tag: respect `pager.tag` in list-mode only

Using, e.g., `git -c pager.tag tag -a new-tag` results in errors such as
"Vim: Warning: Output is not to a terminal" and a garbled terminal.
Someone who makes use of both `git tag -a` and `git tag -l` will
probably not set `pager.tag`, so that `git tag -a` will actually work,
at the cost of not paging output of `git tag -l`.

Use the mechanisms introduced in two earlier patches to ignore
`pager.tag` in git.c and let the `git tag` builtin handle it on its own.
Only respect `pager.tag` when running in list-mode.

There is a window between where the pager is started before and after
this patch. This means that early errors can behave slightly different
before and after this patch. Since operation-parsing has to happen
inside this window, this can be seen with `git -c pager.tag="echo pager
is used" tag -l --unknown-option`. This change in paging-behavior should
be acceptable since it only affects erroneous usages.

Update the documentation and update tests.

If an alias is used to run `git tag -a`, then `pager.tag` will still be
respected. Document this known breakage. It will be fixed in a later
commit. Add a similar test for `-l`, which works.

Noticed-by: Anatoly Borodin <anatoly.borodin@gmail.com>
Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-tag.txt

@@ -205,6 +205,9 @@ it in the repository configuration as follows:
     signingKey = <gpg-keyid>
 -------------------------------------
 
+`pager.tag` is only respected when listing tags, i.e., when `-l` is
+used or implied.
+See linkgit:git-config[1].
 
 DISCUSSION
 ----------

builtin/tag.c

@@ -461,6 +461,9 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 			cmdmode = 'l';
 	}
 
+	if (cmdmode == 'l')
+		setup_auto_pager("tag", 0);
+
 	if ((create_tag_object || force) && (cmdmode != 0))
 		usage_with_options(git_tag_usage, options);
 

git.c

@@ -466,7 +466,7 @@ static struct cmd_struct commands[] = {
 	{ "stripspace", cmd_stripspace },
 	{ "submodule--helper", cmd_submodule__helper, RUN_SETUP | SUPPORT_SUPER_PREFIX},
 	{ "symbolic-ref", cmd_symbolic_ref, RUN_SETUP },
-	{ "tag", cmd_tag, RUN_SETUP },
+	{ "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },
 	{ "unpack-file", cmd_unpack_file, RUN_SETUP },
 	{ "unpack-objects", cmd_unpack_objects, RUN_SETUP },
 	{ "update-index", cmd_update_index, RUN_SETUP },

t/t7006-pager.sh

@@ -187,7 +187,7 @@ test_expect_success TTY 'git tag -a defaults to not paging' '
 	! test -e paginated.out
 '
 
-test_expect_failure TTY 'git tag -a ignores pager.tag' '
+test_expect_success TTY 'git tag -a ignores pager.tag' '
 	test_when_finished "git tag -d newtag" &&
 	rm -f paginated.out &&
 	test_terminal git -c pager.tag tag -am message newtag &&
@@ -201,6 +201,19 @@ test_expect_success TTY 'git tag -a respects --paginate' '
 	test -e paginated.out
 '
 
+test_expect_failure TTY 'git tag as alias ignores pager.tag with -a' '
+	test_when_finished "git tag -d newtag" &&
+	rm -f paginated.out &&
+	test_terminal git -c pager.tag -c alias.t=tag t -am message newtag &&
+	! test -e paginated.out
+'
+
+test_expect_success TTY 'git tag as alias respects pager.tag with -l' '
+	rm -f paginated.out &&
+	test_terminal git -c pager.tag -c alias.t=tag t -l &&
+	test -e paginated.out
+'
+
 # A colored commit log will begin with an appropriate ANSI escape
 # for the first color; the text "commit" comes later.
 colorful() {