Add note regarding argument ordering

Author: varkor

src/librustc_typeck/astconv.rs

@@ -464,15 +464,17 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// Report an error that a generic argument did not match the generic parameter that was
     /// expected.
     fn generic_arg_mismatch_err(sess: &Session, arg: &GenericArg<'_>, kind: &'static str) {
-        struct_span_err!(
+        let mut err = struct_span_err!(
             sess,
             arg.span(),
             E0747,
             "{} provided when a {} was expected",
             arg.descr(),
             kind,
-        )
-        .emit();
+        );
+        // This note will be true as long as generic parameters are strictly ordered by their kind.
+        err.note(&format!("{} arguments must be provided before {} arguments", kind, arg.descr()));
+        err.emit();
     }
 
     /// Creates the relevant generic argument substitutions

src/test/ui/const-generics/const-arg-type-arg-misordered.stderr

@@ -11,6 +11,8 @@ error[E0747]: constant provided when a type was expected
    |
 LL | fn foo<const N: usize>() -> Array<N, ()> {
    |                                   ^
+   |
+   = note: type arguments must be provided before constant arguments
 
 error: aborting due to previous error
 

src/test/ui/const-generics/const-param-before-other-params.stderr

@@ -10,13 +10,5 @@ error: type parameters must be declared prior to const parameters
 LL | fn foo<const X: (), T>(_: &T) {
    |       --------------^- help: reorder the parameters: lifetimes, then types, then consts: `<T, const X: ()>`
 
-warning: the feature `const_generics` is incomplete and may cause the compiler to crash
-  --> $DIR/const-param-before-other-params.rs:1:12
-   |
-LL | #![feature(const_generics)]
-   |            ^^^^^^^^^^^^^^
-   |
-   = note: `#[warn(incomplete_features)]` on by default
-
 error: aborting due to 2 previous errors
 

src/test/ui/parser/issue-14303-fncall.stderr

@@ -3,6 +3,8 @@ error[E0747]: type provided when a lifetime was expected
    |
 LL |         .collect::<Vec<S<_, 'a>>>();
    |                          ^
+   |
+   = note: lifetime arguments must be provided before type arguments
 
 error: aborting due to previous error
 

src/test/ui/parser/issue-14303-path.stderr

@@ -3,6 +3,8 @@ error[E0747]: type provided when a lifetime was expected
    |
 LL | fn bar<'a, 'b, 'c, T>(x: foo::X<'a, T, 'b, 'c>) {}
    |                                     ^
+   |
+   = note: lifetime arguments must be provided before type arguments
 
 error: aborting due to previous error
 

src/test/ui/suggestions/suggest-move-types.stderr

@@ -79,24 +79,32 @@ error[E0747]: type provided when a lifetime was expected
    |
 LL | struct Al<'a, T, M: OneWithLifetime<A=(), T, 'a>> {
    |                                           ^
+   |
+   = note: lifetime arguments must be provided before type arguments
 
 error[E0747]: type provided when a lifetime was expected
   --> $DIR/suggest-move-types.rs:48:71
    |
 LL | struct Bl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<A=(), B=(), C=(), T, U, V, 'a, 'b, 'c>> {
    |                                                                       ^
+   |
+   = note: lifetime arguments must be provided before type arguments
 
 error[E0747]: lifetime provided when a type was expected
   --> $DIR/suggest-move-types.rs:64:56
    |
 LL | struct Cl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), C=(), U, 'b, V, 'c>> {
    |                                                        ^^
+   |
+   = note: type arguments must be provided before lifetime arguments
 
 error[E0747]: lifetime provided when a type was expected
   --> $DIR/suggest-move-types.rs:80:56
    |
 LL | struct Dl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), U, 'b, C=(), V, 'c>> {
    |                                                        ^^
+   |
+   = note: type arguments must be provided before lifetime arguments
 
 error: aborting due to 12 previous errors
 

src/test/ui/traits/trait-object-vs-lifetime.stderr

@@ -27,6 +27,8 @@ error[E0747]: type provided when a lifetime was expected
    |
 LL |     let _: S<dyn 'static +, 'static>;
    |              ^^^^^^^^^^^^^
+   |
+   = note: lifetime arguments must be provided before type arguments
 
 error: aborting due to 5 previous errors