From 0f473b58504cf85ccaafe5bb414a37983d957a56 Mon Sep 17 00:00:00 2001
From: Lars Eggert <lars@eggert.org>
Date: Thu, 14 Mar 2024 10:37:10 +0200
Subject: [PATCH] ci: Run `cargo mutants` on changed code (#1742)

* ci: Run `cargo mutants` on changed code

See https://mutants.rs/, esp. https://mutants.rs/pr-diff.html

* Fixes

* Fix trigger
---
 .github/actions/rust/action.yml |  2 +-
 .github/workflows/mutants.yml   | 36 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 .github/workflows/mutants.yml

diff --git a/.github/actions/rust/action.yml b/.github/actions/rust/action.yml
index dce4923678..bfb09d332d 100644
--- a/.github/actions/rust/action.yml
+++ b/.github/actions/rust/action.yml
@@ -30,7 +30,7 @@ runs:
 
     - name: Install Rust tools
       shell: bash
-      run: cargo +${{ inputs.version }} binstall --no-confirm cargo-llvm-cov cargo-nextest flamegraph cargo-hack
+      run: cargo +${{ inputs.version }} binstall --no-confirm cargo-llvm-cov cargo-nextest flamegraph cargo-hack cargo-mutants
 
     # sccache slows CI down, so we leave it disabled.
     # Leaving the steps below commented out, so we can re-evaluate enabling it later.
diff --git a/.github/workflows/mutants.yml b/.github/workflows/mutants.yml
new file mode 100644
index 0000000000..4e757b267f
--- /dev/null
+++ b/.github/workflows/mutants.yml
@@ -0,0 +1,36 @@
+name: Find mutants
+on:
+  pull_request:
+    branches: ["main"]
+    paths-ignore: ["*.md", "*.png", "*.svg", "LICENSE-*"]
+  merge_group:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}
+  cancel-in-progress: true
+
+jobs:
+  incremental-mutants:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Relative diff
+        run: git diff origin/${{ github.base_ref }}.. > pr.diff
+
+      - name: Install Rust
+        uses: ./.github/actions/rust
+        with:
+          version: stable
+
+      - name: Mutants
+        run: cargo mutants --test-tool=nextest --no-shuffle -j 2 -vV --in-diff pr.diff
+
+      - name: Archive mutants.out
+        uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: mutants-incremental.out
+          path: mutants.out