Fix ICE in eval_body_using_ecx

Return`Err` instead of `assert`ing when
layout is not sized.

Author: gurry

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -7,7 +7,7 @@ use rustc_middle::mir::interpret::{AllocId, ErrorHandled, InterpErrorInfo};
 use rustc_middle::mir::{self, ConstAlloc, ConstValue};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::traits::Reveal;
-use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::layout::{LayoutError, LayoutOf};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::LocalDefId;
@@ -49,8 +49,12 @@ fn eval_body_using_ecx<'mir, 'tcx, R: InterpretationResult<'tcx>>(
         "Unexpected DefKind: {:?}",
         ecx.tcx.def_kind(cid.instance.def_id())
     );
-    let layout = ecx.layout_of(body.bound_return_ty().instantiate(tcx, cid.instance.args))?;
-    assert!(layout.is_sized());
+
+    let body_ty = body.bound_return_ty().instantiate(tcx, cid.instance.args);
+    let layout = ecx.layout_of(body_ty)?;
+    if !layout.is_sized() {
+        return Err((err_inval!(Layout(LayoutError::Unknown(body_ty)))).into());
+    }
 
     let intern_kind = if cid.promoted.is_some() {
         InternKind::Promoted

tests/ui/consts/const-eval/ice-unsized-struct-const-eval-123154.rs

@@ -0,0 +1,15 @@
+// Regression test for #123154
+
+struct AA {
+    pub data: [&usize]
+    //~^ ERROR missing lifetime specifier
+}
+
+impl AA {
+    const fn new() -> Self { }
+    //~^ ERROR mismatched types
+}
+
+static ST: AA = AA::new();
+
+fn main() {}

tests/ui/consts/const-eval/ice-unsized-struct-const-eval-123154.stderr

@@ -0,0 +1,24 @@
+error[E0106]: missing lifetime specifier
+  --> $DIR/ice-unsized-struct-const-eval-123154.rs:4:16
+   |
+LL |     pub data: [&usize]
+   |                ^ expected named lifetime parameter
+   |
+help: consider introducing a named lifetime parameter
+   |
+LL ~ struct AA<'a> {
+LL ~     pub data: [&'a usize]
+   |
+
+error[E0308]: mismatched types
+  --> $DIR/ice-unsized-struct-const-eval-123154.rs:9:23
+   |
+LL |     const fn new() -> Self { }
+   |              ---      ^^^^ expected `AA`, found `()`
+   |              |
+   |              implicitly returns `()` as its body has no tail or `return` expression
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0106, E0308.
+For more information about an error, try `rustc --explain E0106`.