test-lib: have the "check" mode for SANITIZE=leak consider leak logs

As noted in previous on-list discussions[1] we have various tests that
will falsely report being leak-free because we're missing the relevant
exit code from LSAN as summarized below.

We should fix those issues, but in the meantime and as an additional
sanity check we can and should consider our own ASAN logs before
reporting that a test is leak-free.

Before this compiling with SANITIZE=leak and running:

    ./t6407-merge-binary.sh

Will exit successfully, now we'll get an error and an informative
message on:

    GIT_TEST_SANITIZE_LEAK_LOG=true ./t6407-merge-binary.sh

Even better, as noted in the updated t/README we'll now error out when
combined with the "check" mode:

    GIT_TEST_PASSING_SANITIZE_LEAK=check \
    GIT_TEST_SANITIZE_LEAK_LOG=true \
	./t4058-diff-duplicates.sh

Why do we miss these leaks? Because:

 * We have leaks inside "test_expect_failure" blocks, which by design
   will not distinguish a "normal" failure from an abort() or
   segfault. See [1] for a discussion of it shortcomings.

 * We have "git" invocations outside of "test_expect_success",
   e.g. setup code in the main body of the test, or in test helper
   functions that don't use &&-chaining.

 * Our tests will otherwise catch segfaults and abort(), but if we
   invoke a command that invokes another command it needs to ferry the
   exit code up to us.

   Notably a command that e.g. might invoke "git pack-objects" might
   itself exit with status 128 if that "pack-objects" segfaults or
   abort()'s. If the test invoking the parent command(s) is using
   "test_must_fail" we'll consider it an expected "ok" failure.

 * run-command.c doesn't (but probably should) ferry up such exit
   codes, so for e.g. "git push" tests where we expect a failure and an
   underlying "git" command fails we won't ferry up the segfault or
   abort exit code.

 * We have gitweb.perl and some other perl code ignoring return values
   from close(), i.e. ignoring exit codes from "git rev-parse" et al.

 * We have in-tree shellscripts like "git-merge-one-file.sh" invoking
   git commands, they'll usually return their own exit codes on "git"
   failure, rather then ferrying up segfault or abort() exit code.

   E.g. these invocations in git-merge-one-file.sh leak, but aren't
   reflected in the "git merge" exit code:

	src1=$(git unpack-file $2)
	src2=$(git unpack-file $3)

   That case would be easily "fixed" by adding a line like this after
   each assignment:

	test $? -ne 0 && exit $?

   But we'd then in e.g. "t6407-merge-binary.sh" run into
   write_tree_trivial() in "builtin/merge.c" calling die() instead of
   ferrying up the relevant exit code.

Let's remove "TEST_PASSES_SANITIZE_LEAK=true" from tests we
were falsely marking as leak-free.

In the case of t6407-merge-binary.sh it was marked as leak-free in
9081a421a6d (checkout: fix "branch info" memory leaks,
2021-11-16). I'd previously removed other bad
"TEST_PASSES_SANITIZE_LEAK=true" opt-ins in the series merged in
ea05fd5fbf7 (Merge branch 'ab/keep-git-exit-codes-in-tests',
2022-03-16). The case of t1060-object-corruption.sh is more subtle,
and will be discussed in a subsequent commit.

1. https://lore.kernel.org/git/cover-0.7-00000000000-20220318T002951Z-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/t/README b/t/README
index e13063195e..2f439f9658 100644
--- a/t/README
+++ b/t/README
@@ -385,6 +385,12 @@ GIT_TEST_SANITIZE_LEAK_LOG=true will log memory leaks to
 "dedup_token" (see +"ASAN_OPTIONS=help=1 ./git") and other options to
 make logs +machine-readable.
 
+With GIT_TEST_SANITIZE_LEAK_LOG=true we'll look at the leak logs
+before exiting and exit on failure if the logs showed that we had a
+memory leak, even if the test itself would have otherwise passed. This
+allows us to catch e.g. missing &&-chaining. This is especially useful
+when combined with "GIT_TEST_PASSING_SANITIZE_LEAK", see below.
+
 GIT_TEST_PASSING_SANITIZE_LEAK=check when combined with "--immediate"
 will run to completion faster, and result in the same failing
 tests. The only practical reason to run
@@ -393,6 +399,15 @@ combine it with "GIT_TEST_SANITIZE_LEAK_LOG=true". If we stop at the
 first failing test case our leak logs won't show subsequent leaks we
 might have run into.
 
+GIT_TEST_PASSING_SANITIZE_LEAK=(true|check) will not catch all memory
+leaks unless combined with GIT_TEST_SANITIZE_LEAK_LOG=true. Some tests
+run "git" (or "test-tool" etc.) without properly checking the exit
+code, or git will invoke itself and fail to ferry the abort() exit
+code to the original caller. When the two modes are combined we'll
+look at the "test-results/$TEST_NAME.leak/trace.*" files at the end of
+the test run to see if had memory leaks which the test itself didn't
+catch.
+
 GIT_TEST_PROTOCOL_VERSION=<n>, when set, makes 'protocol.version'
 default to n.