add more config options for no_merges

src/config.rs

@@ -94,8 +94,18 @@ pub(crate) struct AssignConfig {
 
 #[derive(PartialEq, Eq, Debug, serde::Deserialize)]
 pub(crate) struct NoMergesConfig {
+    /// No action will be taken on PRs with these labels.
     #[serde(default)]
-    _empty: (),
+    pub(crate) exclude_labels: Vec<String>,
+    /// Set these labels on the PR when merge commits are detected.
+    #[serde(default)]
+    pub(crate) labels: Vec<String>,
+    /// Override the default message to post when merge commits are detected.
+    ///
+    /// This message will always be followed up with
+    /// "The following commits are merge commits:" and then
+    /// a list of the merge commits.
+    pub(crate) message: Option<String>,
 }
 
 #[derive(PartialEq, Eq, Debug, serde::Deserialize)]

src/handlers/no_merges.rs

@@ -4,7 +4,7 @@
 use crate::{
     config::NoMergesConfig,
     db::issue_data::IssueData,
-    github::{IssuesAction, IssuesEvent},
+    github::{IssuesAction, IssuesEvent, Label},
     handlers::Context,
 };
 use anyhow::Context as _;
@@ -38,16 +38,23 @@ pub(super) async fn parse_input(
         return Ok(None);
     }
 
-    // Require an empty configuration block to enable no-merges notifications.
-    if config.is_none() {
+    // Require a `[no_merges]` configuration block to enable no-merges notifications.
+    let Some(config) = config else {
         return Ok(None);
-    }
+    };
 
     // Don't ping on rollups or draft PRs.
     if event.issue.title.starts_with("Rollup of") || event.issue.draft {
         return Ok(None);
     }
 
+    // Don't trigger if the PR has any of the excluded labels.
+    for label in event.issue.labels() {
+        if config.exclude_labels.contains(&label.name) {
+            return Ok(None);
+        }
+    }
+
     let mut merge_commits = HashSet::new();
     let commits = event
         .issue
@@ -71,53 +78,74 @@ pub(super) async fn parse_input(
     })
 }
 
+const DEFAULT_MESSAGE: &str = "
+There are merge commits (commits with multiple parents) in your changes. We have a \
+[no merge policy](https://rustc-dev-guide.rust-lang.org/git.html#no-merge-policy) \
+so these commits will need to be removed for this pull request to be merged.
+
+You can start a rebase with the following commands:
+```shell-session
+$ # rebase
+$ git rebase -i master
+$ # delete any merge commits in the editor that appears
+$ git push --force-with-lease
+```
+
+";
+
 pub(super) async fn handle_input(
     ctx: &Context,
-    _config: &NoMergesConfig,
+    config: &NoMergesConfig,
     event: &IssuesEvent,
     input: NoMergesInput,
 ) -> anyhow::Result<()> {
     let mut client = ctx.db.get().await;
     let mut state: IssueData<'_, NoMergesState> =
         IssueData::load(&mut client, &event.issue, NO_MERGES_KEY).await?;
 
+    let mut message = config
+        .message
+        .as_deref()
+        .unwrap_or(DEFAULT_MESSAGE)
+        .to_string();
+
     let since_last_posted = if state.data.mentioned_merge_commits.is_empty() {
         ""
     } else {
         " (since this message was last posted)"
     };
+    writeln!(
+        message,
+        "The following commits are merge commits{since_last_posted}:"
+    )
+    .unwrap();
 
     let mut should_send = false;
-    let mut message = format!(
-        "
-        There are merge commits (commits with multiple parents) in your changes. We have a
-        [no merge policy](https://rustc-dev-guide.rust-lang.org/git.html#no-merge-policy) so
-        these commits will need to be removed for this pull request to be merged.
-
-        You can start a rebase with the following commands:
-
-        ```shell-session
-        $ # rebase
-        $ git rebase -i master
-        $ # delete any merge commits in the editor that appears
-        $ git push --force-with-lease
-        ```
-
-        The following commits are merge commits{since_last_posted}:
-
-    "
-    );
     for commit in &input.merge_commits {
         if state.data.mentioned_merge_commits.contains(commit) {
             continue;
         }
 
         should_send = true;
         state.data.mentioned_merge_commits.insert((*commit).clone());
-        write!(message, "- {commit}").unwrap();
+        writeln!(message, "- {commit}").unwrap();
     }
 
     if should_send {
+        // Set labels
+        let labels = config
+            .labels
+            .iter()
+            .cloned()
+            .map(|name| Label { name })
+            .collect();
+        event
+            .issue
+            .add_labels(&ctx.github, labels)
+            .await
+            .context("failed to set no_merges labels")?;
+
+        // Post comment
         event
             .issue
             .post_comment(&ctx.github, &message)
@@ -127,3 +155,40 @@ pub(super) async fn handle_input(
     }
     Ok(())
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn message() {
+        let mut message = DEFAULT_MESSAGE.to_string();
+
+        writeln!(message, "The following commits are merge commits:").unwrap();
+
+        for n in 1..5 {
+            writeln!(message, "- commit{n}").unwrap();
+        }
+
+        assert_eq!(
+            message,
+            "
+There are merge commits (commits with multiple parents) in your changes. We have a [no merge policy](https://rustc-dev-guide.rust-lang.org/git.html#no-merge-policy) so these commits will need to be removed for this pull request to be merged.
+
+You can start a rebase with the following commands:
+```shell-session
+$ # rebase
+$ git rebase -i master
+$ # delete any merge commits in the editor that appears
+$ git push --force-with-lease
+```
+
+The following commits are merge commits:
+- commit1
+- commit2
+- commit3
+- commit4
+"
+        );
+    }
+}