Auto merge of #146104 - fmease:rollup-xhh06pd, r=fmease

Rollup of 10 pull requests

Successful merges:

 - #144066 (stabilize c-style varargs for sysv64, win64, efiapi, aapcs)
 - #145783 (add span to struct pattern rest (..))
 - #145961 (resolve: Avoid a regression from splitting prelude into two scopes)
 - #145962 (Ensure we emit an allocator shim when only some crate types need one)
 - #146064 (Add compiler error when trying to use concat metavar expr in repetitions)
 - #146067 (alloc: make Cow From impls const)
 - #146070 (rustdoc-search: skip loading unneeded fnData)
 - #146089 (fix a constness ordering bug in rustfmt)
 - #146094 (Make `Parser::parse_for_head` public for rustfmt usage)
 - #146102 (Remove dead code stemming from an old effects desugaring)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_abi/src/extern_abi.rs

@@ -6,6 +6,8 @@ use std::hash::{Hash, Hasher};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableOrd};
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable, Encodable};
+#[cfg(feature = "nightly")]
+use rustc_span::Symbol;
 
 use crate::AbiFromStrErr;
 
@@ -226,6 +228,13 @@ impl StableOrd for ExternAbi {
 #[cfg(feature = "nightly")]
 rustc_error_messages::into_diag_arg_using_display!(ExternAbi);
 
+#[cfg(feature = "nightly")]
+pub enum CVariadicStatus {
+    NotSupported,
+    Stable,
+    Unstable { feature: Symbol },
+}
+
 impl ExternAbi {
     /// An ABI "like Rust"
     ///
@@ -238,23 +247,33 @@ impl ExternAbi {
         matches!(self, Rust | RustCall | RustCold)
     }
 
-    pub fn supports_varargs(self) -> bool {
+    /// Returns whether the ABI supports C variadics. This only controls whether we allow *imports*
+    /// of such functions via `extern` blocks; there's a separate check during AST construction
+    /// guarding *definitions* of variadic functions.
+    #[cfg(feature = "nightly")]
+    pub fn supports_c_variadic(self) -> CVariadicStatus {
         // * C and Cdecl obviously support varargs.
         // * C can be based on Aapcs, SysV64 or Win64, so they must support varargs.
         // * EfiApi is based on Win64 or C, so it also supports it.
+        // * System automatically falls back to C when used with variadics, therefore supports it.
         //
         // * Stdcall does not, because it would be impossible for the callee to clean
         //   up the arguments. (callee doesn't know how many arguments are there)
         // * Same for Fastcall, Vectorcall and Thiscall.
         // * Other calling conventions are related to hardware or the compiler itself.
+        //
+        // All of the supported ones must have a test in `tests/codegen/cffi/c-variadic-ffi.rs`.
         match self {
             Self::C { .. }
             | Self::Cdecl { .. }
             | Self::Aapcs { .. }
             | Self::Win64 { .. }
             | Self::SysV64 { .. }
-            | Self::EfiApi => true,
-            _ => false,
+            | Self::EfiApi => CVariadicStatus::Stable,
+            Self::System { .. } => {
+                CVariadicStatus::Unstable { feature: rustc_span::sym::extern_system_varargs }
+            }
+            _ => CVariadicStatus::NotSupported,
         }
     }
 }

compiler/rustc_abi/src/lib.rs

@@ -63,6 +63,8 @@ mod tests;
 
 pub use callconv::{Heterogeneous, HomogeneousAggregate, Reg, RegKind};
 pub use canon_abi::{ArmCall, CanonAbi, InterruptKind, X86Call};
+#[cfg(feature = "nightly")]
+pub use extern_abi::CVariadicStatus;
 pub use extern_abi::{ExternAbi, all_names};
 #[cfg(feature = "nightly")]
 pub use layout::{FIRST_VARIANT, FieldIdx, Layout, TyAbiInterface, TyAndLayout, VariantIdx};

compiler/rustc_ast/src/ast.rs

@@ -937,7 +937,7 @@ pub enum PatKind {
 #[derive(Clone, Copy, Encodable, Decodable, Debug, PartialEq, Walkable)]
 pub enum PatFieldsRest {
     /// `module::StructName { field, ..}`
-    Rest,
+    Rest(Span),
     /// `module::StructName { field, syntax error }`
     Recovered(ErrorGuaranteed),
     /// `module::StructName { field }`
@@ -4051,8 +4051,8 @@ mod size_asserts {
     static_assert_size!(Local, 96);
     static_assert_size!(MetaItemLit, 40);
     static_assert_size!(Param, 40);
-    static_assert_size!(Pat, 72);
-    static_assert_size!(PatKind, 48);
+    static_assert_size!(Pat, 80);
+    static_assert_size!(PatKind, 56);
     static_assert_size!(Path, 24);
     static_assert_size!(PathSegment, 24);
     static_assert_size!(Stmt, 32);

compiler/rustc_ast_lowering/src/expr.rs

@@ -1434,10 +1434,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         self.dcx().emit_err(FunctionalRecordUpdateDestructuringAssignment {
                             span: e.span,
                         });
-                        true
+                        Some(self.lower_span(e.span))
                     }
-                    StructRest::Rest(_) => true,
-                    StructRest::None => false,
+                    StructRest::Rest(span) => Some(self.lower_span(*span)),
+                    StructRest::None => None,
                 };
                 let struct_pat = hir::PatKind::Struct(qpath, field_pats, fields_omitted);
                 return self.pat_without_dbm(lhs.span, struct_pat);

compiler/rustc_ast_lowering/src/lib.rs

@@ -2028,7 +2028,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                 (
                     hir::ParamName::Plain(self.lower_ident(param.ident)),
-                    hir::GenericParamKind::Const { ty, default, synthetic: false },
+                    hir::GenericParamKind::Const { ty, default },
                 )
             }
         }
@@ -2508,7 +2508,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         fields: &'hir [hir::PatField<'hir>],
     ) -> &'hir hir::Pat<'hir> {
         let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span));
-        self.pat(span, hir::PatKind::Struct(qpath, fields, false))
+        self.pat(span, hir::PatKind::Struct(qpath, fields, None))
     }
 
     fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, HirId) {

compiler/rustc_ast_lowering/src/pat.rs

@@ -106,10 +106,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         break hir::PatKind::Struct(
                             qpath,
                             fs,
-                            matches!(
-                                etc,
-                                ast::PatFieldsRest::Rest | ast::PatFieldsRest::Recovered(_)
-                            ),
+                            match etc {
+                                ast::PatFieldsRest::Rest(sp) => Some(self.lower_span(*sp)),
+                                ast::PatFieldsRest::Recovered(_) => Some(Span::default()),
+                                _ => None,
+                            },
                         );
                     }
                     PatKind::Tuple(pats) => {

compiler/rustc_ast_passes/messages.ftl

@@ -57,7 +57,7 @@ ast_passes_auto_super_lifetime = auto traits cannot have super traits or lifetim
     .label = {ast_passes_auto_super_lifetime}
     .suggestion = remove the super traits or lifetime bounds
 
-ast_passes_bad_c_variadic = only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+ast_passes_bad_c_variadic = defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 ast_passes_body_in_extern = incorrect `{$kind}` inside `extern` block
     .cannot_have = cannot have a body

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1769,7 +1769,7 @@ impl<'a> State<'a> {
                     },
                     |f| f.pat.span,
                 );
-                if let ast::PatFieldsRest::Rest | ast::PatFieldsRest::Recovered(_) = etc {
+                if let ast::PatFieldsRest::Rest(_) | ast::PatFieldsRest::Recovered(_) = etc {
                     if !fields.is_empty() {
                         self.word_space(",");
                     }

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -58,6 +58,7 @@ use super::linker::{self, Linker};
 use super::metadata::{MetadataPosition, create_wrapper_file};
 use super::rpath::{self, RPathConfig};
 use super::{apple, versioned_llvm_target};
+use crate::base::needs_allocator_shim_for_linking;
 use crate::{
     CodegenResults, CompiledModule, CrateInfo, NativeLib, errors, looks_like_rust_object_file,
 };
@@ -2080,9 +2081,17 @@ fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &Codeg
 }
 
 /// Add object files for allocator code linked once for the whole crate tree.
-fn add_local_crate_allocator_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
-    if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref()) {
-        cmd.add_object(obj);
+fn add_local_crate_allocator_objects(
+    cmd: &mut dyn Linker,
+    codegen_results: &CodegenResults,
+    crate_type: CrateType,
+) {
+    if needs_allocator_shim_for_linking(&codegen_results.crate_info.dependency_formats, crate_type)
+    {
+        if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref())
+        {
+            cmd.add_object(obj);
+        }
     }
 }
 
@@ -2281,7 +2290,7 @@ fn linker_with_args(
         codegen_results,
         metadata,
     );
-    add_local_crate_allocator_objects(cmd, codegen_results);
+    add_local_crate_allocator_objects(cmd, codegen_results, crate_type);
 
     // Avoid linking to dynamic libraries unless they satisfy some undefined symbols
     // at the point at which they are specified on the command line.

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -11,8 +11,9 @@ use rustc_metadata::{
 };
 use rustc_middle::bug;
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_middle::middle::exported_symbols;
-use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
+use rustc_middle::middle::exported_symbols::{
+    self, ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
+};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
@@ -22,6 +23,8 @@ use tracing::{debug, warn};
 
 use super::command::Command;
 use super::symbol_export;
+use crate::back::symbol_export::allocator_shim_symbols;
+use crate::base::needs_allocator_shim_for_linking;
 use crate::errors;
 
 #[cfg(test)]
@@ -1827,7 +1830,7 @@ fn exported_symbols_for_non_proc_macro(
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
         // Do not export mangled symbols from cdylibs and don't attempt to export compiler-builtins
-        // from any cdylib. The latter doesn't work anyway as we use hidden visibility for
+        // from any dylib. The latter doesn't work anyway as we use hidden visibility for
         // compiler-builtins. Most linkers silently ignore it, but ld64 gives a warning.
         if info.level.is_below_threshold(export_threshold) && !tcx.is_compiler_builtins(cnum) {
             symbols.push((
@@ -1838,6 +1841,14 @@ fn exported_symbols_for_non_proc_macro(
         }
     });
 
+    // Mark allocator shim symbols as exported only if they were generated.
+    if export_threshold == SymbolExportLevel::Rust
+        && needs_allocator_shim_for_linking(tcx.dependency_formats(()), crate_type)
+        && tcx.allocator_kind(()).is_some()
+    {
+        symbols.extend(allocator_shim_symbols(tcx));
+    }
+
     symbols
 }