Auto merge of #103877 - oli-obk:const_eval_step_limit, r=fee1-dead

Replace const eval limit by a lint and add an exponential backoff warning

The lint triggers at the first power of 2 that comes after 1 million function calls or traversed back-edges (takes less than a second on usual programs). After the first emission, an unsilenceable warning is repeated at every following power of 2 terminators, causing it to get reported less and less the longer the evaluation runs.

cc `@rust-lang/wg-const-eval`

fixes #93481
closes #67217

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -4,6 +4,7 @@ use std::mem;
 
 use either::{Either, Left, Right};
 
+use hir::CRATE_HIR_ID;
 use rustc_hir::{self as hir, def_id::DefId, definitions::DefPathData};
 use rustc_index::IndexVec;
 use rustc_middle::mir;
@@ -405,6 +406,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.stack().last().map_or(self.tcx.span, |f| f.current_span())
     }
 
+    #[inline(always)]
+    /// Find the first stack frame that is within the current crate, if any, otherwise return the crate's HirId
+    pub fn best_lint_scope(&self) -> hir::HirId {
+        self.stack()
+            .iter()
+            .find_map(|frame| frame.body.source.def_id().as_local())
+            .map_or(CRATE_HIR_ID, |def_id| self.tcx.hir().local_def_id_to_hir_id(def_id))
+    }
+
     #[inline(always)]
     pub(crate) fn stack(&self) -> &[Frame<'mir, 'tcx, M::Provenance, M::FrameExtra>] {
         M::stack(self)