[Outreachy PATCH v4 1/3] parse-options: answer --git-completion-helper before command runs

[Tanga Joris <tangajoris@gmail.com>]

fast-import parses its options only after reading the "feature"
lines from its input, and it creates a temporary pack file before
that. So "git fast-import --git-completion-helper" waits for input,
and each run leaves a tmp_pack_* file behind.

bash completion runs the helper with the terminal as input. The next
commit removes the NO_PARSEOPT flag from fast-import, which would make
"git fast-import --<TAB>" freeze without this patch.

show_usage_with_options_if_asked() already answers -h and --help-all
before a command does any work. Teach it to answer the completion
helper too. Then fast-import, and the other commands that call it,
reply without reading input.

Reported-by: René Scharfe <l.s.r@web.de>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Helped-by: Cynthia Uche <herroyalpriestess@gmail.com>
Signed-off-by: Tanga Joris <tangajoris@gmail.com>
---
Changes since v3:
 - Added a sentence to the log message saying that the next commit
   removes NO_PARSEOPT from fast-import, as Kaartic suggested.
 - Added a comment above show_usage_with_options_if_asked() in
   parse-options.h, as Kaartic suggested.
 - Added Cynthia's test for --git-completion-helper-all. I also added
   the tmp_pack_* check from the first test to it, because without
   it the test still passes when the fix is reverted.
 - 2/3 is unchanged.
 - 3/3 is new, it adds the test Kaartic suggested.

 parse-options.c        |  6 ++++++
 parse-options.h        |  6 ++++++
 t/t9300-fast-import.sh | 16 ++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/parse-options.c b/parse-options.c
index 283a0f1dc2..f2a23b79a4 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -1536,6 +1536,12 @@ void show_usage_with_options_if_asked(int ac, const char **av,
 			usage_with_options_internal(NULL, usagestr, opts,
 						    USAGE_FULL, USAGE_TO_STDOUT);
 			exit(0);
+		} else if (!strcmp(av[1], "--git-completion-helper")) {
+			show_gitcomp(opts, 0);
+			exit(0);
+		} else if (!strcmp(av[1], "--git-completion-helper-all")) {
+			show_gitcomp(opts, 1);
+			exit(0);
 		}
 	}
 }
diff --git a/parse-options.h b/parse-options.h
index f68b51ceca..7ad33801fe 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -427,6 +427,12 @@ int parse_options(int argc, const char **argv, const char *prefix,
 NORETURN void usage_with_options(const char * const *usagestr,
 				 const struct option *options);
 
+/*
+ * If the only argument is -h, --help-all, --git-completion-helper or
+ * --git-completion-helper-all, print the answer and exit. Call this
+ * before the command does any work. Then asking for help or for the
+ * completion list does not wait for input or leave files behind.
+ */
 void show_usage_with_options_if_asked(int ac, const char **av,
 				      const char * const *usage,
 				      const struct option *options);
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 73c6e3d448..1305614381 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -2914,6 +2914,22 @@ test_expect_success 'R: blob appears only once' '
 	test 1 = $n
 '
 
+test_expect_success 'R: --git-completion-helper does not read from stdin' '
+	find .git/objects/pack -name "tmp_pack_*" >before &&
+	echo garbage | git fast-import --git-completion-helper >out &&
+	test_grep -e "--date-format=" out &&
+	find .git/objects/pack -name "tmp_pack_*" >after &&
+	test_cmp before after
+'
+
+test_expect_success 'R: --git-completion-helper-all does not read from stdin' '
+	find .git/objects/pack -name "tmp_pack_*" >before &&
+	echo garbage | git fast-import --git-completion-helper-all >all &&
+	test_grep -e "--allow-unsafe-features" all &&
+	find .git/objects/pack -name "tmp_pack_*" >after &&
+	test_cmp before after
+'
+
 ###
 ### series S (mark and path parsing)
 ###
-- 
2.43.0