Disallow shadowing const parameters

3 files changed, 47 insertions, 15 deletions

diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 6ea46f5c528..a1eafd65d64 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -425,24 +425,29 @@ impl<'a> Resolver<'a> {
                 }
                 err
             }
-            ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
-                let res = binding.res();
-                let shadows_what = res.descr();
+            ResolutionError::BindingShadowsSomethingUnacceptable {
+                shadowing_binding_descr,
+                name,
+                participle,
+                article,
+                shadowed_binding_descr,
+                shadowed_binding_span,
+            } => {
                 let mut err = struct_span_err!(
                     self.session,
                     span,
                     E0530,
                     "{}s cannot shadow {}s",
-                    what_binding,
-                    shadows_what
+                    shadowing_binding_descr,
+                    shadowed_binding_descr,
                 );
                 err.span_label(
                     span,
-                    format!("cannot be named the same as {} {}", res.article(), shadows_what),
+                    format!("cannot be named the same as {} {}", article, shadowed_binding_descr),
                 );
-                let participle = if binding.is_import() { "imported" } else { "defined" };
-                let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
-                err.span_label(binding.span, msg);
+                let msg =
+                    format!("the {} `{}` is {} here", shadowed_binding_descr, name, participle);
+                err.span_label(shadowed_binding_span, msg);
                 err
             }
             ResolutionError::ForwardDeclaredTyParam => {
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index ffa825b7d46..662d39f6ef3 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1763,13 +1763,33 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // to something unusable as a pattern (e.g., constructor function),
                 // but we still conservatively report an error, see
                 // issues/33118#issuecomment-233962221 for one reason why.
+                let binding = binding.expect("no binding for a ctor or static");
                 self.report_error(
                     ident.span,
-                    ResolutionError::BindingShadowsSomethingUnacceptable(
-                        pat_src.descr(),
-                        ident.name,
-                        binding.expect("no binding for a ctor or static"),
-                    ),
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding_descr: pat_src.descr(),
+                        name: ident.name,
+                        participle: if binding.is_import() { "imported" } else { "defined" },
+                        article: binding.res().article(),
+                        shadowed_binding_descr: binding.res().descr(),
+                        shadowed_binding_span: binding.span,
+                    },
+                );
+                None
+            }
+            Res::Def(DefKind::ConstParam, def_id) => {
+                // Same as for DefKind::Const above, but here, `binding` is `None`, so we
+                // have to construct the error differently
+                self.report_error(
+                    ident.span,
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding_descr: pat_src.descr(),
+                        name: ident.name,
+                        participle: "defined",
+                        article: res.article(),
+                        shadowed_binding_descr: res.descr(),
+                        shadowed_binding_span: self.r.opt_span(def_id).expect("const parameter defined outside of local crate"),
+                    }
                 );
                 None
             }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 300d2c01cb5..05c69892504 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -234,7 +234,14 @@ enum ResolutionError<'a> {
         /* current */ &'static str,
     ),
     /// Error E0530: `X` bindings cannot shadow `Y`s.
-    BindingShadowsSomethingUnacceptable(&'static str, Symbol, &'a NameBinding<'a>),
+    BindingShadowsSomethingUnacceptable {
+        shadowing_binding_descr: &'static str,
+        name: Symbol,
+        participle: &'static str,
+        article: &'static str,
+        shadowed_binding_descr: &'static str,
+        shadowed_binding_span: Span,
+    },
     /// Error E0128: generic parameters with a default cannot use forward-declared identifiers.
     ForwardDeclaredTyParam, // FIXME(const_generics_defaults)
     /// ERROR E0770: the type of const parameters must not depend on other generic parameters.