Parse negative literals in const generic arguments

src/libsyntax/parse/parser.rs

@@ -5796,8 +5796,7 @@ impl<'a> Parser<'a> {
                 } else {
                     // FIXME(const_generics): this currently conflicts with emplacement syntax
                     // with negative integer literals.
-                    let lit = self.parse_lit()?;
-                    self.mk_expr(lit.span, ExprKind::Lit(lit), ThinVec::new())
+                    self.parse_literal_maybe_minus()?
                 };
                 let value = AnonConst {
                     id: ast::DUMMY_NODE_ID,

src/test/ui/const-generics/const-expression-parameter.rs

@@ -14,6 +14,10 @@ fn foo_b() {
     u32_identity::<1 + 2>(); //~ ERROR expected one of `,` or `>`, found `+`
 }
 
+fn foo_c() {
+    u32_identity::< -1 >(); // ok
+}
+
 fn main() {
     u32_identity::<5>(); // ok
 }