Rollup of 10 pull requests

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1782,7 +1782,10 @@ fn exported_symbols_for_non_proc_macro(tcx: TyCtxt<'_>, crate_type: CrateType) -
     let mut symbols = Vec::new();
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
-        if info.level.is_below_threshold(export_threshold) {
+        // 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
+        // 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(symbol_export::exporting_symbol_name_for_instance_in_crate(
                 tcx, symbol, cnum,
             ));
@@ -1821,7 +1824,9 @@ pub(crate) fn linked_symbols(
 
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
-        if info.level.is_below_threshold(export_threshold) || info.used {
+        if info.level.is_below_threshold(export_threshold) && !tcx.is_compiler_builtins(cnum)
+            || info.used
+        {
             symbols.push((
                 symbol_export::linking_symbol_name_for_instance_in_crate(tcx, symbol, cnum),
                 info.kind,

compiler/rustc_codegen_ssa/src/mir/naked_asm.rs

@@ -332,7 +332,7 @@ fn wasm_functype<'tcx>(tcx: TyCtxt<'tcx>, fn_abi: &FnAbi<'tcx, Ty<'tcx>>, def_id
     // please also add `wasm32-unknown-unknown` back in `tests/assembly/wasm32-naked-fn.rs`
     // basically the commit introducing this comment should be reverted
     if let PassMode::Pair { .. } = fn_abi.ret.mode {
-        let _ = WasmCAbi::Legacy;
+        let _ = WasmCAbi::Legacy { with_lint: true };
         span_bug!(
             tcx.def_span(def_id),
             "cannot return a pair (the wasm32-unknown-unknown ABI is broken, see https://github.com/rust-lang/rust/issues/115666"
@@ -384,7 +384,7 @@ fn wasm_type<'tcx>(
                 BackendRepr::SimdVector { .. } => "v128",
                 BackendRepr::Memory { .. } => {
                     // FIXME: remove this branch once the wasm32-unknown-unknown ABI is fixed
-                    let _ = WasmCAbi::Legacy;
+                    let _ = WasmCAbi::Legacy { with_lint: true };
                     span_bug!(
                         tcx.def_span(def_id),
                         "cannot use memory args (the wasm32-unknown-unknown ABI is broken, see https://github.com/rust-lang/rust/issues/115666"

compiler/rustc_lint_defs/src/builtin.rs

@@ -143,6 +143,7 @@ declare_lint_pass! {
         UNUSED_VARIABLES,
         USELESS_DEPRECATED,
         WARNINGS,
+        WASM_C_ABI,
         // tidy-alphabetical-end
     ]
 }
@@ -5082,6 +5083,8 @@ declare_lint! {
     /// }
     /// ```
     ///
+    /// This will produce:
+    ///
     /// ```text
     /// warning: ABI error: this function call uses a avx vector type, which is not enabled in the caller
     ///  --> lint_example.rs:18:12
@@ -5125,3 +5128,46 @@ declare_lint! {
         reference: "issue #116558 <https://github.com/rust-lang/rust/issues/116558>",
     };
 }
+
+declare_lint! {
+    /// The `wasm_c_abi` lint detects usage of the `extern "C"` ABI of wasm that is affected
+    /// by a planned ABI change that has the goal of aligning Rust with the standard C ABI
+    /// of this target.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (needs wasm32-unknown-unknown)
+    /// #[repr(C)]
+    /// struct MyType(i32, i32);
+    ///
+    /// extern "C" my_fun(x: MyType) {}
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// error: this function function definition is affected by the wasm ABI transition: it passes an argument of non-scalar type `MyType`
+    /// --> $DIR/wasm_c_abi_transition.rs:17:1
+    ///  |
+    ///  | pub extern "C" fn my_fun(_x: MyType) {}
+    ///  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    ///  |
+    ///  = 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 #138762 <https://github.com/rust-lang/rust/issues/138762>
+    ///  = help: the "C" ABI Rust uses on wasm32-unknown-unknown will change to align with the standard "C" ABI for this target
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// Rust has historically implemented a non-spec-compliant C ABI on wasm32-unknown-unknown. This
+    /// has caused incompatibilities with other compilers and Wasm targets. In a future version
+    /// of Rust, this will be fixed, and therefore code relying on the non-spec-compliant C ABI will
+    /// stop functioning.
+    pub WASM_C_ABI,
+    Warn,
+    "detects code relying on rustc's non-spec-compliant wasm C ABI",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
+        reference: "issue #138762 <https://github.com/rust-lang/rust/issues/138762>",
+    };
+}

compiler/rustc_mir_build/src/builder/expr/as_constant.rs

@@ -105,23 +105,19 @@ fn lit_to_mir_constant<'tcx>(tcx: TyCtxt<'tcx>, lit_input: LitToConstInput<'tcx>
         return Const::Ty(Ty::new_error(tcx, guar), ty::Const::new_error(tcx, guar));
     }
 
-    let trunc = |n, width: ty::UintTy| {
-        let width = width
-            .normalize(tcx.data_layout.pointer_size.bits().try_into().unwrap())
-            .bit_width()
-            .unwrap();
-        let width = Size::from_bits(width);
+    let lit_ty = match *ty.kind() {
+        ty::Pat(base, _) => base,
+        _ => ty,
+    };
+
+    let trunc = |n| {
+        let width = lit_ty.primitive_size(tcx);
         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
         let result = width.truncate(n);
         trace!("trunc result: {}", result);
         ConstValue::Scalar(Scalar::from_uint(result, width))
     };
 
-    let lit_ty = match *ty.kind() {
-        ty::Pat(base, _) => base,
-        _ => ty,
-    };
-
     let value = match (lit, lit_ty.kind()) {
         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
             let s = s.as_str();
@@ -149,11 +145,10 @@ fn lit_to_mir_constant<'tcx>(tcx: TyCtxt<'tcx>, lit_input: LitToConstInput<'tcx>
         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
         }
-        (ast::LitKind::Int(n, _), ty::Uint(ui)) if !neg => trunc(n.get(), *ui),
-        (ast::LitKind::Int(n, _), ty::Int(i)) => trunc(
-            if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() },
-            i.to_unsigned(),
-        ),
+        (ast::LitKind::Int(n, _), ty::Uint(_)) if !neg => trunc(n.get()),
+        (ast::LitKind::Int(n, _), ty::Int(_)) => {
+            trunc(if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() })
+        }
         (ast::LitKind::Float(n, _), ty::Float(fty)) => {
             parse_float_into_constval(*n, *fty, neg).unwrap()
         }

compiler/rustc_mir_build/src/builder/scope.rs

@@ -305,27 +305,25 @@ impl DropTree {
     }
 
     /// Builds the MIR for a given drop tree.
-    ///
-    /// `blocks` should have the same length as `self.drops`, and may have its
-    /// first value set to some already existing block.
     fn build_mir<'tcx, T: DropTreeBuilder<'tcx>>(
         &mut self,
         cfg: &mut CFG<'tcx>,
-        blocks: &mut IndexVec<DropIdx, Option<BasicBlock>>,
-    ) {
+        root_node: Option<BasicBlock>,
+    ) -> IndexVec<DropIdx, Option<BasicBlock>> {
         debug!("DropTree::build_mir(drops = {:#?})", self);
-        assert_eq!(blocks.len(), self.drops.len());
 
-        self.assign_blocks::<T>(cfg, blocks);
-        self.link_blocks(cfg, blocks)
+        let mut blocks = self.assign_blocks::<T>(cfg, root_node);
+        self.link_blocks(cfg, &mut blocks);
+
+        blocks
     }
 
     /// Assign blocks for all of the drops in the drop tree that need them.
     fn assign_blocks<'tcx, T: DropTreeBuilder<'tcx>>(
         &mut self,
         cfg: &mut CFG<'tcx>,
-        blocks: &mut IndexVec<DropIdx, Option<BasicBlock>>,
-    ) {
+        root_node: Option<BasicBlock>,
+    ) -> IndexVec<DropIdx, Option<BasicBlock>> {
         // StorageDead statements can share blocks with each other and also with
         // a Drop terminator. We iterate through the drops to find which drops
         // need their own block.
@@ -342,8 +340,11 @@ impl DropTree {
             Own,
         }
 
+        let mut blocks = IndexVec::from_elem(None, &self.drops);
+        blocks[ROOT_NODE] = root_node;
+
         let mut needs_block = IndexVec::from_elem(Block::None, &self.drops);
-        if blocks[ROOT_NODE].is_some() {
+        if root_node.is_some() {
             // In some cases (such as drops for `continue`) the root node
             // already has a block. In this case, make sure that we don't
             // override it.
@@ -385,6 +386,8 @@ impl DropTree {
 
         debug!("assign_blocks: blocks = {:#?}", blocks);
         assert!(entry_points.is_empty());
+
+        blocks
     }
 
     fn link_blocks<'tcx>(
@@ -1574,10 +1577,7 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
         span: Span,
         continue_block: Option<BasicBlock>,
     ) -> Option<BlockAnd<()>> {
-        let mut blocks = IndexVec::from_elem(None, &drops.drops);
-        blocks[ROOT_NODE] = continue_block;
-
-        drops.build_mir::<ExitScopes>(&mut self.cfg, &mut blocks);
+        let blocks = drops.build_mir::<ExitScopes>(&mut self.cfg, continue_block);
         let is_coroutine = self.coroutine.is_some();
 
         // Link the exit drop tree to unwind drop tree.
@@ -1633,8 +1633,7 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
         let drops = &mut self.scopes.coroutine_drops;
         let cfg = &mut self.cfg;
         let fn_span = self.fn_span;
-        let mut blocks = IndexVec::from_elem(None, &drops.drops);
-        drops.build_mir::<CoroutineDrop>(cfg, &mut blocks);
+        let blocks = drops.build_mir::<CoroutineDrop>(cfg, None);
         if let Some(root_block) = blocks[ROOT_NODE] {
             cfg.terminate(
                 root_block,
@@ -1670,9 +1669,7 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
         fn_span: Span,
         resume_block: &mut Option<BasicBlock>,
     ) {
-        let mut blocks = IndexVec::from_elem(None, &drops.drops);
-        blocks[ROOT_NODE] = *resume_block;
-        drops.build_mir::<Unwind>(cfg, &mut blocks);
+        let blocks = drops.build_mir::<Unwind>(cfg, *resume_block);
         if let (None, Some(resume)) = (*resume_block, blocks[ROOT_NODE]) {
             cfg.terminate(resume, SourceInfo::outermost(fn_span), TerminatorKind::UnwindResume);
 

compiler/rustc_monomorphize/messages.ftl

@@ -63,4 +63,11 @@ monomorphize_symbol_already_defined = symbol `{$symbol}` is already defined
 monomorphize_unknown_cgu_collection_mode =
     unknown codegen-item collection mode '{$mode}', falling back to 'lazy' mode
 
+monomorphize_wasm_c_abi_transition =
+    this function {$is_call ->
+      [true] call
+      *[false] definition
+    } involves an argument of type `{$ty}` which is affected by the wasm ABI transition
+    .help = the "C" ABI Rust uses on wasm32-unknown-unknown will change to align with the standard "C" ABI for this target
+
 monomorphize_written_to_path = the full type name has been written to '{$path}'

compiler/rustc_monomorphize/src/errors.rs

@@ -103,3 +103,12 @@ pub(crate) struct AbiRequiredTargetFeature<'a> {
     /// Whether this is a problem at a call site or at a declaration.
     pub is_call: bool,
 }
+
+#[derive(LintDiagnostic)]
+#[diag(monomorphize_wasm_c_abi_transition)]
+#[help]
+pub(crate) struct WasmCAbiTransition<'a> {
+    pub ty: Ty<'a>,
+    /// Whether this is a problem at a call site or at a declaration.
+    pub is_call: bool,
+}

compiler/rustc_monomorphize/src/mono_checks/abi_check.rs

@@ -3,11 +3,13 @@
 use rustc_abi::{BackendRepr, RegKind};
 use rustc_hir::CRATE_HIR_ID;
 use rustc_middle::mir::{self, traversal};
-use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt};
-use rustc_session::lint::builtin::ABI_UNSUPPORTED_VECTOR_TYPES;
+use rustc_middle::ty::layout::LayoutCx;
+use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt, TypingEnv};
+use rustc_session::lint::builtin::{ABI_UNSUPPORTED_VECTOR_TYPES, WASM_C_ABI};
 use rustc_span::def_id::DefId;
 use rustc_span::{DUMMY_SP, Span, Symbol, sym};
-use rustc_target::callconv::{Conv, FnAbi, PassMode};
+use rustc_target::callconv::{ArgAbi, Conv, FnAbi, PassMode};
+use rustc_target::spec::{HasWasmCAbiOpt, WasmCAbi};
 
 use crate::errors;
 
@@ -26,13 +28,15 @@ fn uses_vector_registers(mode: &PassMode, repr: &BackendRepr) -> bool {
 /// for a certain function.
 /// `is_call` indicates whether this is a call-site check or a definition-site check;
 /// this is only relevant for the wording in the emitted error.
-fn do_check_abi<'tcx>(
+fn do_check_simd_vector_abi<'tcx>(
     tcx: TyCtxt<'tcx>,
     abi: &FnAbi<'tcx, Ty<'tcx>>,
     def_id: DefId,
     is_call: bool,
     span: impl Fn() -> Span,
 ) {
+    // We check this on all functions, including those using the "Rust" ABI.
+    // For the "Rust" ABI it would be a bug if the lint ever triggered, but better safe than sorry.
     let feature_def = tcx.sess.target.features_for_correct_vector_abi();
     let codegen_attrs = tcx.codegen_fn_attrs(def_id);
     let have_feature = |feat: Symbol| {
@@ -88,6 +92,61 @@ fn do_check_abi<'tcx>(
     }
 }
 
+/// Determines whether the given argument is passed the same way on the old and new wasm ABIs.
+fn wasm_abi_safe<'tcx>(tcx: TyCtxt<'tcx>, arg: &ArgAbi<'tcx, Ty<'tcx>>) -> bool {
+    if matches!(arg.layout.backend_repr, BackendRepr::Scalar(_)) {
+        return true;
+    }
+
+    // This matches `unwrap_trivial_aggregate` in the wasm ABI logic.
+    if arg.layout.is_aggregate() {
+        let cx = LayoutCx::new(tcx, TypingEnv::fully_monomorphized());
+        if let Some(unit) = arg.layout.homogeneous_aggregate(&cx).ok().and_then(|ha| ha.unit()) {
+            let size = arg.layout.size;
+            // Ensure there's just a single `unit` element in `arg`.
+            if unit.size == size {
+                return true;
+            }
+        }
+    }
+
+    false
+}
+
+/// Warns against usage of `extern "C"` on wasm32-unknown-unknown that is affected by the
+/// ABI transition.
+fn do_check_wasm_abi<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    abi: &FnAbi<'tcx, Ty<'tcx>>,
+    is_call: bool,
+    span: impl Fn() -> Span,
+) {
+    // Only proceed for `extern "C" fn` on wasm32-unknown-unknown (same check as what `adjust_for_foreign_abi` uses to call `compute_wasm_abi_info`),
+    // and only proceed if `wasm_c_abi_opt` indicates we should emit the lint.
+    if !(tcx.sess.target.arch == "wasm32"
+        && tcx.sess.target.os == "unknown"
+        && tcx.wasm_c_abi_opt() == WasmCAbi::Legacy { with_lint: true }
+        && abi.conv == Conv::C)
+    {
+        return;
+    }
+    // Warn against all types whose ABI will change. Return values are not affected by this change.
+    for arg_abi in abi.args.iter() {
+        if wasm_abi_safe(tcx, arg_abi) {
+            continue;
+        }
+        let span = span();
+        tcx.emit_node_span_lint(
+            WASM_C_ABI,
+            CRATE_HIR_ID,
+            span,
+            errors::WasmCAbiTransition { ty: arg_abi.layout.ty, is_call },
+        );
+        // Let's only warn once per function.
+        break;
+    }
+}
+
 /// Checks that the ABI of a given instance of a function does not contain vector-passed arguments
 /// or return values for which the corresponding target feature is not enabled.
 fn check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
@@ -98,13 +157,10 @@ fn check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
         // function.
         return;
     };
-    do_check_abi(
-        tcx,
-        abi,
-        instance.def_id(),
-        /*is_call*/ false,
-        || tcx.def_span(instance.def_id()),
-    )
+    do_check_simd_vector_abi(tcx, abi, instance.def_id(), /*is_call*/ false, || {
+        tcx.def_span(instance.def_id())
+    });
+    do_check_wasm_abi(tcx, abi, /*is_call*/ false, || tcx.def_span(instance.def_id()));
 }
 
 /// Checks that a call expression does not try to pass a vector-passed argument which requires a
@@ -141,7 +197,8 @@ fn check_call_site_abi<'tcx>(
         // ABI failed to compute; this will not get through codegen.
         return;
     };
-    do_check_abi(tcx, callee_abi, caller.def_id(), /*is_call*/ true, || span);
+    do_check_simd_vector_abi(tcx, callee_abi, caller.def_id(), /*is_call*/ true, || span);
+    do_check_wasm_abi(tcx, callee_abi, /*is_call*/ true, || span);
 }
 
 fn check_callees_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>, body: &mir::Body<'tcx>) {

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1115,7 +1115,6 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 }
             });
         } else {
-            #[allow(rustc::potential_query_instability)] // FIXME
             for ident in single_imports.iter().cloned() {
                 let result = self.r.maybe_resolve_ident_in_module(
                     ModuleOrUniformRoot::Module(module),