Rollup merge of #107777 - compiler-errors:derive_const-actually-derive-const, r=fee1-dead

Make `derive_const` derive properly const-if-const impls

Fixes #107774
Fixes #107666

Also fixes rendering of const-if-const bounds in pretty printing.

r? ```@oli-obk``` or ```@fee1-dead```

9 files changed, 69 insertions, 17 deletions

diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index d7767efa984..cd621bc67a1 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -1567,8 +1567,18 @@ impl<'a> State<'a> {
 
             match bound {
                 GenericBound::Trait(tref, modifier) => {
-                    if modifier == &TraitBoundModifier::Maybe {
-                        self.word("?");
+                    match modifier {
+                        TraitBoundModifier::None => {}
+                        TraitBoundModifier::Maybe => {
+                            self.word("?");
+                        }
+                        TraitBoundModifier::MaybeConst => {
+                            self.word_space("~const");
+                        }
+                        TraitBoundModifier::MaybeConstMaybe => {
+                            self.word_space("~const");
+                            self.word("?");
+                        }
                     }
                     self.print_poly_trait_ref(tref);
                 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index 74e2597830e..e8a353b1c8f 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -153,7 +153,10 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
         let ty_dyn_debug = cx.ty(
             span,
-            ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
+            ast::TyKind::TraitObject(
+                vec![cx.trait_bound(path_debug, false)],
+                ast::TraitObjectSyntax::Dyn,
+            ),
         );
         let ty_slice = cx.ty(
             span,
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index 97de40bac34..a8c0aeb7870 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -605,18 +605,26 @@ impl<'a> TraitDef<'a> {
                     let bounds: Vec<_> = self
                         .additional_bounds
                         .iter()
-                        .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                        .map(|p| {
+                            cx.trait_bound(
+                                p.to_path(cx, self.span, type_ident, generics),
+                                self.is_const,
+                            )
+                        })
                         .chain(
                             // Add a bound for the current trait.
                             self.skip_path_as_bound
                                 .not()
-                                .then(|| cx.trait_bound(trait_path.clone())),
+                                .then(|| cx.trait_bound(trait_path.clone(), self.is_const)),
                         )
                         .chain({
                             // Add a `Copy` bound if required.
                             if is_packed && self.needs_copy_as_bound_if_packed {
                                 let p = deriving::path_std!(marker::Copy);
-                                Some(cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                                Some(cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                ))
                             } else {
                                 None
                             }
@@ -694,18 +702,24 @@ impl<'a> TraitDef<'a> {
                         let mut bounds: Vec<_> = self
                             .additional_bounds
                             .iter()
-                            .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                            .map(|p| {
+                                cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                )
+                            })
                             .collect();
 
                         // Require the current trait.
-                        bounds.push(cx.trait_bound(trait_path.clone()));
+                        bounds.push(cx.trait_bound(trait_path.clone(), self.is_const));
 
                         // Add a `Copy` bound if required.
                         if is_packed && self.needs_copy_as_bound_if_packed {
                             let p = deriving::path_std!(marker::Copy);
-                            bounds.push(
-                                cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)),
-                            );
+                            bounds.push(cx.trait_bound(
+                                p.to_path(cx, self.span, type_ident, generics),
+                                self.is_const,
+                            ));
                         }
 
                         let predicate = ast::WhereBoundPredicate {
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
index c6f5f5d0807..aabd5b1f773 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -154,7 +154,7 @@ fn mk_ty_param(
         .iter()
         .map(|b| {
             let path = b.to_path(cx, span, self_ident, self_generics);
-            cx.trait_bound(path)
+            cx.trait_bound(path, false)
         })
         .collect();
     cx.typaram(span, Ident::new(name, span), bounds, None)
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index 6cd56852f9d..b4c12651e7a 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -131,10 +131,14 @@ impl<'a> ExtCtxt<'a> {
         }
     }
 
-    pub fn trait_bound(&self, path: ast::Path) -> ast::GenericBound {
+    pub fn trait_bound(&self, path: ast::Path, is_const: bool) -> ast::GenericBound {
         ast::GenericBound::Trait(
             self.poly_trait_ref(path.span, path),
-            ast::TraitBoundModifier::None,
+            if is_const {
+                ast::TraitBoundModifier::MaybeConst
+            } else {
+                ast::TraitBoundModifier::None
+            },
         )
     }
 
diff --git a/tests/ui/macros/stringify.rs b/tests/ui/macros/stringify.rs
index 5cd217df6fc..fdc2a7666d6 100644
--- a/tests/ui/macros/stringify.rs
+++ b/tests/ui/macros/stringify.rs
@@ -626,7 +626,7 @@ fn test_item() {
         stringify_item!(
             impl ~const Struct {}
         ),
-        "impl Struct {}", // FIXME
+        "impl ~const Struct {}",
     );
 
     // ItemKind::MacCall
@@ -838,7 +838,7 @@ fn test_ty() {
     assert_eq!(stringify_ty!(dyn Send + 'a), "dyn Send + 'a");
     assert_eq!(stringify_ty!(dyn 'a + Send), "dyn 'a + Send");
     assert_eq!(stringify_ty!(dyn ?Sized), "dyn ?Sized");
-    assert_eq!(stringify_ty!(dyn ~const Clone), "dyn Clone"); // FIXME
+    assert_eq!(stringify_ty!(dyn ~const Clone), "dyn ~const Clone");
     assert_eq!(stringify_ty!(dyn for<'a> Send), "dyn for<'a> Send");
 
     // TyKind::ImplTrait
@@ -846,7 +846,7 @@ fn test_ty() {
     assert_eq!(stringify_ty!(impl Send + 'a), "impl Send + 'a");
     assert_eq!(stringify_ty!(impl 'a + Send), "impl 'a + Send");
     assert_eq!(stringify_ty!(impl ?Sized), "impl ?Sized");
-    assert_eq!(stringify_ty!(impl ~const Clone), "impl Clone"); // FIXME
+    assert_eq!(stringify_ty!(impl ~const Clone), "impl ~const Clone");
     assert_eq!(stringify_ty!(impl for<'a> Send), "impl for<'a> Send");
 
     // TyKind::Paren
diff --git a/tests/ui/rfc-2632-const-trait-impl/const_derives/derive-const-with-params.rs b/tests/ui/rfc-2632-const-trait-impl/const_derives/derive-const-with-params.rs
new file mode 100644
index 00000000000..72edfbc97e4
--- /dev/null
+++ b/tests/ui/rfc-2632-const-trait-impl/const_derives/derive-const-with-params.rs
@@ -0,0 +1,13 @@
+// check-pass
+
+#![feature(derive_const)]
+#![feature(const_trait_impl)]
+
+#[derive_const(PartialEq)]
+pub struct Reverse<T>(T);
+
+const fn foo(a: Reverse<i32>, b: Reverse<i32>) -> bool {
+    a == b
+}
+
+fn main() {}
diff --git a/tests/ui/unpretty/ast-const-trait-bound.rs b/tests/ui/unpretty/ast-const-trait-bound.rs
new file mode 100644
index 00000000000..dbcba7871ec
--- /dev/null
+++ b/tests/ui/unpretty/ast-const-trait-bound.rs
@@ -0,0 +1,4 @@
+// compile-flags: -Zunpretty=normal
+// check-pass
+
+fn foo() where T: ~const Bar {}
diff --git a/tests/ui/unpretty/ast-const-trait-bound.stdout b/tests/ui/unpretty/ast-const-trait-bound.stdout
new file mode 100644
index 00000000000..dbcba7871ec
--- /dev/null
+++ b/tests/ui/unpretty/ast-const-trait-bound.stdout
@@ -0,0 +1,4 @@
+// compile-flags: -Zunpretty=normal
+// check-pass
+
+fn foo() where T: ~const Bar {}