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

@@ -55,6 +55,7 @@ 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

@@ -1434,12 +1434,31 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                 }
             };
 
+            // 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_from_def_id(local_def_id).to_local_def_id()
+                    {
+                        "???FIXME???"
+                    } else if vis_def_id.is_top_level_module() {
+                        "pub(crate)"
+                    } else {
+                        "???FIXME???"
+                    }
+                }
+            };
+
             self.tcx.dcx().emit_err(InPublicInterface {
                 span,
                 vis_descr,
                 kind,
+                vis_sugg,
                 descr: descr.into(),
                 vis_span,
+                suggestion: vis_span,
             });
             return false;
         }

tests/ui/error-codes/E0446.stderr

@@ -2,7 +2,10 @@ error[E0446]: private type `Bar` in public interface
   --> $DIR/E0446.rs:10:5
    |
 LL | struct Bar;
-   | ---------- `Bar` declared as private
+   | ----------
+   | |
+   | `Bar` declared as private
+   | help: consider adding `pub` in front of it
 ...
 LL |     type Alias1 = Bar;
    |     ^^^^^^^^^^^ can't leak private type
@@ -11,7 +14,10 @@ error[E0446]: private trait `PrivTr` in public interface
   --> $DIR/E0446.rs:11:5
    |
 LL | trait PrivTr {}
-   | ------------ `PrivTr` declared as private
+   | ------------
+   | |
+   | `PrivTr` declared as private
+   | help: consider adding `pub` in front of it
 ...
 LL |     type Alias2 = Box<dyn PrivTr>;
    |     ^^^^^^^^^^^ can't leak private trait

tests/ui/privacy/issue-30079.stderr

@@ -18,7 +18,7 @@ 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
@@ -30,7 +30,7 @@ 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/private-in-public-assoc-ty.stderr

@@ -75,7 +75,10 @@ error[E0446]: private trait `PrivTr` in public interface
   --> $DIR/private-in-public-assoc-ty.rs:41:9
    |
 LL |     trait PrivTr {}
-   |     ------------ `PrivTr` declared as private
+   |     ------------
+   |     |
+   |     `PrivTr` declared as private
+   |     help: consider adding `pub` in front of it
 ...
 LL |         type Exist = impl PrivTr;
    |         ^^^^^^^^^^ can't leak private trait

tests/ui/privacy/where-priv-type.stderr

@@ -75,7 +75,10 @@ LL |     type AssocTy = Const<{ my_const_fn(U) }>;
    |     ^^^^^^^^^^^^ can't leak private type
 ...
 LL | const fn my_const_fn(val: u8) -> u8 {
-   | ----------------------------------- `fn(u8) -> u8 {my_const_fn}` declared as private
+   | -----------------------------------
+   | |
+   | `fn(u8) -> u8 {my_const_fn}` declared as private
+   | help: consider adding `pub` in front of it
 
 error: aborting due to 1 previous error; 5 warnings emitted