gpush/gpick: attempt to recycle commits from previous pushes

when we rebase the exact same source commit to the same base and retain
the committer info, the resulting commit will be the same as well.

Change-Id: I496305e544306e7b3fb10b8c3a6dfcb20610105a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 34 insertions, 4 deletions

diff --git a/bin/git-gpush b/bin/git-gpush
index 19936f2..79168f9 100755
--- a/bin/git-gpush
+++ b/bin/git-gpush
@@ -544,6 +544,8 @@ sub scan_pushed_group($$)
             last;
         }
         push @$commits, $pcommit;
+        my $ocommit = $$change{orig};
+        push @$commits, $ocommit if (defined($ocommit));
     }
 }
 
@@ -859,9 +861,9 @@ sub commits_equal($$$$)
         && ("@{$$commit{author}}" eq "@{$$old_commit{author}}");
 }
 
-sub rebase_commit($$$)
+sub rebase_commit($$$$$)
 {
-    my ($commit, $base_id, $old_commit) = @_;
+    my ($commit, $base_id, $old_commit, $old_base_id, $orig_id) = @_;
 
     my $parents = $$commit{parents};
     my $parent_id = get_1st_commit($parents);
@@ -883,6 +885,32 @@ sub rebase_commit($$$)
 
     my ($tree, $errors);
     my $parent = $commit_by_id{$parent_id};
+    if ($old_commit && ($base_id eq $old_base_id) && defined($orig_id)) {
+        if ($$commit{id} eq $orig_id) {
+            # We are picking the same commit to the same base, so
+            # we can just recycle the previously created commit.
+            return ($old_commit, 'recycled unmodified');
+        }
+        my $orig_commit = $commit_by_id{$orig_id};
+        if ($orig_commit && ($$commit{tree} eq $$orig_commit{tree})) {
+            # Upstream commits are not visited, so we get no tree id. However,
+            # as this code aims at series which were not rebased, using the base
+            # commit itself will work just as well for the series' first commit.
+            if (($parent ? $$parent{tree} : $parent_id)
+                    eq get_1st_parent_tree($orig_commit)) {
+                if (($$commit{message} eq $$orig_commit{message})
+                        && ("@{$$commit{author}}" eq "@{$$orig_commit{author}}")) {
+                    # We are picking the same content to the same base, so
+                    # we can just recycle the previously created commit.
+                    return ($old_commit, 'recycled amended');
+                }
+                # We are picking the same diff to the same base, so
+                # we can recycle the previously created tree.
+                $tree = $$old_commit{tree};
+                goto COMMIT;
+            }
+        }
+    }
     my $base = $commit_by_id{$base_id};
     if ($base && $parent && ($$base{tree} eq $$parent{tree})) {
         # The parent commits differ, but their trees are the same.
@@ -901,6 +929,7 @@ sub rebase_commit($$$)
 
     # No previously pushed commit or it does not match,
     # so create a new one.
+  COMMIT:
     my $new_parents = ($base_id eq 'ROOT') ? [] : [ $base_id ];
     my $new_commit = create_commit(
             $new_parents, $tree, $$commit{message},
@@ -927,9 +956,9 @@ sub do_rebase_changes($)
         # We attempt to re-create the exact same commits we pushed previously,
         # so we don't create new PatchSets for umodified Changes regardless of
         # any local rebasing.
-        my $old_commit = prepare_rebase($change, $base);
+        my ($old_commit, $old_base) = prepare_rebase($change, $base);
         my ($new_commit, $did, $errors) =
-                rebase_commit($commit, $base, $old_commit);
+                rebase_commit($commit, $base, $old_commit, $old_base, $$change{orig});
         if (!$new_commit) {
             if (!defined($errors)) {
                 set_change_error($change, 'oneline',
@@ -1246,6 +1275,7 @@ sub update_state($)
         }
         $$change{tgt} = $branch;
         my $commit = $$change{local};
+        $$change{orig} = $$commit{id};
         # --rebase would be required after redoing a merge with a different
         # 1st parent anyway, so just don't save the base for merges.
         # Regular commits on top of merges are auto-rebased as well.