In many projects the number of contributors is low enough that users know
each other and the full email address doesn't need to be displayed.
Displaying only the author's username saves a lot of columns on the screen.

Existing 'e/E' (as in "%ae" and "%aE") placeholders would show the
author's address as "prarit@redhat.com", which would waste columns to show
the same domain-part for all contributors when used in redhat-only
project.  Introduce 'l/L' placeholders that strip '@' and domain part from
the e-mail address.

Signed-off-by: Prarit Bhargava <redacted>
---
Changes in v2:
- Changed option to 'L' based on https://www.ietf.org/rfc/rfc2822.txt
  definition of 'local-part' of email addresses.
- added additional information to documentation for %cL and %cl
- added mailmap output test
- modified code to use mailmap output for "L" option
- modified code to check if email address field has '@' symbol
- modified tests based on input from Peff

Changes in v3:
- Adjust Documentation descriptions for %aL and %cL
- remove exports of TEST* variables from test-lib.sh
- move testing to t6006 and t4203

Changes in v4:
- Change subject and patch description
- Update Documentation descriptions for %aL and %cL

 Documentation/pretty-formats.txt |  6 ++++++
 pretty.c                         |  9 ++++++++-
 t/t4203-mailmap.sh               | 28 ++++++++++++++++++++++++++++
 t/t6006-rev-list-format.sh       |  8 ++++++--
 t/test-lib.sh                    |  8 ++++++--
 5 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/Documentation/pretty-formats.txt b/Documentation/pretty-formats.txt
index b87e2e83e6d0..31c6e8d2b86a 100644
--- a/Documentation/pretty-formats.txt
+++ b/Documentation/pretty-formats.txt

@@ -163,6 +163,9 @@ The placeholders are:
 '%ae':: author email
 '%aE':: author email (respecting .mailmap, see linkgit:git-shortlog[1]
 	or linkgit:git-blame[1])
+'%al':: author email local-part (the part before the '@' sign)
+'%aL':: author local-part (see '%al') respecting .mailmap, see
+	linkgit:git-shortlog[1] or linkgit:git-blame[1])
 '%ad':: author date (format respects --date= option)
 '%aD':: author date, RFC2822 style
 '%ar':: author date, relative

@@ -175,6 +178,9 @@ The placeholders are:
 '%ce':: committer email
 '%cE':: committer email (respecting .mailmap, see
 	linkgit:git-shortlog[1] or linkgit:git-blame[1])
+'%cl':: author email local-part (the part before the '@' sign)
+'%cL':: author local-part (see '%cl') respecting .mailmap, see
+	linkgit:git-shortlog[1] or linkgit:git-blame[1])
 '%cd':: committer date (format respects --date= option)
 '%cD':: committer date, RFC2822 style
 '%cr':: committer date, relative

diff --git a/pretty.c b/pretty.c
index b32f0369531c..93eb6e837071 100644
--- a/pretty.c
+++ b/pretty.c

@@ -696,7 +696,7 @@ static size_t format_person_part(struct strbuf *sb, char part,
 	mail = s.mail_begin;
 	maillen = s.mail_end - s.mail_begin;
 
-	if (part == 'N' || part == 'E') /* mailmap lookup */
+	if (part == 'N' || part == 'E' || part == 'L') /* mailmap lookup */
 		mailmap_name(&mail, &maillen, &name, &namelen);
 	if (part == 'n' || part == 'N') {	/* name */
 		strbuf_add(sb, name, namelen);

@@ -706,6 +706,13 @@ static size_t format_person_part(struct strbuf *sb, char part,
 		strbuf_add(sb, mail, maillen);
 		return placeholder_len;
 	}
+	if (part == 'l' || part == 'L') {	/* local-part */
+		const char *at = memchr(mail, '@', maillen);
+		if (at)
+			maillen = at - mail;
+		strbuf_add(sb, mail, maillen);
+		return placeholder_len;
+	}
 
 	if (!s.date_begin)
 		goto skip;

diff --git a/t/t4203-mailmap.sh b/t/t4203-mailmap.sh
index e8f9c0f5bc8c..586c3a86b1d2 100755
--- a/t/t4203-mailmap.sh
+++ b/t/t4203-mailmap.sh

@@ -412,6 +412,34 @@ test_expect_success 'Log output (complex mapping)' '
 	test_cmp expect actual
 '
 
+cat >expect << EOF
+Author email cto@coompany.xx has local-part cto
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email me@company.xx has local-part me
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email me@company.xx has local-part me
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email nick2@company.xx has local-part nick2
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email bugs@company.xx has local-part bugs
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email bugs@company.xx has local-part bugs
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+
+Author email author@example.com has local-part author
+Committer email $GIT_COMMITTER_EMAIL has local-part $TEST_COMMITTER_LOCALNAME
+EOF
+
+test_expect_success 'Log output (local-part email address)' '
+	git log --pretty=format:"Author email %ae has local-part %al%nCommitter email %ce has local-part %cl%n" >actual &&
+	test_cmp expect actual
+'
+
 cat >expect << EOF
 Author: CTO <cto@company.xx>
 Author: Santa Claus <santa.claus@northpole.xx>

diff --git a/t/t6006-rev-list-format.sh b/t/t6006-rev-list-format.sh
index 1f7d3f7acc9c..ebdc49c4965e 100755
--- a/t/t6006-rev-list-format.sh
+++ b/t/t6006-rev-list-format.sh

@@ -109,31 +109,35 @@ commit $head1
 EOF
 
 # we don't test relative here
-test_format author %an%n%ae%n%ad%n%aD%n%at <<EOF
+test_format author %an%n%ae%n%al%n%ad%n%aD%n%at <<EOF
 commit $head2
 $GIT_AUTHOR_NAME
 $GIT_AUTHOR_EMAIL
+$TEST_AUTHOR_LOCALNAME
 Thu Apr 7 15:13:13 2005 -0700
 Thu, 7 Apr 2005 15:13:13 -0700
 1112911993
 commit $head1
 $GIT_AUTHOR_NAME
 $GIT_AUTHOR_EMAIL
+$TEST_AUTHOR_LOCALNAME
 Thu Apr 7 15:13:13 2005 -0700
 Thu, 7 Apr 2005 15:13:13 -0700
 1112911993
 EOF
 
-test_format committer %cn%n%ce%n%cd%n%cD%n%ct <<EOF
+test_format committer %cn%n%ce%n%cl%n%cd%n%cD%n%ct <<EOF
 commit $head2
 $GIT_COMMITTER_NAME
 $GIT_COMMITTER_EMAIL
+$TEST_COMMITTER_LOCALNAME
 Thu Apr 7 15:13:13 2005 -0700
 Thu, 7 Apr 2005 15:13:13 -0700
 1112911993
 commit $head1
 $GIT_COMMITTER_NAME
 $GIT_COMMITTER_EMAIL
+$TEST_COMMITTER_LOCALNAME
 Thu Apr 7 15:13:13 2005 -0700
 Thu, 7 Apr 2005 15:13:13 -0700
 1112911993

diff --git a/t/test-lib.sh b/t/test-lib.sh
index e06fa02a0eec..46c44408432e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh

@@ -404,9 +404,13 @@ unset VISUAL EMAIL LANGUAGE COLUMNS $("$PERL_PATH" -e '
 unset XDG_CACHE_HOME
 unset XDG_CONFIG_HOME
 unset GITPERLLIB
-GIT_AUTHOR_EMAIL=author@example.com
+TEST_AUTHOR_LOCALNAME=author
+TEST_AUTHOR_DOMAIN=example.com
+GIT_AUTHOR_EMAIL=${TEST_AUTHOR_LOCALNAME}@${TEST_AUTHOR_DOMAIN}
 GIT_AUTHOR_NAME='A U Thor'
-GIT_COMMITTER_EMAIL=committer@example.com
+TEST_COMMITTER_LOCALNAME=committer
+TEST_COMMITTER_DOMAIN=example.com
+GIT_COMMITTER_EMAIL=${TEST_COMMITTER_LOCALNAME}@${TEST_COMMITTER_DOMAIN}
 GIT_COMMITTER_NAME='C O Mitter'
 GIT_MERGE_VERBOSITY=5
 GIT_MERGE_AUTOEDIT=no