rustc_skip_during_method_dispatch: decouple receiver & edition

Author: GrigorenkoPV

Cargo.lock

@@ -3745,6 +3745,7 @@ dependencies = [
  "rustc_trait_selection",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -969,11 +969,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
     ),
     rustc_attr!(
-        rustc_skip_during_method_dispatch, Normal, template!(List: "array, boxed_slice"), WarnFollowing,
-        EncodeCrossCrate::No,
+        rustc_skip_during_method_dispatch, Normal,
+        template!(List: r#"receiver = "name", before_edition = "N""#),
+        DuplicatesOk, EncodeCrossCrate::No,
         "the `#[rustc_skip_during_method_dispatch]` attribute is used to exclude a trait \
-        from method dispatch when the receiver is of the following type, for compatibility in \
-        editions < 2021 (array) or editions < 2024 (boxed_slice)."
+        from method dispatch when the receiver is of the type `receiver`, \
+        for compatibility in editions < `before_edition`."
     ),
     rustc_attr!(
         rustc_must_implement_one_of, Normal, template!(List: "function1, function2, ..."),

compiler/rustc_hir_analysis/Cargo.toml

@@ -30,5 +30,6 @@ rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_type_ir = { path = "../rustc_type_ir" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
+thin-vec = "0.2.12"
 tracing = "0.1"
 # tidy-alphabetical-end

compiler/rustc_hir_analysis/src/collect.rs

@@ -18,7 +18,9 @@ use std::cell::Cell;
 use std::iter;
 use std::ops::Bound;
 
-use rustc_ast::Recovered;
+use rustc_ast::{
+    self as ast, Attribute, MetaItem, MetaItemKind, MetaItemLit, NestedMetaItem, Recovered,
+};
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::unord::UnordMap;
@@ -33,15 +35,18 @@ use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::query::Providers;
+use rustc_middle::ty::trait_def::GatedReceiver;
 use rustc_middle::ty::util::{Discr, IntTypeExt};
 use rustc_middle::ty::{self, AdtKind, Const, IsSuggestable, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
+use rustc_span::edition::Edition;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi;
 use rustc_trait_selection::error_reporting::traits::suggestions::NextTypeParamName;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::ObligationCtxt;
+use thin_vec::ThinVec;
 use tracing::{debug, instrument};
 
 use crate::check::intrinsic::intrinsic_operation_unsafety;
@@ -1205,6 +1210,60 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
     tcx.mk_adt_def(def_id.to_def_id(), kind, variants, repr, is_anonymous)
 }
 
+fn parse_rustc_skip_during_method_dispatch(
+    dcx: DiagCtxtHandle<'_>,
+    attr: &Attribute,
+) -> Result<(GatedReceiver, Edition), ErrorGuaranteed> {
+    debug_assert!(attr.has_name(sym::rustc_skip_during_method_dispatch));
+    let mut receiver: Option<GatedReceiver> = None;
+    let mut before: Option<Edition> = None;
+    for arg in attr.meta_item_list().unwrap_or_default() {
+        let arg_span = arg.span();
+        if let NestedMetaItem::MetaItem(MetaItem {
+            path: ast::Path { segments, span: key_span, .. },
+            kind: MetaItemKind::NameValue(MetaItemLit { symbol: value, span: value_span, .. }),
+            ..
+        }) = arg
+            && let [ast::PathSegment { ident: key, .. }] = segments.as_slice()
+        {
+            match key.as_str() {
+                "receiver" => {
+                    if receiver
+                        .replace(value.as_str().parse().map_err(|()| {
+                            dcx.span_err(value_span, "Expected `array` or `boxed_slice`")
+                        })?)
+                        .is_some()
+                    {
+                        Err(dcx.span_err(arg_span, "`receiver` should be specified only once"))?
+                    }
+                }
+
+                "before" => {
+                    if before
+                        .replace(
+                            value.as_str().parse().map_err(|()| {
+                                dcx.span_err(value_span, "Could not parse edition")
+                            })?,
+                        )
+                        .is_some()
+                    {
+                        Err(dcx.span_err(arg_span, "`before` should be specified only once"))?
+                    }
+                }
+                _ => Err(dcx.span_err(key_span, "Expected either `receiver` or `before`"))?,
+            }
+        } else {
+            Err(dcx
+                .span_err(arg_span, "Expected either `receiver = \"...\"` or `before = \"...\"`"))?
+        };
+    }
+
+    Ok((
+        receiver.ok_or_else(|| dcx.span_err(attr.span, "Missing `receiver`"))?,
+        before.ok_or_else(|| dcx.span_err(attr.span, "Missing `before`"))?,
+    ))
+}
+
 fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
     let item = tcx.hir().expect_item(def_id);
 
@@ -1234,20 +1293,19 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
     let rustc_coinductive = tcx.has_attr(def_id, sym::rustc_coinductive);
     let is_fundamental = tcx.has_attr(def_id, sym::fundamental);
 
-    // FIXME: We could probably do way better attribute validation here.
-    let mut skip_array_during_method_dispatch = false;
-    let mut skip_boxed_slice_during_method_dispatch = false;
+    let mut skip_during_method_dispatch: ThinVec<(GatedReceiver, Edition)> = ThinVec::new();
     for attr in tcx.get_attrs(def_id, sym::rustc_skip_during_method_dispatch) {
-        if let Some(lst) = attr.meta_item_list() {
-            for item in lst {
-                if let Some(ident) = item.ident() {
-                    match ident.as_str() {
-                        "array" => skip_array_during_method_dispatch = true,
-                        "boxed_slice" => skip_boxed_slice_during_method_dispatch = true,
-                        _ => (),
-                    }
-                }
+        if let Ok(parsed) = parse_rustc_skip_during_method_dispatch(tcx.dcx(), attr) {
+            if skip_during_method_dispatch.iter().any(|prev| prev.0 == parsed.0) {
+                tcx.dcx().span_err(
+                    attr.span,
+                    format!(
+                        "Duplicate `#[rustc_skip_during_method_dispatch(receiver = \"{}\")]`",
+                        parsed.0
+                    ),
+                );
             }
+            skip_during_method_dispatch.push(parsed);
         }
     }
 
@@ -1386,8 +1444,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
         is_marker,
         is_coinductive: rustc_coinductive || is_auto,
         is_fundamental,
-        skip_array_during_method_dispatch,
-        skip_boxed_slice_during_method_dispatch,
+        skip_during_method_dispatch,
         specialization_kind,
         must_implement_one_of,
         implement_via_object,

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -1473,24 +1473,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     ));
                 }
                 TraitCandidate(poly_trait_ref) => {
-                    // Some trait methods are excluded for arrays before 2021.
-                    // (`array.into_iter()` wants a slice iterator for compatibility.)
+                    // Handle `#[rustc_skip_during_method_dispatch]`
                     if let Some(method_name) = self.method_name {
-                        if self_ty.is_array() && !method_name.span.at_least_rust_2021() {
-                            let trait_def = self.tcx.trait_def(poly_trait_ref.def_id());
-                            if trait_def.skip_array_during_method_dispatch {
-                                return ProbeResult::NoMatch;
-                            }
-                        }
-
-                        // Some trait methods are excluded for boxed slices before 2024.
-                        // (`boxed_slice.into_iter()` wants a slice iterator for compatibility.)
-                        if self_ty.is_box()
-                            && self_ty.boxed_ty().is_slice()
-                            && !method_name.span.at_least_rust_2024()
-                        {
-                            let trait_def = self.tcx.trait_def(poly_trait_ref.def_id());
-                            if trait_def.skip_boxed_slice_during_method_dispatch {
+                        let trait_def = self.tcx.trait_def(poly_trait_ref.def_id());
+                        for &(receiver, edition) in &trait_def.skip_during_method_dispatch {
+                            if method_name.span.edition() < edition && receiver.matches(self_ty) {
                                 return ProbeResult::NoMatch;
                             }
                         }

compiler/rustc_middle/src/ty/trait_def.rs

@@ -1,18 +1,63 @@
 use std::iter;
+use std::str::FromStr;
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_macros::{Decodable, Encodable, HashStable};
+use rustc_span::edition::Edition;
+use thin_vec::ThinVec;
 use tracing::debug;
 
 use crate::query::LocalCrate;
 use crate::traits::specialization_graph;
 use crate::ty::fast_reject::{self, SimplifiedType, TreatParams};
 use crate::ty::{Ident, Ty, TyCtxt};
 
+/// The `receiver` from the `#[rustc_skip_during_method_dispatch]` attribute.
+/// Effectively represents a set of types.
+#[derive(Copy, Clone, PartialEq, Eq, HashStable, Encodable, Decodable)]
+pub enum GatedReceiver {
+    Array,
+    BoxedSlice,
+}
+
+impl GatedReceiver {
+    #[must_use]
+    /// Checks whether a method call with a receiver of the given type
+    /// falls under `#[rustc_skip_during_method_dispatch]`'s jurisdiction
+    /// and should be dispatched only past a certain edition.
+    pub fn matches(self, ty: Ty<'_>) -> bool {
+        match self {
+            GatedReceiver::Array => ty.is_array(),
+            GatedReceiver::BoxedSlice => ty.is_box() && ty.boxed_ty().is_slice(),
+        }
+    }
+}
+
+impl std::fmt::Display for GatedReceiver {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(match self {
+            Self::Array => "array",
+            Self::BoxedSlice => "boxed_slice",
+        })
+    }
+}
+
+impl FromStr for GatedReceiver {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "array" => Ok(Self::Array),
+            "boxed_slice" => Ok(Self::BoxedSlice),
+            _ => Err(()),
+        }
+    }
+}
+
 /// A trait's definition with type information.
 #[derive(HashStable, Encodable, Decodable)]
 pub struct TraitDef {
@@ -50,15 +95,10 @@ pub struct TraitDef {
     /// added in the future.
     pub is_fundamental: bool,
 
-    /// If `true`, then this trait has the `#[rustc_skip_during_method_dispatch(array)]`
-    /// attribute, indicating that editions before 2021 should not consider this trait
-    /// during method dispatch if the receiver is an array.
-    pub skip_array_during_method_dispatch: bool,
-
-    /// If `true`, then this trait has the `#[rustc_skip_during_method_dispatch(boxed_slice)]`
-    /// attribute, indicating that editions before 2024 should not consider this trait
-    /// during method dispatch if the receiver is a boxed slice.
-    pub skip_boxed_slice_during_method_dispatch: bool,
+    /// If not empty, then this trait has the `#[rustc_skip_during_method_dispatch]` attribute,
+    /// indicating it should not be considered during method dispatch
+    /// for certain receivers before a specific edition.
+    pub skip_during_method_dispatch: ThinVec<(GatedReceiver, Edition)>,
 
     /// Used to determine whether the standard library is allowed to specialize
     /// on this trait.

compiler/rustc_smir/src/rustc_smir/convert/ty.rs

@@ -1,7 +1,9 @@
 //! Conversion of internal Rust compiler `ty` items to stable ones.
 
+use rustc_middle::ty::trait_def::GatedReceiver;
 use rustc_middle::ty::Ty;
 use rustc_middle::{mir, ty};
+use rustc_span::edition::Edition;
 use stable_mir::ty::{
     AdtKind, FloatTy, GenericArgs, GenericParamDef, IntTy, Region, RigidTy, TyKind, UintTy,
 };
@@ -532,6 +534,30 @@ impl<'tcx> Stable<'tcx> for ty::trait_def::TraitSpecializationKind {
     }
 }
 
+impl Stable<'_> for Edition {
+    type T = stable_mir::edition::Edition;
+
+    fn stable(&self, _: &mut Tables<'_>) -> Self::T {
+        match self {
+            Self::Edition2015 => Self::T::Edition2015,
+            Self::Edition2018 => Self::T::Edition2018,
+            Self::Edition2021 => Self::T::Edition2021,
+            Self::Edition2024 => Self::T::Edition2024,
+        }
+    }
+}
+
+impl Stable<'_> for GatedReceiver {
+    type T = stable_mir::ty::GatedReceiver;
+
+    fn stable(&self, _: &mut Tables<'_>) -> Self::T {
+        match self {
+            Self::Array => Self::T::Array,
+            Self::BoxedSlice => Self::T::BoxedSlice,
+        }
+    }
+}
+
 impl<'tcx> Stable<'tcx> for ty::TraitDef {
     type T = stable_mir::ty::TraitDecl;
     fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
@@ -545,8 +571,11 @@ impl<'tcx> Stable<'tcx> for ty::TraitDef {
             has_auto_impl: self.has_auto_impl,
             is_marker: self.is_marker,
             is_coinductive: self.is_coinductive,
-            skip_array_during_method_dispatch: self.skip_array_during_method_dispatch,
-            skip_boxed_slice_during_method_dispatch: self.skip_boxed_slice_during_method_dispatch,
+            skip_during_method_dispatch: self
+                .skip_during_method_dispatch
+                .iter()
+                .map(|x| x.stable(tables))
+                .collect(),
             specialization_kind: self.specialization_kind.stable(tables),
             must_implement_one_of: self
                 .must_implement_one_of

compiler/stable_mir/src/edition.rs

@@ -0,0 +1,10 @@
+use serde::Serialize;
+
+#[non_exhaustive]
+#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
+pub enum Edition {
+    Edition2015,
+    Edition2018,
+    Edition2021,
+    Edition2024,
+}

compiler/stable_mir/src/lib.rs

@@ -32,6 +32,7 @@ pub mod abi;
 #[macro_use]
 pub mod crate_def;
 pub mod compiler_interface;
+pub mod edition;
 #[macro_use]
 pub mod error;
 pub mod mir;

compiler/stable_mir/src/ty.rs

@@ -7,6 +7,7 @@ use super::mir::{Body, Mutability, Safety};
 use super::{with, DefId, Error, Symbol};
 use crate::abi::{FnAbi, Layout};
 use crate::crate_def::{CrateDef, CrateDefType};
+use crate::edition::Edition;
 use crate::mir::alloc::{read_target_int, read_target_uint, AllocId};
 use crate::mir::mono::StaticDef;
 use crate::target::MachineInfo;
@@ -1317,6 +1318,13 @@ pub enum TraitSpecializationKind {
     AlwaysApplicable,
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize)]
+#[non_exhaustive]
+pub enum GatedReceiver {
+    Array,
+    BoxedSlice,
+}
+
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
 pub struct TraitDecl {
     pub def_id: TraitDef,
@@ -1325,8 +1333,7 @@ pub struct TraitDecl {
     pub has_auto_impl: bool,
     pub is_marker: bool,
     pub is_coinductive: bool,
-    pub skip_array_during_method_dispatch: bool,
-    pub skip_boxed_slice_during_method_dispatch: bool,
+    pub skip_during_method_dispatch: Vec<(GatedReceiver, Edition)>,
     pub specialization_kind: TraitSpecializationKind,
     pub must_implement_one_of: Option<Vec<Ident>>,
     pub implement_via_object: bool,

library/alloc/src/boxed.rs

@@ -2304,7 +2304,7 @@ impl<'a, I, A: Allocator> !Iterator for &'a Box<[I], A> {}
 #[stable(feature = "boxed_slice_into_iter", since = "1.80.0")]
 impl<'a, I, A: Allocator> !Iterator for &'a mut Box<[I], A> {}
 
-// Note: the `#[rustc_skip_during_method_dispatch(boxed_slice)]` on `trait IntoIterator`
+// Note: the `rustc_skip_during_method_dispatch` attribute on `trait IntoIterator`
 // hides this implementation from explicit `.into_iter()` calls on editions < 2024,
 // so those calls will still resolve to the slice implementation, by reference.
 #[stable(feature = "boxed_slice_into_iter", since = "1.80.0")]