Subject: [PATCH 0/3] Add a static analysis job to prevent assertions with side effects

From: "Elijah Newren via GitGitGadget" <[email-masked]>
Date: Fri, 14 Mar 2025 00:20:49 +0000

We have several hundred assert() invocations in our code base. Some have
suggested that we should add a recommendation in our CodingGuidelines to
avoid their use, because there is a risk that someone might include
something with a side-effect in their assertion, which can lead to a very
difficult to debug problem. However, CodingGuidelines are going to be less
effective at preventing that foot-gun than a CI job which can warn of
assertions that possibly have side-effects. So, let's add a CI job instead.

While it is difficult to perfectly determine whether any expression has side
effects, a simple compiler/linker hack can prove that all but 9 of our
several hundred assert() calls are indeed free from them. While I believe
the remaining 9 are also free of side effects, it's easier to just convert
those 9 to a new macro (which will not be compiled out when NDEBUG is
defined), and instruct any future assertion writers to likewise switch to
that alternative macro if they have a slightly more involved assert()
invocation.

See
https://github.com/newren/git/actions/runs/13845548634/job/38743076293#step:4:1938
for an example of it running in CI and reporting possibly problematic
assertions (sample output also included in the commit message of the middle
commit in this series if you don't have access to view the link; I'm not
sure what the rules on that are).

Elijah Newren (3):
  git-compat-util: introduce BUG_IF_NOT() macro
  ci: add build checking for side-effects in assert() calls
  treewide: replace assert() with BUG_IF_NOT() in special cases

 Makefile                      |  4 ++++
 ci/check-unsafe-assertions.sh | 18 ++++++++++++++++++
 ci/run-static-analysis.sh     |  2 ++
 diffcore-rename.c             |  2 +-
 git-compat-util.h             |  7 +++++++
 merge-ort.c                   |  4 ++--
 merge-recursive.c             |  2 +-
 object-file.c                 |  2 +-
 parallel-checkout.c           |  2 +-
 scalar.c                      |  4 ++--
 sequencer.c                   |  2 +-
 11 files changed, 40 insertions(+), 9 deletions(-)
 create mode 100755 ci/check-unsafe-assertions.sh

base-commit: 4b68faf6b93311254efad80e554780e372deb42f
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1881%2Fnewren%2Fassertion-side-effects-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1881/newren/assertion-side-effects-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1881
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