Auto merge of rust-lang#119927 - matthiaskrgr:rollup-885ws57, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#119587 (Varargs support for system ABI)
 - rust-lang#119891 (rename `reported_signature_mismatch` to reflect its use)
 - rust-lang#119894 (Allow `~const` on associated type bounds again)
 - rust-lang#119896 (Taint `_` placeholder types in trait impl method signatures)
 - rust-lang#119898 (Remove unused `ErrorReporting` variant from overflow handling)
 - rust-lang#119902 (fix typo in `fn()` docs)

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

Author: bors

Diff for: compiler/rustc_ast_passes/messages.ftl

@@ -232,6 +232,9 @@ ast_passes_tilde_const_disallowed = `~const` is not allowed here
     .trait = this trait is not a `#[const_trait]`, so it cannot have `~const` trait bounds
     .trait_impl = this impl is not `const`, so it cannot have `~const` trait bounds
     .impl = inherent impls cannot have `~const` trait bounds
+    .trait_assoc_ty = associated types in non-`#[const_trait]` traits cannot have `~const` trait bounds
+    .trait_impl_assoc_ty = associated types in non-const impls cannot have `~const` trait bounds
+    .inherent_assoc_ty = inherent associated types cannot have `~const` trait bounds
     .object = trait objects cannot have `~const` trait bounds
     .item = this item cannot have `~const` trait bounds
 

Diff for: compiler/rustc_ast_passes/src/ast_validation.rs

@@ -37,12 +37,17 @@ enum SelfSemantic {
 }
 
 /// What is the context that prevents using `~const`?
+// FIXME(effects): Consider getting rid of this in favor of `errors::TildeConstReason`, they're
+// almost identical. This gets rid of an abstraction layer which might be considered bad.
 enum DisallowTildeConstContext<'a> {
     TraitObject,
     Fn(FnKind<'a>),
     Trait(Span),
     TraitImpl(Span),
     Impl(Span),
+    TraitAssocTy(Span),
+    TraitImplAssocTy(Span),
+    InherentAssocTy(Span),
     Item,
 }
 
@@ -316,6 +321,7 @@ impl<'a> AstValidator<'a> {
                 constness: Const::No,
                 polarity: ImplPolarity::Positive,
                 trait_ref,
+                ..
             } = parent
         {
             Some(trait_ref.path.span.shrink_to_lo())
@@ -1286,6 +1292,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                             // suggestion for moving such bounds to the assoc const fns if available.
                             errors::TildeConstReason::Impl { span }
                         }
+                        &DisallowTildeConstContext::TraitAssocTy(span) => {
+                            errors::TildeConstReason::TraitAssocTy { span }
+                        }
+                        &DisallowTildeConstContext::TraitImplAssocTy(span) => {
+                            errors::TildeConstReason::TraitImplAssocTy { span }
+                        }
+                        &DisallowTildeConstContext::InherentAssocTy(span) => {
+                            errors::TildeConstReason::InherentAssocTy { span }
+                        }
                         DisallowTildeConstContext::TraitObject => {
                             errors::TildeConstReason::TraitObject
                         }
@@ -1483,13 +1498,12 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             self.check_item_named(item.ident, "const");
         }
 
+        let parent_is_const =
+            self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+
         match &item.kind {
             AssocItemKind::Fn(box Fn { sig, generics, body, .. })
-                if self
-                    .outer_trait_or_trait_impl
-                    .as_ref()
-                    .and_then(TraitOrTraitImpl::constness)
-                    .is_some()
+                if parent_is_const
                     || ctxt == AssocCtxt::Trait
                     || matches!(sig.header.constness, Const::Yes(_)) =>
             {
@@ -1505,6 +1519,20 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 );
                 self.visit_fn(kind, item.span, item.id);
             }
+            AssocItemKind::Type(_) => {
+                let disallowed = (!parent_is_const).then(|| match self.outer_trait_or_trait_impl {
+                    Some(TraitOrTraitImpl::Trait { .. }) => {
+                        DisallowTildeConstContext::TraitAssocTy(item.span)
+                    }
+                    Some(TraitOrTraitImpl::TraitImpl { .. }) => {
+                        DisallowTildeConstContext::TraitImplAssocTy(item.span)
+                    }
+                    None => DisallowTildeConstContext::InherentAssocTy(item.span),
+                });
+                self.with_tilde_const(disallowed, |this| {
+                    this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+                })
+            }
             _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
         }
     }

Diff for: compiler/rustc_ast_passes/src/errors.rs

@@ -565,6 +565,8 @@ pub struct ConstBoundTraitObject {
     pub span: Span,
 }
 
+// FIXME(effects): Consider making the note/reason the message of the diagnostic.
+// FIXME(effects): Provide structured suggestions (e.g., add `const` / `#[const_trait]` here).
 #[derive(Diagnostic)]
 #[diag(ast_passes_tilde_const_disallowed)]
 pub struct TildeConstDisallowed {
@@ -598,6 +600,21 @@ pub enum TildeConstReason {
         #[primary_span]
         span: Span,
     },
+    #[note(ast_passes_trait_assoc_ty)]
+    TraitAssocTy {
+        #[primary_span]
+        span: Span,
+    },
+    #[note(ast_passes_trait_impl_assoc_ty)]
+    TraitImplAssocTy {
+        #[primary_span]
+        span: Span,
+    },
+    #[note(ast_passes_inherent_assoc_ty)]
+    InherentAssocTy {
+        #[primary_span]
+        span: Span,
+    },
     #[note(ast_passes_object)]
     TraitObject,
     #[note(ast_passes_item)]

Diff for: compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2659,7 +2659,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
                     {
                         infer_replacements.push((a.span, suggested_ty.to_string()));
-                        return suggested_ty;
+                        return Ty::new_error_with_message(
+                            self.tcx(),
+                            a.span,
+                            suggested_ty.to_string(),
+                        );
                     }
                 }
 
@@ -2677,7 +2681,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
                 {
                     infer_replacements.push((output.span, suggested_ty.to_string()));
-                    suggested_ty
+                    Ty::new_error_with_message(self.tcx(), output.span, suggested_ty.to_string())
                 } else {
                     visitor.visit_ty(output);
                     self.ast_ty_to_ty(output)

Diff for: compiler/rustc_hir_analysis/src/lib.rs

@@ -116,7 +116,8 @@ use rustc_hir::def::DefKind;
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
-    const CONVENTIONS_UNSTABLE: &str = "`C`, `cdecl`, `aapcs`, `win64`, `sysv64` or `efiapi`";
+    const CONVENTIONS_UNSTABLE: &str =
+        "`C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`";
     const CONVENTIONS_STABLE: &str = "`C` or `cdecl`";
     const UNSTABLE_EXPLAIN: &str =
         "using calling conventions other than `C` or `cdecl` for varargs functions is unstable";

Diff for: compiler/rustc_infer/src/infer/at.rs

@@ -84,7 +84,7 @@ impl<'tcx> InferCtxt<'tcx> {
             selection_cache: self.selection_cache.clone(),
             evaluation_cache: self.evaluation_cache.clone(),
             reported_trait_errors: self.reported_trait_errors.clone(),
-            reported_closure_mismatch: self.reported_closure_mismatch.clone(),
+            reported_signature_mismatch: self.reported_signature_mismatch.clone(),
             tainted_by_errors: self.tainted_by_errors.clone(),
             err_count_on_creation: self.err_count_on_creation,
             universe: self.universe.clone(),

Diff for: compiler/rustc_infer/src/infer/mod.rs

@@ -278,7 +278,7 @@ pub struct InferCtxt<'tcx> {
     /// avoid reporting the same error twice.
     pub reported_trait_errors: RefCell<FxIndexMap<Span, Vec<ty::Predicate<'tcx>>>>,
 
-    pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
+    pub reported_signature_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
 
     /// When an error occurs, we want to avoid reporting "derived"
     /// errors that are due to this original failure. Normally, we
@@ -702,7 +702,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             selection_cache: Default::default(),
             evaluation_cache: Default::default(),
             reported_trait_errors: Default::default(),
-            reported_closure_mismatch: Default::default(),
+            reported_signature_mismatch: Default::default(),
             tainted_by_errors: Cell::new(None),
             err_count_on_creation: tcx.dcx().err_count(),
             universe: Cell::new(ty::UniverseIndex::ROOT),

Diff for: compiler/rustc_metadata/src/native_libs.rs

@@ -520,11 +520,23 @@ impl<'tcx> Collector<'tcx> {
     ) -> DllImport {
         let span = self.tcx.def_span(item);
 
+        // this logic is similar to `Target::adjust_abi` (in rustc_target/src/spec/mod.rs) but errors on unsupported inputs
         let calling_convention = if self.tcx.sess.target.arch == "x86" {
             match abi {
                 Abi::C { .. } | Abi::Cdecl { .. } => DllCallingConvention::C,
-                Abi::Stdcall { .. } | Abi::System { .. } => {
-                    DllCallingConvention::Stdcall(self.i686_arg_list_size(item))
+                Abi::Stdcall { .. } => DllCallingConvention::Stdcall(self.i686_arg_list_size(item)),
+                // On Windows, `extern "system"` behaves like msvc's `__stdcall`.
+                // `__stdcall` only applies on x86 and on non-variadic functions:
+                // https://learn.microsoft.com/en-us/cpp/cpp/stdcall?view=msvc-170
+                Abi::System { .. } => {
+                    let c_variadic =
+                        self.tcx.type_of(item).instantiate_identity().fn_sig(self.tcx).c_variadic();
+
+                    if c_variadic {
+                        DllCallingConvention::C
+                    } else {
+                        DllCallingConvention::Stdcall(self.i686_arg_list_size(item))
+                    }
                 }
                 Abi::Fastcall { .. } => {
                     DllCallingConvention::Fastcall(self.i686_arg_list_size(item))

Diff for: compiler/rustc_middle/src/traits/mod.rs

@@ -611,9 +611,6 @@ pub enum SelectionError<'tcx> {
     NotConstEvaluatable(NotConstEvaluatable),
     /// Exceeded the recursion depth during type projection.
     Overflow(OverflowError),
-    /// Signaling that an error has already been emitted, to avoid
-    /// multiple errors being shown.
-    ErrorReporting,
     /// Computing an opaque type's hidden type caused an error (e.g. a cycle error).
     /// We can thus not know whether the hidden type implements an auto trait, so
     /// we should not presume anything about it.

Diff for: compiler/rustc_middle/src/traits/select.rs

@@ -302,7 +302,6 @@ impl EvaluationResult {
 pub enum OverflowError {
     Error(ErrorGuaranteed),
     Canonical,
-    ErrorReporting,
 }
 
 impl From<ErrorGuaranteed> for OverflowError {
@@ -318,7 +317,6 @@ impl<'tcx> From<OverflowError> for SelectionError<'tcx> {
         match overflow_error {
             OverflowError::Error(e) => SelectionError::Overflow(OverflowError::Error(e)),
             OverflowError::Canonical => SelectionError::Overflow(OverflowError::Canonical),
-            OverflowError::ErrorReporting => SelectionError::ErrorReporting,
         }
     }
 }

Diff for: compiler/rustc_target/src/abi/call/mod.rs

@@ -840,7 +840,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "sparc" => sparc::compute_abi_info(cx, self),
             "sparc64" => sparc64::compute_abi_info(cx, self),
             "nvptx64" => {
-                if cx.target_spec().adjust_abi(abi) == spec::abi::Abi::PtxKernel {
+                if cx.target_spec().adjust_abi(abi, self.c_variadic) == spec::abi::Abi::PtxKernel {
                     nvptx64::compute_ptx_kernel_abi_info(cx, self)
                 } else {
                     nvptx64::compute_abi_info(self)
@@ -849,7 +849,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "hexagon" => hexagon::compute_abi_info(self),
             "riscv32" | "riscv64" => riscv::compute_abi_info(cx, self),
             "wasm32" | "wasm64" => {
-                if cx.target_spec().adjust_abi(abi) == spec::abi::Abi::Wasm {
+                if cx.target_spec().adjust_abi(abi, self.c_variadic) == spec::abi::Abi::Wasm {
                     wasm::compute_wasm_abi_info(self)
                 } else {
                     wasm::compute_c_abi_info(cx, self)

Diff for: compiler/rustc_target/src/spec/abi/mod.rs

@@ -70,15 +70,16 @@ impl Abi {
         // * 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 falls back to C for functions with varargs.
         //
         // * 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.
-        // * System can become Stdcall, so is also a no-no.
         // * Other calling conventions are related to hardware or the compiler itself.
         match self {
             Self::C { .. }
             | Self::Cdecl { .. }
+            | Self::System { .. }
             | Self::Aapcs { .. }
             | Self::Win64 { .. }
             | Self::SysV64 { .. }

Diff for: compiler/rustc_target/src/spec/mod.rs

@@ -2401,10 +2401,14 @@ impl DerefMut for Target {
 
 impl Target {
     /// Given a function ABI, turn it into the correct ABI for this target.
-    pub fn adjust_abi(&self, abi: Abi) -> Abi {
+    pub fn adjust_abi(&self, abi: Abi, c_variadic: bool) -> Abi {
         match abi {
             Abi::C { .. } => self.default_adjusted_cabi.unwrap_or(abi),
-            Abi::System { unwind } if self.is_like_windows && self.arch == "x86" => {
+
+            // On Windows, `extern "system"` behaves like msvc's `__stdcall`.
+            // `__stdcall` only applies on x86 and on non-variadic functions:
+            // https://learn.microsoft.com/en-us/cpp/cpp/stdcall?view=msvc-170
+            Abi::System { unwind } if self.is_like_windows && self.arch == "x86" && !c_variadic => {
                 Abi::Stdcall { unwind }
             }
             Abi::System { unwind } => Abi::C { unwind },

Diff for: compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -947,9 +947,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             Overflow(_) => {
                 bug!("overflow should be handled before the `report_selection_error` path");
             }
-            SelectionError::ErrorReporting => {
-                bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
-            }
         };
 
         self.note_obligation_cause(&mut err, &obligation);
@@ -3459,14 +3456,12 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let found_node = found_did.and_then(|did| self.tcx.hir().get_if_local(did));
         let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
 
-        if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
+        if !self.reported_signature_mismatch.borrow_mut().insert((span, found_span)) {
             // We check closures twice, with obligations flowing in different directions,
             // but we want to complain about them only once.
             return None;
         }
 
-        self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
-
         let mut not_tupled = false;
 
         let found = match found_trait_ref.skip_binder().args.type_at(1).kind() {

Diff for: compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -116,11 +116,9 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                             r,
                         )
                     }
-                    OverflowError::ErrorReporting => EvaluationResult::EvaluatedToErr,
                     OverflowError::Error(_) => EvaluationResult::EvaluatedToErr,
                 })
             }
-            Err(OverflowError::ErrorReporting) => EvaluationResult::EvaluatedToErr,
             Err(OverflowError::Error(_)) => EvaluationResult::EvaluatedToErr,
         }
     }

Diff for: compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -14,9 +14,9 @@ use super::util;
 use super::util::closure_trait_ref_and_return_type;
 use super::wf;
 use super::{
-    ErrorReporting, ImplDerivedObligation, ImplDerivedObligationCause, Normalized, Obligation,
-    ObligationCause, ObligationCauseCode, Overflow, PolyTraitObligation, PredicateObligation,
-    Selection, SelectionError, SelectionResult, TraitQueryMode,
+    ImplDerivedObligation, ImplDerivedObligationCause, Normalized, Obligation, ObligationCause,
+    ObligationCauseCode, Overflow, PolyTraitObligation, PredicateObligation, Selection,
+    SelectionError, SelectionResult, TraitQueryMode,
 };
 
 use crate::infer::{InferCtxt, InferOk, TypeFreshener};
@@ -496,7 +496,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
                 Ok(_) => Ok(None),
                 Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
-                Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
                 Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
             })
             .flat_map(Result::transpose)
@@ -1233,7 +1232,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             Ok(Some(c)) => self.evaluate_candidate(stack, &c),
             Ok(None) => Ok(EvaluatedToAmbig),
             Err(Overflow(OverflowError::Canonical)) => Err(OverflowError::Canonical),
-            Err(ErrorReporting) => Err(OverflowError::ErrorReporting),
             Err(..) => Ok(EvaluatedToErr),
         }
     }

Diff for: compiler/rustc_ty_utils/src/abi.rs

@@ -228,9 +228,9 @@ fn fn_sig_for_fn_abi<'tcx>(
 }
 
 #[inline]
-fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi) -> Conv {
+fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi, c_variadic: bool) -> Conv {
     use rustc_target::spec::abi::Abi::*;
-    match tcx.sess.target.adjust_abi(abi) {
+    match tcx.sess.target.adjust_abi(abi, c_variadic) {
         RustIntrinsic | PlatformIntrinsic | Rust | RustCall => Conv::Rust,
 
         // This is intentionally not using `Conv::Cold`, as that has to preserve
@@ -488,7 +488,7 @@ fn fn_abi_new_uncached<'tcx>(
 ) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, &'tcx FnAbiError<'tcx>> {
     let sig = cx.tcx.normalize_erasing_late_bound_regions(cx.param_env, sig);
 
-    let conv = conv_from_spec_abi(cx.tcx(), sig.abi);
+    let conv = conv_from_spec_abi(cx.tcx(), sig.abi, sig.c_variadic);
 
     let mut inputs = sig.inputs();
     let extra_args = if sig.abi == RustCall {

Diff for: library/core/src/primitive_docs.rs

@@ -1605,9 +1605,9 @@ mod prim_ref {}
 /// type in the function pointer to the type at the function declaration, and the return value is
 /// [`transmute`d][mem::transmute] from the type in the declaration to the type in the
 /// pointer. All the usual caveats and concerns around transmutation apply; for instance, if the
-/// function expects a `NonNullI32` and the function pointer uses the ABI-compatible type
-/// `Option<NonNullI32>`, and the value used for the argument is `None`, then this call is Undefined
-/// Behavior since transmuting `None::<NonNullI32>` to `NonNullI32` violates the non-null
+/// function expects a `NonZeroI32` and the function pointer uses the ABI-compatible type
+/// `Option<NonZeroI32>`, and the value used for the argument is `None`, then this call is Undefined
+/// Behavior since transmuting `None::<NonZeroI32>` to `NonZeroI32` violates the non-zero
 /// requirement.
 ///
 /// #### Requirements concerning target features

Diff for: src/librustdoc/clean/blanket_impl.rs

@@ -81,7 +81,6 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                     match infcx.evaluate_obligation(&obligation) {
                         Ok(eval_result) if eval_result.may_apply() => {}
                         Err(traits::OverflowError::Canonical) => {}
-                        Err(traits::OverflowError::ErrorReporting) => {}
                         _ => continue 'blanket_impls,
                     }
                 }