Create E0774

compiler/rustc_error_codes/src/error_codes.rs

@@ -455,6 +455,7 @@ E0769: include_str!("./error_codes/E0769.md"),
 E0770: include_str!("./error_codes/E0770.md"),
 E0771: include_str!("./error_codes/E0771.md"),
 E0773: include_str!("./error_codes/E0773.md"),
+E0774: include_str!("./error_codes/E0774.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

compiler/rustc_error_codes/src/error_codes/E0774.md

@@ -0,0 +1,24 @@
+`derive` was applied on something which is not a struct, a union or an enum.
+
+Erroneous code example:
+
+```compile_fail,E0774
+trait Foo {
+    #[derive(Clone)] // error!
+    type Bar;
+}
+```
+
+As said above, the `derive` attribute is only allowed on structs, unions or
+enums:
+
+```
+#[derive(Clone)] // ok!
+struct Bar {
+    field: u32,
+}
+```
+
+You can find more information about `derive` in the [Rust Book].
+
+[Rust Book]: https://doc.rust-lang.org/book/appendix-03-derivable-traits.html

compiler/rustc_expand/src/expand.rs

@@ -529,9 +529,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     fn error_derive_forbidden_on_non_adt(&self, derives: &[Path], item: &Annotatable) {
         let attr = self.cx.sess.find_by_name(item.attrs(), sym::derive);
         let span = attr.map_or(item.span(), |attr| attr.span);
-        let mut err = self
-            .cx
-            .struct_span_err(span, "`derive` may only be applied to structs, enums and unions");
+        let mut err = rustc_errors::struct_span_err!(
+            self.cx.sess,
+            span,
+            E0774,
+            "`derive` may only be applied to structs, enums and unions",
+        );
         if let Some(ast::Attribute { style: ast::AttrStyle::Inner, .. }) = attr {
             let trait_list = derives.iter().map(|t| pprust::path_to_string(t)).collect::<Vec<_>>();
             let suggestion = format!("#[derive({})]", trait_list.join(", "));

src/test/ui/derives/derive-on-trait-item-or-impl-item.stderr

@@ -1,14 +1,15 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/derive-on-trait-item-or-impl-item.rs:2:5
    |
 LL |     #[derive(Clone)]
    |     ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/derive-on-trait-item-or-impl-item.rs:10:5
    |
 LL |     #[derive(Clone)]
    |     ^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/derives/deriving-non-type.stderr

@@ -1,56 +1,57 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:5:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:8:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:11:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:14:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:17:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:20:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:23:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:26:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/deriving-non-type.rs:29:1
    |
 LL | #[derive(PartialEq)]
    | ^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 9 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/feature-gate/issue-43106-gating-of-derive.stderr

@@ -1,32 +1,33 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43106-gating-of-derive.rs:4:1
    |
 LL | #[derive(Debug)]
    | ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43106-gating-of-derive.rs:7:17
    |
 LL |     mod inner { #![derive(Debug)] }
    |                 ^^^^^^^^^^^^^^^^^ help: try an outer attribute: `#[derive(Debug)]`
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43106-gating-of-derive.rs:10:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43106-gating-of-derive.rs:23:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43106-gating-of-derive.rs:27:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
 error: aborting due to 5 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/issues/issue-36617.stderr

@@ -1,4 +1,4 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-36617.rs:1:1
    |
 LL | #![derive(Copy)]
@@ -22,3 +22,4 @@ LL | #![derive(Copy)]
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/issues/issue-43023.stderr

@@ -1,20 +1,21 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43023.rs:4:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43023.rs:11:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43023.rs:16:5
    |
 LL |     #[derive(Debug)]
    |     ^^^^^^^^^^^^^^^^
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/issues/issue-49934-errors.stderr

@@ -1,4 +1,4 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-49934-errors.rs:1:8
    |
 LL | fn foo<#[derive(Debug)] T>() {
@@ -10,7 +10,7 @@ error: expected an inert attribute, found a derive macro
 LL | fn foo<#[derive(Debug)] T>() {
    |                 ^^^^^
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-49934-errors.rs:5:9
    |
 LL |         #[derive(Debug)]
@@ -24,3 +24,4 @@ LL |         #[derive(Debug)]
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/macros/trace_faulty_macros.stderr

@@ -60,7 +60,7 @@ LL |     let a = pat_macro!();
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/trace_faulty_macros.rs:42:1
    |
 LL | #[derive(Debug)]
@@ -79,3 +79,4 @@ LL |     let a = pat_macro!();
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/malformed/issue-69341-malformed-derive-inert.stderr

@@ -4,7 +4,7 @@ error: traits in `#[derive(...)]` don't accept arguments
 LL |     #[derive(parse())]
    |                   ^^ help: remove the arguments
 
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-69341-malformed-derive-inert.rs:8:5
    |
 LL |     path: (),
@@ -24,3 +24,4 @@ LL |     #[derive(parse())]
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/proc-macro/attributes-on-modules-fail.stderr

@@ -1,4 +1,4 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/attributes-on-modules-fail.rs:16:1
    |
 LL | #[derive(Copy)]
@@ -64,5 +64,5 @@ LL | use m::X;
 
 error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0412, E0658.
+Some errors have detailed explanations: E0412, E0658, E0774.
 For more information about an error, try `rustc --explain E0412`.

src/test/ui/proc-macro/macros-in-extern-derive.stderr

@@ -1,8 +1,9 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/macros-in-extern-derive.rs:2:5
    |
 LL |     #[derive(Copy)]
    |     ^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0774`.

src/test/ui/span/issue-43927-non-ADT-derive.stderr

@@ -1,4 +1,4 @@
-error: `derive` may only be applied to structs, enums and unions
+error[E0774]: `derive` may only be applied to structs, enums and unions
   --> $DIR/issue-43927-non-ADT-derive.rs:3:1
    |
 LL | #![derive(Debug, PartialEq, Eq)] // should be an outer attribute!
@@ -54,3 +54,4 @@ LL | #![derive(Debug, PartialEq, Eq)] // should be an outer attribute!
 
 error: aborting due to 7 previous errors
 
+For more information about this error, try `rustc --explain E0774`.