interpret: do not prune requires_caller_location stack frames quite so early

Author: RalfJung

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -82,12 +82,12 @@ impl<'tcx> ConstEvalErr<'tcx> {
         'tcx: 'mir,
     {
         error.print_backtrace();
-        let stacktrace = ecx.generate_stacktrace();
-        ConstEvalErr {
-            error: error.into_kind(),
-            stacktrace,
-            span: span.unwrap_or_else(|| ecx.cur_span()),
-        }
+        let mut stacktrace = ecx.generate_stacktrace();
+        // Filter out `requires_caller_location` frames.
+        stacktrace.retain(|frame| !frame.instance.def.requires_caller_location(*ecx.tcx));
+        // If `span` is missing, use topmost remaining frame, or else the "root" span from `ecx.tcx`.
+        let span = span.or_else(|| stacktrace.first().map(|f| f.span)).unwrap_or(ecx.tcx.span);
+        ConstEvalErr { error: error.into_kind(), stacktrace, span }
     }
 
     pub fn struct_error(

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -337,7 +337,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                     }
                 };
 
-                Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
+                Err(err.report_as_error(ecx.tcx.at(err.span), &msg))
             } else {
                 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
                 Err(err.report_as_lint(

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -428,11 +428,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     #[inline(always)]
     pub fn cur_span(&self) -> Span {
-        self.stack()
-            .iter()
-            .rev()
-            .find(|frame| !frame.instance.def.requires_caller_location(*self.tcx))
-            .map_or(self.tcx.span, |f| f.current_span())
+        // This deliberately does *not* honor `requires_caller_location` since it is used for much
+        // more than just panics.
+        self.stack().last().map_or(self.tcx.span, |f| f.current_span())
     }
 
     #[inline(always)]
@@ -939,12 +937,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     #[must_use]
     pub fn generate_stacktrace(&self) -> Vec<FrameInfo<'tcx>> {
         let mut frames = Vec::new();
-        for frame in self
-            .stack()
-            .iter()
-            .rev()
-            .skip_while(|frame| frame.instance.def.requires_caller_location(*self.tcx))
-        {
+        // This deliberately does *not* honor `requires_caller_location` since it is used for much
+        // more than just panics.
+        for frame in self.stack().iter().rev() {
             let lint_root = frame.current_source_info().and_then(|source_info| {
                 match &frame.body.source_scopes[source_info.scope].local_data {
                     mir::ClearCrossCrate::Set(data) => Some(data.lint_root),