From f67d045b547204c39bf14be377a4967f3b632905 Mon Sep 17 00:00:00 2001
From: Gurinder Singh <frederick.the.fool@gmail.com>
Date: Sun, 16 Jun 2024 16:37:16 +0530
Subject: [PATCH] Do not panic in `ty::consts::Const::try_to_target_usize()` in
 case of size mismatch

Fixes an ICE when we try to relate an array size of type u8 to usize
---
 compiler/rustc_middle/src/ty/consts.rs         |  6 +++++-
 .../ui/consts/ice-const-size-relate-126359.rs  | 14 ++++++++++++++
 .../consts/ice-const-size-relate-126359.stderr | 18 ++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/consts/ice-const-size-relate-126359.rs
 create mode 100644 tests/ui/consts/ice-const-size-relate-126359.stderr

diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index 12f0c38b054a0..aaa2f3c9dc309 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -150,7 +150,11 @@ impl<'tcx> Const<'tcx> {
 
 impl<'tcx> rustc_type_ir::inherent::Const<TyCtxt<'tcx>> for Const<'tcx> {
     fn try_to_target_usize(self, interner: TyCtxt<'tcx>) -> Option<u64> {
-        self.try_to_target_usize(interner)
+        let scalar = self.try_to_valtree()?.try_to_scalar_int()?;
+        if scalar.size() != interner.data_layout.pointer_size {
+            return None;
+        }
+        Some(scalar.to_target_usize(interner))
     }
 
     fn new_infer(tcx: TyCtxt<'tcx>, infer: ty::InferConst) -> Self {
diff --git a/tests/ui/consts/ice-const-size-relate-126359.rs b/tests/ui/consts/ice-const-size-relate-126359.rs
new file mode 100644
index 0000000000000..db09bd228b349
--- /dev/null
+++ b/tests/ui/consts/ice-const-size-relate-126359.rs
@@ -0,0 +1,14 @@
+// Regression test for ICE #126359
+
+// Tests that there is no ICE when the generic const
+// specifying the size of an array is of a non-usize type
+
+struct OppOrder<const N: u8 = 3, T = u32> {
+    arr: [T; N], // Array size is u8 instead of usize
+    //~^ ERROR mismatched types
+}
+
+fn main() {
+    let _ = OppOrder::<3, u32> { arr: [0, 0, 0] };
+    //~^ ERROR mismatched types
+}
diff --git a/tests/ui/consts/ice-const-size-relate-126359.stderr b/tests/ui/consts/ice-const-size-relate-126359.stderr
new file mode 100644
index 0000000000000..b9c057b204472
--- /dev/null
+++ b/tests/ui/consts/ice-const-size-relate-126359.stderr
@@ -0,0 +1,18 @@
+error[E0308]: mismatched types
+  --> $DIR/ice-const-size-relate-126359.rs:12:39
+   |
+LL |     let _ = OppOrder::<3, u32> { arr: [0, 0, 0] };
+   |                                       ^^^^^^^^^ expected `3`, found `3`
+   |
+   = note: expected array `[u32; 3]`
+              found array `[u32; 3]`
+
+error[E0308]: mismatched types
+  --> $DIR/ice-const-size-relate-126359.rs:7:14
+   |
+LL |     arr: [T; N], // Array size is u8 instead of usize
+   |              ^ expected `usize`, found `u8`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.