From e098327271327f86fb6aac22e64136f4a3268d31 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maja=20K=C4=85dzio=C5=82ka?= <maya@compilercrim.es>
Date: Tue, 10 Feb 2026 15:10:04 +0100
Subject: [PATCH] Don't ICE on layout error in vtable computation

---
 compiler/rustc_middle/src/ty/vtable.rs            |  7 ++++---
 .../vtable-try-as-dyn.full-debuginfo.stderr       |  4 ++++
 .../limits/vtable-try-as-dyn.no-debuginfo.stderr  |  4 ++++
 tests/ui/limits/vtable-try-as-dyn.rs              | 15 +++++++++++++++
 tests/ui/limits/vtable.rs                         |  8 ++++++++
 tests/ui/limits/vtable.stderr                     |  4 ++++
 6 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/limits/vtable-try-as-dyn.full-debuginfo.stderr
 create mode 100644 tests/ui/limits/vtable-try-as-dyn.no-debuginfo.stderr
 create mode 100644 tests/ui/limits/vtable-try-as-dyn.rs
 create mode 100644 tests/ui/limits/vtable.rs
 create mode 100644 tests/ui/limits/vtable.stderr

diff --git a/compiler/rustc_middle/src/ty/vtable.rs b/compiler/rustc_middle/src/ty/vtable.rs
index a3e9054fdcb8b..edb1eaea30275 100644
--- a/compiler/rustc_middle/src/ty/vtable.rs
+++ b/compiler/rustc_middle/src/ty/vtable.rs
@@ -99,9 +99,10 @@ pub(super) fn vtable_allocation_provider<'tcx>(
     // This confirms that the layout computation for &dyn Trait has an accurate sizing.
     assert!(vtable_entries.len() >= vtable_min_entries(tcx, poly_trait_ref));
 
-    let layout = tcx
-        .layout_of(ty::TypingEnv::fully_monomorphized().as_query_input(ty))
-        .expect("failed to build vtable representation");
+    let layout = match tcx.layout_of(ty::TypingEnv::fully_monomorphized().as_query_input(ty)) {
+        Ok(layout) => layout,
+        Err(e) => tcx.dcx().emit_fatal(e.into_diagnostic()),
+    };
     assert!(layout.is_sized(), "can't create a vtable for an unsized type");
     let size = layout.size.bytes();
     let align = layout.align.bytes();
diff --git a/tests/ui/limits/vtable-try-as-dyn.full-debuginfo.stderr b/tests/ui/limits/vtable-try-as-dyn.full-debuginfo.stderr
new file mode 100644
index 0000000000000..a3772e509ed67
--- /dev/null
+++ b/tests/ui/limits/vtable-try-as-dyn.full-debuginfo.stderr
@@ -0,0 +1,4 @@
+error: values of the type `[u8; usize::MAX]` are too big for the target architecture
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/limits/vtable-try-as-dyn.no-debuginfo.stderr b/tests/ui/limits/vtable-try-as-dyn.no-debuginfo.stderr
new file mode 100644
index 0000000000000..a3772e509ed67
--- /dev/null
+++ b/tests/ui/limits/vtable-try-as-dyn.no-debuginfo.stderr
@@ -0,0 +1,4 @@
+error: values of the type `[u8; usize::MAX]` are too big for the target architecture
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/limits/vtable-try-as-dyn.rs b/tests/ui/limits/vtable-try-as-dyn.rs
new file mode 100644
index 0000000000000..4df4f92717f9c
--- /dev/null
+++ b/tests/ui/limits/vtable-try-as-dyn.rs
@@ -0,0 +1,15 @@
+// At the time of writing, vtable.rs would ICE only with debuginfo disabled, while this testcase,
+// originally reported as #152030, would ICE even with debuginfo enabled.
+//@ revisions: no-debuginfo full-debuginfo
+//@ compile-flags: --crate-type=lib --emit=mir
+//@[no-debuginfo] compile-flags: -C debuginfo=0
+//@[full-debuginfo] compile-flags: -C debuginfo=2
+#![feature(try_as_dyn)]
+
+trait Trait {}
+impl<T> Trait for T {}
+
+//~? ERROR: values of the type `[u8; usize::MAX]` are too big for the target architecture
+pub fn foo(x: &[u8; usize::MAX]) {
+    let _ = std::any::try_as_dyn::<[u8; usize::MAX], dyn Trait>(x);
+}
diff --git a/tests/ui/limits/vtable.rs b/tests/ui/limits/vtable.rs
new file mode 100644
index 0000000000000..570eaaec491ca
--- /dev/null
+++ b/tests/ui/limits/vtable.rs
@@ -0,0 +1,8 @@
+//@ compile-flags: --crate-type=lib --emit=mir -C debuginfo=0
+pub trait Trait {}
+impl<T> Trait for T {}
+
+//~? ERROR: values of the type `[u8; usize::MAX]` are too big for the target architecture
+pub fn foo(x: &[u8; usize::MAX]) -> &dyn Trait {
+    x as &dyn Trait
+}
diff --git a/tests/ui/limits/vtable.stderr b/tests/ui/limits/vtable.stderr
new file mode 100644
index 0000000000000..a3772e509ed67
--- /dev/null
+++ b/tests/ui/limits/vtable.stderr
@@ -0,0 +1,4 @@
+error: values of the type `[u8; usize::MAX]` are too big for the target architecture
+
+error: aborting due to 1 previous error
+