Simplify parse_self_param

Author: frank-king

compiler/rustc_parse/src/parser/item.rs

@@ -2954,6 +2954,8 @@ impl<'a> Parser<'a> {
             }
             _ => unreachable!(),
         };
+        // is lifetime `n` tokens ahead?
+        let is_lifetime = |this: &Self, n| this.look_ahead(n, |t| t.is_lifetime());
         // Is `self` `n` tokens ahead?
         let is_isolated_self = |this: &Self, n| {
             this.is_keyword_ahead(n, &[kw::SelfLower])
@@ -3023,60 +3025,35 @@ impl<'a> Parser<'a> {
         let eself_lo = self.token.span;
         let (eself, eself_ident, eself_hi) = match self.token.uninterpolate().kind {
             token::And => {
-                let eself = if is_isolated_self(self, 1) {
-                    // `&self`
-                    self.bump();
-                    SelfKind::Region(None, Mutability::Not)
-                } else if is_isolated_mut_self(self, 1) {
-                    // `&mut self`
-                    self.bump();
-                    self.bump();
-                    SelfKind::Region(None, Mutability::Mut)
-                } else if is_isolated_pin_const_self(self, 1) {
-                    // `&pin const self`
+                let has_lifetime = is_lifetime(self, 1);
+                let skip_lifetime_count = has_lifetime as usize;
+                let eself = if is_isolated_self(self, skip_lifetime_count + 1) {
+                    // `&{'lt} self`
                     self.bump(); // &
-                    self.psess.gated_spans.gate(sym::pin_ergonomics, self.token.span);
-                    self.bump(); // pin
-                    self.bump(); // const
-                    SelfKind::Pinned(None, Mutability::Not)
-                } else if is_isolated_pin_mut_self(self, 1) {
-                    // `&pin mut self`
+                    let lifetime = has_lifetime.then(|| self.expect_lifetime());
+                    SelfKind::Region(lifetime, Mutability::Not)
+                } else if is_isolated_mut_self(self, skip_lifetime_count + 1) {
+                    // `&{'lt} mut self`
                     self.bump(); // &
-                    self.psess.gated_spans.gate(sym::pin_ergonomics, self.token.span);
-                    self.bump(); // pin
+                    let lifetime = has_lifetime.then(|| self.expect_lifetime());
                     self.bump(); // mut
-                    SelfKind::Pinned(None, Mutability::Mut)
-                } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_self(self, 2) {
-                    // `&'lt self`
-                    self.bump();
-                    let lt = self.expect_lifetime();
-                    SelfKind::Region(Some(lt), Mutability::Not)
-                } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_mut_self(self, 2) {
-                    // `&'lt mut self`
-                    self.bump();
-                    let lt = self.expect_lifetime();
-                    self.bump();
-                    SelfKind::Region(Some(lt), Mutability::Mut)
-                } else if self.look_ahead(1, |t| t.is_lifetime())
-                    && is_isolated_pin_const_self(self, 2)
-                {
-                    // `&'lt pin const self`
+                    SelfKind::Region(lifetime, Mutability::Mut)
+                } else if is_isolated_pin_const_self(self, skip_lifetime_count + 1) {
+                    // `&{'lt} pin const self`
                     self.bump(); // &
-                    let lt = self.expect_lifetime();
+                    let lifetime = has_lifetime.then(|| self.expect_lifetime());
                     self.psess.gated_spans.gate(sym::pin_ergonomics, self.token.span);
                     self.bump(); // pin
                     self.bump(); // const
-                    SelfKind::Pinned(Some(lt), Mutability::Not)
-                } else if self.look_ahead(1, |t| t.is_lifetime())
-                    && is_isolated_pin_mut_self(self, 2)
-                {
-                    // `&'lt pin mut self`
+                    SelfKind::Pinned(lifetime, Mutability::Not)
+                } else if is_isolated_pin_mut_self(self, skip_lifetime_count + 1) {
+                    // `&{'lt} pin mut self`
                     self.bump(); // &
-                    let lt = self.expect_lifetime();
+                    let lifetime = has_lifetime.then(|| self.expect_lifetime());
                     self.psess.gated_spans.gate(sym::pin_ergonomics, self.token.span);
                     self.bump(); // pin
                     self.bump(); // mut
-                    SelfKind::Pinned(Some(lt), Mutability::Mut)
+                    SelfKind::Pinned(lifetime, Mutability::Mut)
                 } else {
                     // `&not_self`
                     return Ok(None);