Auto merge of #58161 - davidtwco:issue-57960, r=arielb1

Lower constant patterns with ascribed types.

Fixes #57960.

This PR fixes a bug introduced by #55937 which started checking user
type annotations for associated type patterns. Where lowering a
associated constant expression would previously return a
`PatternKind::Constant`, it now returns a `PatternKind::AscribeUserType`
with a `PatternKind::Constant` inside, this PR unwraps that to
access the constant pattern inside and behaves as before.

r? @pnkfelix

src/librustc_mir/hair/pattern/mod.rs

@@ -167,6 +167,17 @@ pub enum PatternKind<'tcx> {
  },
 }
 
+impl<'tcx> PatternKind<'tcx> {
+ /// If this is a `PatternKind::AscribeUserType` then return the subpattern kind, otherwise
+ /// return this pattern kind.
+ fn with_user_type_ascription_subpattern(self) -> Self {
+ match self {
+ PatternKind::AscribeUserType { subpattern: Pattern { box kind, .. }, .. } => kind,
+ kind => kind,
+ }
+ }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub struct PatternRange<'tcx> {
  pub lo: ty::Const<'tcx>,
@@ -403,9 +414,15 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
  PatKind::Lit(ref value) => self.lower_lit(value),
 
  PatKind::Range(ref lo_expr, ref hi_expr, end) => {
- match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
- (PatternKind::Constant { value: lo },
- PatternKind::Constant { value: hi }) => {
+ match (
+ // Look for `PatternKind::Constant` patterns inside of any
+ // `PatternKind::AscribeUserType` patterns. Type ascriptions can be safely
+ // ignored for the purposes of lowering a range correctly - these are checked
+ // elsewhere for well-formedness.
+ self.lower_lit(lo_expr).with_user_type_ascription_subpattern(),
+ self.lower_lit(hi_expr).with_user_type_ascription_subpattern(),
+ ) {
+ (PatternKind::Constant { value: lo }, PatternKind::Constant { value: hi }) => {
  use std::cmp::Ordering;
  let cmp = compare_const_vals(
  self.tcx,
@@ -454,7 +471,15 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
  }
  }
  }
- _ => PatternKind::Wild
+ ref pats => {
+ self.tcx.sess.delay_span_bug(
+ pat.span,
+ &format!("found bad range pattern `{:?}` outside of error recovery",
+ pats),
+ );
+
+ PatternKind::Wild
+ }
  }
  }
 

src/test/ui/nll/issue-57960.rs

@@ -0,0 +1,39 @@
+// run-pass
+
+#![allow(dead_code)]
+
+trait Range {
+ const FIRST: u8;
+ const LAST: u8;
+}
+
+struct OneDigit;
+impl Range for OneDigit {
+ const FIRST: u8 = 0;
+ const LAST: u8 = 9;
+}
+
+struct TwoDigits;
+impl Range for TwoDigits {
+ const FIRST: u8 = 10;
+ const LAST: u8 = 99;
+}
+
+struct ThreeDigits;
+impl Range for ThreeDigits {
+ const FIRST: u8 = 100;
+ const LAST: u8 = 255;
+}
+
+fn digits(x: u8) -> u32 {
+ match x {
+ OneDigit::FIRST...OneDigit::LAST => 1,
+ TwoDigits::FIRST...TwoDigits::LAST => 2,
+ ThreeDigits::FIRST...ThreeDigits::LAST => 3,
+ _ => unreachable!(),
+ }
+}
+
+fn main() {
+ assert_eq!(digits(100), 3);
+}