parser: Permit trailing +'s in bound lists

Author: petrochenkov

src/libsyntax/parse/parser.rs

@@ -4003,14 +4003,7 @@ impl<'a> Parser<'a> {
                 break
             }}
 
-            // Trailing plus is not allowed for now and we have to detect it.
-            let is_bound_start = |token: &token::Token| {
-                token == &token::Question || token.is_lifetime() ||
-                token.is_keyword(keywords::For) || token.is_path_start()
-            };
-            if self.check(&token::BinOp(token::Plus)) && self.look_ahead(1, is_bound_start) {
-                self.bump();
-            } else {
+            if !self.eat(&token::BinOp(token::Plus)) {
                 break
             }
         }
@@ -4024,9 +4017,8 @@ impl<'a> Parser<'a> {
         let mut lifetimes = Vec::new();
         while let Some(lifetime) = self.eat_lifetime() {
             lifetimes.push(lifetime);
-            if self.check(&token::BinOp(token::Plus)) && self.look_ahead(1, |t| t.is_lifetime()) {
-                self.bump();
-            } else {
+
+            if !self.eat(&token::BinOp(token::Plus)) {
                 break
             }
         }

src/test/parse-fail/bounds-lifetime-3.rs

@@ -16,6 +16,7 @@ type A where 'a: = u8; // OK
 type A where 'a:, = u8; // OK
 type A where 'a: 'b + 'c = u8; // OK
 type A where = u8; // OK
-type A where 'a: 'b + = u8; //~ ERROR expected one of `,` or `=`, found `+`
+type A where 'a: 'b + = u8; // OK
+type A where , = u8; //~ ERROR expected one of `=`, lifetime, or type, found `,`
 
 fn main() {}

src/test/parse-fail/bounds-lifetime-where-2.rs

@@ -16,8 +16,9 @@ type A = for<'a:> fn(); // OK
 type A = for<'a:,> fn(); // OK
 type A = for<'a> fn(); // OK
 type A = for<> fn(); // OK
+type A = for<'a: 'b +> fn(); // OK
 
 type A = for<'a, T> fn(); //~ ERROR only lifetime parameters can be used in this context
-type A = for<'a: 'b +> fn(); //~ ERROR expected one of `,` or `>`, found `+`
+type A = for<,> fn(); //~ ERROR expected one of `>`, identifier, or lifetime, found `,`
 
 fn main() {}

src/test/parse-fail/bounds-lifetime-where.rs

@@ -16,6 +16,8 @@ type A where T: = u8; // OK
 type A where T:, = u8; // OK
 type A where T: Trait + Trait = u8; // OK
 type A where = u8; // OK
-type A where T: Trait + = u8; //~ ERROR expected one of `(`, `,`, `::`, `<`, or `=`, found `+`
+type A where T: Trait + = u8; // OK
+type A where T, = u8;
+//~^ ERROR expected one of `!`, `(`, `+`, `::`, `:`, `<`, `==`, or `=`, found `,`
 
 fn main() {}

src/test/parse-fail/bounds-lifetime.rs

@@ -16,8 +16,8 @@ struct S<
     T: 'a, // OK
     T:, // OK
     T: ?for<'a: 'b + 'c> Trait, // OK
+    T: Tr +, // OK
     T: ?'a, //~ ERROR `?` may only modify trait bounds, not lifetime bounds
-    T: Tr +, //~ ERROR expected one of `(`, `,`, `::`, `<`, `=`, or `>`, found `+`
 >;
 
 fn main() {}