Rollup merge of #93589 - est31:option_then, r=cjgillot

Use Option::then in two places

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -264,7 +264,7 @@ fn lower_match_tree<'pat>(
         // The set of places that we are creating fake borrows of. If there are
         // no match guards then we don't need any fake borrows, so don't track
         // them.
-        let mut fake_borrows = if match_has_guard { Some(FxHashSet::default()) } else { None };
+        let mut fake_borrows = match_has_guard.then(FxHashSet::default);
 
         let mut otherwise = None;
 

compiler/rustc_query_system/src/dep_graph/serialized.rs

@@ -182,7 +182,7 @@ fn new(encoder: FileEncoder, record_stats: bool) -> Self {
             total_edge_count: 0,
             total_node_count: 0,
             result: Ok(()),
-            stats: if record_stats { Some(FxHashMap::default()) } else { None },
+            stats: record_stats.then(FxHashMap::default),
         }
     }