ADD - migrate InvalidTraitItem and AltInvalidTraitItem errors

Thought of doing this by having a struct and an enum with Default and Alt cases, but not sure if we wanted to have the text in code instead of having “demangling()” and “demangling-alt()” in the ftl file.

Don’t like the current way of having structs representing the same-ish and using long names to distinguish their expectations, instead of putting this in an enum and handling the different cases inside the type.

I am fine with whichever option the team prefers; also understand having them as separate structs keeps it simple.

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

@@ -1 +1,5 @@
 symbol_mangling_invalid_symbol_name = symbol-name({$mangled_formatted})
+
+symbol_mangling_invalid_trait_item = demangling({$demangling_formatted})
+
+symbol_mangling_alt_invalid_trait_item = demangling-alt({$alt_demangling_formatted})

compiler/rustc_symbol_mangling/src/errors.rs

@@ -10,3 +10,19 @@ pub struct InvalidSymbolName<'a> {
     pub span: Span,
     pub mangled_formatted: &'a str,
 }
+
+#[derive(SessionDiagnostic)]
+#[error(symbol_mangling::invalid_trait_item)]
+pub struct InvalidTraitItem<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub demangling_formatted: &'a str,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(symbol_mangling::alt_invalid_trait_item)]
+pub struct AltInvalidTraitItem<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub alt_demangling_formatted: &'a str,
+}

compiler/rustc_symbol_mangling/src/test.rs

@@ -4,7 +4,7 @@
 //! def-path. This is used for unit testing the code that generates
 //! paths etc in all kinds of annoying scenarios.
 
-use crate::errors::InvalidSymbolName;
+use crate::errors::{AltInvalidTraitItem, InvalidSymbolName, InvalidTraitItem};
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{subst::InternalSubsts, Instance, TyCtxt};
@@ -65,8 +65,14 @@ impl SymbolNamesTest<'_> {
                 mangled_formatted: &format!("{mangled}"),
             });
             if let Ok(demangling) = rustc_demangle::try_demangle(mangled.name) {
-                tcx.sess.span_err(attr.span, &format!("demangling({})", demangling));
-                tcx.sess.span_err(attr.span, &format!("demangling-alt({:#})", demangling));
+                tcx.sess.emit_err(InvalidTraitItem {
+                    span: attr.span,
+                    demangling_formatted: &format!("{demangling}"),
+                });
+                tcx.sess.emit_err(AltInvalidTraitItem {
+                    span: attr.span,
+                    alt_demangling_formatted: &format!("{:#}", demangling),
+                });
             }
         }