make pub_use_of_private_extern_crate a hard error

Author: RalfJung

compiler/rustc_lint/messages.ftl

@@ -647,9 +647,6 @@ lint_pattern_in_bodiless = patterns aren't allowed in functions without bodies
 lint_pattern_in_foreign = patterns aren't allowed in foreign function declarations
     .label = pattern not allowed in foreign function
 
-lint_private_extern_crate_reexport = extern crate `{$ident}` is private and cannot be re-exported
-    .suggestion = consider making the `extern crate` item publicly accessible
-
 lint_proc_macro_derive_resolution_fallback = cannot find {$ns} `{$ident}` in this scope
     .label = names from parent modules are not accessible without an explicit import
 

compiler/rustc_lint/src/context/diagnostics.rs

@@ -359,10 +359,6 @@ pub(super) fn decorate_lint(sess: &Session, diagnostic: BuiltinLintDiag, diag: &
             lints::MacroUseDeprecated.decorate_lint(diag);
         }
         BuiltinLintDiag::UnusedMacroUse => lints::UnusedMacroUse.decorate_lint(diag),
-        BuiltinLintDiag::PrivateExternCrateReexport { source: ident, extern_crate_span } => {
-            lints::PrivateExternCrateReexport { ident, sugg: extern_crate_span.shrink_to_lo() }
-                .decorate_lint(diag);
-        }
         BuiltinLintDiag::UnusedLabel => lints::UnusedLabel.decorate_lint(diag),
         BuiltinLintDiag::MacroIsPrivate(ident) => {
             lints::MacroIsPrivate { ident }.decorate_lint(diag);

compiler/rustc_lint/src/lints.rs

@@ -2331,14 +2331,6 @@ pub struct MacroUseDeprecated;
 #[diag(lint_unused_macro_use)]
 pub struct UnusedMacroUse;
 
-#[derive(LintDiagnostic)]
-#[diag(lint_private_extern_crate_reexport, code = E0365)]
-pub struct PrivateExternCrateReexport {
-    pub ident: Ident,
-    #[suggestion(code = "pub ", style = "verbose", applicability = "maybe-incorrect")]
-    pub sugg: Span,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(lint_unused_label)]
 pub struct UnusedLabel;

compiler/rustc_lint_defs/src/lib.rs

@@ -711,10 +711,6 @@ pub enum BuiltinLintDiag {
     },
     MacroUseDeprecated,
     UnusedMacroUse,
-    PrivateExternCrateReexport {
-        source: Ident,
-        extern_crate_span: Span,
-    },
     UnusedLabel,
     MacroIsPrivate(Ident),
     UnusedMacroDefinition(Symbol),

compiler/rustc_resolve/messages.ftl

@@ -1,6 +1,10 @@
+
 resolve_accessible_unsure = not sure whether the path is accessible or not
     .note = the type may have associated items, but we are currently not checking them
 
+resolve_private_extern_crate_reexport = extern crate `{$ident}` is private and cannot be re-exported
+    .suggestion = consider making the `extern crate` item publicly accessible
+
 resolve_add_as_non_derive =
     add as non-Derive macro
     `#[{$macro_path}]`

compiler/rustc_resolve/src/errors.rs

@@ -741,6 +741,16 @@ pub(crate) struct CannotBeReexportedCratePublicNS {
     pub(crate) ident: Ident,
 }
 
+#[derive(Diagnostic)]
+#[diag(resolve_private_extern_crate_reexport, code = E0365)]
+pub struct PrivateExternCrateReexport {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) ident: Ident,
+    #[suggestion(code = "pub ", style = "verbose", applicability = "maybe-incorrect")]
+    pub(crate) sugg: Span,
+}
+
 #[derive(Subdiagnostic)]
 #[help(resolve_consider_adding_macro_export)]
 pub(crate) struct ConsiderAddingMacroExport {

compiler/rustc_resolve/src/imports.rs

@@ -5,7 +5,7 @@ use crate::errors::{
     CannotBeReexportedCratePublic, CannotBeReexportedCratePublicNS, CannotBeReexportedPrivate,
     CannotBeReexportedPrivateNS, CannotDetermineImportResolution, CannotGlobImportAllCrates,
     ConsiderAddingMacroExport, ConsiderMarkingAsPub, IsNotDirectlyImportable,
-    ItemsInTraitsAreNotImportable,
+    ItemsInTraitsAreNotImportable, PrivateExternCrateReexport,
 };
 use crate::Determinacy::{self, *};
 use crate::{module_to_string, names_to_string, ImportSuggestion};
@@ -25,8 +25,7 @@ use rustc_middle::metadata::Reexport;
 use rustc_middle::span_bug;
 use rustc_middle::ty;
 use rustc_session::lint::builtin::{
-    AMBIGUOUS_GLOB_REEXPORTS, HIDDEN_GLOB_REEXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE,
-    UNUSED_IMPORTS,
+    AMBIGUOUS_GLOB_REEXPORTS, HIDDEN_GLOB_REEXPORTS, UNUSED_IMPORTS,
 };
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_span::edit_distance::find_best_match_for_name;
@@ -1249,15 +1248,12 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         if !any_successful_reexport {
             let (ns, binding) = reexport_error.unwrap();
             if let Some(extern_crate_id) = pub_use_of_private_extern_crate_hack(import, binding) {
-                self.lint_buffer.buffer_lint(
-                    PUB_USE_OF_PRIVATE_EXTERN_CRATE,
-                    import_id,
-                    import.span,
-                    BuiltinLintDiag::PrivateExternCrateReexport {
-                        source: ident,
-                        extern_crate_span: self.tcx.source_span(self.local_def_id(extern_crate_id)),
-                    },
-                );
+                let err = self.dcx().create_err(PrivateExternCrateReexport {
+                    span: import.span,
+                    ident,
+                    sugg: self.tcx.source_span(self.local_def_id(extern_crate_id)).shrink_to_lo(),
+                });
+                err.emit();
             } else {
                 if ns == TypeNS {
                     let err = if crate_private_reexport {

tests/ui/pub/pub-reexport-priv-extern-crate.rs

@@ -1,6 +1,5 @@
 extern crate core;
 pub use core as reexported_core; //~ ERROR `core` is private and cannot be re-exported
-                                 //~^ WARN this was previously accepted
 
 mod foo1 {
     extern crate core;

tests/ui/pub/pub-reexport-priv-extern-crate.stderr

@@ -1,41 +1,38 @@
+error[E0365]: extern crate `core` is private and cannot be re-exported
+  --> $DIR/pub-reexport-priv-extern-crate.rs:2:9
+   |
+LL | pub use core as reexported_core;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: consider making the `extern crate` item publicly accessible
+   |
+LL | pub extern crate core;
+   | +++
+
 error[E0603]: crate import `core` is private
-  --> $DIR/pub-reexport-priv-extern-crate.rs:10:15
+  --> $DIR/pub-reexport-priv-extern-crate.rs:9:15
    |
 LL |     use foo1::core;
    |               ^^^^ private crate import
    |
 note: the crate import `core` is defined here
-  --> $DIR/pub-reexport-priv-extern-crate.rs:6:5
+  --> $DIR/pub-reexport-priv-extern-crate.rs:5:5
    |
 LL |     extern crate core;
    |     ^^^^^^^^^^^^^^^^^^
 
 error[E0603]: crate import `core` is private
-  --> $DIR/pub-reexport-priv-extern-crate.rs:17:24
+  --> $DIR/pub-reexport-priv-extern-crate.rs:16:24
    |
 LL |     pub use foo2::bar::core;
    |                        ^^^^ private crate import
    |
 note: the crate import `core` is defined here
-  --> $DIR/pub-reexport-priv-extern-crate.rs:12:9
+  --> $DIR/pub-reexport-priv-extern-crate.rs:11:9
    |
 LL |         extern crate core;
    |         ^^^^^^^^^^^^^^^^^^
 
-error[E0365]: extern crate `core` is private and cannot be re-exported
-  --> $DIR/pub-reexport-priv-extern-crate.rs:2:9
-   |
-LL | pub use core as reexported_core;
-   |         ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #34537 <https://github.com/rust-lang/rust/issues/34537>
-   = note: `#[deny(pub_use_of_private_extern_crate)]` on by default
-help: consider making the `extern crate` item publicly accessible
-   |
-LL | pub extern crate core;
-   | +++
-
 error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0365, E0603.