Auto merge of #39158 - petrochenkov:bounds, r=nikomatsakis

Bounds parsing refactoring 2

See https://github.com/rust-lang/rust/pull/37511 for previous discussion.
cc @matklad

Relaxed parsing rules:
 - zero bounds after `:` are allowed in all contexts.
 - zero predicates are allowed after `where`.
- trailing separator `,` is allowed after predicates in `where` clauses not followed by `{`.

Other parsing rules:
 - trailing separator `+` is still allowed in all bound lists.

Code is also cleaned up and tests added.

I haven't touched parsing of trait object types yet, I'll do it later.

src/librustc_passes/ast_validation.rs

@@ -146,6 +146,12 @@ fn visit_ty(&mut self, ty: &'a Ty) {
             TyKind::TraitObject(ref bounds) => {
                 self.no_questions_in_bounds(bounds, "trait object types", false);
             }
+            TyKind::ImplTrait(ref bounds) => {
+                if !bounds.iter()
+                          .any(|b| if let TraitTyParamBound(..) = *b { true } else { false }) {
+                    self.err_handler().span_err(ty.span, "at least one trait must be specified");
+                }
+            }
             _ => {}
         }
 
@@ -284,6 +290,26 @@ fn visit_vis(&mut self, vis: &'a Visibility) {
 
         visit::walk_vis(self, vis)
     }
+
+    fn visit_generics(&mut self, g: &'a Generics) {
+        let mut seen_default = None;
+        for ty_param in &g.ty_params {
+            if ty_param.default.is_some() {
+                seen_default = Some(ty_param.span);
+            } else if let Some(span) = seen_default {
+                self.err_handler()
+                    .span_err(span, "type parameters with a default must be trailing");
+                break
+            }
+        }
+        for predicate in &g.where_clause.predicates {
+            if let WherePredicate::EqPredicate(ref predicate) = *predicate {
+                self.err_handler().span_err(predicate.span, "equality constraints are not yet \
+                                                             supported in where clauses (#20041)");
+            }
+        }
+        visit::walk_generics(self, g)
+    }
 }
 
 pub fn check_crate(session: &Session, krate: &Crate) {

src/librustc_typeck/collect.rs

@@ -1833,11 +1833,8 @@ fn ty_generic_predicates<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>,
                 }
             }
 
-            &hir::WherePredicate::EqPredicate(ref eq_pred) => {
+            &hir::WherePredicate::EqPredicate(..) => {
                 // FIXME(#20041)
-                span_bug!(eq_pred.span,
-                         "Equality constraints are not yet \
-                          implemented (#20041)")
             }
         }
     }

src/librustdoc/clean/mod.rs

@@ -842,8 +842,11 @@ fn clean(&self, cx: &DocContext) -> WherePredicate {
                 }
             }
 
-            hir::WherePredicate::EqPredicate(_) => {
-                unimplemented!() // FIXME(#20041)
+            hir::WherePredicate::EqPredicate(ref wrp) => {
+                WherePredicate::EqPredicate {
+                    lhs: wrp.lhs_ty.clean(cx),
+                    rhs: wrp.rhs_ty.clean(cx)
+                }
             }
         }
     }

src/libsyntax/parse/token.rs

@@ -187,6 +187,29 @@ pub fn can_begin_expr(&self) -> bool {
         }
     }
 
+    /// Returns `true` if the token can appear at the start of a type.
+    pub fn can_begin_type(&self) -> bool {
+        match *self {
+            OpenDelim(Paren)            => true, // tuple
+            OpenDelim(Bracket)          => true, // array
+            Ident(..)                   => true, // type name or keyword
+            Underscore                  => true, // placeholder
+            Not                         => true, // never
+            BinOp(Star)                 => true, // raw pointer
+            BinOp(And)                  => true, // reference
+            AndAnd                      => true, // double reference
+            Lt | BinOp(Shl)             => true, // associated path
+            ModSep                      => true, // global path
+            Interpolated(ref nt) => match **nt {
+                NtTy(..) => true,
+                NtIdent(..) => true,
+                NtPath(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+
     /// Returns `true` if the token is any literal
     pub fn is_lit(&self) -> bool {
         match *self {

src/test/compile-fail/attrs-with-no-formal-in-generics-2.rs

@@ -17,10 +17,7 @@
 
 struct RefAny<'a, T>(&'a T);
 
-impl<#[rustc_1] 'a, #[rustc_2] T, #[oops]> RefAny<'a, T> {
-    //~^ ERROR expected identifier, found `>`
-}
+impl<#[rustc_1] 'a, #[rustc_2] T, #[oops]> RefAny<'a, T> {}
+//~^ ERROR trailing attribute after type parameters
 
-fn main() {
-
-}
+fn main() {}

src/test/compile-fail/generic-non-trailing-defaults.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Heap;
+
+struct Vec<A = Heap, T>;
+//~^ ERROR type parameters with a default must be trailing
+
+struct Foo<A, B = Vec<C>, C>;
+//~^ ERROR type parameters with a default must be trailing
+//~| ERROR type parameters with a default cannot use forward declared identifiers
+
+fn main() {}

src/test/compile-fail/impl-trait/no-trait.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(conservative_impl_trait)]
+
+fn f() -> impl 'static {} //~ ERROR at least one trait must be specified
+
+fn main() {}

src/test/compile-fail/issue-20616-1.rs

@@ -16,7 +16,7 @@
 type Type_1_<'a, T> = &'a T;
 
 
-type Type_1<'a T> = &'a T; //~ error: expected `,` or `>` after lifetime name, found `T`
+type Type_1<'a T> = &'a T; //~ error: expected one of `,`, `:`, or `>`, found `T`
 
 
 //type Type_2 = Type_1_<'static ()>; // error: expected `,` or `>` after lifetime name, found `(`

src/test/compile-fail/issue-20616-2.rs

@@ -19,7 +19,7 @@
 //type Type_1<'a T> = &'a T; // error: expected `,` or `>` after lifetime name, found `T`
 
 
-type Type_2 = Type_1_<'static ()>; //~ error: expected `,` or `>` after lifetime name, found `(`
+type Type_2 = Type_1_<'static ()>; //~ error: expected one of `,` or `>`, found `(`
 
 
 //type Type_3<T> = Box<T,,>; // error: expected type, found `,`

src/test/compile-fail/issue-20616-3.rs

@@ -22,7 +22,7 @@
 //type Type_2 = Type_1_<'static ()>; // error: expected `,` or `>` after lifetime name, found `(`
 
 
-type Type_3<T> = Box<T,,>; //~ error: expected type, found `,`
+type Type_3<T> = Box<T,,>; //~ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_4<T> = Type_1_<'static,, T>; // error: expected type, found `,`

src/test/compile-fail/issue-20616-4.rs

@@ -25,7 +25,8 @@
 //type Type_3<T> = Box<T,,>; // error: expected type, found `,`
 
 
-type Type_4<T> = Type_1_<'static,, T>; //~ error: expected type, found `,`
+type Type_4<T> = Type_1_<'static,, T>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 type Type_5_<'a> = Type_1_<'a, ()>;

src/test/compile-fail/issue-20616-5.rs

@@ -31,7 +31,8 @@
 type Type_5_<'a> = Type_1_<'a, ()>;
 
 
-type Type_5<'a> = Type_1_<'a, (),,>; //~ error: expected type, found `,`
+type Type_5<'a> = Type_1_<'a, (),,>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_6 = Type_5_<'a,,>; // error: expected type, found `,`

src/test/compile-fail/issue-20616-6.rs

@@ -34,7 +34,8 @@
 //type Type_5<'a> = Type_1_<'a, (),,>; // error: expected type, found `,`
 
 
-type Type_6 = Type_5_<'a,,>; //~ error: expected type, found `,`
+type Type_6 = Type_5_<'a,,>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_7 = Box<(),,>; // error: expected type, found `,`

src/test/compile-fail/issue-20616-7.rs

@@ -37,7 +37,7 @@
 //type Type_6 = Type_5_<'a,,>; // error: expected type, found `,`
 
 
-type Type_7 = Box<(),,>; //~ error: expected type, found `,`
+type Type_7 = Box<(),,>; //~ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_8<'a,,> = &'a (); // error: expected ident, found `,`

src/test/compile-fail/issue-20616-8.rs

@@ -40,7 +40,7 @@
 //type Type_7 = Box<(),,>; // error: expected type, found `,`
 
 
-type Type_8<'a,,> = &'a (); //~ error: expected identifier, found `,`
+type Type_8<'a,,> = &'a (); //~ error: expected one of `>`, identifier, or lifetime, found `,`
 
 
 //type Type_9<T,,> = Box<T>; // error: expected identifier, found `,`

src/test/compile-fail/issue-20616-9.rs

@@ -43,4 +43,4 @@
 //type Type_8<'a,,> = &'a (); // error: expected identifier, found `,`
 
 
-type Type_9<T,,> = Box<T>; //~ error: expected identifier, found `,`
+type Type_9<T,,> = Box<T>; //~ error: expected one of `>`, identifier, or lifetime, found `,`

src/test/compile-fail/where-equality-constraints.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn f() where u8 = u16 {}
+//~^ ERROR equality constraints are not yet supported in where clauses
+fn g() where for<'a> &(u8,) == u16, {}
+//~^ ERROR equality constraints are not yet supported in where clauses
+
+fn main() {}

src/test/compile-fail/where-lifetime-resolution.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+trait Trait1 {}
+trait Trait2 {}
+
+fn f() where
+    for<'a> Trait1<'a>: Trait1<'a>, // OK
+    (for<'a> Trait1<'a>): Trait1<'a>,
+    //~^ ERROR use of undeclared lifetime name `'a`
+    for<'a> for<'b> Trait2<'a, 'b>: Trait2<'a, 'b>,
+    //~^ ERROR use of undeclared lifetime name `'b`
+    //~| ERROR nested quantification of lifetimes
+{}
+
+fn main() {}

src/test/parse-fail/bounds-lifetime-1.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+type A = for<'a 'b> fn(); //~ ERROR expected one of `,`, `:`, or `>`, found `'b`
+
+fn main() {}

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

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+type A = for<'a + 'b> fn(); //~ ERROR expected one of `,`, `:`, or `>`, found `+`
+
+fn main() {}

src/test/parse-fail/bounds-lifetime-where-1.rs

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+type A where 'a; //~ ERROR expected `:`, found `;`
+
+fn main() {}

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

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+type A where 'a: 'b + 'c = u8; // OK
+type A where 'a: 'b, = u8; // OK
+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; // OK
+type A where , = u8; //~ ERROR expected one of `=`, lifetime, or type, found `,`
+
+fn main() {}

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

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only -Z continue-parse-after-error
+
+type A = for<'a: 'b + 'c> fn(); // OK
+type A = for<'a: 'b,> fn(); // OK
+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<,> fn(); //~ ERROR expected one of `>`, identifier, or lifetime, found `,`
+
+fn main() {}

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

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+type A where for<'a> for<'b> Trait1 + ?Trait2: 'a + Trait = u8; // OK
+type A where T: Trait, = u8; // OK
+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; // OK
+type A where T, = u8;
+//~^ ERROR expected one of `!`, `(`, `+`, `::`, `:`, `<`, `==`, or `=`, found `,`
+
+fn main() {}

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

+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only -Z continue-parse-after-error
+
+struct S<
+    T: 'a + Tr, // OK
+    T: Tr + 'a, // OK
+    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
+>;
+
+fn main() {}

src/test/parse-fail/issue-14303-path.rs

@@ -12,4 +12,3 @@
 
 fn bar<'a, T>(x: mymodule::X<'a, T, 'b, 'c>) {}
 //~^ ERROR lifetime parameters must be declared prior to type parameters
-//~^^ ERROR expected pattern, found `'c`

src/test/parse-fail/generic-non-trailing-defaults.rs → src/test/parse-fail/issue-17904-2.rs

@@ -10,10 +10,6 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
-struct Heap;
-
-struct Vec<A = Heap, T>; //~ ERROR type parameters with a default must be trailing
-
-struct Foo<A, B = Vec<C>, C>; //~ ERROR type parameters with a default must be trailing
+struct Bar<T> { x: T } where T: Copy //~ ERROR expected item, found `where`
 
 fn main() {}

src/test/parse-fail/issue-17904.rs

@@ -13,7 +13,6 @@
 struct Baz<U> where U: Eq(U); //This is parsed as the new Fn* style parenthesis syntax.
 struct Baz<U> where U: Eq(U) -> R; // Notice this parses as well.
 struct Baz<U>(U) where U: Eq; // This rightfully signals no error as well.
-struct Foo<T> where T: Copy, (T); //~ ERROR unexpected token in `where` clause
-struct Bar<T> { x: T } where T: Copy //~ ERROR expected item, found `where`
+struct Foo<T> where T: Copy, (T); //~ ERROR expected one of `+`, `:`, `==`, or `=`, found `;`
 
 fn main() {}

src/test/parse-fail/issue-32214.rs

@@ -10,8 +10,7 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
-pub fn test<W, I: Iterator<Item=(), W> >() {
-    //~^ ERROR expected `=`, found `>`
-}
+pub fn test<W, I: Iterator<Item=(), W> >() {}
+//~^ ERROR type parameters must be declared prior to associated type bindings
 
 fn main() { }

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

@@ -15,5 +15,4 @@ struct Foo<'a, 'b> {
 }
 
 fn foo<'a, 'b>(x: &mut Foo<'a; 'b>) {}
-//~^ ERROR expected `,` or `>` after lifetime name, found `;`
-//~^^ NOTE did you mean a single argument type &'a Type, or did you mean the comma-separated
+//~^ ERROR expected one of `,` or `>`, found `;`

src/test/parse-fail/where-clauses-no-bounds-or-predicates.rs

@@ -10,13 +10,13 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
+// Empty predicate list is OK
 fn equal1<T>(_: &T, _: &T) -> bool where {
-//~^ ERROR a `where` clause must have at least one predicate in it
     true
 }
 
+// Empty bound list is OK
 fn equal2<T>(_: &T, _: &T) -> bool where T: {
-//~^ ERROR each predicate in a `where` clause must have at least one bound
     true
 }