don't suggest non-deriveable traits for unions

compiler/rustc_attr_parsing/src/attributes/diagnostic/mod.rs

@@ -460,11 +460,12 @@ fn parse_filter(input: Symbol) -> FilterFormatString {
                 // if the integer type has been resolved, to allow targeting all integers.
                 // `"{integer}"` and `"{float}"` come from numerics that haven't been inferred yet,
                 // from the `Display` impl of `InferTy` to be precise.
+                // `"{union|enum|struct}"` is used as a special selector for ADTs.
                 //
                 // Don't try to format these later!
-                Position::ArgumentNamed(arg @ ("integer" | "integral" | "float")) => {
-                    LitOrArg::Lit(Symbol::intern(&format!("{{{arg}}}")))
-                }
+                Position::ArgumentNamed(
+                    arg @ ("integer" | "integral" | "float" | "union" | "enum" | "struct"),
+                ) => LitOrArg::Lit(Symbol::intern(&format!("{{{arg}}}"))),
 
                 Position::ArgumentNamed(arg) => LitOrArg::Arg(Symbol::intern(arg)),
                 Position::ArgumentImplicitlyIs(_) => LitOrArg::Lit(sym::empty_braces),

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -3460,13 +3460,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let diagnostic_name = self.tcx.get_diagnostic_name(trait_pred.def_id())?;
 
         let can_derive = match diagnostic_name {
+            sym::Copy | sym::Clone => true,
+            _ if adt.is_union() => false,
             sym::Default
             | sym::Eq
             | sym::PartialEq
             | sym::Ord
             | sym::PartialOrd
-            | sym::Clone
-            | sym::Copy
             | sym::Hash
             | sym::Debug => true,
             _ => false,

compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs

@@ -124,8 +124,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
             }
 
-            if let Some(true) = self_ty.ty_adt_def().map(|def| def.did().is_local()) {
-                crate_local = true;
+            if let Some(adt) = self_ty.ty_adt_def() {
+                if adt.did().is_local() {
+                    crate_local = true;
+                }
+                self_types.push(format!("{{{}}}", adt.descr()))
             }
 
             // Allow targeting all integers using `{integral}`, even if the exact type was resolved

compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

@@ -4037,12 +4037,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             _ => return false,
         };
         let is_derivable_trait = match diagnostic_name {
-            sym::Default => !adt.is_enum(),
+            sym::Copy | sym::Clone => true,
+            _ if adt.is_union() => false,
             sym::PartialEq | sym::PartialOrd => {
                 let rhs_ty = trait_pred.skip_binder().trait_ref.args.type_at(1);
                 trait_pred.skip_binder().self_ty() == rhs_ty
             }
-            sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
+            sym::Eq | sym::Ord | sym::Hash | sym::Debug | sym::Default => true,
             _ => false,
         };
         is_derivable_trait &&

library/core/src/fmt/mod.rs

@@ -1037,9 +1037,10 @@ impl Display for Arguments<'_> {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
     on(
-        crate_local,
+        all(crate_local, not(Self = "{union}")),
         note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {This} for {Self}`"
     ),
+    on(all(crate_local, Self = "{union}"), note = "manually `impl {This} for {Self}`"),
     on(
         from_desugaring = "FormatLiteral",
         label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{This}`"

tests/ui/diagnostic_namespace/on_unimplemented/do_not_accept_options_of_the_internal_rustc_attribute.rs

@@ -26,12 +26,15 @@ impl Bar for i32 {}
 // cannot use special rustc_on_unimplement symbols
 // in the format string
 #[diagnostic::on_unimplemented(
-    message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+    message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
     //~^WARN there is no parameter `from_desugaring` on trait `Baz`
     //~|WARN there is no parameter `direct` on trait `Baz`
     //~|WARN there is no parameter `cause` on trait `Baz`
     //~|WARN there is no parameter `integral` on trait `Baz`
     //~|WARN there is no parameter `integer` on trait `Baz`
+    //~|WARN there is no parameter `r#struct` on trait `Baz`
+    //~|WARN there is no parameter `r#enum` on trait `Baz`
+    //~|WARN there is no parameter `union` on trait `Baz`
     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
     //~^WARN there is no parameter `float` on trait `Baz`
     //~|WARN there is no parameter `_Self` on trait `Baz`
@@ -52,5 +55,5 @@ fn main() {
     takes_bar(());
     //~^ERROR the trait bound `(): Bar` is not satisfied
     takes_baz(());
-    //~^ERROR {from_desugaring}{direct}{cause}{integral}{integer}
+    //~^ERROR {from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}
 }

tests/ui/diagnostic_namespace/on_unimplemented/do_not_accept_options_of_the_internal_rustc_attribute.stderr

@@ -9,7 +9,7 @@ LL | #[diagnostic::on_unimplemented(message = "Not allowed to apply it on a impl
 warning: there is no parameter `from_desugaring` on trait `Baz`
   --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:17
    |
-LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
    |                 ^^^^^^^^^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
@@ -18,77 +18,101 @@ LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
 warning: there is no parameter `direct` on trait `Baz`
   --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:34
    |
-LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
    |                                  ^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `cause` on trait `Baz`
   --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:42
    |
-LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
    |                                          ^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `integral` on trait `Baz`
   --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:49
    |
-LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
    |                                                 ^^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `integer` on trait `Baz`
   --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:59
    |
-LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}",
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
    |                                                           ^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
+warning: there is no parameter `r#struct` on trait `Baz`
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:68
+   |
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
+   |                                                                    ^^^^^^
+   |
+   = help: expect either a generic argument name or `{Self}` as format argument
+
+warning: there is no parameter `r#enum` on trait `Baz`
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:76
+   |
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
+   |                                                                            ^^^^
+   |
+   = help: expect either a generic argument name or `{Self}` as format argument
+
+warning: there is no parameter `union` on trait `Baz`
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:29:82
+   |
+LL |     message = "{from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}",
+   |                                                                                  ^^^^^
+   |
+   = help: expect either a generic argument name or `{Self}` as format argument
+
 warning: there is no parameter `float` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:15
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:15
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |               ^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `_Self` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:22
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:22
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |                      ^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `crate_local` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:29
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:29
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |                             ^^^^^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `Trait` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:42
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:42
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |                                          ^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `ItemContext` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:49
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:49
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |                                                 ^^^^^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: there is no parameter `This` on trait `Baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:35:62
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:38:62
    |
 LL |     label = "{float}{_Self}{crate_local}{Trait}{ItemContext}{This}"
    |                                                              ^^^^
@@ -129,7 +153,7 @@ LL | #[diagnostic::on_unimplemented = "Message"]
    = help: only `message`, `note` and `label` are allowed as options
 
 error[E0277]: trait has `()` and `i32` as params
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:50:15
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:53:15
    |
 LL |     takes_foo(());
    |     --------- ^^ trait has `()` and `i32` as params
@@ -144,13 +168,13 @@ help: this trait has no implementations, consider adding one
 LL | trait Foo<T> {}
    | ^^^^^^^^^^^^
 note: required by a bound in `takes_foo`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:45:22
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:48:22
    |
 LL | fn takes_foo(_: impl Foo<i32>) {}
    |                      ^^^^^^^^ required by this bound in `takes_foo`
 
 error[E0277]: the trait bound `(): Bar` is not satisfied
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:52:15
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:55:15
    |
 LL |     takes_bar(());
    |     --------- ^^ the trait `Bar` is not implemented for `()`
@@ -163,13 +187,13 @@ help: the trait `Bar` is implemented for `i32`
 LL | impl Bar for i32 {}
    | ^^^^^^^^^^^^^^^^
 note: required by a bound in `takes_bar`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:46:22
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:49:22
    |
 LL | fn takes_bar(_: impl Bar) {}
    |                      ^^^ required by this bound in `takes_bar`
 
-error[E0277]: {from_desugaring}{direct}{cause}{integral}{integer}
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:54:15
+error[E0277]: {from_desugaring}{direct}{cause}{integral}{integer}{struct}{enum}{union}
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:57:15
    |
 LL |     takes_baz(());
    |     --------- ^^ {float}{_Self}{crate_local}{Trait}{ItemContext}{This}
@@ -178,16 +202,16 @@ LL |     takes_baz(());
    |
    = help: the trait `Baz` is not implemented for `()`
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:43:1
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:46:1
    |
 LL | trait Baz {}
    | ^^^^^^^^^
 note: required by a bound in `takes_baz`
-  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:47:22
+  --> $DIR/do_not_accept_options_of_the_internal_rustc_attribute.rs:50:22
    |
 LL | fn takes_baz(_: impl Baz) {}
    |                      ^^^ required by this bound in `takes_baz`
 
-error: aborting due to 3 previous errors; 16 warnings emitted
+error: aborting due to 3 previous errors; 19 warnings emitted
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/on-unimplemented/self-types.rs

@@ -0,0 +1,30 @@
+#![feature(rustc_attrs)]
+
+#[rustc_on_unimplemented(
+    on(Self = "{union}", message = "union self type"),
+    on(Self = "{enum}", message = "enum self type"),
+    on(Self = "{struct}", message = "struct self type"),
+    message = "fallback self type `{Self}`"
+)]
+trait Trait {}
+
+union Union {
+    value: u8,
+}
+
+enum Enum {
+    Variant,
+}
+
+struct Struct;
+
+fn needs_trait<T: Trait>() {}
+
+fn main() {
+    needs_trait::<Union>();
+    //~^ ERROR union self type
+    needs_trait::<Enum>();
+    //~^ ERROR enum self type
+    needs_trait::<Struct>();
+    //~^ ERROR struct self type
+}

tests/ui/on-unimplemented/self-types.stderr

@@ -0,0 +1,69 @@
+error[E0277]: union self type
+  --> $DIR/self-types.rs:24:19
+   |
+LL |     needs_trait::<Union>();
+   |                   ^^^^^ unsatisfied trait bound
+   |
+help: the trait `Trait` is not implemented for `Union`
+  --> $DIR/self-types.rs:11:1
+   |
+LL | union Union {
+   | ^^^^^^^^^^^
+help: this trait has no implementations, consider adding one
+  --> $DIR/self-types.rs:9:1
+   |
+LL | trait Trait {}
+   | ^^^^^^^^^^^
+note: required by a bound in `needs_trait`
+  --> $DIR/self-types.rs:21:19
+   |
+LL | fn needs_trait<T: Trait>() {}
+   |                   ^^^^^ required by this bound in `needs_trait`
+
+error[E0277]: enum self type
+  --> $DIR/self-types.rs:26:19
+   |
+LL |     needs_trait::<Enum>();
+   |                   ^^^^ unsatisfied trait bound
+   |
+help: the trait `Trait` is not implemented for `Enum`
+  --> $DIR/self-types.rs:15:1
+   |
+LL | enum Enum {
+   | ^^^^^^^^^
+help: this trait has no implementations, consider adding one
+  --> $DIR/self-types.rs:9:1
+   |
+LL | trait Trait {}
+   | ^^^^^^^^^^^
+note: required by a bound in `needs_trait`
+  --> $DIR/self-types.rs:21:19
+   |
+LL | fn needs_trait<T: Trait>() {}
+   |                   ^^^^^ required by this bound in `needs_trait`
+
+error[E0277]: struct self type
+  --> $DIR/self-types.rs:28:19
+   |
+LL |     needs_trait::<Struct>();
+   |                   ^^^^^^ unsatisfied trait bound
+   |
+help: the trait `Trait` is not implemented for `Struct`
+  --> $DIR/self-types.rs:19:1
+   |
+LL | struct Struct;
+   | ^^^^^^^^^^^^^
+help: this trait has no implementations, consider adding one
+  --> $DIR/self-types.rs:9:1
+   |
+LL | trait Trait {}
+   | ^^^^^^^^^^^
+note: required by a bound in `needs_trait`
+  --> $DIR/self-types.rs:21:19
+   |
+LL | fn needs_trait<T: Trait>() {}
+   |                   ^^^^^ required by this bound in `needs_trait`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.