Comment on issues when @rustbot label is given an invalid label

Previously, the label was just silently ignored, along with all other labels
in the same command. This tells the user what went wrong, and also adds all valid labels

Author: jyn514

src/github.rs

@@ -366,13 +366,18 @@ impl IssueRepository {
         )
     }
 
-    async fn has_label(&self, client: &GithubClient, label: &str) -> bool {
+    async fn has_label(&self, client: &GithubClient, label: &str) -> anyhow::Result<bool> {
         #[allow(clippy::redundant_pattern_matching)]
         let url = format!("{}/labels/{}", self.url(), label);
-        match client.send_req(client.get(&url)).await {
-            Ok(_) => true,
-            // XXX: Error handling if the request failed for reasons beyond 'label didn't exist'
-            Err(_) => false,
+        match client._send_req(client.get(&url)).await {
+            Ok((_, _)) => Ok(true),
+            Err(e) => {
+                if e.downcast_ref::<reqwest::Error>().map_or(false, |e| e.status() == Some(StatusCode::NOT_FOUND)) {
+                    Ok(false)
+                } else {
+                    Err(e)
+                }
+            }
         }
     }
 }
@@ -519,20 +524,32 @@ impl Issue {
             return Ok(());
         }
 
-        for label in &labels {
-            if !self.repository().has_label(client, &label).await {
-                anyhow::bail!("Label {} does not exist in {}", label, self.global_id());
+        let mut unknown_labels = vec![];
+        let mut known_labels = vec![];
+        for label in labels {
+            if !self.repository().has_label(client, &label).await? {
+                unknown_labels.push(label);
+            } else {
+                known_labels.push(label);
             }
         }
 
         #[derive(serde::Serialize)]
         struct LabelsReq {
             labels: Vec<String>,
         }
-        client
-            ._send_req(client.post(&url).json(&LabelsReq { labels }))
-            .await
-            .context("failed to add labels")?;
+
+        if !known_labels.is_empty() {
+            client
+                ._send_req(client.post(&url).json(&LabelsReq { labels: known_labels }))
+                .await
+                .context("failed to add labels")?;
+        }
+
+        if !unknown_labels.is_empty() {
+            let comment = String::from("Unknown labels:\n- ") + &unknown_labels.join("\n- ");
+            self.post_comment(client, &comment).await.context("failed to post missing label comment")?;
+        }
 
         Ok(())
     }

src/interactions.rs

@@ -1,6 +1,5 @@
 use crate::github::{GithubClient, Issue};
 use std::fmt::Write;
-use tracing as log;
 
 pub struct ErrorComment<'a> {
     issue: &'a Issue,