fast-import: add support for new 'alias' command

fast-export and fast-import have nice --import-marks flags which allow
for incremental migrations.  However, if there is a mark in
fast-export's file of marks without a corresponding mark in the one for
fast-import, then we run the risk that fast-export tries to send new
objects relative to the mark it knows which fast-import does not,
causing fast-import to fail.

This arises in practice when there is a filter of some sort running
between the fast-export and fast-import processes which prunes some
commits programmatically.  Provide such a filter with the ability to
alias pruned commits to their most recent non-pruned ancestor.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-fast-import.txt b/Documentation/git-fast-import.txt
index 4977869465df646731bfe06f6cdf5425f82a0061..a3f1e0c5e4417d66b4a07269b0dbfff7626ad89b 100644 (file)
--- a/Documentation/git-fast-import.txt
+++ b/Documentation/git-fast-import.txt
@@ -337,6 +337,13 @@ and control the current import process.  More detailed discussion
        `commit` command.  This command is optional and is not
        needed to perform an import.
 
+`alias`::
+       Record that a mark refers to a given object without first
+       creating any new object.  Using --import-marks and referring
+       to missing marks will cause fast-import to fail, so aliases
+       can provide a way to set otherwise pruned commits to a valid
+       value (e.g. the nearest non-pruned ancestor).
+
 `checkpoint`::
        Forces fast-import to close the current packfile, generate its
        unique SHA-1 checksum and index, and start a new packfile.
@@ -914,6 +921,21 @@ a data chunk which does not have an LF as its last byte.
 +
 The `LF` after `<delim> LF` is optional (it used to be required).
 
+`alias`
+~~~~~~~
+Record that a mark refers to a given object without first creating any
+new object.
+
+....
+       'alias' LF
+       mark
+       'to' SP <commit-ish> LF
+       LF?
+....
+
+For a detailed description of `<commit-ish>` see above under `from`.
+
+
 `checkpoint`
 ~~~~~~~~~~~~
 Forces fast-import to close the current packfile, start a new one, and to

diff --git a/fast-import.c b/fast-import.c
index 5b9e9e3b02360083f6213eec7121c78541924992..ac368b3e2b8b81d9ba40de3296636f87f8d30b37 100644 (file)
--- a/fast-import.c
+++ b/fast-import.c
@@ -2491,18 +2491,14 @@ static void parse_from_existing(struct branch *b)
        }
 }
 
-static int parse_from(struct branch *b)
+static int parse_objectish(struct branch *b, const char *objectish)
 {
-       const char *from;
        struct branch *s;
        struct object_id oid;
 
-       if (!skip_prefix(command_buf.buf, "from ", &from))
-               return 0;
-
        oidcpy(&oid, &b->branch_tree.versions[1].oid);
 
-       s = lookup_branch(from);
+       s = lookup_branch(objectish);
        if (b == s)
                die("Can't create a branch from itself: %s", b->name);
        else if (s) {
@@ -2510,8 +2506,8 @@ static int parse_from(struct branch *b)
                oidcpy(&b->oid, &s->oid);
                oidcpy(&b->branch_tree.versions[0].oid, t);
                oidcpy(&b->branch_tree.versions[1].oid, t);
-       } else if (*from == ':') {
-               uintmax_t idnum = parse_mark_ref_eol(from);
+       } else if (*objectish == ':') {
+               uintmax_t idnum = parse_mark_ref_eol(objectish);
                struct object_entry *oe = find_mark(idnum);
                if (oe->type != OBJ_COMMIT)
                        die("Mark :%" PRIuMAX " not a commit", idnum);
@@ -2525,13 +2521,13 @@ static int parse_from(struct branch *b)
                        } else
                                parse_from_existing(b);
                }
-       } else if (!get_oid(from, &b->oid)) {
+       } else if (!get_oid(objectish, &b->oid)) {
                parse_from_existing(b);
                if (is_null_oid(&b->oid))
                        b->delete = 1;
        }
        else
-               die("Invalid ref name or SHA1 expression: %s", from);
+               die("Invalid ref name or SHA1 expression: %s", objectish);
 
        if (b->branch_tree.tree && !oideq(&oid, &b->branch_tree.versions[1].oid)) {
                release_tree_content_recursive(b->branch_tree.tree);
@@ -2542,6 +2538,26 @@ static int parse_from(struct branch *b)
        return 1;
 }
 
+static int parse_from(struct branch *b)
+{
+       const char *from;
+
+       if (!skip_prefix(command_buf.buf, "from ", &from))
+               return 0;
+
+       return parse_objectish(b, from);
+}
+
+static int parse_objectish_with_prefix(struct branch *b, const char *prefix)
+{
+       const char *base;
+
+       if (!skip_prefix(command_buf.buf, prefix, &base))
+               return 0;
+
+       return parse_objectish(b, base);
+}
+
 static struct hash_list *parse_merge(unsigned int *count)
 {
        struct hash_list *list = NULL, **tail = &list, *n;
@@ -3087,6 +3103,28 @@ static void parse_progress(void)
        skip_optional_lf();
 }
 
+static void parse_alias(void)
+{
+       struct object_entry *e;
+       struct branch b;
+
+       skip_optional_lf();
+       read_next_command();
+
+       /* mark ... */
+       parse_mark();
+       if (!next_mark)
+               die(_("Expected 'mark' command, got %s"), command_buf.buf);
+
+       /* to ... */
+       memset(&b, 0, sizeof(b));
+       if (!parse_objectish_with_prefix(&b, "to "))
+               die(_("Expected 'to' command, got %s"), command_buf.buf);
+       e = find_object(&b.oid);
+       assert(e);
+       insert_mark(next_mark, e);
+}
+
 static char* make_fast_import_path(const char *path)
 {
        if (!relative_marks_paths || is_absolute_path(path))
@@ -3214,6 +3252,8 @@ static int parse_one_feature(const char *feature, int from_stream)
                option_import_marks(arg, from_stream, 1);
        } else if (skip_prefix(feature, "export-marks=", &arg)) {
                option_export_marks(arg);
+       } else if (!strcmp(feature, "alias")) {
+               ; /* Don't die - this feature is supported */
        } else if (!strcmp(feature, "get-mark")) {
                ; /* Don't die - this feature is supported */
        } else if (!strcmp(feature, "cat-blob")) {
@@ -3370,6 +3410,8 @@ int cmd_main(int argc, const char **argv)
                        parse_checkpoint();
                else if (!strcmp("done", command_buf.buf))
                        break;
+               else if (!strcmp("alias", command_buf.buf))
+                       parse_alias();
                else if (starts_with(command_buf.buf, "progress "))
                        parse_progress();
                else if (skip_prefix(command_buf.buf, "feature ", &v))

diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 3ad2b2f1baf129ec0ec37d0fc84dc67229ac185b..41f2a1dad95f265093731af874beaca51c7b58e0 100755 (executable)
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -111,6 +111,10 @@ test_expect_success 'A: create pack from stdin' '
        Tag of tag of our lovely commit
        EOF
 
+       alias
+       mark :8
+       to :5
+
        INPUT_END
        git fast-import --export-marks=marks.out <input &&
        git whatchanged master
@@ -195,6 +199,7 @@ test_expect_success 'A: verify marks output' '
        :5 $(git rev-parse --verify master^0)
        :6 $(git cat-file tag nested | grep object | cut -d" " -f 2)
        :7 $(git rev-parse --verify nested)
+       :8 $(git rev-parse --verify master^0)
        EOF
        test_cmp expect marks.out
 '