[PATCH 4/4] trailer: add "move" configuration for trailer.ifExists

[Paolo Bonzini <pbonzini@redhat.com>]

In some cases, people apply patches to a queue branch immediately
with "git am -3 -s", and later collect Reviewed-by or Acked-by
trailers as they come in from the mailing list.

In this case, "where=after" does not have the desired behavior,
because it will add the trailer in an unorthodox position, after the
committer's Signed-off-by line.  The "move" configuration is intended
to be applied in such a case to the Signed-off-by header, like

    git interpret-trailers \
	--where end --if-missing doNothing --if-exists move
	"Signed-off-by: A U Thor <au@thor.example.org>"

or perhaps with an automated configuration

    [trailer "move-sob"]
    command = "'echo \"$(git config user.name) <$(git config user.email)>\"'"
    key = Signed-off-by
    where = end
    ifMissing = doNothing
    ifExists = move

Though this of course makes the most sense if the last Signed-off-by is
from the committer itself, and thus is not necessarily a good idea for
everyone.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Documentation/git-interpret-trailers.txt | 13 ++++++++---
 t/t7513-interpret-trailers.sh            | 37 ++++++++++++++++++++++++++++++++
 trailer.c                                | 26 +++++++++++++++++-----
 trailer.h                                |  1 +
 4 files changed, 69 insertions(+), 8 deletions(-)

diff --git a/Documentation/git-interpret-trailers.txt b/Documentation/git-interpret-trailers.txt
index 9dd19a1dd..1cdde492c 100644
--- a/Documentation/git-interpret-trailers.txt
+++ b/Documentation/git-interpret-trailers.txt
@@ -165,7 +165,7 @@ trailer.ifexists::
 	same <token> in the message.
 +
 The valid values for this option are: `addIfDifferentNeighbor` (this
-is the default), `addIfDifferent`, `add`, `replace` or `doNothing`.
+is the default), `addIfDifferent`, `add`, `replace`, `move` or `doNothing`.
 +
 With `addIfDifferentNeighbor`, a new trailer will be added only if no
 trailer with the same (<token>, <value>) pair is above or below the line
@@ -182,13 +182,20 @@ deleted and the new trailer will be added. The deleted trailer will be
 the closest one (with the same <token>) to the place where the new one
 will be added.
 +
+With `move`, an existing trailer with the same (<token>, <value>) will be
+deleted and the new trailer will be added.  If more equal pairs exists,
+the deleted trailer will be the closest one to the place where the new one
+will be added.
++
 With `doNothing`, nothing will be done; that is no new trailer will be
 added if there is already one with the same <token> in the message.
 
 trailer.ifmissing::
 	This option makes it possible to choose what action will be
-	performed when there is not yet any trailer with the same
-	<token> in the message.
+	performed when the `ifexists` action fails.  This means that
+	there is not yet any trailer with the same <token> in the message
+	or, for the `move` action only, there is no identical trailer
+	in the message.
 +
 The valid values for this option are: `add` (this is the default) and
 `doNothing`.
diff --git a/t/t7513-interpret-trailers.sh b/t/t7513-interpret-trailers.sh
index 164719d1c..a0f21fefd 100755
--- a/t/t7513-interpret-trailers.sh
+++ b/t/t7513-interpret-trailers.sh
@@ -1052,6 +1052,43 @@ test_expect_success 'using "ifExists = doNothing"' '
 	test_cmp expected actual
 '
 
+test_expect_success 'require token and value match when "ifExists = move"' '
+	git config trailer.fix.ifExists "move" &&
+	git config trailer.fix.where "start" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: 22
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Fixes: 53
+	EOF
+	(cat complex_message; echo Fixes: 53) | \
+	git interpret-trailers \
+		--trailer "fix=22" \
+		>actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'look for all trailers when "ifExists = move"' '
+	git config trailer.fix.ifMissing "doNothing" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: 22
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Fixes: 53
+	EOF
+	(cat complex_message; echo Fixes: 22; echo Fixes: 53) | \
+	git interpret-trailers \
+		--trailer "fix=22" \
+		>actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'the default is "ifMissing = add"' '
 	git config trailer.cc.key "Cc: " &&
 	git config trailer.cc.where "before" &&
diff --git a/trailer.c b/trailer.c
index ce0d94074..4915bda8f 100644
--- a/trailer.c
+++ b/trailer.c
@@ -202,6 +202,14 @@ static int check_if_different(struct trailer_item *in_tok,
 	return 0;
 }
 
+static int check_if_same(struct trailer_item *in_tok,
+			 struct trailer_item *neighbor,
+			 struct arg_item *arg_tok,
+			 struct list_head *head)
+{
+	return same_trailer(in_tok, arg_tok);
+}
+
 static int check_if_different_neighbor(struct trailer_item *in_tok,
 				       struct trailer_item *neighbor,
 				       struct arg_item *arg_tok,
@@ -255,6 +263,8 @@ static void apply_item_command(struct trailer_item *in_tok, struct arg_item *arg
 		}
 		arg_tok->value = apply_command(arg_tok->conf.command, arg);
 		free((char *)arg);
+		free(arg_tok->conf.command);
+		arg_tok->conf.command = NULL;
 	}
 }
 
@@ -314,9 +324,9 @@ static int apply_arg(struct trailer_item *in_tok,
 	return 1;
 }
 
-static void apply_arg_if_exists(struct trailer_item *in_tok,
-				struct arg_item *arg_tok,
-				struct list_head *head)
+static int apply_arg_if_exists(struct trailer_item *in_tok,
+			       struct arg_item *arg_tok,
+			       struct list_head *head)
 {
 	switch (arg_tok->conf.if_exists) {
 	case EXISTS_DO_NOTHING:
@@ -324,6 +334,9 @@ static void apply_arg_if_exists(struct trailer_item *in_tok,
 	case EXISTS_REPLACE:
 		apply_arg(in_tok, arg_tok, head, NULL, 1);
 		break;
+	case EXISTS_MOVE:
+		/* Look for another trailer if the match fails.  */
+		return apply_arg(in_tok, arg_tok, head, check_if_same, 1);
 	case EXISTS_ADD:
 		apply_arg(in_tok, arg_tok, head, NULL, 0);
 		break;
@@ -337,6 +350,7 @@ static void apply_arg_if_exists(struct trailer_item *in_tok,
 		die("BUG: trailer.c: unhandled value %d",
 		    arg_tok->conf.if_exists);
 	}
+	return 1;
 }
 
 static void apply_arg_if_missing(struct list_head *head,
@@ -367,8 +381,8 @@ static int find_same_and_apply_arg(struct list_head *head,
 		in_tok = list_entry(pos, struct trailer_item, list);
 		if (!same_token(in_tok, arg_tok))
 			continue;
-		apply_arg_if_exists(in_tok, arg_tok, head);
-		return 1;
+		if (apply_arg_if_exists(in_tok, arg_tok, head))
+			return 1;
 	}
 	return 0;
 }
@@ -423,6 +437,8 @@ int trailer_set_if_exists(enum trailer_if_exists *item, const char *value)
 		*item = EXISTS_ADD;
 	else if (!strcasecmp("replace", value))
 		*item = EXISTS_REPLACE;
+	else if (!strcasecmp("move", value))
+		*item = EXISTS_MOVE;
 	else if (!strcasecmp("doNothing", value))
 		*item = EXISTS_DO_NOTHING;
 	else
diff --git a/trailer.h b/trailer.h
index 6d7f8c2a5..0fbdab38d 100644
--- a/trailer.h
+++ b/trailer.h
@@ -16,6 +16,7 @@ enum trailer_if_exists {
 	EXISTS_ADD_IF_DIFFERENT,
 	EXISTS_ADD,
 	EXISTS_REPLACE,
+	EXISTS_MOVE,
 	EXISTS_DO_NOTHING
 };
 enum trailer_if_missing {
-- 
2.14.2