handle the case when the change-id isn't found

When we switch back and forth between the old and recent branches,
if there was a breaking change in the bootstrap configuration in
between, we have to update the change-id in the build configuration
with each checkout, which can be exhausting. This change fixes that.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/bin/main.rs

@@ -109,31 +109,35 @@ fn check_version(config: &Config) -> Option<String> {
     }
 
     let latest_config_id = CONFIG_CHANGE_HISTORY.last().unwrap();
-    let suggestion = if let Some(id) = config.change_id {
+    if let Some(id) = config.change_id {
         if &id != latest_config_id {
-            msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
             let change_links: Vec<String> = find_recent_config_change_ids(id)
                 .iter()
                 .map(|id| format!("https://github.com/rust-lang/rust/pull/{id}"))
                 .collect();
             if !change_links.is_empty() {
+                msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
                 msg.push_str("To see more detail about these changes, visit the following PRs:\n");
+
                 for link in change_links {
                     msg.push_str(&format!("  - {link}\n"));
                 }
+
+                msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
+
+                msg.push_str("note: to silence this warning, ");
+                msg.push_str(&format!(
+                    "update `config.toml` to use `change-id = {latest_config_id}` instead"
+                ));
             }
-            msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
-            format!("update `config.toml` to use `change-id = {latest_config_id}` instead")
         } else {
             return None;
         }
     } else {
         msg.push_str("WARNING: The `change-id` is missing in the `config.toml`. This means that you will not be able to track the major changes made to the bootstrap configurations.\n");
-        format!("add `change-id = {latest_config_id}` at the top of `config.toml`")
+        msg.push_str("note: to silence this warning, ");
+        msg.push_str(&format!("add `change-id = {latest_config_id}` at the top of `config.toml`"));
     };
 
-    msg.push_str("note: to silence this warning, ");
-    msg.push_str(&suggestion);
-
     Some(msg)
 }

src/bootstrap/src/lib.rs

@@ -1849,10 +1849,19 @@ fn envify(s: &str) -> String {
 }
 
 pub fn find_recent_config_change_ids(current_id: usize) -> Vec<usize> {
-    let index = CONFIG_CHANGE_HISTORY
-        .iter()
-        .position(|&id| id == current_id)
-        .expect(&format!("Value `{}` was not found in `CONFIG_CHANGE_HISTORY`.", current_id));
+    if !CONFIG_CHANGE_HISTORY.contains(&current_id) {
+        // If the current change-id is greater than the most recent one,
+        // return an empty list; otherwise, return the full list.
+        if let Some(max_id) = CONFIG_CHANGE_HISTORY.iter().max() {
+            if &current_id > max_id {
+                return Vec::new();
+            }
+        }
+
+        return CONFIG_CHANGE_HISTORY.to_vec();
+    }
+
+    let index = CONFIG_CHANGE_HISTORY.iter().position(|&id| id == current_id).unwrap();
 
     CONFIG_CHANGE_HISTORY
         .iter()