Rollup merge of #139108 - Nadrieril:simplify-expandedconstant, r=oli-obk

Simplify `thir::PatKind::ExpandedConstant`

I made it a bit less ad-hoc. In particular, I removed `is_inline: bool` that was just caching the output of `tcx.def_kind(def_id)`. This makes inline consts a tiny bit less special in patterns.

r? `@oli-obk`

cc `@Zalathar`

Author: Zalathar

compiler/rustc_middle/src/thir.rs

@@ -815,23 +815,17 @@ pub enum PatKind<'tcx> {
     },
 
     /// Pattern obtained by converting a constant (inline or named) to its pattern
-    /// representation using `const_to_pat`.
+    /// representation using `const_to_pat`. This is used for unsafety checking.
     ExpandedConstant {
-        /// [DefId] of the constant, we need this so that we have a
-        /// reference that can be used by unsafety checking to visit nested
-        /// unevaluated constants and for diagnostics. If the `DefId` doesn't
-        /// correspond to a local crate, it points at the `const` item.
+        /// [DefId] of the constant item.
         def_id: DefId,
-        /// If `false`, then `def_id` points at a `const` item, otherwise it
-        /// corresponds to a local inline const.
-        is_inline: bool,
-        /// If the inline constant is used in a range pattern, this subpattern
-        /// represents the range (if both ends are inline constants, there will
-        /// be multiple InlineConstant wrappers).
+        /// The pattern that the constant lowered to.
         ///
-        /// Otherwise, the actual pattern that the constant lowered to. As with
-        /// other constants, inline constants are matched structurally where
-        /// possible.
+        /// HACK: we need to keep the `DefId` of inline constants around for unsafety checking;
+        /// therefore when a range pattern contains inline constants, we re-wrap the range pattern
+        /// with the `ExpandedConstant` nodes that correspond to the range endpoints. Hence
+        /// `subpattern` may actually be a range pattern, and `def_id` be the constant for one of
+        /// its endpoints.
         subpattern: Box<Pat<'tcx>>,
     },
 

compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs

@@ -145,7 +145,7 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
             let arm = &self.thir[*arm];
             let value = match arm.pattern.kind {
                 PatKind::Constant { value } => value,
-                PatKind::ExpandedConstant { ref subpattern, def_id: _, is_inline: false }
+                PatKind::ExpandedConstant { ref subpattern, def_id: _ }
                     if let PatKind::Constant { value } = subpattern.kind =>
                 {
                     value

compiler/rustc_mir_build/src/builder/matches/match_pair.rs

@@ -201,39 +201,10 @@ impl<'tcx> MatchPairTree<'tcx> {
                 None
             }
 
-            PatKind::ExpandedConstant { subpattern: ref pattern, def_id: _, is_inline: false } => {
+            PatKind::ExpandedConstant { subpattern: ref pattern, .. } => {
                 MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
                 None
             }
-            PatKind::ExpandedConstant { subpattern: ref pattern, def_id, is_inline: true } => {
-                MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
-
-                // Apply a type ascription for the inline constant to the value at `match_pair.place`
-                if let Some(source) = place {
-                    let span = pattern.span;
-                    let parent_id = cx.tcx.typeck_root_def_id(cx.def_id.to_def_id());
-                    let args = ty::InlineConstArgs::new(
-                        cx.tcx,
-                        ty::InlineConstArgsParts {
-                            parent_args: ty::GenericArgs::identity_for_item(cx.tcx, parent_id),
-                            ty: cx.infcx.next_ty_var(span),
-                        },
-                    )
-                    .args;
-                    let user_ty = cx.infcx.canonicalize_user_type_annotation(ty::UserType::new(
-                        ty::UserTypeKind::TypeOf(def_id, ty::UserArgs { args, user_self_ty: None }),
-                    ));
-                    let annotation = ty::CanonicalUserTypeAnnotation {
-                        inferred_ty: pattern.ty,
-                        span,
-                        user_ty: Box::new(user_ty),
-                    };
-                    let variance = ty::Contravariant;
-                    extra_data.ascriptions.push(super::Ascription { annotation, source, variance });
-                }
-
-                None
-            }
 
             PatKind::Array { ref prefix, ref slice, ref suffix } => {
                 cx.prefix_slice_suffix(

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -404,9 +404,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 visit::walk_pat(self, pat);
                 self.inside_adt = old_inside_adt;
             }
-            PatKind::ExpandedConstant { def_id, is_inline, .. } => {
+            PatKind::ExpandedConstant { def_id, .. } => {
                 if let Some(def) = def_id.as_local()
-                    && *is_inline
+                    && matches!(self.tcx.def_kind(def_id), DefKind::InlineConst)
                 {
                     self.visit_inner_body(def);
                 }

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -676,7 +676,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             unpeeled_pat = subpattern;
         }
 
-        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. } = unpeeled_pat.kind
+        if let PatKind::ExpandedConstant { def_id, .. } = unpeeled_pat.kind
             && let DefKind::Const = self.tcx.def_kind(def_id)
             && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(pat.span)
             // We filter out paths with multiple path::segments.
@@ -1296,7 +1296,8 @@ fn report_non_exhaustive_match<'p, 'tcx>(
 
     for &arm in arms {
         let arm = &thir.arms[arm];
-        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. } = arm.pattern.kind
+        if let PatKind::ExpandedConstant { def_id, .. } = arm.pattern.kind
+            && !matches!(cx.tcx.def_kind(def_id), DefKind::InlineConst)
             && let Ok(snippet) = cx.tcx.sess.source_map().span_to_snippet(arm.pattern.span)
             // We filter out paths with multiple path::segments.
             && snippet.chars().all(|c| c.is_alphanumeric() || c == '_')

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -182,7 +182,10 @@ impl<'tcx> ConstToPat<'tcx> {
             }
         }
 
-        inlined_const_as_pat
+        // Wrap the pattern in a marker node to indicate that it is the result of lowering a
+        // constant. This is used for diagnostics, and for unsafety checking of inline const blocks.
+        let kind = PatKind::ExpandedConstant { subpattern: inlined_const_as_pat, def_id: uv.def };
+        Box::new(Pat { kind, ty, span: self.span })
     }
 
     fn field_pats(

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -13,14 +13,15 @@ use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{self as hir, LangItem, RangeEnd};
 use rustc_index::Idx;
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::thir::{
     Ascription, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
 };
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
-use rustc_span::def_id::LocalDefId;
+use rustc_span::def_id::DefId;
 use rustc_span::{ErrorGuaranteed, Span};
 use tracing::{debug, instrument};
 
@@ -124,7 +125,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         expr: Option<&'tcx hir::PatExpr<'tcx>>,
         // Out-parameters collecting extra data to be reapplied by the caller
         ascriptions: &mut Vec<Ascription<'tcx>>,
-        inline_consts: &mut Vec<LocalDefId>,
+        expanded_consts: &mut Vec<DefId>,
     ) -> Result<Option<PatRangeBoundary<'tcx>>, ErrorGuaranteed> {
         let Some(expr) = expr else { return Ok(None) };
 
@@ -139,10 +140,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     ascriptions.push(ascription);
                     kind = subpattern.kind;
                 }
-                PatKind::ExpandedConstant { is_inline, def_id, subpattern } => {
-                    if is_inline {
-                        inline_consts.extend(def_id.as_local());
-                    }
+                PatKind::ExpandedConstant { def_id, subpattern } => {
+                    expanded_consts.push(def_id);
                     kind = subpattern.kind;
                 }
                 _ => break,
@@ -221,10 +220,10 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         // Collect extra data while lowering the endpoints, to be reapplied later.
         let mut ascriptions = vec![];
-        let mut inline_consts = vec![];
+        let mut expanded_consts = vec![];
 
         let mut lower_endpoint =
-            |expr| self.lower_pattern_range_endpoint(expr, &mut ascriptions, &mut inline_consts);
+            |expr| self.lower_pattern_range_endpoint(expr, &mut ascriptions, &mut expanded_consts);
 
         let lo = lower_endpoint(lo_expr)?.unwrap_or(PatRangeBoundary::NegInfinity);
         let hi = lower_endpoint(hi_expr)?.unwrap_or(PatRangeBoundary::PosInfinity);
@@ -269,17 +268,12 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         // `Foo::<'a>::A..=Foo::B`), we need to put the ascriptions for the associated
         // constants somewhere. Have them on the range pattern.
         for ascription in ascriptions {
-            kind = PatKind::AscribeUserType {
-                ascription,
-                subpattern: Box::new(Pat { span, ty, kind }),
-            };
+            let subpattern = Box::new(Pat { span, ty, kind });
+            kind = PatKind::AscribeUserType { ascription, subpattern };
         }
-        for def in inline_consts {
-            kind = PatKind::ExpandedConstant {
-                def_id: def.to_def_id(),
-                is_inline: true,
-                subpattern: Box::new(Pat { span, ty, kind }),
-            };
+        for def_id in expanded_consts {
+            let subpattern = Box::new(Pat { span, ty, kind });
+            kind = PatKind::ExpandedConstant { def_id, subpattern };
         }
         Ok(kind)
     }
@@ -569,15 +563,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         // Lower the named constant to a THIR pattern.
         let args = self.typeck_results.node_args(id);
         let c = ty::Const::new_unevaluated(self.tcx, ty::UnevaluatedConst { def: def_id, args });
-        let subpattern = self.const_to_pat(c, ty, id, span);
-
-        // Wrap the pattern in a marker node to indicate that it is the result
-        // of lowering a named constant. This marker is used for improved
-        // diagnostics in some situations, but has no effect at runtime.
-        let mut pattern = {
-            let kind = PatKind::ExpandedConstant { subpattern, def_id, is_inline: false };
-            Box::new(Pat { span, ty, kind })
-        };
+        let mut pattern = self.const_to_pat(c, ty, id, span);
 
         // If this is an associated constant with an explicit user-written
         // type, add an ascription node (e.g. `<Foo<'a> as MyTrait>::CONST`).
@@ -614,18 +600,37 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let ty = tcx.typeck(def_id).node_type(block.hir_id);
 
         let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
-        let parent_args =
-            tcx.erase_regions(ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id));
+        let parent_args = ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id);
         let args = ty::InlineConstArgs::new(tcx, ty::InlineConstArgsParts { parent_args, ty }).args;
 
-        debug_assert!(!args.has_free_regions());
-
         let ct = ty::UnevaluatedConst { def: def_id.to_def_id(), args };
-        let subpattern = self.const_to_pat(ty::Const::new_unevaluated(self.tcx, ct), ty, id, span);
-
-        // Wrap the pattern in a marker node to indicate that it is the result
-        // of lowering an inline const block.
-        PatKind::ExpandedConstant { subpattern, def_id: def_id.to_def_id(), is_inline: true }
+        let c = ty::Const::new_unevaluated(self.tcx, ct);
+        let pattern = self.const_to_pat(c, ty, id, span);
+
+        // Apply a type ascription for the inline constant.
+        let annotation = {
+            let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
+            let args = ty::InlineConstArgs::new(
+                tcx,
+                ty::InlineConstArgsParts { parent_args, ty: infcx.next_ty_var(span) },
+            )
+            .args;
+            infcx.canonicalize_user_type_annotation(ty::UserType::new(ty::UserTypeKind::TypeOf(
+                def_id.to_def_id(),
+                ty::UserArgs { args, user_self_ty: None },
+            )))
+        };
+        let annotation =
+            CanonicalUserTypeAnnotation { user_ty: Box::new(annotation), span, inferred_ty: ty };
+        PatKind::AscribeUserType {
+            subpattern: pattern,
+            ascription: Ascription {
+                annotation,
+                // Note that we use `Contravariant` here. See the `variance` field documentation
+                // for details.
+                variance: ty::Contravariant,
+            },
+        }
     }
 
     /// Lowers the kinds of "expression" that can appear in a HIR pattern:
@@ -637,43 +642,41 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         expr: &'tcx hir::PatExpr<'tcx>,
         pat_ty: Option<Ty<'tcx>>,
     ) -> PatKind<'tcx> {
-        let (lit, neg) = match &expr.kind {
-            hir::PatExprKind::Path(qpath) => {
-                return self.lower_path(qpath, expr.hir_id, expr.span).kind;
-            }
+        match &expr.kind {
+            hir::PatExprKind::Path(qpath) => self.lower_path(qpath, expr.hir_id, expr.span).kind,
             hir::PatExprKind::ConstBlock(anon_const) => {
-                return self.lower_inline_const(anon_const, expr.hir_id, expr.span);
+                self.lower_inline_const(anon_const, expr.hir_id, expr.span)
             }
-            hir::PatExprKind::Lit { lit, negated } => (lit, *negated),
-        };
-
-        // We handle byte string literal patterns by using the pattern's type instead of the
-        // literal's type in `const_to_pat`: if the literal `b"..."` matches on a slice reference,
-        // the pattern's type will be `&[u8]` whereas the literal's type is `&[u8; 3]`; using the
-        // pattern's type means we'll properly translate it to a slice reference pattern. This works
-        // because slices and arrays have the same valtree representation.
-        // HACK: As an exception, use the literal's type if `pat_ty` is `String`; this can happen if
-        // `string_deref_patterns` is enabled. There's a special case for that when lowering to MIR.
-        // FIXME(deref_patterns): This hack won't be necessary once `string_deref_patterns` is
-        // superseded by a more general implementation of deref patterns.
-        let ct_ty = match pat_ty {
-            Some(pat_ty)
-                if let ty::Adt(def, _) = *pat_ty.kind()
-                    && self.tcx.is_lang_item(def.did(), LangItem::String) =>
-            {
-                if !self.tcx.features().string_deref_patterns() {
-                    span_bug!(
-                        expr.span,
-                        "matching on `String` went through without enabling string_deref_patterns"
-                    );
-                }
-                self.typeck_results.node_type(expr.hir_id)
+            hir::PatExprKind::Lit { lit, negated } => {
+                // We handle byte string literal patterns by using the pattern's type instead of the
+                // literal's type in `const_to_pat`: if the literal `b"..."` matches on a slice reference,
+                // the pattern's type will be `&[u8]` whereas the literal's type is `&[u8; 3]`; using the
+                // pattern's type means we'll properly translate it to a slice reference pattern. This works
+                // because slices and arrays have the same valtree representation.
+                // HACK: As an exception, use the literal's type if `pat_ty` is `String`; this can happen if
+                // `string_deref_patterns` is enabled. There's a special case for that when lowering to MIR.
+                // FIXME(deref_patterns): This hack won't be necessary once `string_deref_patterns` is
+                // superseded by a more general implementation of deref patterns.
+                let ct_ty = match pat_ty {
+                    Some(pat_ty)
+                        if let ty::Adt(def, _) = *pat_ty.kind()
+                            && self.tcx.is_lang_item(def.did(), LangItem::String) =>
+                    {
+                        if !self.tcx.features().string_deref_patterns() {
+                            span_bug!(
+                                expr.span,
+                                "matching on `String` went through without enabling string_deref_patterns"
+                            );
+                        }
+                        self.typeck_results.node_type(expr.hir_id)
+                    }
+                    Some(pat_ty) => pat_ty,
+                    None => self.typeck_results.node_type(expr.hir_id),
+                };
+                let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg: *negated };
+                let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
+                self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
             }
-            Some(pat_ty) => pat_ty,
-            None => self.typeck_results.node_type(expr.hir_id),
-        };
-        let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg };
-        let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
-        self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
+        }
     }
 }

compiler/rustc_mir_build/src/thir/print.rs

@@ -741,10 +741,9 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
                 print_indented!(self, format!("value: {:?}", value), depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
             }
-            PatKind::ExpandedConstant { def_id, is_inline, subpattern } => {
+            PatKind::ExpandedConstant { def_id, subpattern } => {
                 print_indented!(self, "ExpandedConstant {", depth_lvl + 1);
                 print_indented!(self, format!("def_id: {def_id:?}"), depth_lvl + 2);
-                print_indented!(self, format!("is_inline: {is_inline:?}"), depth_lvl + 2);
                 print_indented!(self, "subpattern:", depth_lvl + 2);
                 self.print_pat(subpattern, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);