+use rustc_ast::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
+use rustc_ast::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
+use rustc_ast::attr;
+use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
use rustc_errors::{struct_span_err, Handler};
use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
use rustc_feature::{Features, GateIssue, UnstableFeatures};
use rustc_span::source_map::Spanned;
use rustc_span::symbol::sym;
use rustc_span::Span;
-use syntax::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
-use syntax::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
-use syntax::attr;
-use syntax::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
use log::debug;