Merge branch 'cc/interpret-trailers'

A new filter to programatically edit the tail end of the commit log
messages.

* cc/interpret-trailers:
  Documentation: add documentation for 'git interpret-trailers'
  trailer: add tests for commands in config file
  trailer: execute command from 'trailer.<name>.command'
  trailer: add tests for "git interpret-trailers"
  trailer: add interpret-trailers command
  trailer: put all the processing together and print
  trailer: parse trailers from file or stdin
  trailer: process command line trailer arguments
  trailer: read and process config information
  trailer: process trailers from input message and arguments
  trailer: add data structures and basic functions

.gitignore

@@ -74,6 +74,7 @@
 /git-index-pack
 /git-init
 /git-init-db
+/git-interpret-trailers
 /git-instaweb
 /git-log
 /git-ls-files

Documentation/git-interpret-trailers.txt

@@ -0,0 +1,314 @@
+git-interpret-trailers(1)
+=========================
+
+NAME
+----
+git-interpret-trailers - help add stuctured information into commit messages
+
+SYNOPSIS
+--------
+[verse]
+'git interpret-trailers' [--trim-empty] [(--trailer <token>[(=|:)<value>])...] [<file>...]
+
+DESCRIPTION
+-----------
+Help adding 'trailers' lines, that look similar to RFC 822 e-mail
+headers, at the end of the otherwise free-form part of a commit
+message.
+
+This command reads some patches or commit messages from either the
+<file> arguments or the standard input if no <file> is specified. Then
+this command applies the arguments passed using the `--trailer`
+option, if any, to the commit message part of each input file. The
+result is emitted on the standard output.
+
+Some configuration variables control the way the `--trailer` arguments
+are applied to each commit message and the way any existing trailer in
+the commit message is changed. They also make it possible to
+automatically add some trailers.
+
+By default, a '<token>=<value>' or '<token>:<value>' argument given
+using `--trailer` will be appended after the existing trailers only if
+the last trailer has a different (<token>, <value>) pair (or if there
+is no existing trailer). The <token> and <value> parts will be trimmed
+to remove starting and trailing whitespace, and the resulting trimmed
+<token> and <value> will appear in the message like this:
+
+------------------------------------------------
+token: value
+------------------------------------------------
+
+This means that the trimmed <token> and <value> will be separated by
+`': '` (one colon followed by one space).
+
+By default the new trailer will appear at the end of all the existing
+trailers. If there is no existing trailer, the new trailer will appear
+after the commit message part of the ouput, and, if there is no line
+with only spaces at the end of the commit message part, one blank line
+will be added before the new trailer.
+
+Existing trailers are extracted from the input message by looking for
+a group of one or more lines that contain a colon (by default), where
+the group is preceded by one or more empty (or whitespace-only) lines.
+The group must either be at the end of the message or be the last
+non-whitespace lines before a line that starts with '---'. Such three
+minus signs start the patch part of the message.
+
+When reading trailers, there can be whitespaces before and after the
+token, the separator and the value. There can also be whitespaces
+indide the token and the value.
+
+Note that 'trailers' do not follow and are not intended to follow many
+rules for RFC 822 headers. For example they do not follow the line
+folding rules, the encoding rules and probably many other rules.
+
+OPTIONS
+-------
+--trim-empty::
+	If the <value> part of any trailer contains only whitespace,
+	the whole trailer will be removed from the resulting message.
+	This apply to existing trailers as well as new trailers.
+
+--trailer <token>[(=|:)<value>]::
+	Specify a (<token>, <value>) pair that should be applied as a
+	trailer to the input messages. See the description of this
+	command.
+
+CONFIGURATION VARIABLES
+-----------------------
+
+trailer.separators::
+	This option tells which characters are recognized as trailer
+	separators. By default only ':' is recognized as a trailer
+	separator, except that '=' is always accepted on the command
+	line for compatibility with other git commands.
++
+The first character given by this option will be the default character
+used when another separator is not specified in the config for this
+trailer.
++
+For example, if the value for this option is "%=$", then only lines
+using the format '<token><sep><value>' with <sep> containing '%', '='
+or '$' and then spaces will be considered trailers. And '%' will be
+the default separator used, so by default trailers will appear like:
+'<token>% <value>' (one percent sign and one space will appear between
+the token and the value).
+
+trailer.where::
+	This option tells where a new trailer will be added.
++
+This can be `end`, which is the default, `start`, `after` or `before`.
++
+If it is `end`, then each new trailer will appear at the end of the
+existing trailers.
++
+If it is `start`, then each new trailer will appear at the start,
+instead of the end, of the existing trailers.
++
+If it is `after`, then each new trailer will appear just after the
+last trailer with the same <token>.
++
+If it is `before`, then each new trailer will appear just before the
+first trailer with the same <token>.
+
+trailer.ifexists::
+	This option makes it possible to choose what action will be
+	performed when there is already at least one trailer with the
+	same <token> in the message.
++
+The valid values for this option are: `addIfDifferentNeighbor` (this
+is the default), `addIfDifferent`, `add`, `overwrite` 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
+where the new trailer will be added.
++
+With `addIfDifferent`, a new trailer will be added only if no trailer
+with the same (<token>, <value>) pair is already in the message.
++
+With `add`, a new trailer will be added, even if some trailers with
+the same (<token>, <value>) pair are already in the message.
++
+With `replace`, an existing trailer with the same <token> will be
+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 `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.
++
+The valid values for this option are: `add` (this is the default) and
+`doNothing`.
++
+With `add`, a new trailer will be added.
++
+With `doNothing`, nothing will be done.
+
+trailer.<token>.key::
+	This `key` will be used instead of <token> in the trailer. At
+	the end of this key, a separator can appear and then some
+	space characters. By default the only valid separator is ':',
+	but this can be changed using the `trailer.separators` config
+	variable.
++
+If there is a separator, then the key will be used instead of both the
+<token> and the default separator when adding the trailer.
+
+trailer.<token>.where::
+	This option takes the same values as the 'trailer.where'
+	configuration variable and it overrides what is specified by
+	that option for trailers with the specified <token>.
+
+trailer.<token>.ifexist::
+	This option takes the same values as the 'trailer.ifexist'
+	configuration variable and it overrides what is specified by
+	that option for trailers with the specified <token>.
+
+trailer.<token>.ifmissing::
+	This option takes the same values as the 'trailer.ifmissing'
+	configuration variable and it overrides what is specified by
+	that option for trailers with the specified <token>.
+
+trailer.<token>.command::
+	This option can be used to specify a shell command that will
+	be called to automatically add or modify a trailer with the
+	specified <token>.
++
+When this option is specified, the behavior is as if a special
+'<token>=<value>' argument were added at the beginning of the command
+line, where <value> is taken to be the standard output of the
+specified command with any leading and trailing whitespace trimmed
+off.
++
+If the command contains the `$ARG` string, this string will be
+replaced with the <value> part of an existing trailer with the same
+<token>, if any, before the command is launched.
++
+If some '<token>=<value>' arguments are also passed on the command
+line, when a 'trailer.<token>.command' is configured, the command will
+also be executed for each of these arguments. And the <value> part of
+these arguments, if any, will be used to replace the `$ARG` string in
+the command.
+
+EXAMPLES
+--------
+
+* Configure a 'sign' trailer with a 'Signed-off-by' key, and then
+  add two of these trailers to a message:
++
+------------
+$ git config trailer.sign.key "Signed-off-by"
+$ cat msg.txt
+subject
+
+message
+$ cat msg.txt | git interpret-trailers --trailer 'sign: Alice <alice@example.com>' --trailer 'sign: Bob <bob@example.com>'
+subject
+
+message
+
+Signed-off-by: Alice <alice@example.com>
+Signed-off-by: Bob <bob@example.com>
+------------
+
+* Extract the last commit as a patch, and add a 'Cc' and a
+  'Reviewed-by' trailer to it:
++
+------------
+$ git format-patch -1
+0001-foo.patch
+$ git interpret-trailers --trailer 'Cc: Alice <alice@example.com>' --trailer 'Reviewed-by: Bob <bob@example.com>' 0001-foo.patch >0001-bar.patch
+------------
+
+* Configure a 'sign' trailer with a command to automatically add a
+  'Signed-off-by: ' with the author information only if there is no
+  'Signed-off-by: ' already, and show how it works:
++
+------------
+$ git config trailer.sign.key "Signed-off-by: "
+$ git config trailer.sign.ifmissing add
+$ git config trailer.sign.ifexists doNothing
+$ git config trailer.sign.command 'echo "$(git config user.name) <$(git config user.email)>"'
+$ git interpret-trailers <<EOF
+> EOF
+
+Signed-off-by: Bob <bob@example.com>
+$ git interpret-trailers <<EOF
+> Signed-off-by: Alice <alice@example.com>
+> EOF
+
+Signed-off-by: Alice <alice@example.com>
+------------
+
+* Configure a 'fix' trailer with a key that contains a '#' and no
+  space after this character, and show how it works:
++
+------------
+$ git config trailer.separators ":#"
+$ git config trailer.fix.key "Fix #"
+$ echo "subject" | git interpret-trailers --trailer fix=42
+subject
+
+Fix #42
+------------
+
+* Configure a 'see' trailer with a command to show the subject of a
+  commit that is related, and show how it works:
++
+------------
+$ git config trailer.see.key "See-also: "
+$ git config trailer.see.ifExists "replace"
+$ git config trailer.see.ifMissing "doNothing"
+$ git config trailer.see.command "git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \$ARG"
+$ git interpret-trailers <<EOF
+> subject
+> 
+> message
+> 
+> see: HEAD~2
+> EOF
+subject
+
+message
+
+See-also: fe3187489d69c4 (subject of related commit)
+------------
+
+* Configure a commit template with some trailers with empty values
+  (using sed to show and keep the trailing spaces at the end of the
+  trailers), then configure a commit-msg hook that uses
+  'git interpret-trailers' to remove trailers with empty values and
+  to add a 'git-version' trailer:
++
+------------
+$ sed -e 's/ Z$/ /' >commit_template.txt <<EOF
+> ***subject***
+> 
+> ***message***
+> 
+> Fixes: Z
+> Cc: Z
+> Reviewed-by: Z
+> Signed-off-by: Z
+> EOF
+$ git config commit.template commit_template.txt
+$ cat >.git/hooks/commit-msg <<EOF
+> #!/bin/sh
+> git interpret-trailers --trim-empty --trailer "git-version: \$(git describe)" "\$1" > "\$1.new"
+> mv "\$1.new" "\$1"
+> EOF
+$ chmod +x .git/hooks/commit-msg
+------------
+
+SEE ALSO
+--------
+linkgit:git-commit[1], linkgit:git-format-patch[1], linkgit:git-config[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -764,6 +764,7 @@ LIB_OBJS += submodule.o
 LIB_OBJS += symlinks.o
 LIB_OBJS += tag.o
 LIB_OBJS += trace.o
+LIB_OBJS += trailer.o
 LIB_OBJS += transport.o
 LIB_OBJS += transport-helper.o
 LIB_OBJS += tree-diff.o
@@ -828,6 +829,7 @@ BUILTIN_OBJS += builtin/hash-object.o
 BUILTIN_OBJS += builtin/help.o
 BUILTIN_OBJS += builtin/index-pack.o
 BUILTIN_OBJS += builtin/init-db.o
+BUILTIN_OBJS += builtin/interpret-trailers.o
 BUILTIN_OBJS += builtin/log.o
 BUILTIN_OBJS += builtin/ls-files.o
 BUILTIN_OBJS += builtin/ls-remote.o

builtin.h

@@ -73,6 +73,7 @@ extern int cmd_hash_object(int argc, const char **argv, const char *prefix);
 extern int cmd_help(int argc, const char **argv, const char *prefix);
 extern int cmd_index_pack(int argc, const char **argv, const char *prefix);
 extern int cmd_init_db(int argc, const char **argv, const char *prefix);
+extern int cmd_interpret_trailers(int argc, const char **argv, const char *prefix);
 extern int cmd_log(int argc, const char **argv, const char *prefix);
 extern int cmd_log_reflog(int argc, const char **argv, const char *prefix);
 extern int cmd_ls_files(int argc, const char **argv, const char *prefix);

builtin/interpret-trailers.c

@@ -0,0 +1,44 @@
+/*
+ * Builtin "git interpret-trailers"
+ *
+ * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
+ *
+ */
+
+#include "cache.h"
+#include "builtin.h"
+#include "parse-options.h"
+#include "string-list.h"
+#include "trailer.h"
+
+static const char * const git_interpret_trailers_usage[] = {
+	N_("git interpret-trailers [--trim-empty] [(--trailer <token>[(=|:)<value>])...] [<file>...]"),
+	NULL
+};
+
+int cmd_interpret_trailers(int argc, const char **argv, const char *prefix)
+{
+	int trim_empty = 0;
+	struct string_list trailers = STRING_LIST_INIT_DUP;
+
+	struct option options[] = {
+		OPT_BOOL(0, "trim-empty", &trim_empty, N_("trim empty trailers")),
+		OPT_STRING_LIST(0, "trailer", &trailers, N_("trailer"),
+				N_("trailer(s) to add")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, options,
+			     git_interpret_trailers_usage, 0);
+
+	if (argc) {
+		int i;
+		for (i = 0; i < argc; i++)
+			process_trailers(argv[i], trim_empty, &trailers);
+	} else
+		process_trailers(NULL, trim_empty, &trailers);
+
+	string_list_clear(&trailers, 0);
+
+	return 0;
+}

command-list.txt

@@ -62,6 +62,7 @@ git-imap-send                           foreignscminterface
 git-index-pack                          plumbingmanipulators
 git-init                                mainporcelain common
 git-instaweb                            ancillaryinterrogators
+git-interpret-trailers                  purehelpers
 gitk                                    mainporcelain
 git-log                                 mainporcelain common
 git-ls-files                            plumbinginterrogators

git.c

@@ -417,6 +417,7 @@ static struct cmd_struct commands[] = {
 	{ "index-pack", cmd_index_pack, RUN_SETUP_GENTLY },
 	{ "init", cmd_init_db, NO_SETUP },
 	{ "init-db", cmd_init_db, NO_SETUP },
+	{ "interpret-trailers", cmd_interpret_trailers, RUN_SETUP },
 	{ "log", cmd_log, RUN_SETUP },
 	{ "ls-files", cmd_ls_files, RUN_SETUP },
 	{ "ls-remote", cmd_ls_remote, RUN_SETUP_GENTLY },

t/t7513-interpret-trailers.sh

@@ -0,0 +1,863 @@
+#!/bin/sh
+#
+# Copyright (c) 2013, 2014 Christian Couder
+#
+
+test_description='git interpret-trailers'
+
+. ./test-lib.sh
+
+# When we want one trailing space at the end of each line, let's use sed
+# to make sure that these spaces are not removed by any automatic tool.
+
+test_expect_success 'setup' '
+	: >empty &&
+	cat >basic_message <<-\EOF &&
+		subject
+
+		body
+	EOF
+	cat >complex_message_body <<-\EOF &&
+		my subject
+
+		my body which is long
+		and contains some special
+		chars like : = ? !
+
+	EOF
+	sed -e "s/ Z\$/ /" >complex_message_trailers <<-\EOF &&
+		Fixes: Z
+		Acked-by: Z
+		Reviewed-by: Z
+		Signed-off-by: Z
+	EOF
+	cat >basic_patch <<-\EOF
+		---
+		 foo.txt | 2 +-
+		 1 file changed, 1 insertion(+), 1 deletion(-)
+
+		diff --git a/foo.txt b/foo.txt
+		index 0353767..1d91aa1 100644
+		--- a/foo.txt
+		+++ b/foo.txt
+		@@ -1,3 +1,3 @@
+
+		-bar
+		+baz
+
+		--
+		1.9.rc0.11.ga562ddc
+
+	EOF
+'
+
+test_expect_success 'without config' '
+	sed -e "s/ Z\$/ /" >expected <<-\EOF &&
+
+		ack: Peff
+		Reviewed-by: Z
+		Acked-by: Johan
+	EOF
+	git interpret-trailers --trailer "ack = Peff" --trailer "Reviewed-by" \
+		--trailer "Acked-by: Johan" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'without config in another order' '
+	sed -e "s/ Z\$/ /" >expected <<-\EOF &&
+
+		Acked-by: Johan
+		Reviewed-by: Z
+		ack: Peff
+	EOF
+	git interpret-trailers --trailer "Acked-by: Johan" --trailer "Reviewed-by" \
+		--trailer "ack = Peff" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '--trim-empty without config' '
+	cat >expected <<-\EOF &&
+
+		ack: Peff
+		Acked-by: Johan
+	EOF
+	git interpret-trailers --trim-empty --trailer ack=Peff \
+		--trailer "Reviewed-by" --trailer "Acked-by: Johan" \
+		--trailer "sob:" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with config option on the command line' '
+	cat >expected <<-\EOF &&
+
+		Acked-by: Johan
+		Reviewed-by: Peff
+	EOF
+	echo "Acked-by: Johan" |
+	git -c "trailer.Acked-by.ifexists=addifdifferent" interpret-trailers \
+		--trailer "Reviewed-by: Peff" --trailer "Acked-by: Johan" >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with config setup' '
+	git config trailer.ack.key "Acked-by: " &&
+	cat >expected <<-\EOF &&
+
+		Acked-by: Peff
+	EOF
+	git interpret-trailers --trim-empty --trailer "ack = Peff" empty >actual &&
+	test_cmp expected actual &&
+	git interpret-trailers --trim-empty --trailer "Acked-by = Peff" empty >actual &&
+	test_cmp expected actual &&
+	git interpret-trailers --trim-empty --trailer "Acked-by :Peff" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with config setup and ":=" as separators' '
+	git config trailer.separators ":=" &&
+	git config trailer.ack.key "Acked-by= " &&
+	cat >expected <<-\EOF &&
+
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trim-empty --trailer "ack = Peff" empty >actual &&
+	test_cmp expected actual &&
+	git interpret-trailers --trim-empty --trailer "Acked-by= Peff" empty >actual &&
+	test_cmp expected actual &&
+	git interpret-trailers --trim-empty --trailer "Acked-by : Peff" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with config setup and "%" as separators' '
+	git config trailer.separators "%" &&
+	cat >expected <<-\EOF &&
+
+		bug% 42
+		count% 10
+		bug% 422
+	EOF
+	git interpret-trailers --trim-empty --trailer "bug = 42" \
+		--trailer count%10 --trailer "test: stuff" \
+		--trailer "bug % 422" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with "%" as separators and a message with trailers' '
+	cat >special_message <<-\EOF &&
+		Special Message
+
+		bug% 42
+		count% 10
+		bug% 422
+	EOF
+	cat >expected <<-\EOF &&
+		Special Message
+
+		bug% 42
+		count% 10
+		bug% 422
+		count% 100
+	EOF
+	git interpret-trailers --trailer count%100 \
+		special_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with config setup and ":=#" as separators' '
+	git config trailer.separators ":=#" &&
+	git config trailer.bug.key "Bug #" &&
+	cat >expected <<-\EOF &&
+
+		Bug #42
+	EOF
+	git interpret-trailers --trim-empty --trailer "bug = 42" empty >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with commit basic message' '
+	cat basic_message >expected &&
+	echo >>expected &&
+	git interpret-trailers <basic_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with basic patch' '
+	cat basic_message >input &&
+	cat basic_patch >>input &&
+	cat basic_message >expected &&
+	echo >>expected &&
+	cat basic_patch >>expected &&
+	git interpret-trailers <input >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with commit complex message as argument' '
+	cat complex_message_body complex_message_trailers >complex_message &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by: Z
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with 2 files arguments' '
+	cat basic_message >>expected &&
+	echo >>expected &&
+	cat basic_patch >>expected &&
+	git interpret-trailers complex_message input >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with message that has comments' '
+	cat basic_message >>message_with_comments &&
+	sed -e "s/ Z\$/ /" >>message_with_comments <<-\EOF &&
+		# comment
+
+		# other comment
+		Cc: Z
+		# yet another comment
+		Reviewed-by: Johan
+		Reviewed-by: Z
+		# last comment
+
+	EOF
+	cat basic_patch >>message_with_comments &&
+	cat basic_message >expected &&
+	cat >>expected <<-\EOF &&
+		# comment
+
+		Reviewed-by: Johan
+		Cc: Peff
+	EOF
+	cat basic_patch >>expected &&
+	git interpret-trailers --trim-empty --trailer "Cc: Peff" message_with_comments >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with commit complex message and trailer args' '
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by: Z
+		Signed-off-by: Z
+		Acked-by= Peff
+		Bug #42
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "bug: 42" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with complex patch, args and --trim-empty' '
+	cat complex_message >complex_patch &&
+	cat basic_patch >>complex_patch &&
+	cat complex_message_body >expected &&
+	cat >>expected <<-\EOF &&
+		Acked-by= Peff
+		Bug #42
+	EOF
+	cat basic_patch >>expected &&
+	git interpret-trailers --trim-empty --trailer "ack: Peff" \
+		--trailer "bug: 42" <complex_patch >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = before"' '
+	git config trailer.bug.where "before" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by: Z
+		Signed-off-by: Z
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "bug: 42" complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = after"' '
+	git config trailer.ack.where "after" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Reviewed-by: Z
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "bug: 42" complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = end"' '
+	git config trailer.review.key "Reviewed-by" &&
+	git config trailer.review.where "end" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Reviewed-by: Z
+		Signed-off-by: Z
+		Reviewed-by: Junio
+		Reviewed-by: Johannes
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "Reviewed-by: Junio" --trailer "Reviewed-by: Johannes" \
+		complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = start"' '
+	git config trailer.review.key "Reviewed-by" &&
+	git config trailer.review.where "start" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Reviewed-by: Johannes
+		Reviewed-by: Junio
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Reviewed-by: Z
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "Reviewed-by: Junio" --trailer "Reviewed-by: Johannes" \
+		complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = before" for a token in the middle of the message' '
+	git config trailer.review.key "Reviewed-by:" &&
+	git config trailer.review.where "before" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Reviewed-by:Johan
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "bug: 42" \
+		--trailer "review: Johan" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "where = before" and --trim-empty' '
+	cat complex_message_body >expected &&
+	cat >>expected <<-\EOF &&
+		Bug #46
+		Bug #42
+		Acked-by= Peff
+		Reviewed-by:Johan
+	EOF
+	git interpret-trailers --trim-empty --trailer "ack: Peff" \
+		--trailer "bug: 42" --trailer "review: Johan" \
+		--trailer "Bug: 46" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'the default is "ifExists = addIfDifferentNeighbor"' '
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" --trailer "ack: Peff" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'default "ifExists" is now "addIfDifferent"' '
+	git config trailer.ifexists "addIfDifferent" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Acked-by= Junio
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" --trailer "ack: Peff" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = addIfDifferent" with "where = end"' '
+	git config trailer.ack.ifExists "addIfDifferent" &&
+	git config trailer.ack.where "end" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = addIfDifferent" with "where = before"' '
+	git config trailer.ack.ifExists "addIfDifferent" &&
+	git config trailer.ack.where "before" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Peff
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = addIfDifferentNeighbor" with "where = end"' '
+	git config trailer.ack.ifExists "addIfDifferentNeighbor" &&
+	git config trailer.ack.where "end" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Acked-by= Peff
+		Acked-by= Junio
+		Tested-by: Jakub
+		Acked-by= Junio
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" \
+		--trailer "Tested-by: Jakub" --trailer "ack: Junio" \
+		--trailer "ack: Junio" --trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = addIfDifferentNeighbor"  with "where = after"' '
+	git config trailer.ack.ifExists "addIfDifferentNeighbor" &&
+	git config trailer.ack.where "after" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+		Tested-by: Jakub
+	EOF
+	git interpret-trailers --trailer "ack: Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" \
+		--trailer "Tested-by: Jakub" --trailer "ack: Junio" \
+		--trailer "ack: Junio" --trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = addIfDifferentNeighbor" and --trim-empty' '
+	git config trailer.ack.ifExists "addIfDifferentNeighbor" &&
+	cat complex_message_body >expected &&
+	cat >>expected <<-\EOF &&
+		Bug #42
+		Acked-by= Peff
+		Acked-by= Junio
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trim-empty --trailer "ack: Peff" \
+		--trailer "Acked-by= Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = add" with "where = end"' '
+	git config trailer.ack.ifExists "add" &&
+	git config trailer.ack.where "end" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Acked-by= Peff
+		Acked-by= Peff
+		Tested-by: Jakub
+		Acked-by= Junio
+		Tested-by: Johannes
+		Acked-by= Peff
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "Acked-by= Peff" --trailer "review:" \
+		--trailer "Tested-by: Jakub" --trailer "ack: Junio" \
+		--trailer "bug: 42" --trailer "Tested-by: Johannes" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = add" with "where = after"' '
+	git config trailer.ack.ifExists "add" &&
+	git config trailer.ack.where "after" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Acked-by= Peff
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "Acked-by= Peff" --trailer "review:" \
+		--trailer "ack: Junio" --trailer "bug: 42" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = replace"' '
+	git config trailer.fix.key "Fixes: " &&
+	git config trailer.fix.ifExists "replace" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+		Fixes: 22
+	EOF
+	git interpret-trailers --trailer "review:" \
+		--trailer "fix=53" --trailer "ack: Junio" --trailer "fix=22" \
+		--trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = replace" with "where = after"' '
+	git config trailer.fix.where "after" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: 22
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" \
+		--trailer "fix=53" --trailer "ack: Junio" --trailer "fix=22" \
+		--trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifExists = doNothing"' '
+	git config trailer.fix.ifExists "doNothing" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "ack: Junio" --trailer "fix=22" \
+		--trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >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" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Cc: Linus
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "cc=Linus" --trailer "ack: Junio" \
+		--trailer "fix=22" --trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'when default "ifMissing" is "doNothing"' '
+	git config trailer.ifmissing "doNothing" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "cc=Linus" --trailer "ack: Junio" \
+		--trailer "fix=22" --trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual &&
+	git config trailer.ifmissing "add"
+'
+
+test_expect_success 'using "ifMissing = add" with "where = end"' '
+	git config trailer.cc.key "Cc: " &&
+	git config trailer.cc.where "end" &&
+	git config trailer.cc.ifMissing "add" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+		Cc: Linus
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "ack: Junio" --trailer "fix=22" \
+		--trailer "bug: 42" --trailer "cc=Linus" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifMissing = add" with "where = before"' '
+	git config trailer.cc.key "Cc: " &&
+	git config trailer.cc.where "before" &&
+	git config trailer.cc.ifMissing "add" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Cc: Linus
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "ack: Junio" --trailer "fix=22" \
+		--trailer "bug: 42" --trailer "cc=Linus" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'using "ifMissing = doNothing"' '
+	git config trailer.cc.ifMissing "doNothing" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=53" \
+		--trailer "cc=Linus" --trailer "ack: Junio" \
+		--trailer "fix=22" --trailer "bug: 42" --trailer "ack: Peff" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'default "where" is now "after"' '
+	git config trailer.where "after" &&
+	git config --unset trailer.ack.where &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Bug #42
+		Fixes: Z
+		Acked-by= Z
+		Acked-by= Peff
+		Acked-by= Peff
+		Acked-by= Junio
+		Acked-by= Peff
+		Reviewed-by:
+		Signed-off-by: Z
+		Tested-by: Jakub
+		Tested-by: Johannes
+	EOF
+	git interpret-trailers --trailer "ack: Peff" \
+		--trailer "Acked-by= Peff" --trailer "review:" \
+		--trailer "Tested-by: Jakub" --trailer "ack: Junio" \
+		--trailer "bug: 42" --trailer "Tested-by: Johannes" \
+		--trailer "ack: Peff" <complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with simple command' '
+	git config trailer.sign.key "Signed-off-by: " &&
+	git config trailer.sign.where "after" &&
+	git config trailer.sign.ifExists "addIfDifferentNeighbor" &&
+	git config trailer.sign.command "echo \"A U Thor <author@example.com>\"" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Signed-off-by: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=22" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with command using commiter information' '
+	git config trailer.sign.ifExists "addIfDifferent" &&
+	git config trailer.sign.command "echo \"\$GIT_COMMITTER_NAME <\$GIT_COMMITTER_EMAIL>\"" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Signed-off-by: C O Mitter <committer@example.com>
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=22" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with command using author information' '
+	git config trailer.sign.key "Signed-off-by: " &&
+	git config trailer.sign.where "after" &&
+	git config trailer.sign.ifExists "addIfDifferentNeighbor" &&
+	git config trailer.sign.command "echo \"\$GIT_AUTHOR_NAME <\$GIT_AUTHOR_EMAIL>\"" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-\EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Signed-off-by: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=22" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup a commit' '
+	echo "Content of the first commit." > a.txt &&
+	git add a.txt &&
+	git commit -m "Add file a.txt"
+'
+
+test_expect_success 'with command using $ARG' '
+	git config trailer.fix.ifExists "replace" &&
+	git config trailer.fix.command "git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \$ARG" &&
+	FIXED=$(git log -1 --oneline --format="%h (%s)" --abbrev-commit --abbrev=14 HEAD) &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-EOF &&
+		Fixes: $FIXED
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Signed-off-by: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=HEAD" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with failing command using $ARG' '
+	git config trailer.fix.ifExists "replace" &&
+	git config trailer.fix.command "false \$ARG" &&
+	cat complex_message_body >expected &&
+	sed -e "s/ Z\$/ /" >>expected <<-EOF &&
+		Fixes: Z
+		Acked-by= Z
+		Reviewed-by:
+		Signed-off-by: Z
+		Signed-off-by: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer "review:" --trailer "fix=HEAD" \
+		<complex_message >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'with empty tokens' '
+	git config --unset trailer.fix.command &&
+	cat >expected <<-EOF &&
+
+		Signed-off-by: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer ":" --trailer ":test" >actual <<-EOF &&
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'with command but no key' '
+	git config --unset trailer.sign.key &&
+	cat >expected <<-EOF &&
+
+		sign: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers >actual <<-EOF &&
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'with no command and no key' '
+	git config --unset trailer.review.key &&
+	cat >expected <<-EOF &&
+
+		review: Junio
+		sign: A U Thor <author@example.com>
+	EOF
+	git interpret-trailers --trailer "review:Junio" >actual <<-EOF &&
+	EOF
+	test_cmp expected actual
+'
+
+test_done

trailer.c

@@ -0,0 +1,851 @@
+#include "cache.h"
+#include "string-list.h"
+#include "run-command.h"
+#include "string-list.h"
+#include "trailer.h"
+/*
+ * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
+ */
+
+enum action_where { WHERE_END, WHERE_AFTER, WHERE_BEFORE, WHERE_START };
+enum action_if_exists { EXISTS_ADD_IF_DIFFERENT_NEIGHBOR, EXISTS_ADD_IF_DIFFERENT,
+			EXISTS_ADD, EXISTS_REPLACE, EXISTS_DO_NOTHING };
+enum action_if_missing { MISSING_ADD, MISSING_DO_NOTHING };
+
+struct conf_info {
+	char *name;
+	char *key;
+	char *command;
+	enum action_where where;
+	enum action_if_exists if_exists;
+	enum action_if_missing if_missing;
+};
+
+static struct conf_info default_conf_info;
+
+struct trailer_item {
+	struct trailer_item *previous;
+	struct trailer_item *next;
+	const char *token;
+	const char *value;
+	struct conf_info conf;
+};
+
+static struct trailer_item *first_conf_item;
+
+static char *separators = ":";
+
+#define TRAILER_ARG_STRING "$ARG"
+
+static int after_or_end(enum action_where where)
+{
+	return (where == WHERE_AFTER) || (where == WHERE_END);
+}
+
+/*
+ * Return the length of the string not including any final
+ * punctuation. E.g., the input "Signed-off-by:" would return
+ * 13, stripping the trailing punctuation but retaining
+ * internal punctuation.
+ */
+static size_t token_len_without_separator(const char *token, size_t len)
+{
+	while (len > 0 && !isalnum(token[len - 1]))
+		len--;
+	return len;
+}
+
+static int same_token(struct trailer_item *a, struct trailer_item *b)
+{
+	size_t a_len = token_len_without_separator(a->token, strlen(a->token));
+	size_t b_len = token_len_without_separator(b->token, strlen(b->token));
+	size_t min_len = (a_len > b_len) ? b_len : a_len;
+
+	return !strncasecmp(a->token, b->token, min_len);
+}
+
+static int same_value(struct trailer_item *a, struct trailer_item *b)
+{
+	return !strcasecmp(a->value, b->value);
+}
+
+static int same_trailer(struct trailer_item *a, struct trailer_item *b)
+{
+	return same_token(a, b) && same_value(a, b);
+}
+
+static inline int contains_only_spaces(const char *str)
+{
+	const char *s = str;
+	while (*s && isspace(*s))
+		s++;
+	return !*s;
+}
+
+static inline void strbuf_replace(struct strbuf *sb, const char *a, const char *b)
+{
+	const char *ptr = strstr(sb->buf, a);
+	if (ptr)
+		strbuf_splice(sb, ptr - sb->buf, strlen(a), b, strlen(b));
+}
+
+static void free_trailer_item(struct trailer_item *item)
+{
+	free(item->conf.name);
+	free(item->conf.key);
+	free(item->conf.command);
+	free((char *)item->token);
+	free((char *)item->value);
+	free(item);
+}
+
+static char last_non_space_char(const char *s)
+{
+	int i;
+	for (i = strlen(s) - 1; i >= 0; i--)
+		if (!isspace(s[i]))
+			return s[i];
+	return '\0';
+}
+
+static void print_tok_val(const char *tok, const char *val)
+{
+	char c = last_non_space_char(tok);
+	if (!c)
+		return;
+	if (strchr(separators, c))
+		printf("%s%s\n", tok, val);
+	else
+		printf("%s%c %s\n", tok, separators[0], val);
+}
+
+static void print_all(struct trailer_item *first, int trim_empty)
+{
+	struct trailer_item *item;
+	for (item = first; item; item = item->next) {
+		if (!trim_empty || strlen(item->value) > 0)
+			print_tok_val(item->token, item->value);
+	}
+}
+
+static void update_last(struct trailer_item **last)
+{
+	if (*last)
+		while ((*last)->next != NULL)
+			*last = (*last)->next;
+}
+
+static void update_first(struct trailer_item **first)
+{
+	if (*first)
+		while ((*first)->previous != NULL)
+			*first = (*first)->previous;
+}
+
+static void add_arg_to_input_list(struct trailer_item *on_tok,
+				  struct trailer_item *arg_tok,
+				  struct trailer_item **first,
+				  struct trailer_item **last)
+{
+	if (after_or_end(arg_tok->conf.where)) {
+		arg_tok->next = on_tok->next;
+		on_tok->next = arg_tok;
+		arg_tok->previous = on_tok;
+		if (arg_tok->next)
+			arg_tok->next->previous = arg_tok;
+		update_last(last);
+	} else {
+		arg_tok->previous = on_tok->previous;
+		on_tok->previous = arg_tok;
+		arg_tok->next = on_tok;
+		if (arg_tok->previous)
+			arg_tok->previous->next = arg_tok;
+		update_first(first);
+	}
+}
+
+static int check_if_different(struct trailer_item *in_tok,
+			      struct trailer_item *arg_tok,
+			      int check_all)
+{
+	enum action_where where = arg_tok->conf.where;
+	do {
+		if (!in_tok)
+			return 1;
+		if (same_trailer(in_tok, arg_tok))
+			return 0;
+		/*
+		 * if we want to add a trailer after another one,
+		 * we have to check those before this one
+		 */
+		in_tok = after_or_end(where) ? in_tok->previous : in_tok->next;
+	} while (check_all);
+	return 1;
+}
+
+static void remove_from_list(struct trailer_item *item,
+			     struct trailer_item **first,
+			     struct trailer_item **last)
+{
+	struct trailer_item *next = item->next;
+	struct trailer_item *previous = item->previous;
+
+	if (next) {
+		item->next->previous = previous;
+		item->next = NULL;
+	} else if (last)
+		*last = previous;
+
+	if (previous) {
+		item->previous->next = next;
+		item->previous = NULL;
+	} else if (first)
+		*first = next;
+}
+
+static struct trailer_item *remove_first(struct trailer_item **first)
+{
+	struct trailer_item *item = *first;
+	*first = item->next;
+	if (item->next) {
+		item->next->previous = NULL;
+		item->next = NULL;
+	}
+	return item;
+}
+
+static int read_from_command(struct child_process *cp, struct strbuf *buf)
+{
+	if (run_command(cp))
+		return error("running trailer command '%s' failed", cp->argv[0]);
+	if (strbuf_read(buf, cp->out, 1024) < 1)
+		return error("reading from trailer command '%s' failed", cp->argv[0]);
+	strbuf_trim(buf);
+	return 0;
+}
+
+static const char *apply_command(const char *command, const char *arg)
+{
+	struct strbuf cmd = STRBUF_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	struct child_process cp;
+	const char *argv[] = {NULL, NULL};
+	const char *result;
+
+	strbuf_addstr(&cmd, command);
+	if (arg)
+		strbuf_replace(&cmd, TRAILER_ARG_STRING, arg);
+
+	argv[0] = cmd.buf;
+	memset(&cp, 0, sizeof(cp));
+	cp.argv = argv;
+	cp.env = local_repo_env;
+	cp.no_stdin = 1;
+	cp.out = -1;
+	cp.use_shell = 1;
+
+	if (read_from_command(&cp, &buf)) {
+		strbuf_release(&buf);
+		result = xstrdup("");
+	} else
+		result = strbuf_detach(&buf, NULL);
+
+	strbuf_release(&cmd);
+	return result;
+}
+
+static void apply_item_command(struct trailer_item *in_tok, struct trailer_item *arg_tok)
+{
+	if (arg_tok->conf.command) {
+		const char *arg;
+		if (arg_tok->value && arg_tok->value[0]) {
+			arg = arg_tok->value;
+		} else {
+			if (in_tok && in_tok->value)
+				arg = xstrdup(in_tok->value);
+			else
+				arg = xstrdup("");
+		}
+		arg_tok->value = apply_command(arg_tok->conf.command, arg);
+		free((char *)arg);
+	}
+}
+
+static void apply_arg_if_exists(struct trailer_item *in_tok,
+				struct trailer_item *arg_tok,
+				struct trailer_item *on_tok,
+				struct trailer_item **in_tok_first,
+				struct trailer_item **in_tok_last)
+{
+	switch (arg_tok->conf.if_exists) {
+	case EXISTS_DO_NOTHING:
+		free_trailer_item(arg_tok);
+		break;
+	case EXISTS_REPLACE:
+		apply_item_command(in_tok, arg_tok);
+		add_arg_to_input_list(on_tok, arg_tok,
+				      in_tok_first, in_tok_last);
+		remove_from_list(in_tok, in_tok_first, in_tok_last);
+		free_trailer_item(in_tok);
+		break;
+	case EXISTS_ADD:
+		apply_item_command(in_tok, arg_tok);
+		add_arg_to_input_list(on_tok, arg_tok,
+				      in_tok_first, in_tok_last);
+		break;
+	case EXISTS_ADD_IF_DIFFERENT:
+		apply_item_command(in_tok, arg_tok);
+		if (check_if_different(in_tok, arg_tok, 1))
+			add_arg_to_input_list(on_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		else
+			free_trailer_item(arg_tok);
+		break;
+	case EXISTS_ADD_IF_DIFFERENT_NEIGHBOR:
+		apply_item_command(in_tok, arg_tok);
+		if (check_if_different(on_tok, arg_tok, 0))
+			add_arg_to_input_list(on_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		else
+			free_trailer_item(arg_tok);
+		break;
+	}
+}
+
+static void apply_arg_if_missing(struct trailer_item **in_tok_first,
+				 struct trailer_item **in_tok_last,
+				 struct trailer_item *arg_tok)
+{
+	struct trailer_item **in_tok;
+	enum action_where where;
+
+	switch (arg_tok->conf.if_missing) {
+	case MISSING_DO_NOTHING:
+		free_trailer_item(arg_tok);
+		break;
+	case MISSING_ADD:
+		where = arg_tok->conf.where;
+		in_tok = after_or_end(where) ? in_tok_last : in_tok_first;
+		apply_item_command(NULL, arg_tok);
+		if (*in_tok) {
+			add_arg_to_input_list(*in_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		} else {
+			*in_tok_first = arg_tok;
+			*in_tok_last = arg_tok;
+		}
+		break;
+	}
+}
+
+static int find_same_and_apply_arg(struct trailer_item **in_tok_first,
+				   struct trailer_item **in_tok_last,
+				   struct trailer_item *arg_tok)
+{
+	struct trailer_item *in_tok;
+	struct trailer_item *on_tok;
+	struct trailer_item *following_tok;
+
+	enum action_where where = arg_tok->conf.where;
+	int middle = (where == WHERE_AFTER) || (where == WHERE_BEFORE);
+	int backwards = after_or_end(where);
+	struct trailer_item *start_tok = backwards ? *in_tok_last : *in_tok_first;
+
+	for (in_tok = start_tok; in_tok; in_tok = following_tok) {
+		following_tok = backwards ? in_tok->previous : in_tok->next;
+		if (!same_token(in_tok, arg_tok))
+			continue;
+		on_tok = middle ? in_tok : start_tok;
+		apply_arg_if_exists(in_tok, arg_tok, on_tok,
+				    in_tok_first, in_tok_last);
+		return 1;
+	}
+	return 0;
+}
+
+static void process_trailers_lists(struct trailer_item **in_tok_first,
+				   struct trailer_item **in_tok_last,
+				   struct trailer_item **arg_tok_first)
+{
+	struct trailer_item *arg_tok;
+	struct trailer_item *next_arg;
+
+	if (!*arg_tok_first)
+		return;
+
+	for (arg_tok = *arg_tok_first; arg_tok; arg_tok = next_arg) {
+		int applied = 0;
+
+		next_arg = arg_tok->next;
+		remove_from_list(arg_tok, arg_tok_first, NULL);
+
+		applied = find_same_and_apply_arg(in_tok_first,
+						  in_tok_last,
+						  arg_tok);
+
+		if (!applied)
+			apply_arg_if_missing(in_tok_first,
+					     in_tok_last,
+					     arg_tok);
+	}
+}
+
+static int set_where(struct conf_info *item, const char *value)
+{
+	if (!strcasecmp("after", value))
+		item->where = WHERE_AFTER;
+	else if (!strcasecmp("before", value))
+		item->where = WHERE_BEFORE;
+	else if (!strcasecmp("end", value))
+		item->where = WHERE_END;
+	else if (!strcasecmp("start", value))
+		item->where = WHERE_START;
+	else
+		return -1;
+	return 0;
+}
+
+static int set_if_exists(struct conf_info *item, const char *value)
+{
+	if (!strcasecmp("addIfDifferent", value))
+		item->if_exists = EXISTS_ADD_IF_DIFFERENT;
+	else if (!strcasecmp("addIfDifferentNeighbor", value))
+		item->if_exists = EXISTS_ADD_IF_DIFFERENT_NEIGHBOR;
+	else if (!strcasecmp("add", value))
+		item->if_exists = EXISTS_ADD;
+	else if (!strcasecmp("replace", value))
+		item->if_exists = EXISTS_REPLACE;
+	else if (!strcasecmp("doNothing", value))
+		item->if_exists = EXISTS_DO_NOTHING;
+	else
+		return -1;
+	return 0;
+}
+
+static int set_if_missing(struct conf_info *item, const char *value)
+{
+	if (!strcasecmp("doNothing", value))
+		item->if_missing = MISSING_DO_NOTHING;
+	else if (!strcasecmp("add", value))
+		item->if_missing = MISSING_ADD;
+	else
+		return -1;
+	return 0;
+}
+
+static void duplicate_conf(struct conf_info *dst, struct conf_info *src)
+{
+	*dst = *src;
+	if (src->name)
+		dst->name = xstrdup(src->name);
+	if (src->key)
+		dst->key = xstrdup(src->key);
+	if (src->command)
+		dst->command = xstrdup(src->command);
+}
+
+static struct trailer_item *get_conf_item(const char *name)
+{
+	struct trailer_item *item;
+	struct trailer_item *previous;
+
+	/* Look up item with same name */
+	for (previous = NULL, item = first_conf_item;
+	     item;
+	     previous = item, item = item->next) {
+		if (!strcasecmp(item->conf.name, name))
+			return item;
+	}
+
+	/* Item does not already exists, create it */
+	item = xcalloc(sizeof(struct trailer_item), 1);
+	duplicate_conf(&item->conf, &default_conf_info);
+	item->conf.name = xstrdup(name);
+
+	if (!previous)
+		first_conf_item = item;
+	else {
+		previous->next = item;
+		item->previous = previous;
+	}
+
+	return item;
+}
+
+enum trailer_info_type { TRAILER_KEY, TRAILER_COMMAND, TRAILER_WHERE,
+			 TRAILER_IF_EXISTS, TRAILER_IF_MISSING };
+
+static struct {
+	const char *name;
+	enum trailer_info_type type;
+} trailer_config_items[] = {
+	{ "key", TRAILER_KEY },
+	{ "command", TRAILER_COMMAND },
+	{ "where", TRAILER_WHERE },
+	{ "ifexists", TRAILER_IF_EXISTS },
+	{ "ifmissing", TRAILER_IF_MISSING }
+};
+
+static int git_trailer_default_config(const char *conf_key, const char *value, void *cb)
+{
+	const char *trailer_item, *variable_name;
+
+	if (!skip_prefix(conf_key, "trailer.", &trailer_item))
+		return 0;
+
+	variable_name = strrchr(trailer_item, '.');
+	if (!variable_name) {
+		if (!strcmp(trailer_item, "where")) {
+			if (set_where(&default_conf_info, value) < 0)
+				warning(_("unknown value '%s' for key '%s'"),
+					value, conf_key);
+		} else if (!strcmp(trailer_item, "ifexists")) {
+			if (set_if_exists(&default_conf_info, value) < 0)
+				warning(_("unknown value '%s' for key '%s'"),
+					value, conf_key);
+		} else if (!strcmp(trailer_item, "ifmissing")) {
+			if (set_if_missing(&default_conf_info, value) < 0)
+				warning(_("unknown value '%s' for key '%s'"),
+					value, conf_key);
+		} else if (!strcmp(trailer_item, "separators")) {
+			separators = xstrdup(value);
+		}
+	}
+	return 0;
+}
+
+static int git_trailer_config(const char *conf_key, const char *value, void *cb)
+{
+	const char *trailer_item, *variable_name;
+	struct trailer_item *item;
+	struct conf_info *conf;
+	char *name = NULL;
+	enum trailer_info_type type;
+	int i;
+
+	if (!skip_prefix(conf_key, "trailer.", &trailer_item))
+		return 0;
+
+	variable_name = strrchr(trailer_item, '.');
+	if (!variable_name)
+		return 0;
+
+	variable_name++;
+	for (i = 0; i < ARRAY_SIZE(trailer_config_items); i++) {
+		if (strcmp(trailer_config_items[i].name, variable_name))
+			continue;
+		name = xstrndup(trailer_item,  variable_name - trailer_item - 1);
+		type = trailer_config_items[i].type;
+		break;
+	}
+
+	if (!name)
+		return 0;
+
+	item = get_conf_item(name);
+	conf = &item->conf;
+	free(name);
+
+	switch (type) {
+	case TRAILER_KEY:
+		if (conf->key)
+			warning(_("more than one %s"), conf_key);
+		conf->key = xstrdup(value);
+		break;
+	case TRAILER_COMMAND:
+		if (conf->command)
+			warning(_("more than one %s"), conf_key);
+		conf->command = xstrdup(value);
+		break;
+	case TRAILER_WHERE:
+		if (set_where(conf, value))
+			warning(_("unknown value '%s' for key '%s'"), value, conf_key);
+		break;
+	case TRAILER_IF_EXISTS:
+		if (set_if_exists(conf, value))
+			warning(_("unknown value '%s' for key '%s'"), value, conf_key);
+		break;
+	case TRAILER_IF_MISSING:
+		if (set_if_missing(conf, value))
+			warning(_("unknown value '%s' for key '%s'"), value, conf_key);
+		break;
+	default:
+		die("internal bug in trailer.c");
+	}
+	return 0;
+}
+
+static int parse_trailer(struct strbuf *tok, struct strbuf *val, const char *trailer)
+{
+	size_t len;
+	struct strbuf seps = STRBUF_INIT;
+	strbuf_addstr(&seps, separators);
+	strbuf_addch(&seps, '=');
+	len = strcspn(trailer, seps.buf);
+	strbuf_release(&seps);
+	if (len == 0)
+		return error(_("empty trailer token in trailer '%s'"), trailer);
+	if (len < strlen(trailer)) {
+		strbuf_add(tok, trailer, len);
+		strbuf_trim(tok);
+		strbuf_addstr(val, trailer + len + 1);
+		strbuf_trim(val);
+	} else {
+		strbuf_addstr(tok, trailer);
+		strbuf_trim(tok);
+	}
+	return 0;
+}
+
+static const char *token_from_item(struct trailer_item *item, char *tok)
+{
+	if (item->conf.key)
+		return item->conf.key;
+	if (tok)
+		return tok;
+	return item->conf.name;
+}
+
+static struct trailer_item *new_trailer_item(struct trailer_item *conf_item,
+					     char *tok, char *val)
+{
+	struct trailer_item *new = xcalloc(sizeof(*new), 1);
+	new->value = val ? val : xstrdup("");
+
+	if (conf_item) {
+		duplicate_conf(&new->conf, &conf_item->conf);
+		new->token = xstrdup(token_from_item(conf_item, tok));
+		free(tok);
+	} else {
+		duplicate_conf(&new->conf, &default_conf_info);
+		new->token = tok;
+	}
+
+	return new;
+}
+
+static int token_matches_item(const char *tok, struct trailer_item *item, int tok_len)
+{
+	if (!strncasecmp(tok, item->conf.name, tok_len))
+		return 1;
+	return item->conf.key ? !strncasecmp(tok, item->conf.key, tok_len) : 0;
+}
+
+static struct trailer_item *create_trailer_item(const char *string)
+{
+	struct strbuf tok = STRBUF_INIT;
+	struct strbuf val = STRBUF_INIT;
+	struct trailer_item *item;
+	int tok_len;
+
+	if (parse_trailer(&tok, &val, string))
+		return NULL;
+
+	tok_len = token_len_without_separator(tok.buf, tok.len);
+
+	/* Lookup if the token matches something in the config */
+	for (item = first_conf_item; item; item = item->next) {
+		if (token_matches_item(tok.buf, item, tok_len))
+			return new_trailer_item(item,
+						strbuf_detach(&tok, NULL),
+						strbuf_detach(&val, NULL));
+	}
+
+	return new_trailer_item(NULL,
+				strbuf_detach(&tok, NULL),
+				strbuf_detach(&val, NULL));
+}
+
+static void add_trailer_item(struct trailer_item **first,
+			     struct trailer_item **last,
+			     struct trailer_item *new)
+{
+	if (!new)
+		return;
+	if (!*last) {
+		*first = new;
+		*last = new;
+	} else {
+		(*last)->next = new;
+		new->previous = *last;
+		*last = new;
+	}
+}
+
+static struct trailer_item *process_command_line_args(struct string_list *trailers)
+{
+	struct trailer_item *arg_tok_first = NULL;
+	struct trailer_item *arg_tok_last = NULL;
+	struct string_list_item *tr;
+	struct trailer_item *item;
+
+	/* Add a trailer item for each configured trailer with a command */
+	for (item = first_conf_item; item; item = item->next) {
+		if (item->conf.command) {
+			struct trailer_item *new = new_trailer_item(item, NULL, NULL);
+			add_trailer_item(&arg_tok_first, &arg_tok_last, new);
+		}
+	}
+
+	/* Add a trailer item for each trailer on the command line */
+	for_each_string_list_item(tr, trailers) {
+		struct trailer_item *new = create_trailer_item(tr->string);
+		add_trailer_item(&arg_tok_first, &arg_tok_last, new);
+	}
+
+	return arg_tok_first;
+}
+
+static struct strbuf **read_input_file(const char *file)
+{
+	struct strbuf **lines;
+	struct strbuf sb = STRBUF_INIT;
+
+	if (file) {
+		if (strbuf_read_file(&sb, file, 0) < 0)
+			die_errno(_("could not read input file '%s'"), file);
+	} else {
+		if (strbuf_read(&sb, fileno(stdin), 0) < 0)
+			die_errno(_("could not read from stdin"));
+	}
+
+	lines = strbuf_split(&sb, '\n');
+
+	strbuf_release(&sb);
+
+	return lines;
+}
+
+/*
+ * Return the (0 based) index of the start of the patch or the line
+ * count if there is no patch in the message.
+ */
+static int find_patch_start(struct strbuf **lines, int count)
+{
+	int i;
+
+	/* Get the start of the patch part if any */
+	for (i = 0; i < count; i++) {
+		if (starts_with(lines[i]->buf, "---"))
+			return i;
+	}
+
+	return count;
+}
+
+/*
+ * Return the (0 based) index of the first trailer line or count if
+ * there are no trailers. Trailers are searched only in the lines from
+ * index (count - 1) down to index 0.
+ */
+static int find_trailer_start(struct strbuf **lines, int count)
+{
+	int start, only_spaces = 1;
+
+	/*
+	 * Get the start of the trailers by looking starting from the end
+	 * for a line with only spaces before lines with one separator.
+	 */
+	for (start = count - 1; start >= 0; start--) {
+		if (lines[start]->buf[0] == comment_line_char)
+			continue;
+		if (contains_only_spaces(lines[start]->buf)) {
+			if (only_spaces)
+				continue;
+			return start + 1;
+		}
+		if (strcspn(lines[start]->buf, separators) < lines[start]->len) {
+			if (only_spaces)
+				only_spaces = 0;
+			continue;
+		}
+		return count;
+	}
+
+	return only_spaces ? count : 0;
+}
+
+static int has_blank_line_before(struct strbuf **lines, int start)
+{
+	for (;start >= 0; start--) {
+		if (lines[start]->buf[0] == comment_line_char)
+			continue;
+		return contains_only_spaces(lines[start]->buf);
+	}
+	return 0;
+}
+
+static void print_lines(struct strbuf **lines, int start, int end)
+{
+	int i;
+	for (i = start; lines[i] && i < end; i++)
+		printf("%s", lines[i]->buf);
+}
+
+static int process_input_file(struct strbuf **lines,
+			      struct trailer_item **in_tok_first,
+			      struct trailer_item **in_tok_last)
+{
+	int count = 0;
+	int patch_start, trailer_start, i;
+
+	/* Get the line count */
+	while (lines[count])
+		count++;
+
+	patch_start = find_patch_start(lines, count);
+	trailer_start = find_trailer_start(lines, patch_start);
+
+	/* Print lines before the trailers as is */
+	print_lines(lines, 0, trailer_start);
+
+	if (!has_blank_line_before(lines, trailer_start - 1))
+		printf("\n");
+
+	/* Parse trailer lines */
+	for (i = trailer_start; i < patch_start; i++) {
+		struct trailer_item *new = create_trailer_item(lines[i]->buf);
+		add_trailer_item(in_tok_first, in_tok_last, new);
+	}
+
+	return patch_start;
+}
+
+static void free_all(struct trailer_item **first)
+{
+	while (*first) {
+		struct trailer_item *item = remove_first(first);
+		free_trailer_item(item);
+	}
+}
+
+void process_trailers(const char *file, int trim_empty, struct string_list *trailers)
+{
+	struct trailer_item *in_tok_first = NULL;
+	struct trailer_item *in_tok_last = NULL;
+	struct trailer_item *arg_tok_first;
+	struct strbuf **lines;
+	int patch_start;
+
+	/* Default config must be setup first */
+	git_config(git_trailer_default_config, NULL);
+	git_config(git_trailer_config, NULL);
+
+	lines = read_input_file(file);
+
+	/* Print the lines before the trailers */
+	patch_start = process_input_file(lines, &in_tok_first, &in_tok_last);
+
+	arg_tok_first = process_command_line_args(trailers);
+
+	process_trailers_lists(&in_tok_first, &in_tok_last, &arg_tok_first);
+
+	print_all(in_tok_first, trim_empty);
+
+	free_all(&in_tok_first);
+
+	/* Print the lines after the trailers as is */
+	print_lines(lines, patch_start, INT_MAX);
+
+	strbuf_list_free(lines);
+}

trailer.h

@@ -0,0 +1,6 @@
+#ifndef TRAILER_H
+#define TRAILER_H
+
+void process_trailers(const char *file, int trim_empty, struct string_list *trailers);
+
+#endif /* TRAILER_H */