fix: release squashed release PRs from main branch

crates/git_cmd/src/lib.rs

@@ -342,6 +342,16 @@ impl Repo {
             .context("cannot determine if git tag exists")?;
         Ok(output.lines().count() >= 1)
     }
+
+    pub fn get_branches_of_commit(&self, commit_hash: &str) -> anyhow::Result<Vec<String>> {
+        let output = self.git(&["branch", "--contains", commit_hash])?;
+        let branches = output
+            .lines()
+            .filter_map(|l| l.split_whitespace().last())
+            .map(|s| s.to_string())
+            .collect();
+        Ok(branches)
+    }
 }
 
 pub fn is_file_ignored(repo_path: &Utf8Path, file: &Utf8Path) -> bool {

crates/release_plz_core/src/command/release.rs

@@ -613,8 +613,22 @@ async fn should_release(
             // Get the last commit of the PR, i.e. the last commit that was pushed before the PR was merged
             match pr_commits.last() {
                 Some(commit) if commit.sha != last_commit => {
-                    // I need to checkout the last commit of the PR if it exists
-                    Ok(ShouldRelease::YesWithCommit(commit.sha.clone()))
+                    let is_pr_commit_in_original_branch = {
+                        let branches_of_commit = repo.get_branches_of_commit(&commit.sha);
+                        if let Ok(branches) = branches_of_commit {
+                            branches.contains(&repo.original_branch().to_string())
+                        } else {
+                            false
+                        }
+                    };
+
+                    if is_pr_commit_in_original_branch {
+                        // I need to checkout the last commit of the PR if it exists
+                        Ok(ShouldRelease::YesWithCommit(commit.sha.clone()))
+                    } else {
+                        // The commit is not in the original branch, probably the PR was squashed
+                        Ok(ShouldRelease::Yes)
+                    }
                 }
                 _ => {
                     // I'm already at the right commit