setup_git_directory: delay core.bare/core.worktree errors
[gitweb.git] / tree-diff.c
index 11c3550177dbaab30596be2fc3c1633f2a0485f8..e7b378c8b2c8f145519410bb17811bf60eb29384 100644 (file)
 #include "diffcore.h"
 #include "tree.h"
 
-static void show_entry(struct diff_options *opt, const char *prefix,
-                      struct tree_desc *desc, struct strbuf *base);
+/*
+ * internal mode marker, saying a tree entry != entry of tp[imin]
+ * (see ll_diff_tree_paths for what it means there)
+ *
+ * we will update/use/emit entry for diff only with it unset.
+ */
+#define S_IFXMIN_NEQ   S_DIFFTREE_IFXMIN_NEQ
 
-static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2,
-                             struct strbuf *base, struct diff_options *opt)
-{
-       unsigned mode1, mode2;
-       const char *path1, *path2;
-       const unsigned char *sha1, *sha2;
-       int cmp, pathlen1, pathlen2;
-       int old_baselen = base->len;
 
-       sha1 = tree_entry_extract(t1, &path1, &mode1);
-       sha2 = tree_entry_extract(t2, &path2, &mode2);
+static struct combine_diff_path *ll_diff_tree_paths(
+       struct combine_diff_path *p, const unsigned char *sha1,
+       const unsigned char **parents_sha1, int nparent,
+       struct strbuf *base, struct diff_options *opt);
+static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
+                            struct strbuf *base, struct diff_options *opt);
+
+/*
+ * Compare two tree entries, taking into account only path/S_ISDIR(mode),
+ * but not their sha1's.
+ *
+ * NOTE files and directories *always* compare differently, even when having
+ *      the same name - thanks to base_name_compare().
+ *
+ * NOTE empty (=invalid) descriptor(s) take part in comparison as +infty,
+ *      so that they sort *after* valid tree entries.
+ *
+ *      Due to this convention, if trees are scanned in sorted order, all
+ *      non-empty descriptors will be processed first.
+ */
+static int tree_entry_pathcmp(struct tree_desc *t1, struct tree_desc *t2)
+{
+       struct name_entry *e1, *e2;
+       int cmp;
 
-       pathlen1 = tree_entry_len(&t1->entry);
-       pathlen2 = tree_entry_len(&t2->entry);
-       cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
-       if (cmp < 0) {
-               show_entry(opt, "-", t1, base);
+       /* empty descriptors sort after valid tree entries */
+       if (!t1->size)
+               return t2->size ? 1 : 0;
+       else if (!t2->size)
                return -1;
-       }
-       if (cmp > 0) {
-               show_entry(opt, "+", t2, base);
-               return 1;
-       }
-       if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER) && !hashcmp(sha1, sha2) && mode1 == mode2)
-               return 0;
 
-       /*
-        * If the filemode has changed to/from a directory from/to a regular
-        * file, we need to consider it a remove and an add.
-        */
-       if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
-               show_entry(opt, "-", t1, base);
-               show_entry(opt, "+", t2, base);
-               return 0;
-       }
+       e1 = &t1->entry;
+       e2 = &t2->entry;
+       cmp = base_name_compare(e1->path, tree_entry_len(e1), e1->mode,
+                               e2->path, tree_entry_len(e2), e2->mode);
+       return cmp;
+}
 
-       strbuf_add(base, path1, pathlen1);
-       if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode1)) {
-               if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
-                       opt->change(opt, mode1, mode2,
-                                   sha1, sha2, 1, 1, base->buf, 0, 0);
+
+/*
+ * convert path -> opt->diff_*() callbacks
+ *
+ * emits diff to first parent only, and tells diff tree-walker that we are done
+ * with p and it can be freed.
+ */
+static int emit_diff_first_parent_only(struct diff_options *opt, struct combine_diff_path *p)
+{
+       struct combine_diff_parent *p0 = &p->parent[0];
+       if (p->mode && p0->mode) {
+               opt->change(opt, p0->mode, p->mode, p0->sha1, p->sha1,
+                       1, 1, p->path, 0, 0);
+       }
+       else {
+               const unsigned char *sha1;
+               unsigned int mode;
+               int addremove;
+
+               if (p->mode) {
+                       addremove = '+';
+                       sha1 = p->sha1;
+                       mode = p->mode;
+               } else {
+                       addremove = '-';
+                       sha1 = p0->sha1;
+                       mode = p0->mode;
                }
-               strbuf_addch(base, '/');
-               diff_tree_sha1(sha1, sha2, base->buf, opt);
-       } else {
-               opt->change(opt, mode1, mode2, sha1, sha2, 1, 1, base->buf, 0, 0);
+
+               opt->add_remove(opt, addremove, mode, sha1, 1, p->path, 0);
        }
-       strbuf_setlen(base, old_baselen);
-       return 0;
+
+       return 0;       /* we are done with p */
 }
 
-/* A whole sub-tree went away or appeared */
-static void show_tree(struct diff_options *opt, const char *prefix,
-                     struct tree_desc *desc, struct strbuf *base)
+
+/*
+ * Make a new combine_diff_path from path/mode/sha1
+ * and append it to paths list tail.
+ *
+ * Memory for created elements could be reused:
+ *
+ *     - if last->next == NULL, the memory is allocated;
+ *
+ *     - if last->next != NULL, it is assumed that p=last->next was returned
+ *       earlier by this function, and p->next was *not* modified.
+ *       The memory is then reused from p.
+ *
+ * so for clients,
+ *
+ * - if you do need to keep the element
+ *
+ *     p = path_appendnew(p, ...);
+ *     process(p);
+ *     p->next = NULL;
+ *
+ * - if you don't need to keep the element after processing
+ *
+ *     pprev = p;
+ *     p = path_appendnew(p, ...);
+ *     process(p);
+ *     p = pprev;
+ *     ; don't forget to free tail->next in the end
+ *
+ * p->parent[] remains uninitialized.
+ */
+static struct combine_diff_path *path_appendnew(struct combine_diff_path *last,
+       int nparent, const struct strbuf *base, const char *path, int pathlen,
+       unsigned mode, const unsigned char *sha1)
 {
-       enum interesting match = entry_not_interesting;
-       for (; desc->size; update_tree_entry(desc)) {
-               if (match != all_entries_interesting) {
-                       match = tree_entry_interesting(&desc->entry, base, 0,
-                                                      &opt->pathspec);
-                       if (match == all_entries_not_interesting)
-                               break;
-                       if (match == entry_not_interesting)
-                               continue;
-               }
-               show_entry(opt, prefix, desc, base);
+       struct combine_diff_path *p;
+       int len = base->len + pathlen;
+       int alloclen = combine_diff_path_size(nparent, len);
+
+       /* if last->next is !NULL - it is a pre-allocated memory, we can reuse */
+       p = last->next;
+       if (p && (alloclen > (intptr_t)p->next)) {
+               free(p);
+               p = NULL;
+       }
+
+       if (!p) {
+               p = xmalloc(alloclen);
+
+               /*
+                * until we go to it next round, .next holds how many bytes we
+                * allocated (for faster realloc - we don't need copying old data).
+                */
+               p->next = (struct combine_diff_path *)(intptr_t)alloclen;
        }
+
+       last->next = p;
+
+       p->path = (char *)&(p->parent[nparent]);
+       memcpy(p->path, base->buf, base->len);
+       memcpy(p->path + base->len, path, pathlen);
+       p->path[len] = 0;
+       p->mode = mode;
+       hashcpy(p->sha1, sha1 ? sha1 : null_sha1);
+
+       return p;
 }
 
-/* A file entry went away or appeared */
-static void show_entry(struct diff_options *opt, const char *prefix,
-                      struct tree_desc *desc, struct strbuf *base)
+/*
+ * new path should be added to combine diff
+ *
+ * 3 cases on how/when it should be called and behaves:
+ *
+ *      t, !tp         -> path added, all parents lack it
+ *     !t,  tp         -> path removed from all parents
+ *      t,  tp         -> path modified/added
+ *                        (M for tp[i]=tp[imin], A otherwise)
+ */
+static struct combine_diff_path *emit_path(struct combine_diff_path *p,
+       struct strbuf *base, struct diff_options *opt, int nparent,
+       struct tree_desc *t, struct tree_desc *tp,
+       int imin)
 {
        unsigned mode;
        const char *path;
-       const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
-       int pathlen = tree_entry_len(&desc->entry);
+       const unsigned char *sha1;
+       int pathlen;
        int old_baselen = base->len;
+       int i, isdir, recurse = 0, emitthis = 1;
+
+       /* at least something has to be valid */
+       assert(t || tp);
 
-       strbuf_add(base, path, pathlen);
-       if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
-               enum object_type type;
-               struct tree_desc inner;
-               void *tree;
-               unsigned long size;
+       if (t) {
+               /* path present in resulting tree */
+               sha1 = tree_entry_extract(t, &path, &mode);
+               pathlen = tree_entry_len(&t->entry);
+               isdir = S_ISDIR(mode);
+       } else {
+               /*
+                * a path was removed - take path from imin parent. Also take
+                * mode from that parent, to decide on recursion(1).
+                *
+                * 1) all modes for tp[i]=tp[imin] should be the same wrt
+                *    S_ISDIR, thanks to base_name_compare().
+                */
+               tree_entry_extract(&tp[imin], &path, &mode);
+               pathlen = tree_entry_len(&tp[imin].entry);
 
-               tree = read_sha1_file(sha1, &type, &size);
-               if (!tree || type != OBJ_TREE)
-                       die("corrupt tree sha %s", sha1_to_hex(sha1));
+               isdir = S_ISDIR(mode);
+               sha1 = NULL;
+               mode = 0;
+       }
 
-               if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE))
-                       opt->add_remove(opt, *prefix, mode, sha1, 1, base->buf, 0);
+       if (DIFF_OPT_TST(opt, RECURSIVE) && isdir) {
+               recurse = 1;
+               emitthis = DIFF_OPT_TST(opt, TREE_IN_RECURSIVE);
+       }
 
-               strbuf_addch(base, '/');
+       if (emitthis) {
+               int keep;
+               struct combine_diff_path *pprev = p;
+               p = path_appendnew(p, nparent, base, path, pathlen, mode, sha1);
 
-               init_tree_desc(&inner, tree, size);
-               show_tree(opt, prefix, &inner, base);
-               free(tree);
-       } else
-               opt->add_remove(opt, prefix[0], mode, sha1, 1, base->buf, 0);
+               for (i = 0; i < nparent; ++i) {
+                       /*
+                        * tp[i] is valid, if present and if tp[i]==tp[imin] -
+                        * otherwise, we should ignore it.
+                        */
+                       int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
+
+                       const unsigned char *sha1_i;
+                       unsigned mode_i;
+
+                       p->parent[i].status =
+                               !t ? DIFF_STATUS_DELETED :
+                                       tpi_valid ?
+                                               DIFF_STATUS_MODIFIED :
+                                               DIFF_STATUS_ADDED;
+
+                       if (tpi_valid) {
+                               sha1_i = tp[i].entry.sha1;
+                               mode_i = tp[i].entry.mode;
+                       }
+                       else {
+                               sha1_i = NULL;
+                               mode_i = 0;
+                       }
+
+                       p->parent[i].mode = mode_i;
+                       hashcpy(p->parent[i].sha1, sha1_i ? sha1_i : null_sha1);
+               }
+
+               keep = 1;
+               if (opt->pathchange)
+                       keep = opt->pathchange(opt, p);
+
+               /*
+                * If a path was filtered or consumed - we don't need to add it
+                * to the list and can reuse its memory, leaving it as
+                * pre-allocated element on the tail.
+                *
+                * On the other hand, if path needs to be kept, we need to
+                * correct its .next to NULL, as it was pre-initialized to how
+                * much memory was allocated.
+                *
+                * see path_appendnew() for details.
+                */
+               if (!keep)
+                       p = pprev;
+               else
+                       p->next = NULL;
+       }
+
+       if (recurse) {
+               const unsigned char **parents_sha1;
+
+               parents_sha1 = xalloca(nparent * sizeof(parents_sha1[0]));
+               for (i = 0; i < nparent; ++i) {
+                       /* same rule as in emitthis */
+                       int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
+
+                       parents_sha1[i] = tpi_valid ? tp[i].entry.sha1
+                                                   : NULL;
+               }
+
+               strbuf_add(base, path, pathlen);
+               strbuf_addch(base, '/');
+               p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
+               xalloca_free(parents_sha1);
+       }
 
        strbuf_setlen(base, old_baselen);
+       return p;
 }
 
 static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
-                              struct diff_options *opt,
-                              enum interesting *match)
+                              struct diff_options *opt)
 {
+       enum interesting match;
+
        while (t->size) {
-               *match = tree_entry_interesting(&t->entry, base, 0, &opt->pathspec);
-               if (*match) {
-                       if (*match == all_entries_not_interesting)
+               match = tree_entry_interesting(&t->entry, base, 0, &opt->pathspec);
+               if (match) {
+                       if (match == all_entries_not_interesting)
                                t->size = 0;
                        break;
                }
@@ -128,55 +300,260 @@ static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
        }
 }
 
-int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
-             const char *base_str, struct diff_options *opt)
+
+/*
+ * generate paths for combined diff D(sha1,parents_sha1[])
+ *
+ * Resulting paths are appended to combine_diff_path linked list, and also, are
+ * emitted on the go via opt->pathchange() callback, so it is possible to
+ * process the result as batch or incrementally.
+ *
+ * The paths are generated scanning new tree and all parents trees
+ * simultaneously, similarly to what diff_tree() was doing for 2 trees.
+ * The theory behind such scan is as follows:
+ *
+ *
+ * D(T,P1...Pn) calculation scheme
+ * -------------------------------
+ *
+ * D(T,P1...Pn) = D(T,P1) ^ ... ^ D(T,Pn)      (regarding resulting paths set)
+ *
+ *     D(T,Pj)         - diff between T..Pj
+ *     D(T,P1...Pn)    - combined diff from T to parents P1,...,Pn
+ *
+ *
+ * We start from all trees, which are sorted, and compare their entries in
+ * lock-step:
+ *
+ *      T     P1       Pn
+ *      -     -        -
+ *     |t|   |p1|     |pn|
+ *     |-|   |--| ... |--|      imin = argmin(p1...pn)
+ *     | |   |  |     |  |
+ *     |-|   |--|     |--|
+ *     |.|   |. |     |. |
+ *      .     .        .
+ *      .     .        .
+ *
+ * at any time there could be 3 cases:
+ *
+ *     1)  t < p[imin];
+ *     2)  t > p[imin];
+ *     3)  t = p[imin].
+ *
+ * Schematic deduction of what every case means, and what to do, follows:
+ *
+ * 1)  t < p[imin]  ->  ∀j t ∉ Pj  ->  "+t" ∈ D(T,Pj)  ->  D += "+t";  t↓
+ *
+ * 2)  t > p[imin]
+ *
+ *     2.1) ∃j: pj > p[imin]  ->  "-p[imin]" ∉ D(T,Pj)  ->  D += ø;  ∀ pi=p[imin]  pi↓
+ *     2.2) ∀i  pi = p[imin]  ->  pi ∉ T  ->  "-pi" ∈ D(T,Pi)  ->  D += "-p[imin]";  ∀i pi↓
+ *
+ * 3)  t = p[imin]
+ *
+ *     3.1) ∃j: pj > p[imin]  ->  "+t" ∈ D(T,Pj)  ->  only pi=p[imin] remains to investigate
+ *     3.2) pi = p[imin]  ->  investigate δ(t,pi)
+ *      |
+ *      |
+ *      v
+ *
+ *     3.1+3.2) looking at δ(t,pi) ∀i: pi=p[imin] - if all != ø  ->
+ *
+ *                       ⎧δ(t,pi)  - if pi=p[imin]
+ *              ->  D += ⎨
+ *                       ⎩"+t"     - if pi>p[imin]
+ *
+ *
+ *     in any case t↓  ∀ pi=p[imin]  pi↓
+ *
+ *
+ * ~~~~~~~~
+ *
+ * NOTE
+ *
+ *     Usual diff D(A,B) is by definition the same as combined diff D(A,[B]),
+ *     so this diff paths generator can, and is used, for plain diffs
+ *     generation too.
+ *
+ *     Please keep attention to the common D(A,[B]) case when working on the
+ *     code, in order not to slow it down.
+ *
+ * NOTE
+ *     nparent must be > 0.
+ */
+
+
+/* ∀ pi=p[imin]  pi↓ */
+static inline void update_tp_entries(struct tree_desc *tp, int nparent)
 {
-       struct strbuf base;
-       int baselen = strlen(base_str);
-       enum interesting t1_match = entry_not_interesting;
-       enum interesting t2_match = entry_not_interesting;
+       int i;
+       for (i = 0; i < nparent; ++i)
+               if (!(tp[i].entry.mode & S_IFXMIN_NEQ))
+                       update_tree_entry(&tp[i]);
+}
+
+static struct combine_diff_path *ll_diff_tree_paths(
+       struct combine_diff_path *p, const unsigned char *sha1,
+       const unsigned char **parents_sha1, int nparent,
+       struct strbuf *base, struct diff_options *opt)
+{
+       struct tree_desc t, *tp;
+       void *ttree, **tptree;
+       int i;
+
+       tp     = xalloca(nparent * sizeof(tp[0]));
+       tptree = xalloca(nparent * sizeof(tptree[0]));
+
+       /*
+        * load parents first, as they are probably already cached.
+        *
+        * ( log_tree_diff() parses commit->parent before calling here via
+        *   diff_tree_sha1(parent, commit) )
+        */
+       for (i = 0; i < nparent; ++i)
+               tptree[i] = fill_tree_descriptor(&tp[i], parents_sha1[i]);
+       ttree = fill_tree_descriptor(&t, sha1);
 
        /* Enable recursion indefinitely */
        opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);
 
-       strbuf_init(&base, PATH_MAX);
-       strbuf_add(&base, base_str, baselen);
-
        for (;;) {
+               int imin, cmp;
+
                if (diff_can_quit_early(opt))
                        break;
+
                if (opt->pathspec.nr) {
-                       skip_uninteresting(t1, &base, opt, &t1_match);
-                       skip_uninteresting(t2, &base, opt, &t2_match);
+                       skip_uninteresting(&t, base, opt);
+                       for (i = 0; i < nparent; i++)
+                               skip_uninteresting(&tp[i], base, opt);
                }
-               if (!t1->size) {
-                       if (!t2->size)
+
+               /* comparing is finished when all trees are done */
+               if (!t.size) {
+                       int done = 1;
+                       for (i = 0; i < nparent; ++i)
+                               if (tp[i].size) {
+                                       done = 0;
+                                       break;
+                               }
+                       if (done)
                                break;
-                       show_entry(opt, "+", t2, &base);
-                       update_tree_entry(t2);
-                       continue;
                }
-               if (!t2->size) {
-                       show_entry(opt, "-", t1, &base);
-                       update_tree_entry(t1);
-                       continue;
+
+               /*
+                * lookup imin = argmin(p1...pn),
+                * mark entries whether they =p[imin] along the way
+                */
+               imin = 0;
+               tp[0].entry.mode &= ~S_IFXMIN_NEQ;
+
+               for (i = 1; i < nparent; ++i) {
+                       cmp = tree_entry_pathcmp(&tp[i], &tp[imin]);
+                       if (cmp < 0) {
+                               imin = i;
+                               tp[i].entry.mode &= ~S_IFXMIN_NEQ;
+                       }
+                       else if (cmp == 0) {
+                               tp[i].entry.mode &= ~S_IFXMIN_NEQ;
+                       }
+                       else {
+                               tp[i].entry.mode |= S_IFXMIN_NEQ;
+                       }
+               }
+
+               /* fixup markings for entries before imin */
+               for (i = 0; i < imin; ++i)
+                       tp[i].entry.mode |= S_IFXMIN_NEQ;       /* pi > p[imin] */
+
+
+
+               /* compare t vs p[imin] */
+               cmp = tree_entry_pathcmp(&t, &tp[imin]);
+
+               /* t = p[imin] */
+               if (cmp == 0) {
+                       /* are either pi > p[imin] or diff(t,pi) != ø ? */
+                       if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER)) {
+                               for (i = 0; i < nparent; ++i) {
+                                       /* p[i] > p[imin] */
+                                       if (tp[i].entry.mode & S_IFXMIN_NEQ)
+                                               continue;
+
+                                       /* diff(t,pi) != ø */
+                                       if (hashcmp(t.entry.sha1, tp[i].entry.sha1) ||
+                                           (t.entry.mode != tp[i].entry.mode))
+                                               continue;
+
+                                       goto skip_emit_t_tp;
+                               }
+                       }
+
+                       /* D += {δ(t,pi) if pi=p[imin];  "+a" if pi > p[imin]} */
+                       p = emit_path(p, base, opt, nparent,
+                                       &t, tp, imin);
+
+               skip_emit_t_tp:
+                       /* t↓,  ∀ pi=p[imin]  pi↓ */
+                       update_tree_entry(&t);
+                       update_tp_entries(tp, nparent);
+               }
+
+               /* t < p[imin] */
+               else if (cmp < 0) {
+                       /* D += "+t" */
+                       p = emit_path(p, base, opt, nparent,
+                                       &t, /*tp=*/NULL, -1);
+
+                       /* t↓ */
+                       update_tree_entry(&t);
                }
-               switch (compare_tree_entry(t1, t2, &base, opt)) {
-               case -1:
-                       update_tree_entry(t1);
-                       continue;
-               case 0:
-                       update_tree_entry(t1);
-                       /* Fallthrough */
-               case 1:
-                       update_tree_entry(t2);
-                       continue;
+
+               /* t > p[imin] */
+               else {
+                       /* ∀i pi=p[imin] -> D += "-p[imin]" */
+                       if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER)) {
+                               for (i = 0; i < nparent; ++i)
+                                       if (tp[i].entry.mode & S_IFXMIN_NEQ)
+                                               goto skip_emit_tp;
+                       }
+
+                       p = emit_path(p, base, opt, nparent,
+                                       /*t=*/NULL, tp, imin);
+
+               skip_emit_tp:
+                       /* ∀ pi=p[imin]  pi↓ */
+                       update_tp_entries(tp, nparent);
                }
-               die("git diff-tree: internal error");
        }
 
-       strbuf_release(&base);
-       return 0;
+       free(ttree);
+       for (i = nparent-1; i >= 0; i--)
+               free(tptree[i]);
+       xalloca_free(tptree);
+       xalloca_free(tp);
+
+       return p;
+}
+
+struct combine_diff_path *diff_tree_paths(
+       struct combine_diff_path *p, const unsigned char *sha1,
+       const unsigned char **parents_sha1, int nparent,
+       struct strbuf *base, struct diff_options *opt)
+{
+       p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
+
+       /*
+        * free pre-allocated last element, if any
+        * (see path_appendnew() for details about why)
+        */
+       if (p->next) {
+               free(p->next);
+               p->next = NULL;
+       }
+
+       return p;
 }
 
 /*
@@ -190,7 +567,7 @@ static inline int diff_might_be_rename(void)
                !DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
 }
 
-static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
+static void try_to_follow_renames(const unsigned char *old, const unsigned char *new, struct strbuf *base, struct diff_options *opt)
 {
        struct diff_options diff_opts;
        struct diff_queue_struct *q = &diff_queued_diff;
@@ -228,7 +605,7 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
        diff_opts.break_opt = opt->break_opt;
        diff_opts.rename_score = opt->rename_score;
        diff_setup_done(&diff_opts);
-       diff_tree(t1, t2, base, &diff_opts);
+       ll_diff_tree_sha1(old, new, base, &diff_opts);
        diffcore_std(&diff_opts);
        free_pathspec(&diff_opts.pathspec);
 
@@ -287,25 +664,40 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
        q->nr = 1;
 }
 
-int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
+static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
+                            struct strbuf *base, struct diff_options *opt)
 {
-       void *tree1, *tree2;
-       struct tree_desc t1, t2;
-       unsigned long size1, size2;
-       int retval;
+       struct combine_diff_path phead, *p;
+       pathchange_fn_t pathchange_old = opt->pathchange;
 
-       tree1 = fill_tree_descriptor(&t1, old);
-       tree2 = fill_tree_descriptor(&t2, new);
-       size1 = t1.size;
-       size2 = t2.size;
-       retval = diff_tree(&t1, &t2, base, opt);
-       if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
-               init_tree_desc(&t1, tree1, size1);
-               init_tree_desc(&t2, tree2, size2);
-               try_to_follow_renames(&t1, &t2, base, opt);
+       phead.next = NULL;
+       opt->pathchange = emit_diff_first_parent_only;
+       diff_tree_paths(&phead, new, &old, 1, base, opt);
+
+       for (p = phead.next; p;) {
+               struct combine_diff_path *pprev = p;
+               p = p->next;
+               free(pprev);
        }
-       free(tree1);
-       free(tree2);
+
+       opt->pathchange = pathchange_old;
+       return 0;
+}
+
+int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base_str, struct diff_options *opt)
+{
+       struct strbuf base;
+       int retval;
+
+       strbuf_init(&base, PATH_MAX);
+       strbuf_addstr(&base, base_str);
+
+       retval = ll_diff_tree_sha1(old, new, &base, opt);
+       if (!*base_str && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename())
+               try_to_follow_renames(old, new, &base, opt);
+
+       strbuf_release(&base);
+
        return retval;
 }