Miri stacktrace: record span inside frame, not call-site span

Author: RalfJung

src/librustc_middle/mir/interpret/error.rs

@@ -53,9 +53,8 @@ pub struct ConstEvalErr<'tcx> {
 
 #[derive(Debug)]
 pub struct FrameInfo<'tcx> {
-    /// This span is in the caller.
-    pub call_site: Span,
     pub instance: ty::Instance<'tcx>,
+    pub span: Span,
     pub lint_root: Option<hir::HirId>,
 }
 
@@ -65,12 +64,12 @@ impl<'tcx> fmt::Display for FrameInfo<'tcx> {
             if tcx.def_key(self.instance.def_id()).disambiguated_data.data
                 == DefPathData::ClosureExpr
             {
-                write!(f, "inside call to closure")?;
+                write!(f, "inside closure")?;
             } else {
-                write!(f, "inside call to `{}`", self.instance)?;
+                write!(f, "inside `{}`", self.instance)?;
             }
-            if !self.call_site.is_dummy() {
-                let lo = tcx.sess.source_map().lookup_char_pos(self.call_site.lo());
+            if !self.span.is_dummy() {
+                let lo = tcx.sess.source_map().lookup_char_pos(self.span.lo());
                 write!(f, " at {}:{}:{}", lo.file.name, lo.line, lo.col.to_usize() + 1)?;
             }
             Ok(())
@@ -169,13 +168,9 @@ impl<'tcx> ConstEvalErr<'tcx> {
                 err.span_label(self.span, span_msg);
             }
             // Add spans for the stacktrace.
-            // Skip the last, which is just the environment of the constant.  The stacktrace
-            // is sometimes empty because we create "fake" eval contexts in CTFE to do work
-            // on constant values.
-            if !self.stacktrace.is_empty() {
-                for frame_info in &self.stacktrace[..self.stacktrace.len() - 1] {
-                    err.span_label(frame_info.call_site, frame_info.to_string());
-                }
+            // Skip the first, which is the place of the error.
+            for frame_info in self.stacktrace.iter().skip(1) {
+                err.span_label(frame_info.span, frame_info.to_string());
             }
             // Let the caller finish the job.
             emit(err)

src/librustc_mir/interpret/eval_context.rs

@@ -860,30 +860,18 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     pub fn generate_stacktrace(&self, explicit_span: Option<Span>) -> Vec<FrameInfo<'tcx>> {
-        let mut last_span = None;
         let mut frames = Vec::new();
         for frame in self.stack().iter().rev() {
-            // make sure we don't emit frames that are duplicates of the previous
-            if explicit_span == Some(frame.span) {
-                last_span = Some(frame.span);
-                continue;
-            }
-            if let Some(last) = last_span {
-                if last == frame.span {
-                    continue;
-                }
-            } else {
-                last_span = Some(frame.span);
-            }
-
-            let lint_root = frame.current_source_info().and_then(|source_info| {
+            let source_info = frame.current_source_info();
+            let lint_root = source_info.and_then(|source_info| {
                 match &frame.body.source_scopes[source_info.scope].local_data {
                     mir::ClearCrossCrate::Set(data) => Some(data.lint_root),
                     mir::ClearCrossCrate::Clear => None,
                 }
             });
+            let span = source_info.map_or(DUMMY_SP, |source_info| source_info.span);
 
-            frames.push(FrameInfo { call_site: frame.span, instance: frame.instance, lint_root });
+            frames.push(FrameInfo { span, instance: frame.instance, lint_root });
         }
         trace!("generate stacktrace: {:#?}, {:?}", frames, explicit_span);
         frames