Fix where clauses parsing

Require at least one predicate for a lifetime in a where clause

Author: matklad

src/librustc_borrowck/borrowck/mir/dataflow/graphviz.rs

@@ -88,7 +88,7 @@ pub trait MirWithFlowState<'tcx> {
 }
 
 impl<'a, 'tcx: 'a, BD> MirWithFlowState<'tcx> for MirBorrowckCtxtPreDataflow<'a, 'tcx, BD>
-    where 'a, 'tcx: 'a, BD: BitDenotation<Ctxt=MoveDataParamEnv<'tcx>>
+    where 'tcx: 'a, BD: BitDenotation<Ctxt=MoveDataParamEnv<'tcx>>
 {
     type BD = BD;
     fn node_id(&self) -> NodeId { self.node_id }

src/libsyntax/parse/parser.rs

@@ -4440,14 +4440,20 @@ impl<'a> Parser<'a> {
                     let bounded_lifetime =
                         self.parse_lifetime()?;
 
-                    self.eat(&token::Colon);
+                    self.expect(&token::Colon)?;
 
                     let bounds =
                         self.parse_lifetimes(token::BinOp(token::Plus))?;
 
                     let hi = self.prev_span.hi;
                     let span = mk_sp(lo, hi);
 
+                    if bounds.is_empty() {
+                        self.span_err(span,
+                                      "each predicate in a `where` clause must have \
+                                       at least one bound in it");
+                    }
+
                     where_clause.predicates.push(ast::WherePredicate::RegionPredicate(
                         ast::WhereRegionPredicate {
                             span: span,

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

@@ -1,4 +1,4 @@
-// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z parse-only
+// compile-flags: -Z parse-only -Z continue-parse-after-error
 
 fn equal1<T>(_: &T, _: &T) -> bool where {
 //~^ ERROR a `where` clause must have at least one predicate in it
@@ -20,5 +20,11 @@ fn equal2<T>(_: &T, _: &T) -> bool where T: {
     true
 }
 
+fn foo2<'a>() where 'a: {}
+//~^ ERROR each predicate in a `where` clause must have at least one bound
+
+fn foo1<'a>() where 'a {}
+//~^ ERROR expected `:`, found `{`
+
 fn main() {
 }