tests: disallow the use of abbreviated options (by default)

Git's command-line parsers support uniquely abbreviated options, e.g.
`git init --ba` would automatically expand `--ba` to `--bare`.

This is a very convenient feature in every day life for Git users, in
particular when tab completion is not available.

However, it is not a good idea to rely on that in Git's test suite, as
something that is a unique abbreviation of a command line option today
might no longer be a unique abbreviation tomorrow.

For example, if a future contribution added a new mode
`git init --babyproofing` and a previously-introduced test case used the
fact that `git init --ba` expanded to `git init --bare`, that future
contribution would now have to touch seemingly unrelated tests just to
keep the test suite from failing.

So let's disallow abbreviated options in the test suite by default.

Note: for ease of implementation, this patch really only touches the
`parse-options` machinery: more and more hand-rolled option parsers are
converted to use that internal API, and more and more scripts are
converted to built-ins (naturally using the parse-options API, too), so
in practice this catches most issues, and is definitely the biggest bang
for the buck.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -6,6 +6,8 @@
 #include "color.h"
 #include "utf8.h"
 
+static int disallow_abbreviated_options;
+
 #define OPT_SHORT 1
 #define OPT_UNSET 2
 
@@ -344,6 +346,10 @@ static enum parse_opt_result parse_long_opt(
 		return get_value(p, options, all_opts, flags ^ opt_flags);
 	}
 
+	if (disallow_abbreviated_options && (ambiguous_option || abbrev_option))
+		die("disallowed abbreviated or ambiguous option '%.*s'",
+		    (int)(arg_end - arg), arg);
+
 	if (ambiguous_option) {
 		error(_("ambiguous option: %s "
 			"(could be --%s%s or --%s%s)"),
@@ -708,6 +714,9 @@ int parse_options(int argc, const char **argv, const char *prefix,
 {
 	struct parse_opt_ctx_t ctx;
 
+	disallow_abbreviated_options =
+		git_env_bool("GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS", 0);
+
 	parse_options_start(&ctx, argc, argv, prefix, options, flags);
 	switch (parse_options_step(&ctx, options, usagestr)) {
 	case PARSE_OPT_HELP:

t/README

@@ -399,6 +399,10 @@ GIT_TEST_SIDEBAND_ALL=<boolean>, when true, overrides the
 fetch-pack to not request sideband-all (even if the server advertises
 sideband-all).
 
+GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=<boolean>, when true (which is
+the default when running tests), errors out when an abbreviated option
+is used.
+
 Naming Tests
 ------------
 

t/t0040-parse-options.sh

@@ -203,20 +203,24 @@ file: (not set)
 EOF
 
 test_expect_success 'unambiguously abbreviated option' '
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
 	test-tool parse-options --int 2 --boolean --no-bo >output 2>output.err &&
 	test_must_be_empty output.err &&
 	test_cmp expect output
 '
 
 test_expect_success 'unambiguously abbreviated option with "="' '
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
 	test-tool parse-options --expect="integer: 2" --int=2
 '
 
 test_expect_success 'ambiguously abbreviated option' '
-	test_expect_code 129 test-tool parse-options --strin 123
+	test_expect_code 129 env GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
+	test-tool parse-options --strin 123
 '
 
 test_expect_success 'non ambiguous option (after two options it abbreviates)' '
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
 	test-tool parse-options --expect="string: 123" --st 123
 '
 
@@ -325,6 +329,7 @@ file: (not set)
 EOF
 
 test_expect_success 'negation of OPT_NONEG flags is not ambiguous' '
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
 	test-tool parse-options --no-ambig >output 2>output.err &&
 	test_must_be_empty output.err &&
 	test_cmp expect output
@@ -370,4 +375,11 @@ test_expect_success '--no-verbose resets multiple verbose to 0' '
 	test-tool parse-options --expect="verbose: 0" -v -v -v --no-verbose
 '
 
+test_expect_success 'GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS works' '
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=false \
+		test-tool parse-options --ye &&
+	test_must_fail env GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=true \
+		test-tool parse-options --ye
+'
+
 test_done

t/test-lib.sh

@@ -57,6 +57,13 @@ fi
 . "$GIT_BUILD_DIR"/GIT-BUILD-OPTIONS
 export PERL_PATH SHELL_PATH
 
+# Disallow the use of abbreviated options in the test suite by default
+if test -z "${GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS}"
+then
+	GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=true
+	export GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS
+fi
+
 ################################################################
 # It appears that people try to run tests without building...
 "${GIT_TEST_INSTALLED:-$GIT_BUILD_DIR}/git$X" >/dev/null