[PATCH v2 0/4] test-lib: improve LSAN + ASAN stack traces

A UX improvement for LSAN stack traces. See https://lore.kernel.org/git/cover-0.4-00000000000-20220218T205753Z-avarab@gmail.com/ for the v1.

I think this v2 should address all the comments on the v1, thanks Taylor & Junio!

Changes:
 * Renamed XSAN_OPTIONS to GIT_XSAN_OPTIONS
 * The "prepend_var" now handles an empty $3, as suggested by Junio.
 * I added a new 2/4 updating the $TEST_DIRECTORY commentary to note
   that we depend on it pointing to *the* "t" directory.

Ævar Arnfjörð Bjarmason (4):
  test-lib: add GIT_XSAN_OPTIONS, inherit [AL]SAN_OPTIONS
  test-lib: correct commentary on TEST_DIRECTORY overriding
  test-lib: make $GIT_BUILD_DIR an absolute path
  test-lib: add "fast_unwind_on_malloc=0" to LSAN_OPTIONS

 t/test-lib.sh | 45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

Range-diff against v1:
1:  75c8f7a719c ! 1:  01e63a72231 test-lib: add XSAN_OPTIONS, inherit [AL]SAN_OPTIONS
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    test-lib: add XSAN_OPTIONS, inherit [AL]SAN_OPTIONS
    +    test-lib: add GIT_XSAN_OPTIONS, inherit [AL]SAN_OPTIONS
     
         Change our ASAN_OPTIONS and LSAN_OPTIONS to set defaults for those
         variables, rather than punting out entirely if we already have them in
    @@ t/test-lib.sh: then
      GIT_BUILD_DIR="$TEST_DIRECTORY"/..
      
     +# Prepend a string to a VAR using an arbitrary ":" delimiter, not
    -+# adding the delimiter if VAR is empty. I.e. a generalized:
    ++# adding the delimiter if VAR or VALUE is empty. I.e. a generalized:
     +#
    -+#	VAR=$1${VAR:+$VAR}
    ++#	VAR=$1${VAR:+${1:+$2}$VAR}
     +#
    -+# Usage (using ":" as a delimiter):
    ++# Usage (using ":" as the $2 delimiter):
     +#
    -+#	prepend_var VAR : $1
    ++#	prepend_var VAR : VALUE
     +prepend_var () {
    -+	eval "$1=$3\${$1:+$2\$$1}"
    ++	eval "$1=$3\${$1:+${3:+$2}\$$1}"
     +}
     +
    -+# If [AL]SAN is in effect we want to abort so that we notice problems.
    -+prepend_var XSAN_OPTIONS : abort_on_error=1
    ++# If [AL]SAN is in effect we want to abort so that we notice
    ++# problems. The GIT_XSAN_OPTIONS variable can be used to set common
    ++# defaults shared between [AL]SAN_OPTIONS.
    ++prepend_var GIT_XSAN_OPTIONS : abort_on_error=1
     +
      # If we were built with ASAN, it may complain about leaks
      # of program-lifetime variables. Disable it by default to lower
    @@ t/test-lib.sh: then
      # before we even do our "did we build git yet" check (since we don't
      # want that one to complain to stderr).
     -: ${ASAN_OPTIONS=detect_leaks=0:abort_on_error=1}
    -+prepend_var ASAN_OPTIONS : $XSAN_OPTIONS
    ++prepend_var ASAN_OPTIONS : $GIT_XSAN_OPTIONS
     +prepend_var ASAN_OPTIONS : detect_leaks=0
      export ASAN_OPTIONS
      
     -# If LSAN is in effect we _do_ want leak checking, but we still
     -# want to abort so that we notice the problems.
     -: ${LSAN_OPTIONS=abort_on_error=1}
    -+prepend_var LSAN_OPTIONS : $XSAN_OPTIONS
    ++prepend_var LSAN_OPTIONS : $GIT_XSAN_OPTIONS
      export LSAN_OPTIONS
      
      if test ! -f "$GIT_BUILD_DIR"/GIT-BUILD-OPTIONS
-:  ----------- > 2:  0c2867e30dc test-lib: correct commentary on TEST_DIRECTORY overriding
2:  4c53c6157ac ! 3:  229654027b8 test-lib: make $GIT_BUILD_DIR an absolute path
    @@ Commit message
         "/path/to/build". The "TEST_DIRECTORY" here is already made an
         absolute path a few lines above this.
     
    -    This will be helpful to LSAN_OPTIONS which will want to strip the
    -    build directory path from filenames, which we couldn't do if we had a
    -    "/.." in there.
    +    We could simply do $(cd "$TEST_DIRECTORY"/.." && pwd) here, but as
    +    noted in the preceding commit the "$TEST_DIRECTORY" can't be anything
    +    except the path containing this test-lib.sh file at this point, so we
    +    can more cheaply and equally strip the "/t" off the end.
    +
    +    This change will be helpful to LSAN_OPTIONS which will want to strip
    +    the build directory path from filenames, which we couldn't do if we
    +    had a "/.." in there.
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    @@ t/test-lib.sh: then
     +GIT_BUILD_DIR="${TEST_DIRECTORY%/t}"
      
      # Prepend a string to a VAR using an arbitrary ":" delimiter, not
    - # adding the delimiter if VAR is empty. I.e. a generalized:
    + # adding the delimiter if VAR or VALUE is empty. I.e. a generalized:
    +@@ t/test-lib.sh: prepend_var () {
    + # problems. The GIT_XSAN_OPTIONS variable can be used to set common
    + # defaults shared between [AL]SAN_OPTIONS.
    + prepend_var GIT_XSAN_OPTIONS : abort_on_error=1
    ++prepend_var GIT_XSAN_OPTIONS : strip_path_prefix=\"$GIT_BUILD_DIR/\"
    + 
    + # If we were built with ASAN, it may complain about leaks
    + # of program-lifetime variables. Disable it by default to lower
3:  ec852e6d691 < -:  ----------- test-lib: add "strip_path_prefix" to XSAN_OPTIONS
4:  2becf76a14a ! 4:  e6a48b6e4ce test-lib: add "fast_unwind_on_malloc=0" to LSAN_OPTIONS
    @@ t/test-lib.sh
     @@ t/test-lib.sh: prepend_var ASAN_OPTIONS : detect_leaks=0
      export ASAN_OPTIONS
      
    - prepend_var LSAN_OPTIONS : $XSAN_OPTIONS
    + prepend_var LSAN_OPTIONS : $GIT_XSAN_OPTIONS
     +prepend_var LSAN_OPTIONS : fast_unwind_on_malloc=0
      export LSAN_OPTIONS