merge-tree.c: add --merge-base=<commit> option

This patch will give our callers more flexibility to use `git merge-tree`,
such as:

    git merge-tree --write-tree --merge-base=branch^ HEAD branch

This does a merge of HEAD and branch, but uses branch^ as the merge-base.

And the reason why using an option flag instead of a positional argument
is to allow additional commits passed to merge-tree to be handled via an
octopus merge in the future.

Signed-off-by: Kyle Zhao <kylezhao@tencent.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

diff --git a/Documentation/git-merge-tree.txt b/Documentation/git-merge-tree.txt
index 04bcc416e6e2966b8b83d911cac61307e0f4feaf..d9dacb2ce549dd442b2d869f2a05fd75df1ace9e 100644 (file)
--- a/Documentation/git-merge-tree.txt
+++ b/Documentation/git-merge-tree.txt
@@ -64,6 +64,10 @@ OPTIONS
        share no common history.  This flag can be given to override that
        check and make the merge proceed anyway.
 
+--merge-base=<commit>::
+       Instead of finding the merge-bases for <branch1> and <branch2>,
+       specify a merge-base for the merge.
+
 [[OUTPUT]]
 OUTPUT
 ------

diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index fe853aa8f9147b540d5427af33cec824a54de3df..62c6d43cdb91a5957649d94e8e6b7eea62d48694 100644 (file)
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -3,6 +3,7 @@
 #include "tree-walk.h"
 #include "xdiff-interface.h"
 #include "help.h"
+#include "commit.h"
 #include "commit-reach.h"
 #include "merge-ort.h"
 #include "object-store.h"
@@ -406,6 +407,7 @@ struct merge_tree_options {
 };
 
 static int real_merge(struct merge_tree_options *o,
+                     const char *merge_base,
                      const char *branch1, const char *branch2,
                      const char *prefix)
 {
@@ -432,16 +434,31 @@ static int real_merge(struct merge_tree_options *o,
        opt.branch1 = branch1;
        opt.branch2 = branch2;
 
-       /*
-        * Get the merge bases, in reverse order; see comment above
-        * merge_incore_recursive in merge-ort.h
-        */
-       merge_bases = get_merge_bases(parent1, parent2);
-       if (!merge_bases && !o->allow_unrelated_histories)
-               die(_("refusing to merge unrelated histories"));
-       merge_bases = reverse_commit_list(merge_bases);
+       if (merge_base) {
+               struct commit *base_commit;
+               struct tree *base_tree, *parent1_tree, *parent2_tree;
+
+               base_commit = lookup_commit_reference_by_name(merge_base);
+               if (!base_commit)
+                       die(_("could not lookup commit %s"), merge_base);
+
+               opt.ancestor = merge_base;
+               base_tree = get_commit_tree(base_commit);
+               parent1_tree = get_commit_tree(parent1);
+               parent2_tree = get_commit_tree(parent2);
+               merge_incore_nonrecursive(&opt, base_tree, parent1_tree, parent2_tree, &result);
+       } else {
+               /*
+                * Get the merge bases, in reverse order; see comment above
+                * merge_incore_recursive in merge-ort.h
+                */
+               merge_bases = get_merge_bases(parent1, parent2);
+               if (!merge_bases && !o->allow_unrelated_histories)
+                       die(_("refusing to merge unrelated histories"));
+               merge_bases = reverse_commit_list(merge_bases);
+               merge_incore_recursive(&opt, merge_bases, parent1, parent2, &result);
+       }
 
-       merge_incore_recursive(&opt, merge_bases, parent1, parent2, &result);
        if (result.clean < 0)
                die(_("failure to merge"));
 
@@ -487,6 +504,7 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
        struct merge_tree_options o = { .show_messages = -1 };
        int expected_remaining_argc;
        int original_argc;
+       const char *merge_base = NULL;
 
        const char * const merge_tree_usage[] = {
                N_("git merge-tree [--write-tree] [<options>] <branch1> <branch2>"),
@@ -515,6 +533,10 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
                           &o.use_stdin,
                           N_("perform multiple merges, one per line of input"),
                           PARSE_OPT_NONEG),
+               OPT_STRING(0, "merge-base",
+                          &merge_base,
+                          N_("commit"),
+                          N_("specify a merge-base for the merge")),
                OPT_END()
        };
 
@@ -529,6 +551,8 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 
                if (o.mode == MODE_TRIVIAL)
                        die(_("--trivial-merge is incompatible with all other options"));
+               if (merge_base)
+                       die(_("--merge-base is incompatible with --stdin"));
                line_termination = '\0';
                while (strbuf_getline_lf(&buf, stdin) != EOF) {
                        struct strbuf **split;
@@ -538,7 +562,7 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
                        if (!split[0] || !split[1] || split[2])
                                die(_("malformed input line: '%s'."), buf.buf);
                        strbuf_rtrim(split[0]);
-                       result = real_merge(&o, split[0]->buf, split[1]->buf, prefix);
+                       result = real_merge(&o, merge_base, split[0]->buf, split[1]->buf, prefix);
                        if (result < 0)
                                die(_("merging cannot continue; got unclean result of %d"), result);
                        strbuf_list_free(split);
@@ -581,7 +605,7 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 
        /* Do the relevant type of merge */
        if (o.mode == MODE_REAL)
-               return real_merge(&o, argv[0], argv[1], prefix);
+               return real_merge(&o, merge_base, argv[0], argv[1], prefix);
        else
                return trivial_merge(argv[0], argv[1], argv[2]);
 }

diff --git a/t/t4301-merge-tree-write-tree.sh b/t/t4301-merge-tree-write-tree.sh
index cac85591b52b3b3d7d0a7aa7f5dbc0c32d8ebdda..6db96ccbaaed09633ea1c2c138411df09d80c5e4 100755 (executable)
--- a/t/t4301-merge-tree-write-tree.sh
+++ b/t/t4301-merge-tree-write-tree.sh
@@ -860,4 +860,31 @@ test_expect_success '--stdin with both a successful and a conflicted merge' '
        test_cmp expect actual
 '
 
+# specify merge-base as parent of branch2
+# git merge-tree --write-tree --merge-base=c2 c1 c3
+#   Commit c1: add file1
+#   Commit c2: add file2 after c1
+#   Commit c3: add file3 after c2
+#   Expected: add file3, and file2 does NOT appear
+
+test_expect_success 'specify merge-base as parent of branch2' '
+       # Setup
+       test_when_finished "rm -rf base-b2-p" &&
+       git init base-b2-p &&
+       test_commit -C base-b2-p c1 file1 &&
+       test_commit -C base-b2-p c2 file2 &&
+       test_commit -C base-b2-p c3 file3 &&
+
+       # Testing
+       TREE_OID=$(git -C base-b2-p merge-tree --write-tree --merge-base=c2 c1 c3) &&
+
+       q_to_tab <<-EOF >expect &&
+       100644 blob $(git -C base-b2-p rev-parse c1:file1)Qfile1
+       100644 blob $(git -C base-b2-p rev-parse c3:file3)Qfile3
+       EOF
+
+       git -C base-b2-p ls-tree $TREE_OID >actual &&
+       test_cmp expect actual
+'
+
 test_done