branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
How to add fuzzers (partially cribbed from oss-fuzz[0]):
1) git clone https://github.com/google/oss-fuzz
2) cd oss-fuzz
3) python infra/helper.py build_image mercurial
4) docker run --cap-add=SYS_PTRACE -it -v $HG_REPO_PATH:/hg-new \
gcr.io/oss-fuzz/mercurial bash
5) cd /src
6) rm -r mercurial
7) ln -s /hg-new mercurial
8) cd mercurial
9) compile
10) ls $OUT
Step 9 is literally running the command "compile", which is part of
the docker container. Once you have that working, you can build the
fuzzers like this (in the oss-fuzz repo):
python infra/helper.py build_fuzzers --sanitizer address mercurial $HG_REPO_PATH
(you can also say "memory", "undefined" or "coverage" for
sanitizer). Then run the built fuzzers like this:
python infra/helper.py run_fuzzer mercurial -- $FUZZER
0: https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md