revs,
+static void show_new_file(struct oneway_unpack_data *cbdata,
                          struct cache_entry *new,
                          int cached, int match_missing)
 {
-       unsigned char *sha1;
+       const unsigned char *sha1;
        unsigned int mode;
+       struct rev_info *revs = cbdata->revs;
 
-       /* New file in the index: it might actually be different in
+       /*
+        * New file in the index: it might actually be different in
         * the working copy.
         */
-       if (get_stat_data(new, &sha1, &mode, cached, match_missing) < 0)
+       if (get_stat_data(new, &sha1, &mode, cached, match_missing, cbdata) < 0)
                return;
 
        diff_index_show_file(revs, "+", new, sha1, mode);
 }
 
-static int show_modified(struct rev_info *revs,
+static int show_modified(struct oneway_unpack_data *cbdata,
                         struct cache_entry *old,
                         struct cache_entry *new,
                         int report_missing,
                         int cached, int match_missing)
 {
        unsigned int mode, oldmode;
-       unsigned char *sha1;
+       const unsigned char *sha1;
+       struct rev_info *revs = cbdata->revs;
 
-       if (get_stat_data(new, &sha1, &mode, cached, match_missing) < 0) {
+       if (get_stat_data(new, &sha1, &mode, cached, match_missing, cbdata) < 0) {
                if (report_missing)
                        diff_index_show_file(revs, "-", old,
                                             old->sha1, old->ce_mode);
@@ -550,14 +294,14 @@ static int show_modified(struct rev_info *revs,
                p->len = pathlen;
                memcpy(p->path, new->name, pathlen);
                p->path[pathlen] = 0;
-               p->mode = ntohl(mode);
+               p->mode = mode;
                hashclr(p->sha1);
                memset(p->parent, 0, 2 * sizeof(struct combine_diff_parent));
                p->parent[0].status = DIFF_STATUS_MODIFIED;
-               p->parent[0].mode = ntohl(new->ce_mode);
+               p->parent[0].mode = new->ce_mode;
                hashcpy(p->parent[0].sha1, new->sha1);
                p->parent[1].status = DIFF_STATUS_MODIFIED;
-               p->parent[1].mode = ntohl(old->ce_mode);
+               p->parent[1].mode = old->ce_mode;
                hashcpy(p->parent[1].sha1, old->sha1);
                show_combined_diff(p, 2, revs->dense_combined_merges, revs);
                free(p);
@@ -569,86 +313,8 @@ static int show_modified(struct rev_info *revs,
            !DIFF_OPT_TST(&revs->diffopt, FIND_COPIES_HARDER))
                return 0;
 
-       mode = ntohl(mode);
-       oldmode = ntohl(oldmode);
-
        diff_change(&revs->diffopt, oldmode, mode,
-                   old->sha1, sha1, old->name, NULL);
-       return 0;
-}
-
-static int diff_cache(struct rev_info *revs,
-                     struct cache_entry **ac, int entries,
-                     const char **pathspec,
-                     int cached, int match_missing)
-{
-       while (entries) {
-               struct cache_entry *ce = *ac;
-               int same = (entries > 1) && ce_same_name(ce, ac[1]);
-
-               if (DIFF_OPT_TST(&revs->diffopt, QUIET) &&
-                       DIFF_OPT_TST(&revs->diffopt, HAS_CHANGES))
-                       break;
-
-               if (!ce_path_match(ce, pathspec))
-                       goto skip_entry;
-
-               switch (ce_stage(ce)) {
-               case 0:
-                       /* No stage 1 entry? That means it's a new file */
-                       if (!same) {
-                               show_new_file(revs, ce, cached, match_missing);
-                               break;
-                       }
-                       /* Show difference between old and new */
-                       show_modified(revs, ac[1], ce, 1,
-                                     cached, match_missing);
-                       break;
-               case 1:
-                       /* No stage 3 (merge) entry?
-                        * That means it's been deleted.
-                        */
-                       if (!same) {
-                               diff_index_show_file(revs, "-", ce,
-                                                    ce->sha1, ce->ce_mode);
-                               break;
-                       }
-                       /* We come here with ce pointing at stage 1
-                        * (original tree) and ac[1] pointing at stage
-                        * 3 (unmerged).  show-modified with
-                        * report-missing set to false does not say the
-                        * file is deleted but reports true if work
-                        * tree does not have it, in which case we
-                        * fall through to report the unmerged state.
-                        * Otherwise, we show the differences between
-                        * the original tree and the work tree.
-                        */
-                       if (!cached &&
-                           !show_modified(revs, ce, ac[1], 0,
-                                          cached, match_missing))
-                               break;
-                       diff_unmerge(&revs->diffopt, ce->name,
-                                    ntohl(ce->ce_mode), ce->sha1);
-                       break;
-               case 3:
-                       diff_unmerge(&revs->diffopt, ce->name,
-                                    0, null_sha1);
-                       break;
-
-               default:
-                       die("impossible cache entry stage");
-               }
-
-skip_entry:
-               /*
-                * Ignore all the different stages for this file,
-                * we've handled the relevant cases now.
-                */
-               do {
-                       ac++;
-                       entries--;
-               } while (entries && ce_same_name(ce, ac[0]));
-       }
+                   old->sha1, sha1, old->name);
        return 0;
 }
 
@@ -664,24 +330,123 @@ static void mark_merge_entries(void)
                struct cache_entry *ce = active_cache[i];
                if (!ce_stage(ce))
                        continue;
-               ce->ce_flags |= htons(CE_STAGEMASK);
+               ce->ce_flags |= CE_STAGEMASK;
        }
 }
 
-int run_diff_index(struct rev_info *revs, int cached)
+/*
+ * This gets a mix of an existing index and a tree, one pathname entry
+ * at a time. The index entry may be a single stage-0 one, but it could
+ * also be multiple unmerged entries (in which case idx_pos/idx_nr will
+ * give you the position and number of entries in the index).
+ */
+static void do_oneway_diff(struct unpack_trees_options *o,
+       struct cache_entry *idx,
+       struct cache_entry *tree)
 {
-       int ret;
-       struct object *ent;
-       struct tree *tree;
-       const char *tree_name;
-       int match_missing = 0;
+       struct oneway_unpack_data *cbdata = o->unpack_data;
+       struct rev_info *revs = cbdata->revs;
+       int match_missing, cached;
 
        /*
         * Backward compatibility wart - "diff-index -m" does
-        * not mean "do not ignore merges", but totally different.
+        * not mean "do not ignore merges", but "match_missing".
+        *
+        * But with the revision flag parsing, that's found in
+        * "!revs->ignore_merges".
+        */
+       cached = o->index_only;
+       match_missing = !revs->ignore_merges;
+
+       if (cached && idx && ce_stage(idx)) {
+               if (tree)
+                       diff_unmerge(&revs->diffopt, idx->name, idx->ce_mode, idx->sha1);
+               return;
+       }
+
+       /*
+        * Something added to the tree?
+        */
+       if (!tree) {
+               show_new_file(cbdata, idx, cached, match_missing);
+               return;
+       }
+
+       /*
+        * Something removed from the tree?
         */
-       if (!revs->ignore_merges)
-               match_missing = 1;
+       if (!idx) {
+               diff_index_show_file(revs, "-", tree, tree->sha1, tree->ce_mode);
+               return;
+       }
+
+       /* Show difference between old and new */
+       show_modified(cbdata, tree, idx, 1, cached, match_missing);
+}
+
+static inline void skip_same_name(struct cache_entry *ce, struct unpack_trees_options *o)
+{
+       int len = ce_namelen(ce);
+       const struct index_state *index = o->src_index;
+
+       while (o->pos < index->cache_nr) {
+               struct cache_entry *next = index->cache[o->pos];
+               if (len != ce_namelen(next))
+                       break;
+               if (memcmp(ce->name, next->name, len))
+                       break;
+               o->pos++;
+       }
+}
+
+/*
+ * The unpack_trees() interface is designed for merging, so
+ * the different source entries are designed primarily for
+ * the source trees, with the old index being really mainly
+ * used for being replaced by the result.
+ *
+ * For diffing, the index is more important, and we only have a
+ * single tree.
+ *
+ * We're supposed to return how many index entries we want to skip.
+ *
+ * This wrapper makes it all more readable, and takes care of all
+ * the fairly complex unpack_trees() semantic requirements, including
+ * the skipping, the path matching, the type conflict cases etc.
+ */
+static int oneway_diff(struct cache_entry **src, struct unpack_trees_options *o)
+{
+       struct cache_entry *idx = src[0];
+       struct cache_entry *tree = src[1];
+       struct oneway_unpack_data *cbdata = o->unpack_data;
+       struct rev_info *revs = cbdata->revs;
+
+       if (idx && ce_stage(idx))
+               skip_same_name(idx, o);
+
+       /*
+        * Unpack-trees generates a DF/conflict entry if
+        * there was a directory in the index and a tree
+        * in the tree. From a diff standpoint, that's a
+        * delete of the tree and a create of the file.
+        */
+       if (tree == o->df_conflict_entry)
+               tree = NULL;
+
+       if (ce_path_match(idx ? idx : tree, revs->prune_data))
+               do_oneway_diff(o, idx, tree);
+
+       return 0;
+}
+
+int run_diff_index(struct rev_info *revs, int cached)
+{
+       struct object *ent;
+       struct tree *tree;
+       const char *tree_name;
+       struct unpack_trees_options opts;
+       struct tree_desc t;
+       struct oneway_unpack_data unpack_cb;
 
        mark_merge_entries();
 
@@ -690,13 +455,26 @@ int run_diff_index(struct rev_info *revs, int cached)
        tree = parse_tree_indirect(ent->sha1);
        if (!tree)
                return error("bad tree object %s", tree_name);
-       if (read_tree(tree, 1, revs->prune_data))
-               return error("unable to read tree object %s", tree_name);
-       ret = diff_cache(revs, active_cache, active_nr, revs->prune_data,
-                        cached, match_missing);
+
+       unpack_cb.revs = revs;
+       unpack_cb.symcache[0] = '\0';
+       memset(&opts, 0, sizeof(opts));
+       opts.head_idx = 1;
+       opts.index_only = cached;
+       opts.merge = 1;
+       opts.fn = oneway_diff;
+       opts.unpack_data = &unpack_cb;
+       opts.src_index = &the_index;
+       opts.dst_index = NULL;
+
+       init_tree_desc(&t, tree->buffer, tree->size);
+       if (unpack_trees(1, &t, &opts))
+               exit(128);
+
+       diff_set_mnemonic_prefix(&revs->diffopt, "c/", cached ? "i/" : "w/");
        diffcore_std(&revs->diffopt);
        diff_flush(&revs->diffopt);
-       return ret;
+       return 0;
 }
 
 int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
@@ -706,6 +484,9 @@ int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
        int i;
        struct cache_entry **dst;
        struct cache_entry *last = NULL;
+       struct unpack_trees_options opts;
+       struct tree_desc t;
+       struct oneway_unpack_data unpack_cb;
 
        /*
         * This is used by git-blame to run diff-cache internally;
@@ -722,8 +503,7 @@ int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
                        cache_tree_invalidate_path(active_cache_tree,
                                                   ce->name);
                        last = ce;
-                       ce->ce_mode = 0;
-                       ce->ce_flags &= ~htons(CE_STAGEMASK);
+                       ce->ce_flags |= CE_REMOVE;
                }
                *dst++ = ce;
        }
@@ -734,8 +514,20 @@ int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
        tree = parse_tree_indirect(tree_sha1);
        if (!tree)
                die("bad tree object %s", sha1_to_hex(tree_sha1));
-       if (read_tree(tree, 1, opt->paths))
-               return error("unable to read tree %s", sha1_to_hex(tree_sha1));
-       return diff_cache(&revs, active_cache, active_nr, revs.prune_data,
-                         1, 0);
+
+       unpack_cb.revs = &revs;
+       unpack_cb.symcache[0] = '\0';
+       memset(&opts, 0, sizeof(opts));
+       opts.head_idx = 1;
+       opts.index_only = 1;
+       opts.merge = 1;
+       opts.fn = oneway_diff;
+       opts.unpack_data = &unpack_cb;
+       opts.src_index = &the_index;
+       opts.dst_index = &the_index;
+
+       init_tree_desc(&t, tree->buffer, tree->size);
+       if (unpack_trees(1, &t, &opts))
+               exit(128);
+       return 0;
 }