Reduce boilerplate with the ? operator

Author: LingMan

compiler/rustc_builtin_macros/src/format_foreign.rs

@@ -649,17 +649,13 @@ pub mod shell {
     impl<'a> Iterator for Substitutions<'a> {
         type Item = Substitution<'a>;
         fn next(&mut self) -> Option<Self::Item> {
-            match parse_next_substitution(self.s) {
-                Some((mut sub, tail)) => {
-                    self.s = tail;
-                    if let Some(InnerSpan { start, end }) = sub.position() {
-                        sub.set_position(start + self.pos, end + self.pos);
-                        self.pos += end;
-                    }
-                    Some(sub)
-                }
-                None => None,
+            let (mut sub, tail) = parse_next_substitution(self.s)?;
+            self.s = tail;
+            if let Some(InnerSpan { start, end }) = sub.position() {
+                sub.set_position(start + self.pos, end + self.pos);
+                self.pos += end;
             }
+            Some(sub)
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2364,13 +2364,9 @@ impl<'o, 'tcx> Iterator for TraitObligationStackList<'o, 'tcx> {
     type Item = &'o TraitObligationStack<'o, 'tcx>;
 
     fn next(&mut self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
-        match self.head {
-            Some(o) => {
-                *self = o.previous;
-                Some(o)
-            }
-            None => None,
-        }
+        let o = self.head?;
+        *self = o.previous;
+        Some(o)
     }
 }