typeck: port "manual implementations"

Port the "manual implementations of `X` are experimental" diagnostic to
use the diagnostic derive.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_error_messages/locales/en-US/typeck.ftl

@@ -122,3 +122,8 @@ typeck-missing-type-params =
         *[other] references
     } to {$parameters}
     .note = because of the default `Self` reference, type parameters must be specified on object types
+
+typeck-manual-implementation =
+    manual implementations of `{$trait_name}` are experimental
+    .label = manual implementations of `{$trait_name}` are experimental
+    .help = add `#![feature(unboxed_closures)]` to the crate attributes to enable

compiler/rustc_typeck/src/astconv/errors.rs

@@ -1,5 +1,5 @@
 use crate::astconv::AstConv;
-use crate::errors::MissingTypeParams;
+use crate::errors::{ManualImplementation, MissingTypeParams};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, struct_span_err, Applicability, ErrorGuaranteed};
 use rustc_hir as hir;
@@ -121,19 +121,7 @@ pub(crate) fn complain_about_internal_fn_trait(
 
         if is_impl {
             let trait_name = self.tcx().def_path_str(trait_def_id);
-            struct_span_err!(
-                self.tcx().sess,
-                span,
-                E0183,
-                "manual implementations of `{}` are experimental",
-                trait_name,
-            )
-            .span_label(
-                span,
-                format!("manual implementations of `{}` are experimental", trait_name),
-            )
-            .help("add `#![feature(unboxed_closures)]` to the crate attributes to enable")
-            .emit();
+            self.tcx().sess.emit_err(ManualImplementation { span, trait_name });
         }
     }
 

compiler/rustc_typeck/src/errors.rs

@@ -313,3 +313,13 @@ fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuar
         err
     }
 }
+
+#[derive(SessionDiagnostic)]
+#[error(code = "E0183", slug = "typeck-manual-implementation")]
+#[help]
+pub struct ManualImplementation {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub trait_name: String,
+}