apply: refactor `struct image` to use a `struct strbuf`

The `struct image` uses a character array to track the pre- or postimage
of a patch operation. This has multiple downsides:

  - It is somewhat hard to track memory ownership. In fact, we have
    several memory leaks in git-apply(1) because we do not (and cannot
    easily) free the buffer in all situations.

  - We have to reinvent the wheel and manually implement a lot of
    functionality that would already be provided by `struct strbuf`.

  - We have to carefully track whether `update_pre_post_images()` can do
    an in-place update of the postimage or whether it has to allocate a
    new buffer for it.

This is all rather cumbersome, and especially `update_pre_post_images()`
is really hard to understand as a consequence even though what it is
doing is rather trivial.

Refactor the code to use a `struct strbuf` instead, addressing all of
the above. Like this we can easily perform in-place updates in all
situations, the logic to perform those updates becomes way simpler and
the lifetime of the buffer becomes a ton easier to track.

This refactoring also plugs some leaking buffers as a side effect.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/t/t4138-apply-ws-expansion.sh b/t/t4138-apply-ws-expansion.sh
index 8bbf8260fa..7981931b4e 100755
--- a/t/t4138-apply-ws-expansion.sh
+++ b/t/t4138-apply-ws-expansion.sh
@@ -5,6 +5,7 @@
 
 test_description='git apply test patches with whitespace expansion.'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success setup '