privacy: port "field is private" diag

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

Cargo.lock

@@ -4280,6 +4280,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_errors",
  "rustc_hir",
+ "rustc_macros",
  "rustc_middle",
  "rustc_session",
  "rustc_span",

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

@@ -0,0 +1,3 @@
+privacy-field-is-private = field `{$field_name}` of {$variant_descr} `{$def_path_str}` is private
+privacy-field-is-private-is-update-syntax-label = field `{$field_name}` is private
+privacy-field-is-private-label = private field

compiler/rustc_error_messages/src/lib.rs

@@ -32,6 +32,7 @@
 // Generates `DEFAULT_LOCALE_RESOURCES` static and `fluent_generated` module.
 fluent_messages! {
     parser => "../locales/en-US/parser.ftl",
+    privacy => "../locales/en-US/privacy.ftl",
     typeck => "../locales/en-US/typeck.ftl",
     builtin_macros => "../locales/en-US/builtin_macros.ftl",
 }

compiler/rustc_privacy/Cargo.toml

@@ -4,14 +4,15 @@ version = "0.0.0"
 edition = "2021"
 
 [dependencies]
-rustc_middle = { path = "../rustc_middle" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_attr = { path = "../rustc_attr" }
+rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
-rustc_typeck = { path = "../rustc_typeck" }
+rustc_macros = { path = "../rustc_macros" }
+rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
-rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
+rustc_typeck = { path = "../rustc_typeck" }
 tracing = "0.1"

compiler/rustc_privacy/src/errors.rs

@@ -0,0 +1,29 @@
+use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
+use rustc_span::{Span, Symbol};
+
+#[derive(SessionDiagnostic)]
+#[error(privacy::field_is_private, code = "E0451")]
+pub struct FieldIsPrivate {
+    #[primary_span]
+    pub span: Span,
+    pub field_name: Symbol,
+    pub variant_descr: &'static str,
+    pub def_path_str: String,
+    #[subdiagnostic]
+    pub label: FieldIsPrivateLabel,
+}
+
+#[derive(SessionSubdiagnostic)]
+pub enum FieldIsPrivateLabel {
+    #[label(privacy::field_is_private_is_update_syntax_label)]
+    IsUpdateSyntax {
+        #[primary_span]
+        span: Span,
+        field_name: Symbol,
+    },
+    #[label(privacy::field_is_private_label)]
+    Other {
+        #[primary_span]
+        span: Span,
+    },
+}

compiler/rustc_privacy/src/lib.rs

@@ -5,6 +5,8 @@
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 
+mod errors;
+
 use rustc_ast::MacroDef;
 use rustc_attr as attr;
 use rustc_data_structures::fx::FxHashSet;
@@ -34,6 +36,8 @@
 use std::ops::ControlFlow;
 use std::{cmp, fmt, mem};
 
+use errors::{FieldIsPrivate, FieldIsPrivateLabel};
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Generic infrastructure used to implement specific visitors below.
 ////////////////////////////////////////////////////////////////////////////////
@@ -935,23 +939,17 @@ fn check_field(
         let hir_id = self.tcx.hir().local_def_id_to_hir_id(self.current_item);
         let def_id = self.tcx.adjust_ident_and_get_scope(ident, def.did(), hir_id).1;
         if !field.vis.is_accessible_from(def_id, self.tcx) {
-            let label = if in_update_syntax {
-                format!("field `{}` is private", field.name)
-            } else {
-                "private field".to_string()
-            };
-
-            struct_span_err!(
-                self.tcx.sess,
+            self.tcx.sess.emit_err(FieldIsPrivate {
                 span,
-                E0451,
-                "field `{}` of {} `{}` is private",
-                field.name,
-                def.variant_descr(),
-                self.tcx.def_path_str(def.did())
-            )
-            .span_label(span, label)
-            .emit();
+                field_name: field.name,
+                variant_descr: def.variant_descr(),
+                def_path_str: self.tcx.def_path_str(def.did()),
+                label: if in_update_syntax {
+                    FieldIsPrivateLabel::IsUpdateSyntax { span, field_name: field.name }
+                } else {
+                    FieldIsPrivateLabel::Other { span }
+                },
+            });
         }
     }
 }