Streamline find_lang_feature_issue.

It currently processes `ACTIVE_FEATURES` separately from
`ACCEPTED_FEATURES`, `REMOVED_FEATURES`, and `STABLE_REMOVED_FEATURES`,
for no good reason. This commit treats them uniformly.

Author: nnethercote

compiler/rustc_feature/src/lib.rs

@@ -79,8 +79,8 @@ pub enum UnstableFeatures {
 impl UnstableFeatures {
     /// This takes into account `RUSTC_BOOTSTRAP`.
     ///
-    /// If `krate` is [`Some`], then setting `RUSTC_BOOTSTRAP=krate` will enable the nightly features.
-    /// Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
+    /// If `krate` is [`Some`], then setting `RUSTC_BOOTSTRAP=krate` will enable the nightly
+    /// features. Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
     pub fn from_environment(krate: Option<&str>) -> Self {
         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
         let disable_unstable_features =
@@ -107,19 +107,18 @@ impl UnstableFeatures {
 }
 
 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
-    if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
-        info.issue
-    } else {
-        // search in Accepted, Removed, or Stable Removed features
-        let found = ACCEPTED_FEATURES
-            .iter()
-            .chain(REMOVED_FEATURES)
-            .chain(STABLE_REMOVED_FEATURES)
-            .find(|t| t.name == feature);
-        match found {
-            Some(found) => found.issue,
-            None => panic!("feature `{feature}` is not declared anywhere"),
-        }
+    // Search in all the feature lists.
+    let found = []
+        .iter()
+        .chain(ACTIVE_FEATURES)
+        .chain(ACCEPTED_FEATURES)
+        .chain(REMOVED_FEATURES)
+        .chain(STABLE_REMOVED_FEATURES)
+        .find(|t| t.name == feature);
+
+    match found {
+        Some(found) => found.issue,
+        None => panic!("feature `{feature}` is not declared anywhere"),
     }
 }