feat: Prevent spam from GitHub mentions in merge commits

Author: xosnrdev

Cargo.toml

@@ -54,6 +54,9 @@ chrono = "0.4"
 
 itertools = "0.14"
 
+# Text processing
+regex = "1"
+
 [dev-dependencies]
 insta = "1.26"
 wiremock = "0.6"

src/bors/handlers/trybuild.rs

@@ -20,6 +20,7 @@ use crate::github::{
     CommitSha, GithubUser, LabelTrigger, MergeError, PullRequest, PullRequestNumber,
 };
 use crate::permissions::PermissionType;
+use crate::utils::suppress_github_mentions;
 
 use super::deny_request;
 use super::has_permission;
@@ -286,7 +287,7 @@ fn auto_merge_commit_message(
 {pr_message}"#,
         pr_label = pr.head_label,
         pr_title = pr.title,
-        pr_message = pr.message,
+        pr_message = suppress_github_mentions(&pr.message),
         repo_owner = name.owner(),
         repo_name = name.name()
     );

src/utils/mod.rs

@@ -1,2 +1,99 @@
 pub mod logging;
 pub mod timing;
+
+/// Converts GitHub @mentions to markdown-backticked text to prevent notifications.
+/// For example, "@user" becomes "`user`".
+///
+/// Handles GitHub mention formats:
+/// - Usernames (@username)
+/// - Teams (@org/team)
+/// - Nested teams (@org/team/subteam)
+///
+/// GitHub's nested team documentation:
+/// https://docs.github.com/en/organizations/organizing-members-into-teams/about-teams#nested-teams
+///
+/// Ignores email addresses and other @ symbols that don't match GitHub mention patterns.
+pub fn suppress_github_mentions(text: &str) -> String {
+    if text.is_empty() || !text.contains('@') {
+        return text.to_string();
+    }
+
+    let segment = r"[A-Za-z0-9][A-Za-z0-9\-]{0,38}";
+    let pattern = format!(r"@{0}(?:/{0})*", segment);
+
+    let re = regex::Regex::new(&pattern).unwrap();
+    re.replace_all(text, |caps: &regex::Captures| {
+        let mention = &caps[0];
+        let position = caps.get(0).unwrap().start();
+
+        if !is_github_mention(text, mention, position) {
+            return mention.to_string();
+        }
+
+        let name = &mention[1..]; // Drop the @ symbol
+        format!("`{}`", name)
+    })
+    .to_string()
+}
+
+// Determines if a potential mention would actually trigger a notification
+fn is_github_mention(text: &str, mention: &str, pos: usize) -> bool {
+    // Not a valid mention if preceded by alphanumeric or underscore (email)
+    if pos > 0 {
+        let c = text.chars().nth(pos - 1).unwrap();
+        if c.is_alphanumeric() || c == '_' {
+            return false;
+        }
+    }
+
+    // Check if followed by invalid character
+    let end = pos + mention.len();
+    if end < text.len() {
+        let next_char = text.chars().nth(end).unwrap();
+        if next_char.is_alphanumeric() || next_char == '_' || next_char == '-' {
+            return false;
+        }
+    }
+
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_suppress_github_mentions() {
+        // User mentions
+        assert_eq!(suppress_github_mentions("Hello @user"), "Hello `user`");
+
+        // Org team mentions
+        assert_eq!(suppress_github_mentions("@org/team"), "`org/team`");
+        assert_eq!(
+            suppress_github_mentions("@org/team/subteam"),
+            "`org/team/subteam`"
+        );
+        assert_eq!(
+            suppress_github_mentions("@big/team/sub/group"),
+            "`big/team/sub/group`"
+        );
+        assert_eq!(
+            suppress_github_mentions("Thanks @user, @rust-lang/libs and @github/docs/content!"),
+            "Thanks `user`, `rust-lang/libs` and `github/docs/content`!"
+        );
+
+        // Non mentions
+        assert_eq!(suppress_github_mentions("@"), "@");
+        assert_eq!(suppress_github_mentions(""), "");
+        assert_eq!(
+            suppress_github_mentions("No mentions here"),
+            "No mentions here"
+        );
+        assert_eq!(
+            suppress_github_mentions("[email protected]"),
+            "[email protected]"
+        );
+
+        assert_eq!(suppress_github_mentions("@user_test"), "@user_test");
+    }
+}