patcht/perf/run: fix bin-wrappers computation

From: Derrick Stolee <dstolee@microsoft.com>

The GIT_TEST_INSTALLED was moved from perf-lib.sh to run in df0f5021 (perf-lib.sh: remove GIT_TEST_INSTALLED from perf-lib.sh, 2019-05-07) and that included a change to how it inspected the existence of a bin-wrappers directory. However, that included a typo that made the match of bin-wrappers never work. Specifically, the assignment was

	mydir_abs_wrappers="$mydir_abs_wrappers/bin-wrappers"

which uses the same variable before it is initialized. By changing it to

	mydir_abs_wrappers="$mydir_abs/bin-wrappers"

We can correctly use the bin-wrappers directory.

This is critical to successfully computing performance of commands that execute subcommands. The bin-wrappers ensure that the --exec-path is set correctly.

Reported-by: Victoria Dye <vdye@github.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
    t/perf/run: fix bin-wrappers computation
    
    Found this while we were testing sparse index improvements to 'git
    stash', which uses a lot of subcommands.
    
    Thanks, -Stolee

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1044%2Fderrickstolee%2Fperf-run-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1044/derrickstolee/perf-run-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1044

 t/perf/run | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Tue, Sep 21, 2021 at 03:46:12PM +0000, Derrick Stolee via GitGitGadget wrote:

Just sanity-checking everything you said: with this bug, we'll set mydir_abs_wrappers to "/bin-wrappers", then realize that directory doesn't exist, and fall back to GIT_TEST_INSTALLED=$mydir_abs. Putting 'set -x' at the top of t/perf/run, we can see the relevant section:

  + mydir=build/73cd7d9420bb7d75207e8149521db375c789a81c
  + cd build/73cd7d9420bb7d75207e8149521db375c789a81c
  + pwd
  + mydir_abs=/home/ttaylorr/src/git/t/perf/build/73cd7d9420bb7d75207e8149521db375c789a81c
  + mydir_abs_wrappers=/bin-wrappers
  + test -d /bin-wrappers
  + GIT_TEST_INSTALLED=/home/ttaylorr/src/git/t/perf/build/73cd7d9420bb7d75207e8149521db375c789a81c
  + export GIT_TEST_INSTALLED

OK. But the real problem is in t/test-lib.sh where we read "$GIT_TEST_INSTALLED". There we ask for the `--exec-path`, which appears to be wrong, at least in my setup. Printing out the $GIT_EXEC_PATH and $GIT_TEST_INSTALLED, I get:

  /home/ttaylorr/local/git/ds.sparse-checkout/libexec/git-core,
  /home/ttaylorr/src/git/t/perf/build/73cd7d9420bb7d75207e8149521db375c789a81c

where the former is the branch I happen to have checked out, and the latter is the revision that I asked to run performance tests on via t/perf/run.

So I think we'll run the right top-level Git command since the latter path ends up first in our $PATH, but the exec path is definitely wrong.

This fix looks obviously right to me (and gives me the expected output from above when I apply it locally).

Thanks, Taylor

On 9/21/2021 1:50 PM, Taylor Blau wrote:

Thanks for digging into this more. This issue with GIT_EXEC_PATH explains some strangeness I was seeing.

Perhaps there is something more robust to be done around GIT_EXEC_PATH,
but the current fix satisfies my needs.
 

Thanks, -Stolee