Pattern types: Avoid having to handle an Option for range ends in the type system or the HIR

compiler/rustc_ast_lowering/src/lib.rs

@@ -136,6 +136,7 @@ struct LoweringContext<'a, 'hir> {
 
     allow_try_trait: Arc<[Symbol]>,
     allow_gen_future: Arc<[Symbol]>,
+    allow_pattern_type: Arc<[Symbol]>,
     allow_async_iterator: Arc<[Symbol]>,
     allow_for_await: Arc<[Symbol]>,
     allow_async_fn_traits: Arc<[Symbol]>,
@@ -176,6 +177,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             impl_trait_defs: Vec::new(),
             impl_trait_bounds: Vec::new(),
             allow_try_trait: [sym::try_trait_v2, sym::yeet_desugar_details].into(),
+            allow_pattern_type: [sym::pattern_types, sym::pattern_type_range_trait].into(),
             allow_gen_future: if tcx.features().async_fn_track_caller() {
                 [sym::gen_future, sym::closure_track_caller].into()
             } else {
@@ -1357,7 +1359,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 }
             }
             TyKind::Pat(ty, pat) => {
-                hir::TyKind::Pat(self.lower_ty(ty, itctx), self.lower_ty_pat(pat))
+                hir::TyKind::Pat(self.lower_ty(ty, itctx), self.lower_ty_pat(pat, ty.span))
             }
             TyKind::MacCall(_) => {
                 span_bug!(t.span, "`TyKind::MacCall` should have been expanded by now")

compiler/rustc_ast_lowering/src/pat.rs

@@ -3,11 +3,11 @@ use std::sync::Arc;
 use rustc_ast::ptr::P;
 use rustc_ast::*;
 use rustc_data_structures::stack::ensure_sufficient_stack;
-use rustc_hir as hir;
-use rustc_hir::def::Res;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::{self as hir, LangItem};
 use rustc_middle::span_bug;
 use rustc_span::source_map::{Spanned, respan};
-use rustc_span::{Ident, Span};
+use rustc_span::{DesugaringKind, Ident, Span, kw};
 
 use super::errors::{
     ArbitraryExpressionInPattern, ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding,
@@ -430,22 +430,124 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.arena.alloc(hir::PatExpr { hir_id: self.lower_node_id(expr.id), span, kind })
     }
 
-    pub(crate) fn lower_ty_pat(&mut self, pattern: &TyPat) -> &'hir hir::TyPat<'hir> {
-        self.arena.alloc(self.lower_ty_pat_mut(pattern))
+    pub(crate) fn lower_ty_pat(
+        &mut self,
+        pattern: &TyPat,
+        base_type: Span,
+    ) -> &'hir hir::TyPat<'hir> {
+        self.arena.alloc(self.lower_ty_pat_mut(pattern, base_type))
     }
 
-    fn lower_ty_pat_mut(&mut self, pattern: &TyPat) -> hir::TyPat<'hir> {
+    fn lower_ty_pat_mut(&mut self, pattern: &TyPat, base_type: Span) -> hir::TyPat<'hir> {
         // loop here to avoid recursion
         let pat_hir_id = self.lower_node_id(pattern.id);
         let node = match &pattern.kind {
-            TyPatKind::Range(e1, e2, Spanned { node: end, .. }) => hir::TyPatKind::Range(
-                e1.as_deref().map(|e| self.lower_anon_const_to_const_arg(e)),
-                e2.as_deref().map(|e| self.lower_anon_const_to_const_arg(e)),
-                self.lower_range_end(end, e2.is_some()),
+            TyPatKind::Range(e1, e2, Spanned { node: end, span }) => hir::TyPatKind::Range(
+                e1.as_deref().map(|e| self.lower_anon_const_to_const_arg(e)).unwrap_or_else(|| {
+                    self.lower_ty_pat_range_end(
+                        hir::LangItem::RangeMin,
+                        span.shrink_to_lo(),
+                        base_type,
+                    )
+                }),
+                e2.as_deref()
+                    .map(|e| match end {
+                        RangeEnd::Included(..) => self.lower_anon_const_to_const_arg(e),
+                        RangeEnd::Excluded => self.lower_excluded_range_end(e),
+                    })
+                    .unwrap_or_else(|| {
+                        self.lower_ty_pat_range_end(
+                            hir::LangItem::RangeMax,
+                            span.shrink_to_hi(),
+                            base_type,
+                        )
+                    }),
             ),
             TyPatKind::Err(guar) => hir::TyPatKind::Err(*guar),
         };
 
         hir::TyPat { hir_id: pat_hir_id, kind: node, span: self.lower_span(pattern.span) }
     }
+
+    /// Lowers the range end of an exclusive range (`2..5`) to an inclusive range 2..=(5 - 1).
+    /// This way the type system doesn't have to handle the distinction between inclusive/exclusive ranges.
+    fn lower_excluded_range_end(&mut self, e: &AnonConst) -> &'hir hir::ConstArg<'hir> {
+        let span = self.lower_span(e.value.span);
+        let unstable_span = self.mark_span_with_reason(
+            DesugaringKind::PatTyRange,
+            span,
+            Some(Arc::clone(&self.allow_pattern_type)),
+        );
+        let anon_const = self.with_new_scopes(span, |this| {
+            let def_id = this.local_def_id(e.id);
+            let hir_id = this.lower_node_id(e.id);
+            let body = this.lower_body(|this| {
+                // Need to use a custom function as we can't just subtract `1` from a `char`.
+                let kind = hir::ExprKind::Path(this.make_lang_item_qpath(
+                    hir::LangItem::RangeSub,
+                    unstable_span,
+                    None,
+                ));
+                let fn_def = this.arena.alloc(hir::Expr { hir_id: this.next_id(), kind, span });
+                let args = this.arena.alloc([this.lower_expr_mut(&e.value)]);
+                (
+                    &[],
+                    hir::Expr {
+                        hir_id: this.next_id(),
+                        kind: hir::ExprKind::Call(fn_def, args),
+                        span,
+                    },
+                )
+            });
+            hir::AnonConst { def_id, hir_id, body, span }
+        });
+        self.arena.alloc(hir::ConstArg {
+            hir_id: self.next_id(),
+            kind: hir::ConstArgKind::Anon(self.arena.alloc(anon_const)),
+        })
+    }
+
+    /// When a range has no end specified (`1..` or `1..=`) or no start specified (`..5` or `..=5`),
+    /// we instead use a constant of the MAX/MIN of the type.
+    /// This way the type system does not have to handle the lack of a start/end.
+    fn lower_ty_pat_range_end(
+        &mut self,
+        lang_item: LangItem,
+        span: Span,
+        base_type: Span,
+    ) -> &'hir hir::ConstArg<'hir> {
+        let parent_def_id = self.current_hir_id_owner.def_id;
+        let node_id = self.next_node_id();
+
+        // Add a definition for the in-band const def.
+        // We're generating a range end that didn't exist in the AST,
+        // so the def collector didn't create the def ahead of time. That's why we have to do
+        // it here.
+        let def_id = self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, span);
+        let hir_id = self.lower_node_id(node_id);
+
+        let unstable_span = self.mark_span_with_reason(
+            DesugaringKind::PatTyRange,
+            self.lower_span(span),
+            Some(Arc::clone(&self.allow_pattern_type)),
+        );
+        let span = self.lower_span(base_type);
+
+        let path_expr = hir::Expr {
+            hir_id: self.next_id(),
+            kind: hir::ExprKind::Path(self.make_lang_item_qpath(lang_item, unstable_span, None)),
+            span,
+        };
+
+        let ct = self.with_new_scopes(span, |this| {
+            self.arena.alloc(hir::AnonConst {
+                def_id,
+                hir_id,
+                body: this.lower_body(|_this| (&[], path_expr)),
+                span,
+            })
+        });
+        let hir_id = self.next_id();
+        self.arena.alloc(hir::ConstArg { kind: hir::ConstArgKind::Anon(ct), hir_id })
+    }
 }

compiler/rustc_hir/src/hir.rs

@@ -1600,7 +1600,7 @@ pub struct PatField<'hir> {
     pub span: Span,
 }
 
-#[derive(Copy, Clone, PartialEq, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Debug, HashStable_Generic, Hash, Eq, Encodable, Decodable)]
 pub enum RangeEnd {
     Included,
     Excluded,
@@ -1668,7 +1668,7 @@ pub enum PatExprKind<'hir> {
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum TyPatKind<'hir> {
     /// A range pattern (e.g., `1..=2` or `1..2`).
-    Range(Option<&'hir ConstArg<'hir>>, Option<&'hir ConstArg<'hir>>, RangeEnd),
+    Range(&'hir ConstArg<'hir>, &'hir ConstArg<'hir>),
 
     /// A placeholder for a pattern that wasn't well formed in some way.
     Err(ErrorGuaranteed),

compiler/rustc_hir/src/intravisit.rs

@@ -708,9 +708,9 @@ pub fn walk_arm<'v, V: Visitor<'v>>(visitor: &mut V, arm: &'v Arm<'v>) -> V::Res
 pub fn walk_ty_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v TyPat<'v>) -> V::Result {
     try_visit!(visitor.visit_id(pattern.hir_id));
     match pattern.kind {
-        TyPatKind::Range(lower_bound, upper_bound, _) => {
-            visit_opt!(visitor, visit_const_arg_unambig, lower_bound);
-            visit_opt!(visitor, visit_const_arg_unambig, upper_bound);
+        TyPatKind::Range(lower_bound, upper_bound) => {
+            try_visit!(visitor.visit_const_arg_unambig(lower_bound));
+            try_visit!(visitor.visit_const_arg_unambig(upper_bound));
         }
         TyPatKind::Err(_) => (),
     }

compiler/rustc_hir/src/lang_items.rs

@@ -418,6 +418,9 @@ language_item_table! {
     Range,                   sym::Range,               range_struct,               Target::Struct,         GenericRequirement::None;
     RangeToInclusive,        sym::RangeToInclusive,    range_to_inclusive_struct,  Target::Struct,         GenericRequirement::None;
     RangeTo,                 sym::RangeTo,             range_to_struct,            Target::Struct,         GenericRequirement::None;
+    RangeMax,                sym::RangeMax,            range_max,                  Target::AssocConst,     GenericRequirement::Exact(0);
+    RangeMin,                sym::RangeMin,            range_min,                  Target::AssocConst,     GenericRequirement::Exact(0);
+    RangeSub,                sym::RangeSub,            range_sub,                  Target::Method(MethodKind::Trait { body: false }),     GenericRequirement::Exact(0);
 
     // `new_range` types that are `Copy + IntoIterator`
     RangeFromCopy,           sym::RangeFromCopy,       range_from_copy_struct,     Target::Struct,         GenericRequirement::None;

compiler/rustc_hir_analysis/messages.ftl

@@ -244,9 +244,6 @@ hir_analysis_inherent_ty_outside_relevant = cannot define inherent `impl` for a
     .help = consider moving this inherent impl into the crate defining the type if possible
     .span_help = alternatively add `#[rustc_allow_incoherent_impl]` to the relevant impl items
 
-hir_analysis_invalid_base_type = `{$ty}` is not a valid base type for range patterns
-    .note = range patterns only support integers
-
 hir_analysis_invalid_generic_receiver_ty = invalid generic `self` parameter type: `{$receiver_ty}`
     .note = type of `self` must not be a method generic parameter type
 

compiler/rustc_hir_analysis/src/errors.rs

@@ -11,8 +11,6 @@ use rustc_middle::ty::Ty;
 use rustc_span::{Ident, Span, Symbol};
 
 use crate::fluent_generated as fluent;
-mod pattern_types;
-pub(crate) use pattern_types::*;
 pub(crate) mod wrong_number_of_generic_args;
 
 mod precise_captures;

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -53,9 +53,7 @@ use rustc_type_ir::Upcast;
 use tracing::{debug, instrument};
 
 use crate::check::check_abi_fn_ptr;
-use crate::errors::{
-    AmbiguousLifetimeBound, BadReturnTypeNotation, InvalidBaseType, NoVariantNamed,
-};
+use crate::errors::{AmbiguousLifetimeBound, BadReturnTypeNotation, NoVariantNamed};
 use crate::hir_ty_lowering::errors::{GenericsArgsErrExtend, prohibit_assoc_item_constraint};
 use crate::hir_ty_lowering::generics::{check_generic_arg_count, lower_generic_args};
 use crate::middle::resolve_bound_vars as rbv;
@@ -2452,28 +2450,26 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let ty_span = ty.span;
                 let ty = self.lower_ty(ty);
                 let pat_ty = match pat.kind {
-                    hir::TyPatKind::Range(start, end, include_end) => {
-                        let ty = match ty.kind() {
-                            ty::Int(_) | ty::Uint(_) | ty::Char => ty,
-                            _ => Ty::new_error(
-                                tcx,
-                                self.dcx().emit_err(InvalidBaseType {
-                                    ty,
-                                    pat: "range",
+                    hir::TyPatKind::Range(start, end) => {
+                        let (ty, start, end) = match ty.kind() {
+                            // Keep this list of types in sync with the list of types that
+                            // the `RangePattern` trait is implemented for.
+                            ty::Int(_) | ty::Uint(_) | ty::Char => {
+                                let start = self.lower_const_arg(start, FeedConstTy::No);
+                                let end = self.lower_const_arg(end, FeedConstTy::No);
+                                (ty, start, end)
+                            }
+                            _ => {
+                                let guar = self.dcx().span_delayed_bug(
                                     ty_span,
-                                    pat_span: pat.span,
-                                }),
-                            ),
-                        };
-                        let start = start.map(|expr| self.lower_const_arg(expr, FeedConstTy::No));
-                        let end = end.map(|expr| self.lower_const_arg(expr, FeedConstTy::No));
-
-                        let include_end = match include_end {
-                            hir::RangeEnd::Included => true,
-                            hir::RangeEnd::Excluded => false,
+                                    "invalid base type for range pattern",
+                                );
+                                let errc = ty::Const::new_error(tcx, guar);
+                                (Ty::new_error(tcx, guar), errc, errc)
+                            }
                         };
 
-                        let pat = tcx.mk_pat(ty::PatternKind::Range { start, end, include_end });
+                        let pat = tcx.mk_pat(ty::PatternKind::Range { start, end });
                         Ty::new_pat(tcx, ty, pat)
                     }
                     hir::TyPatKind::Err(e) => Ty::new_error(tcx, e),

compiler/rustc_hir_analysis/src/variance/constraints.rs

@@ -252,13 +252,9 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
 
             ty::Pat(typ, pat) => {
                 match *pat {
-                    ty::PatternKind::Range { start, end, include_end: _ } => {
-                        if let Some(start) = start {
-                            self.add_constraints_from_const(current, start, variance);
-                        }
-                        if let Some(end) = end {
-                            self.add_constraints_from_const(current, end, variance);
-                        }
+                    ty::PatternKind::Range { start, end } => {
+                        self.add_constraints_from_const(current, start, variance);
+                        self.add_constraints_from_const(current, end, variance);
                     }
                 }
                 self.add_constraints_from_ty(current, typ, variance);

compiler/rustc_hir_pretty/src/lib.rs

@@ -1869,17 +1869,10 @@ impl<'a> State<'a> {
         // Pat isn't normalized, but the beauty of it
         // is that it doesn't matter
         match pat.kind {
-            TyPatKind::Range(begin, end, end_kind) => {
-                if let Some(expr) = begin {
-                    self.print_const_arg(expr);
-                }
-                match end_kind {
-                    RangeEnd::Included => self.word("..."),
-                    RangeEnd::Excluded => self.word(".."),
-                }
-                if let Some(expr) = end {
-                    self.print_const_arg(expr);
-                }
+            TyPatKind::Range(begin, end) => {
+                self.print_const_arg(begin);
+                self.word("..=");
+                self.print_const_arg(end);
             }
             TyPatKind::Err(_) => {
                 self.popen();

compiler/rustc_lint/src/types.rs

@@ -882,27 +882,13 @@ fn ty_is_known_nonnull<'tcx>(
                 || Option::unwrap_or_default(
                     try {
                         match **pat {
-                            ty::PatternKind::Range { start, end, include_end } => {
-                                match (start, end) {
-                                    (Some(start), None) => {
-                                        start.try_to_value()?.try_to_bits(tcx, typing_env)? > 0
-                                    }
-                                    (Some(start), Some(end)) => {
-                                        let start =
-                                            start.try_to_value()?.try_to_bits(tcx, typing_env)?;
-                                        let end =
-                                            end.try_to_value()?.try_to_bits(tcx, typing_env)?;
-
-                                        if include_end {
-                                            // This also works for negative numbers, as we just need
-                                            // to ensure we aren't wrapping over zero.
-                                            start > 0 && end >= start
-                                        } else {
-                                            start > 0 && end > start
-                                        }
-                                    }
-                                    _ => false,
-                                }
+                            ty::PatternKind::Range { start, end } => {
+                                let start = start.try_to_value()?.try_to_bits(tcx, typing_env)?;
+                                let end = end.try_to_value()?.try_to_bits(tcx, typing_env)?;
+
+                                // This also works for negative numbers, as we just need
+                                // to ensure we aren't wrapping over zero.
+                                start > 0 && end >= start
                             }
                         }
                     },

compiler/rustc_middle/src/ty/flags.rs

@@ -220,13 +220,9 @@ impl FlagComputation {
             &ty::Pat(ty, pat) => {
                 self.add_ty(ty);
                 match *pat {
-                    ty::PatternKind::Range { start, end, include_end: _ } => {
-                        if let Some(start) = start {
-                            self.add_const(start)
-                        }
-                        if let Some(end) = end {
-                            self.add_const(end)
-                        }
+                    ty::PatternKind::Range { start, end } => {
+                        self.add_const(start);
+                        self.add_const(end);
                     }
                 }
             }