Make lifetime ordering error pretty print const param defaults

Author: BoxyUwU

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -938,8 +938,11 @@ fn validate_generic_param_order(
                 }
                 GenericParamKind::Type { default: None } => (),
                 GenericParamKind::Lifetime => (),
-                // FIXME(const_generics_defaults)
-                GenericParamKind::Const { ty: _, kw_span: _, default: _ } => (),
+                GenericParamKind::Const { ty: _, kw_span: _, default: Some(default) } => {
+                    ordered_params += " = ";
+                    ordered_params += &pprust::expr_to_string(&*default.value);
+                }
+                GenericParamKind::Const { ty: _, kw_span: _, default: None } => (),
             }
             first = false;
         }
@@ -959,7 +962,7 @@ fn validate_generic_param_order(
             span,
             &format!(
                 "reorder the parameters: lifetimes, {}",
-                if sess.features_untracked().const_generics {
+                if sess.features_untracked().unordered_const_ty_params() {
                     "then consts and types"
                 } else {
                     "then types, then consts"

src/test/ui/const-generics/defaults/intermixed-lifetime.min.stderr

@@ -2,13 +2,13 @@ error: lifetime parameters must be declared prior to const parameters
   --> $DIR/intermixed-lifetime.rs:7:28
    |
 LL | struct Foo<const N: usize, 'a, T = u32>(&'a (), T);
-   |           -----------------^^---------- help: reorder the parameters: lifetimes, then types, then consts: `<'a, const N: usize, T = u32>`
+   |           -----------------^^---------- help: reorder the parameters: lifetimes, then consts and types: `<'a, const N: usize, T = u32>`
 
 error: lifetime parameters must be declared prior to type parameters
   --> $DIR/intermixed-lifetime.rs:10:37
    |
 LL | struct Bar<const N: usize, T = u32, 'a>(&'a (), T);
-   |           --------------------------^^- help: reorder the parameters: lifetimes, then types, then consts: `<'a, const N: usize, T = u32>`
+   |           --------------------------^^- help: reorder the parameters: lifetimes, then consts and types: `<'a, const N: usize, T = u32>`
 
 error: aborting due to 2 previous errors
 

src/test/ui/const-generics/defaults/param-order-err-pretty-prints-default.rs

@@ -0,0 +1,5 @@
+#![feature(const_generics_defaults)]
+struct Foo<const M: usize = 10, 'a>(&'a u32);
+//~^ Error lifetime parameters must be declared prior to const parameters
+
+fn main() {}

src/test/ui/const-generics/defaults/param-order-err-pretty-prints-default.stderr

@@ -0,0 +1,8 @@
+error: lifetime parameters must be declared prior to const parameters
+  --> $DIR/param-order-err-pretty-prints-default.rs:2:33
+   |
+LL | struct Foo<const M: usize = 10, 'a>(&'a u32);
+   |           ----------------------^^- help: reorder the parameters: lifetimes, then consts and types: `<'a, const M: usize = 10>`
+
+error: aborting due to previous error
+