prefer `if let` to match with `None => {}` arm in some places

This is a spiritual succesor to #34268/8531d581, in which we replaced a
number of matches of None to the unit value with `if let` conditionals
where it was judged that this made for clearer/simpler code (as would be
recommended by Manishearth/rust-clippy's `single_match` lint). The same
rationale applies to matches of None to the empty block.

1 files changed, 5 insertions, 8 deletions

diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index fdaf182c605..57c4af6bed5 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -250,15 +250,12 @@ impl Session {
                     msg: String) {
         let lint_id = lint::LintId::of(lint);
         let mut lints = self.lints.borrow_mut();
-        match lints.get_mut(&id) {
-            Some(arr) => {
-                let tuple = (lint_id, sp, msg);
-                if !arr.contains(&tuple) {
-                    arr.push(tuple);
-                }
-                return;
+        if let Some(arr) = lints.get_mut(&id) {
+            let tuple = (lint_id, sp, msg);
+            if !arr.contains(&tuple) {
+                arr.push(tuple);
             }
-            None => {}
+            return;
         }
         lints.insert(id, vec!((lint_id, sp, msg)));
     }