Explicitly export core and std macros

Currently all core and std macros are automatically added to the prelude
via #[macro_use]. However a situation arose where we want to add a new macro
`assert_matches` but don't want to pull it into the standard prelude for
compatibility reasons. By explicitly exporting the macros found in the core and
std crates we get to decide on a per macro basis and can later add them via
the rust_20xx preludes.

Author: Voultapher

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -43,7 +43,7 @@ pub fn inject(
 
     let item = cx.item(
         span,
-        thin_vec![cx.attr_word(sym::macro_use, span)],
+        ast::AttrVec::new(),
         ast::ItemKind::ExternCrate(None, Ident::new(name, ident_span)),
     );
 

compiler/rustc_lint_defs/src/builtin.rs

@@ -19,6 +19,7 @@ declare_lint_pass! {
         AMBIGUOUS_ASSOCIATED_ITEMS,
         AMBIGUOUS_GLOB_IMPORTS,
         AMBIGUOUS_GLOB_REEXPORTS,
+        AMBIGUOUS_PANIC_IMPORTS,
         ARITHMETIC_OVERFLOW,
         ASM_SUB_REGISTER,
         BAD_ASM_STYLE,
@@ -4472,6 +4473,42 @@ declare_lint! {
     };
 }
 
+declare_lint! {
+    /// The `ambiguous_panic_imports` lint detects ambiguous core and std panic imports, but
+    /// previously didn't do that due to `#[macro_use]` prelude macro import.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(ambiguous_panic_imports)]
+    /// #![no_std]
+    ///
+    /// extern crate std;
+    /// use std::prelude::v1::*;
+    ///
+    /// fn xx() {
+    ///     panic!(); // resolves to core::panic
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Future versions of Rust will no longer accept the ambiguous resolution.
+    ///
+    /// 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_PANIC_IMPORTS,
+    Warn,
+    "detects ambiguous core and std panic imports",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: fcw!(FutureReleaseError #147319),
+        report_in_deps: false,
+    };
+}
+
 declare_lint! {
     /// The `refining_impl_trait_reachable` lint detects `impl Trait` return
     /// types in method signatures that are refined by a publically reachable

compiler/rustc_resolve/src/diagnostics.rs

@@ -24,7 +24,7 @@ use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::{
-    ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE, AMBIGUOUS_GLOB_IMPORTS,
+    ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE, AMBIGUOUS_GLOB_IMPORTS, AMBIGUOUS_PANIC_IMPORTS,
     MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
 };
 use rustc_session::utils::was_invoked_from_cargo;
@@ -44,10 +44,11 @@ use crate::errors::{
 use crate::imports::{Import, ImportKind};
 use crate::late::{DiagMetadata, PatternSource, Rib};
 use crate::{
-    AmbiguityError, AmbiguityKind, BindingError, BindingKey, Decl, DeclKind, Finalize,
-    ForwardGenericParamBanReason, HasGenericParams, LateDecl, MacroRulesScope, Module, ModuleKind,
-    ModuleOrUniformRoot, ParentScope, PathResult, PrivacyError, ResolutionError, Resolver, Scope,
-    ScopeSet, Segment, UseError, Used, VisResolutionError, errors as errs, path_names_to_string,
+    AmbiguityError, AmbiguityKind, AmbiguityWarning, BindingError, BindingKey, Decl, DeclKind,
+    Finalize, ForwardGenericParamBanReason, HasGenericParams, LateDecl, MacroRulesScope, Module,
+    ModuleKind, ModuleOrUniformRoot, ParentScope, PathResult, PrivacyError, ResolutionError,
+    Resolver, Scope, ScopeSet, Segment, UseError, Used, VisResolutionError, errors as errs,
+    path_names_to_string,
 };
 
 type Res = def::Res<ast::NodeId>;
@@ -146,17 +147,18 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         for ambiguity_error in &self.ambiguity_errors {
             let diag = self.ambiguity_diagnostic(ambiguity_error);
 
-            if ambiguity_error.warning {
+            if let Some(ambiguity_warning) = ambiguity_error.warning {
                 let node_id = match ambiguity_error.b1.0.kind {
                     DeclKind::Import { import, .. } => import.root_id,
                     DeclKind::Def(_) => CRATE_NODE_ID,
                 };
-                self.lint_buffer.buffer_lint(
-                    AMBIGUOUS_GLOB_IMPORTS,
-                    node_id,
-                    diag.ident.span,
-                    diag,
-                );
+
+                let lint = match ambiguity_warning {
+                    AmbiguityWarning::GlobImport => AMBIGUOUS_GLOB_IMPORTS,
+                    AmbiguityWarning::PanicImport => AMBIGUOUS_PANIC_IMPORTS,
+                };
+
+                self.lint_buffer.buffer_lint(lint, node_id, diag.ident.span, diag);
             } else {
                 self.dcx().emit_err(diag);
             }

compiler/rustc_resolve/src/ident.rs

@@ -8,6 +8,7 @@ use rustc_hir::def::{DefKind, MacroKinds, Namespace, NonMacroAttrKind, PartialRe
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
 use rustc_session::parse::feature_err;
+use rustc_span::edition::Edition;
 use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
 use rustc_span::{Ident, Macros20NormalizedIdent, Span, kw, sym};
 use smallvec::SmallVec;
@@ -20,9 +21,10 @@ use crate::late::{
 };
 use crate::macros::{MacroRulesScope, sub_namespace_match};
 use crate::{
-    AmbiguityError, AmbiguityKind, BindingKey, CmResolver, Decl, DeclKind, Determinacy, Finalize,
-    ImportKind, LateDecl, Module, ModuleKind, ModuleOrUniformRoot, ParentScope, PathResult,
-    PrivacyError, Res, ResolutionError, Resolver, Scope, ScopeSet, Segment, Stage, Used, errors,
+    AmbiguityError, AmbiguityKind, AmbiguityWarning, BindingKey, CmResolver, Decl, DeclKind,
+    Determinacy, Finalize, ImportKind, LateDecl, Module, ModuleKind, ModuleOrUniformRoot,
+    ParentScope, PathResult, PrivacyError, Res, ResolutionError, Resolver, Scope, ScopeSet,
+    Segment, Stage, Used, errors,
 };
 
 #[derive(Copy, Clone)]
@@ -841,14 +843,27 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             if issue_145575_hack || issue_149681_hack {
                 self.issue_145575_hack_applied = true;
             } else {
+                // Turn ambiguity errors for core vs std panic into warnings.
+                // FIXME: Remove with lang team approval.
+                let is_issue_147319_hack = orig_ident.span.edition() <= Edition::Edition2024
+                    && matches!(orig_ident.name, sym::panic)
+                    && matches!(scope, Scope::StdLibPrelude)
+                    && matches!(innermost_scope, Scope::ModuleGlobs(_, _))
+                    && ((self.is_specific_builtin_macro(res, sym::std_panic)
+                        && self.is_specific_builtin_macro(innermost_res, sym::core_panic))
+                        || (self.is_specific_builtin_macro(res, sym::core_panic)
+                            && self.is_specific_builtin_macro(innermost_res, sym::std_panic)));
+
+                let warning = is_issue_147319_hack.then_some(AmbiguityWarning::PanicImport);
+
                 self.ambiguity_errors.push(AmbiguityError {
                     kind,
                     ident: orig_ident,
                     b1: innermost_decl,
                     b2: decl,
                     scope1: innermost_scope,
                     scope2: scope,
-                    warning: false,
+                    warning,
                 });
                 return true;
             }

compiler/rustc_resolve/src/imports.rs

@@ -959,8 +959,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ImportKind::Single { decls, .. } => decls[TypeNS].get().decl(),
             _ => None,
         };
-        let ambiguity_errors_len =
-            |errors: &Vec<AmbiguityError<'_>>| errors.iter().filter(|error| !error.warning).count();
+        let ambiguity_errors_len = |errors: &Vec<AmbiguityError<'_>>| {
+            errors.iter().filter(|error| error.warning.is_none()).count()
+        };
         let prev_ambiguity_errors_len = ambiguity_errors_len(&self.ambiguity_errors);
         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 
@@ -1176,7 +1177,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         });
                         let res = binding.res();
                         let has_ambiguity_error =
-                            this.ambiguity_errors.iter().any(|error| !error.warning);
+                            this.ambiguity_errors.iter().any(|error| error.warning.is_none());
                         if res == Res::Err || has_ambiguity_error {
                             this.dcx()
                                 .span_delayed_bug(import.span, "some error happened for an import");

compiler/rustc_resolve/src/lib.rs

@@ -911,6 +911,12 @@ impl AmbiguityKind {
     }
 }
 
+#[derive(Clone, Copy, PartialEq)]
+enum AmbiguityWarning {
+    GlobImport,
+    PanicImport,
+}
+
 struct AmbiguityError<'ra> {
     kind: AmbiguityKind,
     ident: Ident,
@@ -919,7 +925,7 @@ struct AmbiguityError<'ra> {
     // `empty_module` in module scope serves as an unknown module here.
     scope1: Scope<'ra>,
     scope2: Scope<'ra>,
-    warning: bool,
+    warning: Option<AmbiguityWarning>,
 }
 
 impl<'ra> DeclData<'ra> {
@@ -1871,6 +1877,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         self.get_macro(res).is_some_and(|macro_data| macro_data.ext.builtin_name.is_some())
     }
 
+    fn is_specific_builtin_macro(&self, res: Res, symbol: Symbol) -> bool {
+        self.get_macro(res).is_some_and(|macro_data| macro_data.ext.builtin_name == Some(symbol))
+    }
+
     fn macro_def(&self, mut ctxt: SyntaxContext) -> DefId {
         loop {
             match ctxt.outer_expn_data().macro_def_id {
@@ -2063,7 +2073,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 b2,
                 scope1: Scope::ModuleGlobs(self.empty_module, None),
                 scope2: Scope::ModuleGlobs(self.empty_module, None),
-                warning: warn_ambiguity,
+                warning: if warn_ambiguity { Some(AmbiguityWarning::GlobImport) } else { None },
             };
             if !self.matches_previous_ambiguity_error(&ambiguity_error) {
                 // avoid duplicated span information to be emit out

compiler/rustc_resolve/src/macros.rs

@@ -835,10 +835,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                  res: Res| {
             if let Some(initial_res) = initial_res {
                 if res != initial_res {
-                    // Make sure compilation does not succeed if preferred macro resolution
-                    // has changed after the macro had been expanded. In theory all such
-                    // situations should be reported as errors, so this is a bug.
-                    this.dcx().span_delayed_bug(span, "inconsistent resolution for a macro");
+                    if this.ambiguity_errors.is_empty() {
+                        // Make sure compilation does not succeed if preferred macro resolution
+                        // has changed after the macro had been expanded. In theory all such
+                        // situations should be reported as errors, so this is a bug.
+                        this.dcx().span_delayed_bug(span, "inconsistent resolution for a macro");
+                    }
                 }
             } else if this.tcx.dcx().has_errors().is_none() && this.privacy_errors.is_empty() {
                 // It's possible that the macro was unresolved (indeterminate) and silently

library/alloctests/lib.rs

@@ -65,6 +65,7 @@
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(optimize_attribute)]
+#![feature(prelude_import)]
 #![feature(rustc_allow_const_fn_unstable)]
 #![feature(rustc_attrs)]
 #![feature(staged_api)]
@@ -74,11 +75,17 @@
 
 // Allow testing this library
 extern crate alloc as realalloc;
-#[macro_use]
+
+// This is needed to provide macros to the directly imported alloc modules below.
 extern crate std;
+#[prelude_import]
+#[allow(unused_imports)]
+use std::prelude::rust_2024::*;
+
 #[cfg(test)]
 extern crate test;
 mod testing;
+
 use realalloc::*;
 
 // We are directly including collections, raw_vec, and wtf8 here as they use non-public
@@ -102,8 +109,7 @@ pub(crate) mod test_helpers {
         let mut hasher = std::hash::RandomState::new().build_hasher();
         std::panic::Location::caller().hash(&mut hasher);
         let hc64 = hasher.finish();
-        let seed_vec =
-            hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<crate::vec::Vec<u8>>();
+        let seed_vec = hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<std::vec::Vec<u8>>();
         let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
         rand::SeedableRng::from_seed(seed)
     }

library/core/src/prelude/v1.rs

@@ -59,12 +59,31 @@ pub use crate::hash::macros::Hash;
 
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
 #[doc(no_inline)]
+#[expect(deprecated)]
 pub use crate::{
-    assert, cfg, column, compile_error, concat, env, file, format_args,
-    format_args_nl, include, include_bytes, include_str, line, log_syntax, module_path, option_env,
-    stringify, trace_macros,
+    assert, assert_eq, assert_ne, cfg, column, compile_error, concat, debug_assert, debug_assert_eq,
+    debug_assert_ne, file, format_args, include, include_bytes, include_str, line, matches,
+    module_path, option_env, stringify, todo, r#try, unimplemented, unreachable, write, writeln,
 };
 
+// These macros need special handling, so that we don't export them *and* the modules of the same
+// name. We only want the macros in the prelude so we shadow the original modules with private
+// modules with the same names.
+mod ambiguous_macros_only {
+    mod env {}
+    #[expect(hidden_glob_reexports)]
+    mod panic {}
+    #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+    pub use crate::*;
+}
+#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+#[doc(no_inline)]
+pub use self::ambiguous_macros_only::{env, panic};
+
+#[unstable(feature = "cfg_select", issue = "115585")]
+#[doc(no_inline)]
+pub use crate::cfg_select;
+
 #[unstable(
     feature = "concat_bytes",
     issue = "87555",
@@ -73,6 +92,30 @@ pub use crate::{
 #[doc(no_inline)]
 pub use crate::concat_bytes;
 
+#[unstable(feature = "const_format_args", issue = "none")]
+#[doc(no_inline)]
+pub use crate::const_format_args;
+
+#[unstable(
+    feature = "log_syntax",
+    issue = "29598",
+    reason = "`log_syntax!` is not stable enough for use and is subject to change"
+)]
+#[doc(no_inline)]
+pub use crate::log_syntax;
+
+#[unstable(feature = "pattern_type_macro", issue = "123646")]
+#[doc(no_inline)]
+pub use crate::pattern_type;
+
+#[unstable(
+    feature = "trace_macros",
+    issue = "29598",
+    reason = "`trace_macros` is not stable enough for use and is subject to change"
+)]
+#[doc(no_inline)]
+pub use crate::trace_macros;
+
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]

library/std/src/prelude/mod.rs

@@ -54,9 +54,9 @@
 //! * <code>[std::convert]::{[AsRef], [AsMut], [Into], [From]}</code>, generic
 //!   conversions, used by savvy API authors to create overloaded methods.
 //! * <code>[std::default]::[Default]</code>, types that have default values.
-//! * <code>[std::iter]::{[Iterator], [Extend], [IntoIterator], [DoubleEndedIterator], [ExactSizeIterator]}</code>,
-//!   iterators of various
-//!   kinds.
+//! * <code>[std::iter]::{[Iterator], [Extend], [IntoIterator], [DoubleEndedIterator],
+//!   [ExactSizeIterator]}</code>, iterators of various kinds.
+//! * Most of the standard macros.
 //! * <code>[std::option]::[Option]::{[self][Option], [Some], [None]}</code>, a
 //!   type which expresses the presence or absence of a value. This type is so
 //!   commonly used, its variants are also exported.
@@ -145,6 +145,11 @@ pub mod rust_2021 {
     #[stable(feature = "prelude_2021", since = "1.55.0")]
     #[doc(no_inline)]
     pub use core::prelude::rust_2021::*;
+
+    // There are two different panic macros, one in `core` and one in `std`. They are slightly
+    // different. For `std` we explicitly want the one defined in `std`.
+    #[stable(feature = "prelude_2021", since = "1.55.0")]
+    pub use super::v1::panic;
 }
 
 /// The 2024 version of the prelude of The Rust Standard Library.
@@ -159,6 +164,11 @@ pub mod rust_2024 {
     #[stable(feature = "prelude_2024", since = "1.85.0")]
     #[doc(no_inline)]
     pub use core::prelude::rust_2024::*;
+
+    // There are two different panic macros, one in `core` and one in `std`. They are slightly
+    // different. For `std` we explicitly want the one defined in `std`.
+    #[stable(feature = "prelude_2024", since = "1.85.0")]
+    pub use super::v1::panic;
 }
 
 /// The Future version of the prelude of The Rust Standard Library.
@@ -174,4 +184,9 @@ pub mod rust_future {
     #[unstable(feature = "prelude_next", issue = "none")]
     #[doc(no_inline)]
     pub use core::prelude::rust_future::*;
+
+    // There are two different panic macros, one in `core` and one in `std`. They are slightly
+    // different. For `std` we explicitly want the one defined in `std`.
+    #[unstable(feature = "prelude_next", issue = "none")]
+    pub use super::v1::panic;
 }