[PATCH v6 5/7] builtin/grep.c: add '--column' option to 'git-grep(1)'

[Taylor Blau <me@ttaylorr.com>]

Teach 'git-grep(1)' a new option, '--column', to show the column
number of the first match on a non-context line. This makes it possible
to teach 'contrib/git-jump/git-jump' how to seek to the first matching
position of a grep match in your editor, and allows similar additional
scripting capabilities.

For example:

  $ git grep -n --column foo | head -n3
  .clang-format:51:14:# myFunction(foo, bar, baz);
  .clang-format:64:7:# int foo();
  .clang-format:75:8:# void foo()

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 Documentation/git-grep.txt |  7 ++++++-
 builtin/grep.c             |  4 ++++
 grep.c                     |  5 +++--
 t/t7810-grep.sh            | 39 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index 18b494731f..cec4665df5 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -13,7 +13,7 @@ SYNOPSIS
 	   [-v | --invert-match] [-h|-H] [--full-name]
 	   [-E | --extended-regexp] [-G | --basic-regexp]
 	   [-P | --perl-regexp]
-	   [-F | --fixed-strings] [-n | --line-number]
+	   [-F | --fixed-strings] [-n | --line-number] [--column]
 	   [-l | --files-with-matches] [-L | --files-without-match]
 	   [(-O | --open-files-in-pager) [<pager>]]
 	   [-z | --null]
@@ -169,6 +169,11 @@ providing this option will cause it to die.
 --line-number::
 	Prefix the line number to matching lines.
 
+--column::
+	Prefix the 1-indexed byte-offset of the first match from the start of the
+	matching line. This option is incompatible with '--invert-match', and
+	ignored with expressions using '--and', '--or', '--not'.
+
 -l::
 --files-with-matches::
 --name-only::
diff --git a/builtin/grep.c b/builtin/grep.c
index 5f32d2ce84..f9f516dfc4 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -829,6 +829,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 			    GREP_PATTERN_TYPE_PCRE),
 		OPT_GROUP(""),
 		OPT_BOOL('n', "line-number", &opt.linenum, N_("show line numbers")),
+		OPT_BOOL(0, "column", &opt.columnnum, N_("show column number of first match")),
 		OPT_NEGBIT('h', NULL, &opt.pathname, N_("don't show filenames"), 1),
 		OPT_BIT('H', NULL, &opt.pathname, N_("show filenames"), 1),
 		OPT_NEGBIT(0, "full-name", &opt.relative,
@@ -1111,6 +1112,9 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		hit = grep_objects(&opt, &pathspec, the_repository, &list);
 	}
 
+	if (opt.columnnum && opt.invert)
+		die(_("--column and --invert-match cannot be combined"));
+
 	if (num_threads)
 		hit |= wait_all();
 	if (hit && show_in_pager)
diff --git a/grep.c b/grep.c
index f3fe416791..7396b49a2d 100644
--- a/grep.c
+++ b/grep.c
@@ -1402,9 +1402,10 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 	/*
 	 * Treat 'cno' as the 1-indexed offset from the start of a non-context
 	 * line to its first match. Otherwise, 'cno' is 0 indicating that we are
-	 * being called with a context line.
+	 * being called with a context line, or we are --extended, and cannot
+	 * always show an answer.
 	 */
-	if (opt->columnnum && cno) {
+	if (opt->columnnum && sign == ':' && !opt->extended) {
 		char buf[32];
 		xsnprintf(buf, sizeof(buf), "%d", cno);
 		output_color(opt, buf, strlen(buf), opt->color_columnno);
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 1797f632a3..491b2e044a 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -99,6 +99,40 @@ do
 		test_cmp expected actual
 	'
 
+	test_expect_success "grep -w $L (with --column)" '
+		{
+			echo ${HC}file:5:foo mmap bar
+			echo ${HC}file:14:foo_mmap bar mmap
+			echo ${HC}file:5:foo mmap bar_mmap
+			echo ${HC}file:14:foo_mmap bar mmap baz
+		} >expected &&
+		git grep --column -w -e mmap $H >actual &&
+		test_cmp expected actual
+	'
+
+	test_expect_success "grep -w $L (with --column, -C)" '
+		{
+			echo ${HC}file:5:foo mmap bar
+			echo ${HC}file-foo_mmap bar
+			echo ${HC}file:14:foo_mmap bar mmap
+			echo ${HC}file:5:foo mmap bar_mmap
+			echo ${HC}file:14:foo_mmap bar mmap baz
+		} >expected &&
+		git grep --column -w -C1 -e mmap $H >actual &&
+		test_cmp expected actual
+	'
+
+	test_expect_success "grep -w $L (with --line-number, --column)" '
+		{
+			echo ${HC}file:1:5:foo mmap bar
+			echo ${HC}file:3:14:foo_mmap bar mmap
+			echo ${HC}file:4:5:foo mmap bar_mmap
+			echo ${HC}file:5:14:foo_mmap bar mmap baz
+		} >expected &&
+		git grep -n --column -w -e mmap $H >actual &&
+		test_cmp expected actual
+	'
+
 	test_expect_success "grep -w $L" '
 		{
 			echo ${HC}file:1:foo mmap bar
@@ -1590,4 +1624,9 @@ test_expect_success 'grep does not report i-t-a and assume unchanged with -L' '
 	test_cmp expected actual
 '
 
+test_expect_success 'grep does not allow --column, --invert-match' '
+	test_must_fail git grep --column --invert-match pat 2>err &&
+	test_i18ngrep "\-\-column and \-\-invert-match cannot be combined" err
+'
+
 test_done
-- 
2.17.0