Adjust parser generic parameter errors

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

@@ -0,0 +1,19 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+fn u32_identity<const X: u32>() -> u32 {
+    //~^ ERROR const generics in any position are currently unsupported
+    5
+}
+
+fn foo_a() {
+    u32_identity::<-1>(); //~ ERROR expected identifier, found `<-`
+}
+
+fn foo_b() {
+    u32_identity::<1 + 2>(); //~ ERROR expected one of `,` or `>`, found `+`
+}
+
+fn main() {
+    u32_identity::<5>(); // ok
+}