[PATCH v2] t0001: fix broken not-quite getcwd(3) test in bed67874e2

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

With a54e938e5b (strbuf: support long paths w/o read rights in
strbuf_getcwd() on FreeBSD, 2017-03-26) we had t0001 break on systems
like OpenBSD and AIX whose getcwd(3) has standard (but not like glibc
et al) behavior.

This was partially fixed in bed67874e2 (t0001: skip test with
restrictive permissions if getpwd(3) respects them, 2017-08-07).

The problem with that fix is that while its analysis of the problem is
correct, it doesn't actually call getcwd(3), instead it invokes "pwd
-P". There is no guarantee that "pwd -P" is going to call getcwd(3),
as opposed to e.g. being a shell built-in.

On AIX under both bash and ksh this test breaks because "pwd -P" will
happily display the current working directory, but getcwd(3) called by
the "git init" we're testing here will fail to get it.

I checked whether clobbering the $PWD environment variable would
affect it, and it didn't. Presumably these shells keep track of their
working directory internally.

There's possible follow-up work here in teaching strbuf_getcwd() to
get the working directory with whatever method "pwd" uses on these
platforms. See [1] for a discussion of that, but let's take the easy
way out here and just skip these tests by fixing the
GETCWD_IGNORES_PERMS prerequisite to match the limitations of
strbuf_getcwd().

1. https://lore.kernel.org/git/b650bef5-d739-d98d-e9f1-fa292b6ce982@web.de/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

Junio: I tried to get this in around the v2.32.0 release, see previous
proddings at:

  https://lore.kernel.org/git/871r9d6hhy.fsf@evledraar.gmail.com/
  https://lore.kernel.org/git/87y2bl52v4.fsf@evledraar.gmail.com/

Here's another try with a slightly updated commit message discussing
that there's a possible more perfect solution here (per René's reply),
but that this fixes the immediate bug on AIX/OpenBSD etc.

Range-diff against v1:
1:  c70791bbd3a ! 1:  d7d071441b0 t0001: fix broken not-quite getcwd(3) test in bed67874e2
    @@ Commit message
     
         The problem with that fix is that while its analysis of the problem is
         correct, it doesn't actually call getcwd(3), instead it invokes "pwd
    -    -P". There is no guarantee that "pwd -P" is actually going to call
    -    getcwd(3), as opposed to e.g. being a shell built-in.
    +    -P". There is no guarantee that "pwd -P" is going to call getcwd(3),
    +    as opposed to e.g. being a shell built-in.
     
         On AIX under both bash and ksh this test breaks because "pwd -P" will
         happily display the current working directory, but getcwd(3) called by
    @@ Commit message
         affect it, and it didn't. Presumably these shells keep track of their
         working directory internally.
     
    -    Let's change the test to a new "test-tool getcwd".
    +    There's possible follow-up work here in teaching strbuf_getcwd() to
    +    get the working directory with whatever method "pwd" uses on these
    +    platforms. See [1] for a discussion of that, but let's take the easy
    +    way out here and just skip these tests by fixing the
    +    GETCWD_IGNORES_PERMS prerequisite to match the limitations of
    +    strbuf_getcwd().
    +
    +    1. https://lore.kernel.org/git/b650bef5-d739-d98d-e9f1-fa292b6ce982@web.de/
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     

 Makefile               |  1 +
 t/helper/test-getcwd.c | 26 ++++++++++++++++++++++++++
 t/helper/test-tool.c   |  1 +
 t/helper/test-tool.h   |  1 +
 t/t0001-init.sh        |  5 ++++-
 5 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 t/helper/test-getcwd.c

diff --git a/Makefile b/Makefile
index c6f6246bf63..9573190f1d7 100644
--- a/Makefile
+++ b/Makefile
@@ -715,6 +715,7 @@ TEST_BUILTINS_OBJS += test-example-decorate.o
 TEST_BUILTINS_OBJS += test-fast-rebase.o
 TEST_BUILTINS_OBJS += test-genrandom.o
 TEST_BUILTINS_OBJS += test-genzeros.o
+TEST_BUILTINS_OBJS += test-getcwd.o
 TEST_BUILTINS_OBJS += test-hash-speed.o
 TEST_BUILTINS_OBJS += test-hash.o
 TEST_BUILTINS_OBJS += test-hashmap.o
diff --git a/t/helper/test-getcwd.c b/t/helper/test-getcwd.c
new file mode 100644
index 00000000000..d680038a780
--- /dev/null
+++ b/t/helper/test-getcwd.c
@@ -0,0 +1,26 @@
+#include "test-tool.h"
+#include "git-compat-util.h"
+#include "parse-options.h"
+
+static const char *getcwd_usage[] = {
+	"test-tool getcwd",
+	NULL
+};
+
+int cmd__getcwd(int argc, const char **argv)
+{
+	struct option options[] = {
+		OPT_END()
+	};
+	char *cwd;
+
+	argc = parse_options(argc, argv, "test-tools", options, getcwd_usage, 0);
+	if (argc > 0)
+		usage_with_options(getcwd_usage, options);
+
+	cwd = xgetcwd();
+	puts(cwd);
+	free(cwd);
+
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 490ac026c51..3ce5585e53a 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -33,6 +33,7 @@ static struct test_cmd cmds[] = {
 	{ "fast-rebase", cmd__fast_rebase },
 	{ "genrandom", cmd__genrandom },
 	{ "genzeros", cmd__genzeros },
+	{ "getcwd", cmd__getcwd },
 	{ "hashmap", cmd__hashmap },
 	{ "hash-speed", cmd__hash_speed },
 	{ "index-version", cmd__index_version },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index f8dc266721f..9f0f5228508 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -23,6 +23,7 @@ int cmd__example_decorate(int argc, const char **argv);
 int cmd__fast_rebase(int argc, const char **argv);
 int cmd__genrandom(int argc, const char **argv);
 int cmd__genzeros(int argc, const char **argv);
+int cmd__getcwd(int argc, const char **argv);
 int cmd__hashmap(int argc, const char **argv);
 int cmd__hash_speed(int argc, const char **argv);
 int cmd__index_version(int argc, const char **argv);
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index acd662e403b..df544bb321f 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -356,7 +356,10 @@ test_lazy_prereq GETCWD_IGNORES_PERMS '
 	chmod 100 $base ||
 	BUG "cannot prepare $base"
 
-	(cd $base/dir && /bin/pwd -P)
+	(
+		cd $base/dir &&
+		test-tool getcwd
+	)
 	status=$?
 
 	chmod 700 $base &&
-- 
2.32.0.1071.g36f34456314