gpick: add support for resolving easy conflicts

Change-Id: I703e26fdf3527ef13b5f4702b6efae52b20f6eba
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

2 files changed, 115 insertions, 11 deletions

diff --git a/bin/git-gpick b/bin/git-gpick
index 5e07140..433ee6a 100755
--- a/bin/git-gpick
+++ b/bin/git-gpick
@@ -72,6 +72,13 @@ Description:
     follow the usual instructions on screen.
 
 Options:
+    -m, --merge
+        Attempt to merge concurrent local and remote modifications to
+        the same Changes. Use only once you are sure that there are no
+        logical conflicts.
+        This currently works only when each side touches different parts
+        of the Change (author, commit message, or diff).
+
     -f, --force
         Replace or merge the local commits even in case of conflicting
         modifications.
@@ -162,6 +169,7 @@ use constant {
 
 my $branch;
 my $upstream_branch;
+my $merge = 0;
 my $force = 0;
 my $ignore = 0;
 my @commit_specs;
@@ -186,6 +194,8 @@ sub parse_arguments(@)
         } elsif ($arg eq "-b" || $arg eq "--branch") {
             fail("--branch needs an argument.\n") if (!@_ || ($_[0] =~ /^-/));
             $branch = shift @_;
+        } elsif ($arg eq "-m" || $arg eq "--merge") {
+            $merge = 1;
         } elsif ($arg eq "-f" || $arg eq "--force") {
             $force = 1;
         } elsif ($arg eq "-i" || $arg eq "--ignore") {
@@ -203,8 +213,8 @@ sub parse_arguments(@)
     fail("--quiet and --verbose/--debug are mutually exclusive.\n")
         if ($quiet && $verbose);
 
-    fail("--force and --ignore are mutually exclusive.\n")
-        if ($force && $ignore);
+    fail("--merge/--force and --ignore are mutually exclusive.\n")
+        if (($merge || $force) && $ignore);
 }
 
 sub determine_local_branch()
@@ -1171,10 +1181,10 @@ sub verify_delete($$$$$$$)
     return (UPD_DROP, $pfx, $annot);
 }
 
-sub verify_update($$$$$$$)
+sub verify_update($$$$$$$$)
 {
     my ($reports, $lcl_commit, $rmt_commit, $rmt_ps, $pushed_commit, $pushed_ps,
-        $need_force_repl) = @_;
+        $need_force_repl, $can_merge) = @_;
 
     my ($pfx, $annot, $forcing) = (undef, "", 0);
     # First make a direct comparison. This should be the common case (the user
@@ -1226,6 +1236,35 @@ sub verify_update($$$$$$$)
         if ($lcl_parts) {
             # The current local commit differs from the previously pushed one,
             # and we already know that the current remote commit also differs.
+            # However, individual parts may be unmodified on either side.
+            if (!$fc && $merge) {
+                # No textual conflict, as each side modified different parts.
+                # We do not merge without being asked to, as the modifications
+                # might still conflict logically.
+                $pfx = "Merge     " if (!$quiet);
+                return (UPD_PUSHED | UPD_META | UPD_INFO, $rmt_parts, $pfx, $annot);
+            }
+            if (!$force) {
+                my $pfx;
+                if (!$fc) {
+                    $$can_merge = 1;
+                    $pfx = "(Merge)   ";
+                } elsif ($fl) {
+                    $$can_merge = 1 if (!$merge);
+                    $$need_force_repl = 1;
+                    $pfx = "(MERGE)   ";
+                } else {
+                    # TODO: We could still attempt 3-way merges here.
+                    $$need_force_repl = 1;
+                    $pfx = "(REPLACE) ";
+                }
+                return (UPD_INFO, NO_PARTS, $pfx, $annot);
+            }
+            if ($fl && $merge) {
+                # Retain the non-conflicting local modifications.
+                $pfx = "MERGE     " if (!$quiet);
+                return (UPD_PUSHED | UPD_META | UPD_INFO, $rmt_parts, $pfx, $annot);
+            }
             $forcing = 1;
         } elsif ($pushed_ps eq "?") {
             # The previously pushed commit disappeared from Gerrit.
@@ -1251,6 +1290,33 @@ sub verify_update($$$$$$$)
     return (UPD_PUSHED | UPD_META | UPD_INFO, ALL_PARTS, $pfx, $annot);
 }
 
+# Create a new commit by replacing named parts of the
+# source commit with these from the reference commit.
+sub merge_commits($$$)
+{
+    my ($commit, $ref_commit, $parts) = @_;
+
+    my ($parents, $tree, $message, $author, $committer) =
+        ($$commit{parents}, $$commit{tree}, $$commit{message},
+         $$commit{author}, $$commit{committer});
+    if ($parts & AUTHOR_PART) {
+        $author = $$ref_commit{author};
+    }
+    if ($parts & MESSAGE_PART) {
+        # This is probably the most common case: commit message edited
+        # directly on Gerrit, while amending the diff locally.
+        $message = $$ref_commit{message};
+    }
+    if ($parts & DIFF_PART) {
+        # To get the correct diff, we need to replace both the parent(s)
+        # and the tree. The implicit rebasing does not matter, as the
+        # result is going to be cherry-picked anyway.
+        $parents = $$ref_commit{parents};
+        $tree = $$ref_commit{tree};
+    }
+    return create_commit($parents, $tree, $message, $author, $committer);
+}
+
 # Turn the list of local Changes into the final list of commits the
 # local branch should be reconstructed from.
 sub do_adjust_changes($)
@@ -1259,7 +1325,7 @@ sub do_adjust_changes($)
 
     print "Adjusting Changes ...\n" if ($debug);
 
-    my ($need_force_del, $need_force_repl);
+    my ($need_force_del, $need_force_repl, $can_merge);
     my ($any_missing, $any_crossed, $any_merged);
     my (@commits, @reports);
     foreach my $pair (@$pairs) {
@@ -1309,7 +1375,7 @@ sub do_adjust_changes($)
             } else {
                 ($upd, $parts, $pfx, $annot) =
                     verify_update(\@reports, $lcl_commit, $rmt_commit, $rmt_ps,
-                                  $pushed_commit, $pushed_ps, \$need_force_repl);
+                                  $pushed_commit, $pushed_ps, \$need_force_repl, \$can_merge);
             }
             report_update(\@reports, $pfx, $annot, $lcl_commit, $ginfo) if (defined($pfx));
             # Note: we don't clear the diff cache here, so entries filled
@@ -1325,6 +1391,8 @@ sub do_adjust_changes($)
             my $commit;
             if ($parts == NO_PARTS) {
                 $commit = $lcl_commit;
+            } elsif ($parts != ALL_PARTS) {
+                $commit = merge_commits($lcl_commit, $rmt_commit, $parts);
             } else {
                 $commit = $rmt_commit;
             }
@@ -1369,15 +1437,26 @@ sub do_adjust_changes($)
         $any_msg = 1;
     }
 
-    if ($need_force_repl || $need_force_del) {
+    if ($can_merge || $need_force_repl || $need_force_del) {
         my $err;
         if ($need_force_del) {
             $err .= "\nLocal modifications found in Change(s) scheduled for deletion;"
                     ." add --force to proceed nonetheless.";
         }
-        if ($need_force_repl) {
-            $err .= "\nConflicting local modifications found in Change(s) scheduled for update;"
-                    ." use --force to overwrite them, or --ignore to disregard any new PatchSet(s).";
+        if ($can_merge || $need_force_repl) {
+            my $lmt = " local modifications found in Change(s) scheduled for update;";
+            my $ipt = " or --ignore to disregard any new PatchSet(s).";
+            if ($can_merge) {
+                my $mmt = " add --merge after verifying compatibility,";
+                if ($need_force_repl) {
+                    $err .= "\nMergeable and conflicting".$lmt.$mmt
+                            ." and/or --force to overwrite unmerged modifications,".$ipt;
+                } else {
+                    $err .= "\nMergeable".$lmt.$mmt." --force to overwrite them,".$ipt;
+                }
+            } else {
+                $err .= "\nConflicting".$lmt." use --force to overwrite them,".$ipt;
+            }
         }
         nwfail($err."\n");
     }
@@ -1479,7 +1558,9 @@ sub invoke_rebase($$)
     $ENV{GPICK_DEBUG} = $debug;
     $ENV{GIT_EDITOR} = $script;
 
-    my @gitcmd = ('git', 'rebase', '-i', $base);
+    # Make sure that every commit is picked, otherwise the state todo might
+    # not match if we constructed a first commit that needs no rebasing.
+    my @gitcmd = ('git', 'rebase', '-i', '--no-ff', $base);
     push @gitcmd, '-q' if ($quiet);
     if (!$dry_run) {
         print "+ @gitcmd\n" if ($debug);
diff --git a/bin/git_gpush.pm b/bin/git_gpush.pm
index d349db4..b6f9b1c 100644
--- a/bin/git_gpush.pm
+++ b/bin/git_gpush.pm
@@ -1343,6 +1343,29 @@ sub apply_diff($$$)
     return ($curr_tree, undef);
 }
 
+# Create a commit object from the specified metadata.
+sub create_commit($$$$$)
+{
+    my ($parents, $tree, $commit_msg, $author, $committer) = @_;
+
+    ($ENV{GIT_AUTHOR_NAME}, $ENV{GIT_AUTHOR_EMAIL}, $ENV{GIT_AUTHOR_DATE}) = @$author;
+    ($ENV{GIT_COMMITTER_NAME}, $ENV{GIT_COMMITTER_EMAIL}, $ENV{GIT_COMMITTER_DATE}) = @$committer;
+    my @pargs = map { ('-p', $_) } @$parents;
+    my $proc = open_process(USE_STDIN | SILENT_STDIN | USE_STDOUT | FWD_STDERR,
+                            'git', 'commit-tree', $tree, @pargs);
+    write_process($proc, $commit_msg);
+    my $sha1 = read_process($proc);
+    close_process($proc);
+
+    my $commit = {
+        id => $sha1,
+        parents => $parents,
+        tree => $tree
+    };
+    init_commit($commit);
+    return $commit;
+}
+
 ###################
 # branch tracking #
 ###################