commit f87d6bd4c8242eca92b03c6948e66e29820befd1
Author: Sven van Heugten <sven@memcmp.org>
Date:   Fri Feb 20 15:55:21 2026 +0100

    Initial commit

diff --git a/LICENSE b/LICENSE
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+MIT License
+
+Copyright (c) 2026 Sven van Heugten
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
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+# git-check-assertions
+
+🚧 Merely a proof-of-concept right now.
+
+I recently wrote two blogs posts arguing that there might be some value in writing verifiable claims, i.e. assertions, inside of our commit messages:
+
+* [Should we start writing verifiable claims in commit message?](https://sven.memcmp.org/2026-02-19-should-we-start-writing-verifiable-claims-in-commit-messages/)
+* [Writing the steps to validate a test in the commit message](https://sven.memcmp.org/2026-02-20-writing-the-steps-to-validate-a-test-in-the-commit-message/)
+
+This is a simple verifier for such assertions.
+
+You include a small bash script inside your commit messages, and `git-check-assertions` will then check out every commit (from the point that your branch diverged from `main`), and verify that the script in the commit message runs successfully.
+
+⚠️ Only run this on repositories and branches that you trust, since the `bash` scripts in the commit messages can do whatever they want.
+
+## Examples of commit messages
+
+Assert that a commit builds:
+
+~~~
+```git-check-assertions
+dotnet build
+```
+~~~
+
+Assert that a commit builds and that the tests succeed:
+
+~~~
+```git-check-assertions
+dotnet build
+dotnet test --no-build
+```
+~~~
+
+Assert that a commit builds, but that the tests do not succeed (`assert_fails` is a helper function included in `git-check-assertions`):
+
+~~~
+```git-check-assertions
+dotnet build
+assert_fails dotnet test --no-build
+```
+~~~
+
+Assert that a commit builds, and that the tests fail with exactly the error that you expect:
+
+~~~
+```git-check-assertions
+dotnet build
+(assert_fails dotnet test --no-build) | grep "Invalid URL"
+```
+~~~
diff --git a/git-check-assertions.sh b/git-check-assertions.sh
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+#!/usr/bin/env bash
+
+# Copyright (c) 2026 Sven van Heugten
+#
+# Repository: https://codeberg.org/svenvanheugten/git-check-assertions
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+set -euo pipefail
+
+assert_fails() {
+  ! "$@" || { echo "Expected command to fail, but it succeeded."; exit 1; }
+}
+export -f assert_fails
+
+orig_ref="$(git symbolic-ref --quiet --short HEAD || git rev-parse HEAD)"
+base="$(git merge-base main HEAD)"
+mapfile -t commits < <(git rev-list --reverse "${base}..HEAD")
+
+echo "Base: $base"
+echo "Commits to visit: ${#commits[@]}"
+echo
+
+for commit_hash in "${commits[@]}"; do
+  echo "Checking out $commit_hash"
+  git -c advice.detachedHead=false checkout -q "$commit_hash"
+  commit_msg="$(git log -1 --format=%B "$commit_hash")"
+  block="$(printf '%s\n' "$commit_msg" \
+    | sed -n '/^```git-check-assertions[[:space:]]*$/,/^```[[:space:]]*$/p' \
+    | sed '1d;$d')"
+  if [ -n "$block" ]; then
+    echo "git-check-assertions block in $commit_hash:"
+    printf '%s\n' "$block" | sed 's/^/> /'
+    if ! bash -euo pipefail -c "$block"; then
+      echo "git-check-assertions block failed in $commit_hash" >&2
+      echo "Returning to $orig_ref"
+      git checkout -q "$orig_ref"
+      exit 1
+    fi
+  fi
+  echo
+done
+
+echo
+echo "Returning to $orig_ref"
+git checkout -q "$orig_ref"