Prevent stack overflow for deeply nested consts.

Author: cjgillot

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -2,6 +2,7 @@ use std::mem;
 
 use either::{Left, Right};
 
+use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def::DefKind;
 use rustc_middle::mir::interpret::{AllocId, ErrorHandled, InterpErrorInfo};
 use rustc_middle::mir::pretty::write_allocation_bytes;
@@ -305,10 +306,13 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
         // they do not have to behave "as if" they were evaluated at runtime.
         CompileTimeInterpreter::new(CanAccessStatics::from(is_static), CheckAlignment::Error),
     );
-    eval_in_interpreter(ecx, cid, is_static)
+    // Evaluating this MIR in the interpreter may in turn require evaluating constants to
+    // allocations. As the recursion depends on what the user wrote, we need to protect ourselves
+    // from stack overflow.
+    ensure_sufficient_stack(|| eval_in_interpreter(ecx, cid, is_static))
 }
 
-pub fn eval_in_interpreter<'mir, 'tcx>(
+fn eval_in_interpreter<'mir, 'tcx>(
     mut ecx: InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
     cid: GlobalId<'tcx>,
     is_static: bool,