make bounds on higher-kinded lifetimes a hard error in ast_validation

Also move the check for not having type parameters into ast_validation.

I was not sure what to do with compile-fail/issue-23046.rs: The issue looks like
maybe the bounds actually played a role in triggering the ICE, but that seems
unlikely given that the compiler seems to entirely ignore them.  However, I
couldn't find a testcase without the bounds, so I figured the best I could do is
to just remove the bounds and make sure at least that keeps working.

1 files changed, 2 insertions, 12 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 09dd00fa5fa..ba8ccc2256f 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5484,18 +5484,8 @@ impl<'a> Parser<'a> {
             self.expect_lt()?;
             let params = self.parse_generic_params()?;
             self.expect_gt()?;
-
-            let first_non_lifetime_param_span = params.iter()
-                .filter_map(|param| match *param {
-                    ast::GenericParam::Lifetime(_) => None,
-                    ast::GenericParam::Type(ref t) => Some(t.span),
-                })
-                .next();
-
-            if let Some(span) = first_non_lifetime_param_span {
-                self.span_err(span, "only lifetime parameters can be used in this context");
-            }
-
+            // We rely on AST validation to rule out invalid cases: There must not be type
+            // parameters, and the lifetime parameters must not have bounds.
             Ok(params)
         } else {
             Ok(Vec::new())