Suggest proper vis type in the help message

Author: nyurik

compiler/rustc_privacy/messages.ftl

@@ -8,7 +8,7 @@ privacy_from_private_dep_in_public_interface =
 privacy_in_public_interface = {$vis_descr} {$kind} `{$descr}` in public interface
     .label = can't leak {$vis_descr} {$kind}
     .visibility_label = `{$descr}` declared as {$vis_descr}
-    .suggestion = consider adding `pub` in front of it
+    .suggestion = consider adding `{$vis_sugg}` in front of it
 
 privacy_item_is_private = {$kind} `{$descr}` is private
     .label = private {$kind}

compiler/rustc_privacy/src/errors.rs

@@ -56,6 +56,7 @@ pub struct InPublicInterfaceTraits<'a> {
     pub span: Span,
     pub vis_descr: &'static str,
     pub kind: &'a str,
+    pub vis_sugg: &'static str,
     pub descr: DiagnosticArgFromDisplay<'a>,
     #[label(privacy_visibility_label)]
     pub vis_span: Span,
@@ -70,6 +71,7 @@ pub struct InPublicInterface<'a> {
     pub span: Span,
     pub vis_descr: &'static str,
     pub kind: &'a str,
+    pub vis_sugg: &'static str,
     pub descr: DiagnosticArgFromDisplay<'a>,
     #[label(privacy_visibility_label)]
     pub vis_span: Span,

compiler/rustc_privacy/src/lib.rs

@@ -1814,11 +1814,27 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                 || self.in_assoc_ty
                 || self.tcx.resolutions(()).has_pub_restricted
             {
+                // FIXME: this code was adapted from the above `vis_descr` computation,
+                //        but it's not clear if it's correct.
+                let vis_sugg = match self.required_visibility {
+                    ty::Visibility::Public => "pub",
+                    ty::Visibility::Restricted(vis_def_id) => {
+                        if vis_def_id == self.tcx.parent_module(hir_id) {
+                            "???FIXME???"
+                        } else if vis_def_id.is_top_level_module() {
+                            "pub(crate)"
+                        } else {
+                            "???FIXME???"
+                        }
+                    }
+                };
+
                 if kind == "trait" {
                     self.tcx.sess.emit_err(InPublicInterfaceTraits {
                         span,
                         vis_descr,
                         kind,
+                        vis_sugg,
                         descr: descr.into(),
                         vis_span,
                     });
@@ -1827,6 +1843,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                         span,
                         vis_descr,
                         kind,
+                        vis_sugg,
                         descr: descr.into(),
                         vis_span,
                         suggestion: vis_span,

tests/ui/privacy/issue-30079.stderr

@@ -15,7 +15,7 @@ LL |     struct Priv;
    |     -----------
    |     |
    |     `m2::Priv` declared as private
-   |     help: consider adding `pub` in front of it
+   |     help: consider adding `pub(crate)` in front of it
 LL |     impl ::std::ops::Deref for ::SemiPriv {
 LL |         type Target = Priv;
    |         ^^^^^^^^^^^ can't leak private type
@@ -27,7 +27,7 @@ LL |     struct Priv;
    |     -----------
    |     |
    |     `m3::Priv` declared as private
-   |     help: consider adding `pub` in front of it
+   |     help: consider adding `pub(crate)` in front of it
 LL |     impl ::SemiPrivTrait for () {
 LL |         type Assoc = Priv;
    |         ^^^^^^^^^^ can't leak private type

tests/ui/privacy/restricted/private-in-public.stderr

@@ -5,7 +5,7 @@ LL |     struct Priv;
    |     -----------
    |     |
    |     `Priv` declared as private
-   |     help: consider adding `pub` in front of it
+   |     help: consider adding `pub(crate)` in front of it
 ...
 LL |         pub(crate) fn g(_: Priv) {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type
@@ -17,7 +17,7 @@ LL |     struct Priv;
    |     -----------
    |     |
    |     `Priv` declared as private
-   |     help: consider adding `pub` in front of it
+   |     help: consider adding `pub(crate)` in front of it
 ...
 LL |         pub(crate) fn h(_: Priv) {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type

tests/ui/transmutability/visibility/assume/should_accept_if_dst_has_unreachable_field.stderr

@@ -5,7 +5,7 @@ LL |     #[repr(C)] pub(self) struct Zst; // <- unreachable type
    |                --------------------
    |                |
    |                `dst::Zst` declared as private
-   |                help: consider adding `pub` in front of it
+   |                help: consider adding `pub(crate)` in front of it
 ...
 LL |         pub(in super) field: Zst,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type

tests/ui/transmutability/visibility/should_accept_if_src_has_unreachable_field.stderr

@@ -5,7 +5,7 @@ LL |     #[repr(C)] pub(self) struct Zst; // <- unreachable type
    |                --------------------
    |                |
    |                `src::Zst` declared as private
-   |                help: consider adding `pub` in front of it
+   |                help: consider adding `pub(crate)` in front of it
 ...
 LL |         pub(in super) field: Zst,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type

tests/ui/type-alias-impl-trait/privacy.stderr

@@ -2,7 +2,10 @@ error[E0446]: private type alias `Foo` in public interface
   --> $DIR/privacy.rs:4:1
    |
 LL | type Foo = (impl Sized, u8);
-   | -------- `Foo` declared as private
+   | --------
+   | |
+   | `Foo` declared as private
+   | help: consider adding `pub` in front of it
 LL | pub fn foo() -> Foo {
    | ^^^^^^^^^^^^^^^^^^^ can't leak private type alias