Remove E0719

This hard error serves no purpose.
Fixes #143143

Author: Jules-Bertholet

compiler/rustc_error_codes/src/error_codes/E0719.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 An associated type value was specified more than once.
 
 Erroneous code example:
 
-```compile_fail,E0719
+```
 trait FooTrait {}
 trait BarTrait {}
 

compiler/rustc_error_codes/src/lib.rs

@@ -464,7 +464,7 @@ E0716: 0716,
 E0711: 0711,
 E0717: 0717,
 E0718: 0718,
-E0719: 0719,
+E0719: 0719, // REMOVED: no longer an error
 E0720: 0720,
 E0722: 0722,
 E0724: 0724,

compiler/rustc_hir_analysis/messages.ftl

@@ -591,11 +591,6 @@ hir_analysis_unused_generic_parameter_ty_alias_help =
 
 hir_analysis_useless_impl_item = this item cannot be used as its where bounds are not satisfied for the `Self` type
 
-hir_analysis_value_of_associated_struct_already_specified =
-    the value of the associated type `{$item_name}` in trait `{$def_path}` is already specified
-    .label = re-bound here
-    .previous_bound_label = `{$item_name}` bound here first
-
 hir_analysis_variadic_function_compatible_convention = C-variadic functions with the {$convention} calling convention are not supported
     .label = C-variadic function must have a compatible calling convention
 

compiler/rustc_hir_analysis/src/errors.rs

@@ -388,18 +388,6 @@ pub(crate) struct TypeofReservedKeywordUsed<'tcx> {
     pub opt_sugg: Option<(Span, Applicability)>,
 }
 
-#[derive(Diagnostic)]
-#[diag(hir_analysis_value_of_associated_struct_already_specified, code = E0719)]
-pub(crate) struct ValueOfAssociatedStructAlreadySpecified {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-    #[label(hir_analysis_previous_bound_label)]
-    pub prev_span: Span,
-    pub item_name: Ident,
-    pub def_path: String,
-}
-
 #[derive(Diagnostic)]
 #[diag(hir_analysis_unconstrained_opaque_type)]
 #[note]

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -1,6 +1,6 @@
 use std::ops::ControlFlow;
 
-use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
@@ -509,14 +509,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// the `trait_ref` here will be `for<'a> T: Iterator`.
     /// The `constraint` data however is from *inside* the binder
     /// (e.g., `&'a u32`) and hence may reference bound regions.
-    #[instrument(level = "debug", skip(self, bounds, duplicates, path_span))]
+    #[instrument(level = "debug", skip(self, bounds, path_span))]
     pub(super) fn lower_assoc_item_constraint(
         &self,
         hir_ref_id: hir::HirId,
         trait_ref: ty::PolyTraitRef<'tcx>,
         constraint: &hir::AssocItemConstraint<'tcx>,
         bounds: &mut Vec<(ty::Clause<'tcx>, Span)>,
-        duplicates: &mut FxIndexMap<DefId, Span>,
         path_span: Span,
         predicate_filter: PredicateFilter,
     ) -> Result<(), ErrorGuaranteed> {
@@ -572,18 +571,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             )
             .expect("failed to find associated item");
 
-        duplicates
-            .entry(assoc_item.def_id)
-            .and_modify(|prev_span| {
-                self.dcx().emit_err(errors::ValueOfAssociatedStructAlreadySpecified {
-                    span: constraint.span,
-                    prev_span: *prev_span,
-                    item_name: constraint.ident,
-                    def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
-                });
-            })
-            .or_insert(constraint.span);
-
         let projection_term = if let ty::AssocTag::Fn = assoc_tag {
             let bound_vars = tcx.late_bound_vars(constraint.hir_id);
             ty::Binder::bind_with_vars(

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -132,10 +132,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 self.dcx()
                     .struct_span_err(
                         span,
-                        format!(
-                            "conflicting associated type bounds for `{item}` when \
-                            expanding trait alias"
-                        ),
+                        format!("conflicting associated type bounds for `{item}`"),
                     )
                     .with_span_label(
                         old_proj_span,

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -24,7 +24,7 @@ use std::assert_matches::assert_matches;
 use std::slice;
 
 use rustc_ast::TraitObjectSyntax;
-use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, ErrorGuaranteed, FatalError, struct_span_code_err,
@@ -910,7 +910,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
         }
 
-        let mut dup_constraints = FxIndexMap::default();
         for constraint in trait_segment.args().constraints {
             // Don't register any associated item constraints for negative bounds,
             // since we should have emitted an error for them earlier, and they
@@ -929,7 +928,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 poly_trait_ref,
                 constraint,
                 bounds,
-                &mut dup_constraints,
                 constraint.span,
                 predicate_filter,
             );