From 920a973bdbb0aece426b85cf03a377108e064524 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 20 Sep 2024 20:16:49 -0400
Subject: [PATCH] Don't emit spurious error for pattern matched array with
 erroneous len const

---
 compiler/rustc_hir_typeck/src/pat.rs | 13 +------------
 tests/ui/consts/issue-116186.rs      |  2 +-
 tests/ui/consts/issue-116186.stderr  | 11 ++---------
 3 files changed, 4 insertions(+), 22 deletions(-)

diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 45a6efc7a6a32..7dd6deb4fe6fd 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -11,7 +11,6 @@ use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{self as hir, BindingMode, ByRef, HirId, LangItem, Mutability, Pat, PatKind};
 use rustc_infer::infer;
-use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
@@ -2413,17 +2412,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         len: ty::Const<'tcx>,
         min_len: u64,
     ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
-        let len = match len.eval(self.tcx, self.param_env, span) {
-            Ok((_, val)) => val
-                .try_to_scalar()
-                .and_then(|scalar| scalar.try_to_scalar_int().ok())
-                .map(|int| int.to_target_usize(self.tcx)),
-            Err(ErrorHandled::Reported(..)) => {
-                let guar = self.error_scrutinee_unfixed_length(span);
-                return (Some(Ty::new_error(self.tcx, guar)), arr_ty);
-            }
-            Err(ErrorHandled::TooGeneric(..)) => None,
-        };
+        let len = len.try_eval_target_usize(self.tcx, self.param_env);
 
         let guar = if let Some(len) = len {
             // Now we know the length...
diff --git a/tests/ui/consts/issue-116186.rs b/tests/ui/consts/issue-116186.rs
index a77c38c64dc57..8bfb47629e7f4 100644
--- a/tests/ui/consts/issue-116186.rs
+++ b/tests/ui/consts/issue-116186.rs
@@ -4,7 +4,7 @@
 fn something(path: [usize; N]) -> impl Clone {
     //~^ ERROR cannot find value `N` in this scope
     match path {
-        [] => 0, //~ ERROR cannot pattern-match on an array without a fixed length
+        [] => 0,
         _ => 1,
     };
 }
diff --git a/tests/ui/consts/issue-116186.stderr b/tests/ui/consts/issue-116186.stderr
index e6eae2d9f55ef..46931f79dd0cb 100644
--- a/tests/ui/consts/issue-116186.stderr
+++ b/tests/ui/consts/issue-116186.stderr
@@ -9,13 +9,6 @@ help: you might be missing a const parameter
 LL | fn something<const N: /* Type */>(path: [usize; N]) -> impl Clone {
    |             +++++++++++++++++++++
 
-error[E0730]: cannot pattern-match on an array without a fixed length
-  --> $DIR/issue-116186.rs:7:9
-   |
-LL |         [] => 0,
-   |         ^^
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0425, E0730.
-For more information about an error, try `rustc --explain E0425`.
+For more information about this error, try `rustc --explain E0425`.