fix(resolve): update the ambiguity glob binding as warning recursively

compiler/rustc_errors/src/lib.rs

@@ -1871,6 +1871,22 @@ pub fn add_elided_lifetime_in_path_suggestion(
     });
 }
 
+pub fn report_ambiguity_error<'a, G: EmissionGuarantee>(
+    db: &mut DiagnosticBuilder<'a, G>,
+    ambiguity: rustc_lint_defs::AmbiguityErrorDiag,
+) {
+    db.span_label(ambiguity.label_span, ambiguity.label_msg);
+    db.note(ambiguity.note_msg);
+    db.span_note(ambiguity.b1_span, ambiguity.b1_note_msg);
+    for help_msg in ambiguity.b1_help_msgs {
+        db.help(help_msg);
+    }
+    db.span_note(ambiguity.b2_span, ambiguity.b2_note_msg);
+    for help_msg in ambiguity.b2_help_msgs {
+        db.help(help_msg);
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum TerminalUrl {
     No,

compiler/rustc_lint/src/context.rs

@@ -946,6 +946,9 @@ pub trait LintContext: Sized {
                         Applicability::MachineApplicable,
                     );
                 }
+                BuiltinLintDiagnostics::AmbiguousGlobImports { diag } => {
+                    rustc_errors::report_ambiguity_error(db, diag);
+                }
                 BuiltinLintDiagnostics::AmbiguousGlobReexports { name, namespace, first_reexport_span, duplicate_reexport_span } => {
                     db.span_label(first_reexport_span, format!("the name `{name}` in the {namespace} namespace is first re-exported here"));
                     db.span_label(duplicate_reexport_span, format!("but the name `{name}` in the {namespace} namespace is also re-exported here"));

compiler/rustc_lint_defs/src/builtin.rs

@@ -3316,6 +3316,7 @@ declare_lint_pass! {
         // tidy-alphabetical-start
         ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
         AMBIGUOUS_ASSOCIATED_ITEMS,
+        AMBIGUOUS_GLOB_IMPORTS,
         AMBIGUOUS_GLOB_REEXPORTS,
         ARITHMETIC_OVERFLOW,
         ASM_SUB_REGISTER,
@@ -4405,3 +4406,46 @@ declare_lint! {
     Warn,
     "unrecognized diagnostic attribute"
 }
+
+declare_lint! {
+    /// The `ambiguous_glob_imports` lint detects glob imports that should report ambiguity
+    /// errors, but previously didn't do that due to rustc bugs.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    ///
+    /// #![deny(ambiguous_glob_imports)]
+    /// pub fn foo() -> u32 {
+    ///     use sub::*;
+    ///     C
+    /// }
+    ///
+    /// mod sub {
+    ///     mod mod1 { pub const C: u32 = 1; }
+    ///     mod mod2 { pub const C: u32 = 2; }
+    ///
+    ///     pub use mod1::*;
+    ///     pub use mod2::*;
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Previous versions of Rust compile it successfully because it
+    /// had lost the ambiguity error when resolve `use sub::mod2::*`.
+    ///
+    /// This is a [future-incompatible] lint to transition this to a
+    /// hard error in the future.
+    ///
+    /// [future-incompatible]: ../index.md#future-incompatible-lints
+    pub AMBIGUOUS_GLOB_IMPORTS,
+    Warn,
+    "detects certain glob imports that require reporting an ambiguity error",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseError,
+        reference: "issue #114095 <https://github.com/rust-lang/rust/issues/114095>",
+    };
+}

compiler/rustc_lint_defs/src/lib.rs

@@ -467,6 +467,21 @@ impl<HCX> ToStableHashKey<HCX> for LintId {
     }
 }
 
+#[derive(Debug)]
+pub struct AmbiguityErrorDiag {
+    pub msg: String,
+    pub span: Span,
+    pub label_span: Span,
+    pub label_msg: String,
+    pub note_msg: String,
+    pub b1_span: Span,
+    pub b1_note_msg: String,
+    pub b1_help_msgs: Vec<String>,
+    pub b2_span: Span,
+    pub b2_note_msg: String,
+    pub b2_help_msgs: Vec<String>,
+}
+
 // This could be a closure, but then implementing derive trait
 // becomes hacky (and it gets allocated).
 #[derive(Debug)]
@@ -530,6 +545,9 @@ pub enum BuiltinLintDiagnostics {
         vis_span: Span,
         ident_span: Span,
     },
+    AmbiguousGlobImports {
+        diag: AmbiguityErrorDiag,
+    },
     AmbiguousGlobReexports {
         /// The name for which collision(s) have occurred.
         name: String,

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -41,6 +41,7 @@ impl<'a, Id: Into<DefId>> ToNameBinding<'a>
         arenas.alloc_name_binding(NameBindingData {
             kind: NameBindingKind::Module(self.0),
             ambiguity: None,
+            warn_ambiguity: false,
             vis: self.1.to_def_id(),
             span: self.2,
             expansion: self.3,
@@ -53,6 +54,7 @@ impl<'a, Id: Into<DefId>> ToNameBinding<'a> for (Res, ty::Visibility<Id>, Span,
         arenas.alloc_name_binding(NameBindingData {
             kind: NameBindingKind::Res(self.0),
             ambiguity: None,
+            warn_ambiguity: false,
             vis: self.1.to_def_id(),
             span: self.2,
             expansion: self.3,
@@ -69,7 +71,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
     {
         let binding = def.to_name_binding(self.arenas);
         let key = self.new_disambiguated_key(ident, ns);
-        if let Err(old_binding) = self.try_define(parent, key, binding) {
+        if let Err(old_binding) = self.try_define(parent, key, binding, false) {
             self.report_conflict(parent, ident, ns, old_binding, binding);
         }
     }

compiler/rustc_resolve/src/diagnostics.rs

@@ -5,10 +5,8 @@ use rustc_ast::{self as ast, Crate, ItemKind, ModKind, NodeId, Path, CRATE_NODE_
 use rustc_ast::{MetaItemKind, NestedMetaItem};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{
-    pluralize, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
-};
-use rustc_errors::{struct_span_err, SuggestionStyle};
+use rustc_errors::{pluralize, report_ambiguity_error, struct_span_err, SuggestionStyle};
+use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind, PerNS};
@@ -17,8 +15,9 @@ use rustc_hir::PrimTy;
 use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint::builtin::ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE;
+use rustc_session::lint::builtin::AMBIGUOUS_GLOB_IMPORTS;
 use rustc_session::lint::builtin::MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS;
-use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_session::lint::{AmbiguityErrorDiag, BuiltinLintDiagnostics};
 use rustc_session::Session;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
@@ -135,7 +134,23 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
 
         for ambiguity_error in &self.ambiguity_errors {
-            self.report_ambiguity_error(ambiguity_error);
+            let diag = self.ambiguity_diagnostics(ambiguity_error);
+            if ambiguity_error.warning {
+                let NameBindingKind::Import { import, .. } = ambiguity_error.b1.0.kind else {
+                    unreachable!()
+                };
+                self.lint_buffer.buffer_lint_with_diagnostic(
+                    AMBIGUOUS_GLOB_IMPORTS,
+                    import.root_id,
+                    ambiguity_error.ident.span,
+                    diag.msg.to_string(),
+                    BuiltinLintDiagnostics::AmbiguousGlobImports { diag },
+                );
+            } else {
+                let mut err = struct_span_err!(self.tcx.sess, diag.span, E0659, "{}", &diag.msg);
+                report_ambiguity_error(&mut err, diag);
+                err.emit();
+            }
         }
 
         let mut reported_spans = FxHashSet::default();
@@ -1540,20 +1555,15 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
     }
 
-    fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
-        let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
+    fn ambiguity_diagnostics(&self, ambiguity_error: &AmbiguityError<'_>) -> AmbiguityErrorDiag {
+        let AmbiguityError { kind, ident, b1, b2, misc1, misc2, .. } = *ambiguity_error;
         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
             // We have to print the span-less alternative first, otherwise formatting looks bad.
             (b2, b1, misc2, misc1, true)
         } else {
             (b1, b2, misc1, misc2, false)
         };
-
-        let mut err = struct_span_err!(self.tcx.sess, ident.span, E0659, "`{ident}` is ambiguous");
-        err.span_label(ident.span, "ambiguous name");
-        err.note(format!("ambiguous because of {}", kind.descr()));
-
-        let mut could_refer_to = |b: NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
+        let could_refer_to = |b: NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
             let note_msg = format!("`{ident}` could{also} refer to {what}");
 
@@ -1579,16 +1589,35 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 AmbiguityErrorMisc::FromPrelude | AmbiguityErrorMisc::None => {}
             }
 
-            err.span_note(b.span, note_msg);
-            for (i, help_msg) in help_msgs.iter().enumerate() {
-                let or = if i == 0 { "" } else { "or " };
-                err.help(format!("{}{}", or, help_msg));
-            }
+            (
+                b.span,
+                note_msg,
+                help_msgs
+                    .iter()
+                    .enumerate()
+                    .map(|(i, help_msg)| {
+                        let or = if i == 0 { "" } else { "or " };
+                        format!("{}{}", or, help_msg)
+                    })
+                    .collect::<Vec<_>>(),
+            )
         };
-
-        could_refer_to(b1, misc1, "");
-        could_refer_to(b2, misc2, " also");
-        err.emit();
+        let (b1_span, b1_note_msg, b1_help_msgs) = could_refer_to(b1, misc1, "");
+        let (b2_span, b2_note_msg, b2_help_msgs) = could_refer_to(b2, misc2, " also");
+
+        AmbiguityErrorDiag {
+            msg: format!("`{ident}` is ambiguous"),
+            span: ident.span,
+            label_span: ident.span,
+            label_msg: "ambiguous name".to_string(),
+            note_msg: format!("ambiguous because of {}", kind.descr()),
+            b1_span,
+            b1_note_msg,
+            b1_help_msgs,
+            b2_span,
+            b2_note_msg,
+            b2_help_msgs,
+        }
     }
 
     /// If the binding refers to a tuple struct constructor with fields,

compiler/rustc_resolve/src/ident.rs

@@ -677,6 +677,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                         ident: orig_ident,
                                         b1: innermost_binding,
                                         b2: binding,
+                                        warning: false,
                                         misc1: misc(innermost_flags),
                                         misc2: misc(flags),
                                     });
@@ -905,6 +906,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     ident,
                     b1: binding,
                     b2: shadowed_glob,
+                    warning: false,
                     misc1: AmbiguityErrorMisc::None,
                     misc2: AmbiguityErrorMisc::None,
                 });