+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
#include "cache.h"
-static int unpack(unsigned char *sha1)
+static int stage = 0;
+static int update = 0;
+
+static int unpack_tree(unsigned char *sha1)
{
void *buffer;
unsigned long size;
- char type[20];
+ int ret;
- buffer = read_sha1_file(sha1, type, &size);
+ buffer = read_object_with_reference(sha1, "tree", &size, NULL);
if (!buffer)
- usage("unable to read sha1 file");
- if (strcmp(type, "tree"))
- usage("expected a 'tree' node");
- while (size) {
- int len = strlen(buffer)+1;
- unsigned char *sha1 = buffer + len;
- char *path = strchr(buffer, ' ')+1;
- unsigned int mode;
- if (size < len + 20 || sscanf(buffer, "%o", &mode) != 1)
- usage("corrupt 'tree' file");
- buffer = sha1 + 20;
- size -= len + 20;
- printf("%o %s (%s)\n", mode, path, sha1_to_hex(sha1));
+ return -1;
+ ret = read_tree(buffer, size, stage);
+ free(buffer);
+ return ret;
+}
+
+static int path_matches(struct cache_entry *a, struct cache_entry *b)
+{
+ int len = ce_namelen(a);
+ return ce_namelen(b) == len &&
+ !memcmp(a->name, b->name, len);
+}
+
+static int same(struct cache_entry *a, struct cache_entry *b)
+{
+ return a->ce_mode == b->ce_mode &&
+ !memcmp(a->sha1, b->sha1, 20);
+}
+
+
+/*
+ * This removes all trivial merges that don't change the tree
+ * and collapses them to state 0.
+ */
+static struct cache_entry *merge_entries(struct cache_entry *a,
+ struct cache_entry *b,
+ struct cache_entry *c)
+{
+ /*
+ * Ok, all three entries describe the same
+ * filename, but maybe the contents or file
+ * mode have changed?
+ *
+ * The trivial cases end up being the ones where two
+ * out of three files are the same:
+ * - both destinations the same, trivially take either
+ * - one of the destination versions hasn't changed,
+ * take the other.
+ *
+ * The "all entries exactly the same" case falls out as
+ * a special case of any of the "two same" cases.
+ *
+ * Here "a" is "original", and "b" and "c" are the two
+ * trees we are merging.
+ */
+ if (a && b && c) {
+ if (same(b,c))
+ return c;
+ if (same(a,b))
+ return c;
+ if (same(a,c))
+ return b;
+ }
+ return NULL;
+}
+
+/*
+ * When a CE gets turned into an unmerged entry, we
+ * want it to be up-to-date
+ */
+static void verify_uptodate(struct cache_entry *ce)
+{
+ struct stat st;
+
+ if (!lstat(ce->name, &st)) {
+ unsigned changed = ce_match_stat(ce, &st);
+ if (!changed)
+ return;
+ errno = 0;
+ }
+ if (errno == ENOENT)
+ return;
+ die("Entry '%s' not uptodate. Cannot merge.", ce->name);
+}
+
+/*
+ * If the old tree contained a CE that isn't even in the
+ * result, that's always a problem, regardless of whether
+ * it's up-to-date or not (ie it can be a file that we
+ * have updated but not committed yet).
+ */
+static void reject_merge(struct cache_entry *ce)
+{
+ die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
+}
+
+static int merged_entry_internal(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst, int allow_dirty)
+{
+ merge->ce_flags |= htons(CE_UPDATE);
+ if (old) {
+ /*
+ * See if we can re-use the old CE directly?
+ * That way we get the uptodate stat info.
+ *
+ * This also removes the UPDATE flag on
+ * a match.
+ */
+ if (same(old, merge)) {
+ *merge = *old;
+ } else if (!allow_dirty) {
+ verify_uptodate(old);
+ }
+ }
+ merge->ce_flags &= ~htons(CE_STAGEMASK);
+ *dst++ = merge;
+ return 1;
+}
+
+static int merged_entry_allow_dirty(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
+{
+ return merged_entry_internal(merge, old, dst, 1);
+}
+
+static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
+{
+ return merged_entry_internal(merge, old, dst, 0);
+}
+
+static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
+{
+ if (old)
+ verify_uptodate(old);
+ ce->ce_mode = 0;
+ *dst++ = ce;
+ return 1;
+}
+
+static int causes_df_conflict(struct cache_entry *ce, int stage,
+ struct cache_entry **dst_,
+ struct cache_entry **next_,
+ int tail)
+{
+ /* This is called during the merge operation and walking
+ * the active_cache[] array is messy, because it is in the
+ * middle of overlapping copy operation. The invariants
+ * are:
+ * (1) active_cache points at the first (zeroth) entry.
+ * (2) up to dst pointer are resolved entries.
+ * (3) from the next pointer (head-inclusive) to the tail
+ * of the active_cache array have the remaining paths
+ * to be processed. There can be a gap between dst
+ * and next. Note that next is called "src" in the
+ * merge_cache() function, and tail is the original
+ * end of active_cache array when merge_cache() started.
+ * (4) the path corresponding to *ce is not found in (2)
+ * or (3). It is in the gap.
+ *
+ * active_cache -----......+++++++++++++.
+ * ^dst ^next ^tail
+ */
+ int i, next, dst;
+ const char *path = ce->name;
+ int namelen = ce_namelen(ce);
+
+ next = next_ - active_cache;
+ dst = dst_ - active_cache;
+
+ for (i = 0; i < tail; i++) {
+ int entlen, len;
+ const char *one, *two;
+ if (dst <= i && i < next)
+ continue;
+ ce = active_cache[i];
+ if (ce_stage(ce) != stage)
+ continue;
+ /* If ce->name is a prefix of path, then path is a file
+ * that hangs underneath ce->name, which is bad.
+ * If path is a prefix of ce->name, then it is the
+ * other way around which also is bad.
+ */
+ entlen = ce_namelen(ce);
+ if (namelen == entlen)
+ continue;
+ if (namelen < entlen) {
+ len = namelen;
+ one = path;
+ two = ce->name;
+ } else {
+ len = entlen;
+ one = ce->name;
+ two = path;
+ }
+ if (memcmp(one, two, len))
+ continue;
+ if (two[len] == '/')
+ return 1;
}
return 0;
}
+static int threeway_merge(struct cache_entry *stages[4],
+ struct cache_entry **dst,
+ struct cache_entry **next, int tail)
+{
+ struct cache_entry *old = stages[0];
+ struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
+ struct cache_entry *merge;
+ int count;
+
+ /* #5ALT */
+ if (!a && b && c && same(b, c)) {
+ if (old && !same(b, old))
+ return -1;
+ return merged_entry_allow_dirty(b, old, dst);
+ }
+ /* #2ALT and #3ALT */
+ if (!a && (!!b != !!c)) {
+ /*
+ * The reason we need to worry about directory/file
+ * conflicts only in #2ALT and #3ALT case is this:
+ *
+ * (1) For all other cases that read-tree internally
+ * resolves a path, we always have such a path in
+ * *both* stage2 and stage3 when we begin.
+ * Traditionally, the behaviour has been even
+ * stricter and we did not resolve a path without
+ * initially being in all of stage1, 2, and 3.
+ *
+ * (2) When read-tree finishes, all resolved paths (i.e.
+ * the paths that are in stage0) must have come from
+ * either stage2 or stage3. It is not possible to
+ * have a stage0 path as a result of a merge if
+ * neither stage2 nor stage3 had that path.
+ *
+ * (3) It is guaranteed that just after reading the
+ * stages, each stage cannot have directory/file
+ * conflicts on its own, because they are populated
+ * by reading hierarchy of a tree. Combined with
+ * (1) and (2) above, this means that no matter what
+ * combination of paths we take from stage2 and
+ * stage3 as a result of a merge, they cannot cause
+ * a directory/file conflict situation (otherwise
+ * the "guilty" path would have already had such a
+ * conflict in the original stage, either stage2
+ * or stage3). Although its stage2 is synthesized
+ * by overlaying the current index on top of "our
+ * head" tree, --emu23 case also has this guarantee,
+ * by calling add_cache_entry() to create such stage2
+ * entries.
+ *
+ * (4) Only #2ALT and #3ALT lack the guarantee (1).
+ * They resolve paths that exist only in stage2
+ * or stage3. The stage2 tree may have a file DF
+ * while stage3 tree may have a file DF/DF. If
+ * #2ALT and #3ALT rules happen to apply to both
+ * of them, we would end up having DF (coming from
+ * stage2) and DF/DF (from stage3) in the result.
+ * When we attempt to resolve a path that exists
+ * only in stage2, we need to make sure there is
+ * no path that would conflict with it in stage3
+ * and vice versa.
+ */
+ if (c) { /* #2ALT */
+ if (!causes_df_conflict(c, 2, dst, next, tail) &&
+ (!old || same(c, old)))
+ return merged_entry_allow_dirty(c, old, dst);
+ }
+ else { /* #3ALT */
+ if (!causes_df_conflict(b, 3, dst, next, tail) &&
+ (!old || same(b, old)))
+ return merged_entry_allow_dirty(b, old, dst);
+ }
+ /* otherwise we will apply the original rule */
+ }
+ /* #14ALT */
+ if (a && b && c && same(a, b) && !same(a, c)) {
+ if (old && same(old, c))
+ return merged_entry_allow_dirty(c, old, dst);
+ /* otherwise the regular rule applies */
+ }
+ /*
+ * If we have an entry in the index cache ("old"), then we want
+ * to make sure that it matches any entries in stage 2 ("first
+ * branch", aka "b").
+ */
+ if (old) {
+ if (!b || !same(old, b))
+ return -1;
+ }
+ merge = merge_entries(a, b, c);
+ if (merge)
+ return merged_entry(merge, old, dst);
+ if (old)
+ verify_uptodate(old);
+ count = 0;
+ if (a) { *dst++ = a; count++; }
+ if (b) { *dst++ = b; count++; }
+ if (c) { *dst++ = c; count++; }
+ return count;
+}
+
+/*
+ * Two-way merge.
+ *
+ * The rule is to "carry forward" what is in the index without losing
+ * information across a "fast forward", favoring a successful merge
+ * over a merge failure when it makes sense. For details of the
+ * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
+ *
+ */
+static int twoway_merge(struct cache_entry **src, struct cache_entry **dst,
+ struct cache_entry **next, int tail)
+{
+ struct cache_entry *current = src[0];
+ struct cache_entry *oldtree = src[1], *newtree = src[2];
+
+ if (src[3])
+ return -1;
+
+ if (current) {
+ if ((!oldtree && !newtree) || /* 4 and 5 */
+ (!oldtree && newtree &&
+ same(current, newtree)) || /* 6 and 7 */
+ (oldtree && newtree &&
+ same(oldtree, newtree)) || /* 14 and 15 */
+ (oldtree && newtree &&
+ !same(oldtree, newtree) && /* 18 and 19*/
+ same(current, newtree))) {
+ *dst++ = current;
+ return 1;
+ }
+ else if (oldtree && !newtree && same(current, oldtree)) {
+ /* 10 or 11 */
+ return deleted_entry(oldtree, current, dst);
+ }
+ else if (oldtree && newtree &&
+ same(current, oldtree) && !same(current, newtree)) {
+ /* 20 or 21 */
+ return merged_entry(newtree, current, dst);
+ }
+ else
+ /* all other failures */
+ return -1;
+ }
+ else if (newtree)
+ return merged_entry(newtree, current, dst);
+ else
+ return deleted_entry(oldtree, current, dst);
+}
+
+/*
+ * Two-way merge emulated with three-way merge.
+ *
+ * This treats "read-tree -m H M" by transforming it internally
+ * into "read-tree -m H I+H M", where I+H is a tree that would
+ * contain the contents of the current index file, overlayed on
+ * top of H. Unlike the traditional two-way merge, this leaves
+ * the stages in the resulting index file and lets the user resolve
+ * the merge conflicts using standard tools for three-way merge.
+ *
+ * This function is just to set-up such an arrangement, and the
+ * actual merge uses threeway_merge() function.
+ */
+static void setup_emu23(void)
+{
+ /* stage0 contains I, stage1 H, stage2 M.
+ * move stage2 to stage3, and create stage2 entries
+ * by scanning stage0 and stage1 entries.
+ */
+ int i, namelen, size;
+ struct cache_entry *ce, *stage2;
+
+ for (i = 0; i < active_nr; i++) {
+ ce = active_cache[i];
+ if (ce_stage(ce) != 2)
+ continue;
+ /* hoist them up to stage 3 */
+ namelen = ce_namelen(ce);
+ ce->ce_flags = create_ce_flags(namelen, 3);
+ }
+
+ for (i = 0; i < active_nr; i++) {
+ ce = active_cache[i];
+ if (ce_stage(ce) > 1)
+ continue;
+ namelen = ce_namelen(ce);
+ size = cache_entry_size(namelen);
+ stage2 = xmalloc(size);
+ memcpy(stage2, ce, size);
+ stage2->ce_flags = create_ce_flags(namelen, 2);
+ if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
+ die("cannot merge index and our head tree");
+
+ /* We are done with this name, so skip to next name */
+ while (i < active_nr &&
+ ce_namelen(active_cache[i]) == namelen &&
+ !memcmp(active_cache[i]->name, ce->name, namelen))
+ i++;
+ i--; /* compensate for the loop control */
+ }
+}
+
+/*
+ * One-way merge.
+ *
+ * The rule is:
+ * - take the stat information from stage0, take the data from stage1
+ */
+static int oneway_merge(struct cache_entry **src, struct cache_entry **dst,
+ struct cache_entry **next, int tail)
+{
+ struct cache_entry *old = src[0];
+ struct cache_entry *a = src[1];
+
+ if (src[2] || src[3])
+ return -1;
+
+ if (!a)
+ return 0;
+ if (old && same(old, a)) {
+ *dst++ = old;
+ return 1;
+ }
+ return merged_entry(a, NULL, dst);
+}
+
+static void check_updates(struct cache_entry **src, int nr)
+{
+ static struct checkout state = {
+ .base_dir = "",
+ .force = 1,
+ .quiet = 1,
+ .refresh_cache = 1,
+ };
+ unsigned short mask = htons(CE_UPDATE);
+ while (nr--) {
+ struct cache_entry *ce = *src++;
+ if (!ce->ce_mode) {
+ if (update)
+ unlink(ce->name);
+ continue;
+ }
+ if (ce->ce_flags & mask) {
+ ce->ce_flags &= ~mask;
+ if (update)
+ checkout_entry(ce, &state);
+ }
+ }
+}
+
+typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **, struct cache_entry **, int);
+
+static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
+{
+ struct cache_entry **dst = src;
+ int tail = nr;
+
+ while (nr) {
+ int entries;
+ struct cache_entry *name, *ce, *stages[4] = { NULL, };
+
+ name = ce = *src;
+ for (;;) {
+ int stage = ce_stage(ce);
+ stages[stage] = ce;
+ ce = *++src;
+ active_nr--;
+ if (!--nr)
+ break;
+ if (!path_matches(ce, name))
+ break;
+ }
+
+ entries = fn(stages, dst, src, tail);
+ if (entries < 0)
+ reject_merge(name);
+ dst += entries;
+ active_nr += entries;
+ }
+ check_updates(active_cache, active_nr);
+}
+
+static int read_cache_unmerged(void)
+{
+ int i, deleted;
+ struct cache_entry **dst;
+
+ read_cache();
+ dst = active_cache;
+ deleted = 0;
+ for (i = 0; i < active_nr; i++) {
+ struct cache_entry *ce = active_cache[i];
+ if (ce_stage(ce)) {
+ deleted++;
+ continue;
+ }
+ if (deleted)
+ *dst = ce;
+ dst++;
+ }
+ active_nr -= deleted;
+ return deleted;
+}
+
+static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
+
+static struct cache_file cache_file;
+
int main(int argc, char **argv)
{
- int fd;
+ int i, newfd, merge, reset, emu23;
unsigned char sha1[20];
- if (argc != 2)
- usage("read-tree <key>");
- if (get_sha1_hex(argv[1], sha1) < 0)
- usage("read-tree <key>");
- sha1_file_directory = getenv(DB_ENVIRONMENT);
- if (!sha1_file_directory)
- sha1_file_directory = DEFAULT_DB_ENVIRONMENT;
- if (unpack(sha1) < 0)
- usage("unpack failed");
+ newfd = hold_index_file_for_update(&cache_file, get_index_file());
+ if (newfd < 0)
+ die("unable to create new cachefile");
+
+ merge = 0;
+ reset = 0;
+ emu23 = 0;
+ for (i = 1; i < argc; i++) {
+ const char *arg = argv[i];
+
+ /* "-u" means "update", meaning that a merge will update the working directory */
+ if (!strcmp(arg, "-u")) {
+ update = 1;
+ continue;
+ }
+
+ /* This differs from "-m" in that we'll silently ignore unmerged entries */
+ if (!strcmp(arg, "--reset")) {
+ if (stage || merge || emu23)
+ usage(read_tree_usage);
+ reset = 1;
+ merge = 1;
+ stage = 1;
+ read_cache_unmerged();
+ continue;
+ }
+
+ /* "-m" stands for "merge", meaning we start in stage 1 */
+ if (!strcmp(arg, "-m")) {
+ if (stage || merge || emu23)
+ usage(read_tree_usage);
+ if (read_cache_unmerged())
+ die("you need to resolve your current index first");
+ stage = 1;
+ merge = 1;
+ continue;
+ }
+
+ /* "-emu23" uses 3-way merge logic to perform fast-forward */
+ if (!strcmp(arg, "--emu23")) {
+ if (stage || merge || emu23)
+ usage(read_tree_usage);
+ if (read_cache_unmerged())
+ die("you need to resolve your current index first");
+ merge = emu23 = stage = 1;
+ continue;
+ }
+
+ if (get_sha1(arg, sha1) < 0)
+ usage(read_tree_usage);
+ if (stage > 3)
+ usage(read_tree_usage);
+ if (unpack_tree(sha1) < 0)
+ die("failed to unpack tree object %s", arg);
+ stage++;
+ }
+ if (update && !merge)
+ usage(read_tree_usage);
+ if (merge) {
+ static const merge_fn_t merge_function[] = {
+ [1] = oneway_merge,
+ [2] = twoway_merge,
+ [3] = threeway_merge,
+ };
+ merge_fn_t fn;
+
+ if (stage < 2 || stage > 4)
+ die("just how do you expect me to merge %d trees?", stage-1);
+ if (emu23 && stage != 3)
+ die("--emu23 takes only two trees");
+ fn = merge_function[stage-1];
+ if (stage == 3 && emu23) {
+ setup_emu23();
+ fn = merge_function[3];
+ }
+ merge_cache(active_cache, active_nr, fn);
+ }
+ if (write_cache(newfd, active_cache, active_nr) ||
+ commit_index_file(&cache_file))
+ die("unable to write new index file");
return 0;
}