From cdebf02e5490989efc159cd1b4bc0645713e1dfc Mon Sep 17 00:00:00 2001
From: dragfire <asem.devajit@gmail.com>
Date: Mon, 24 Aug 2020 15:17:00 -0600
Subject: Add a test that forbids merge commits

---
 .github/workflows/ci.yaml |  3 +++
 xtask/tests/tidy.rs       | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index fb077e28d..fa276e2bf 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -30,6 +30,9 @@ jobs:
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+        fetch-depth: 5
 
     # We need to disable the existing toolchain to avoid updating rust-docs
     # which takes a long time. The fastest way to do this is to rename the
diff --git a/xtask/tests/tidy.rs b/xtask/tests/tidy.rs
index fd9645c23..c276b6307 100644
--- a/xtask/tests/tidy.rs
+++ b/xtask/tests/tidy.rs
@@ -50,6 +50,20 @@ fn rust_files_are_tidy() {
     tidy_docs.finish();
 }
 
+#[test]
+fn check_merge_commits() {
+    let cmd_output =
+        run!("git rev-list --merges --invert-grep --author 'bors\\[bot\\]' HEAD~4.."; echo = false);
+    match cmd_output {
+        Ok(out) => {
+            if !out.is_empty() {
+                panic!("Please rebase your branch on top of master by running `git rebase master`");
+            }
+        }
+        Err(e) => panic!("{}", e),
+    }
+}
+
 fn deny_clippy(path: &PathBuf, text: &String) {
     if text.contains("[\u{61}llow(clippy") {
         panic!(
-- 
cgit v1.2.3