[RFC PATCH 0/7] ls-tree --format

On Fri, Dec 17 2021, Teng Long wrote:

FWIW here's the changes I had locally & cleaned up now that did the alternate --format approach.

I think you'll probably want to steal some of this, e.g. you're patching the dead comment I removed in 1/6, 2-4/6 can be skipped, but I thought they were nice.

Back when I last looked at this series, your --object-name patch was much shorter, but now it's about the same size as the generic --format support. So maybe it's worth considering implementing the more generic path.

One reason I didn't submit this before is that I couldn't get past the
performance regression this would inttroduce, i.e. if moved entirely
to strbuf_expand(). Here though I'm keeping the old code, so it's no
slower than "master", unlike your patch. But I haven't dug into why
yours is slower:
    
    $ git hyperfine -L rev origin/master,tl/object-name,avar/ls-tree-format -s 'make CFLAGS=-O3' './git -C /run/user/1001/linux ls-tree -r HEAD' --warmup 10 -r 10
    Benchmark 1: ./git -C /run/user/1001/linux ls-tree -r HEAD' in 'origin/master
      Time (mean ± σ):      67.8 ms ±   0.3 ms    [User: 48.8 ms, System: 18.9 ms]
      Range (min … max):    67.4 ms …  68.4 ms    10 runs
    
    Benchmark 2: ./git -C /run/user/1001/linux ls-tree -r HEAD' in 'tl/object-name
      Time (mean ± σ):      72.8 ms ±   0.4 ms    [User: 50.6 ms, System: 22.1 ms]
      Range (min … max):    72.0 ms …  73.2 ms    10 runs
    
    Benchmark 3: ./git -C /run/user/1001/linux ls-tree -r HEAD' in 'avar/ls-tree-format
      Time (mean ± σ):      67.6 ms ±   0.4 ms    [User: 50.5 ms, System: 17.0 ms]
      Range (min … max):    67.1 ms …  68.4 ms    10 runs
    
    Summary
      './git -C /run/user/1001/linux ls-tree -r HEAD' in 'avar/ls-tree-format' ran
        1.00 ± 0.01 times faster than './git -C /run/user/1001/linux ls-tree -r HEAD' in 'origin/master'
        1.08 ± 0.01 times faster than './git -C /run/user/1001/linux ls-tree -r HEAD' in 'tl/object-name'

I then tacket a 6/6 at the end here to implement your --object-name in
terms of --format (but didn't update the comimt message etc.). That's
slower as expected:
    
    $ git hyperfine -L rev tl/object-name,avar/ls-tree-format -s 'make CFLAGS=-O3' './git -C /run/user/1001/linux ls-tree --object-only -r HEAD' --warmup 10 -r 10
    Benchmark 1: ./git -C /run/user/1001/linux ls-tree --object-only -r HEAD' in 'tl/object-name
      Time (mean ± σ):      58.7 ms ±   0.4 ms    [User: 43.0 ms, System: 15.6 ms]
      Range (min … max):    58.4 ms …  59.6 ms    10 runs
     
    Benchmark 2: ./git -C /run/user/1001/linux ls-tree --object-only -r HEAD' in 'avar/ls-tree-format
      Time (mean ± σ):      65.6 ms ±   0.2 ms    [User: 42.4 ms, System: 23.0 ms]
      Range (min … max):    65.1 ms …  65.9 ms    10 runs
     
    Summary
      './git -C /run/user/1001/linux ls-tree --object-only -r HEAD' in 'tl/object-name' ran
        1.12 ± 0.01 times faster than './git -C /run/user/1001/linux ls-tree --object-only -r HEAD' in 'avar/ls-tree-format'

But it's not too bad, so maybe it's fine & worth making it more generic?

Anyway. Just food for thought and and FYI in case you're interested. Junio noted already that he'd like the --object-name approach first, so if you still want to pursue your current implementation I don't mind.

I do think you should be making performance testing a part of your testing & cover letter writing though. A 8-10% slowdown isn't nothing, especially for exactly the sort of plumbing command that'll likely to be used to e.g. slurp up all paths in a very large repo.

These patches really aren't "ready". There's no docs, and as I noted in some earlier thread the tests for ls-tree are really lacking. E.g. I seem to have a rather obvious bug in how -t and the --format interact here, but no test catches it.

Well, that one's me not having added a test, but I'm fairly sure there might also be hidden bugs here due to lack of testing.

Teng Long (1):
  ls-tree.c: support `--object-only` option for "git-ls-tree"

Ævar Arnfjörð Bjarmason (6):
  ls-tree: remove commented-out code
  ls-tree: add missing braces to "else" arms
  ls-tree: use "enum object_type", not {blob,tree,commit}_type
  ls-tree: use "size_t", not "int" for "struct strbuf"'s "len"
  ls-tree: split up the "init" part of show_tree()
  ls-tree: add a --format=<fmt> option

 Documentation/git-ls-tree.txt |   7 +-
 builtin/ls-tree.c             | 226 ++++++++++++++++++++++++++++++----
 t/t3103-ls-tree-misc.sh       |   8 ++
 t/t3104-ls-tree-oid.sh        |  51 ++++++++
 t/t3105-ls-tree-format.sh     |  49 ++++++++
 5 files changed, 313 insertions(+), 28 deletions(-)
 create mode 100755 t/t3104-ls-tree-oid.sh
 create mode 100755 t/t3105-ls-tree-format.sh