add and use helper method to get SourceInfo of current instruction in frame

Author: RalfJung

src/librustc_mir/interpret/eval_context.rs

@@ -164,6 +164,20 @@ impl<'tcx, Tag: Copy + 'static> LocalState<'tcx, Tag> {
     }
 }
 
+impl<'mir, 'tcx, Tag, Extra> Frame<'mir, 'tcx, Tag, Extra> {
+    /// Return the `SourceInfo` of the current instruction.
+    pub fn current_source_info(&self) -> Option<mir::SourceInfo> {
+        self.block.map(|block| {
+            let block = &self.body.basic_blocks()[block];
+            if self.stmt < block.statements.len() {
+                block.statements[self.stmt].source_info
+            } else {
+                block.terminator().source_info
+            }
+        })
+    }
+}
+
 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> HasDataLayout for InterpCx<'mir, 'tcx, M> {
     #[inline]
     fn data_layout(&self) -> &layout::TargetDataLayout {
@@ -828,34 +842,28 @@ 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 { instance, span, body, block, stmt, .. } in self.stack().iter().rev() {
+        for frame in self.stack().iter().rev() {
             // make sure we don't emit frames that are duplicates of the previous
-            if explicit_span == Some(span) {
-                last_span = Some(span);
+            if explicit_span == Some(frame.span) {
+                last_span = Some(frame.span);
                 continue;
             }
             if let Some(last) = last_span {
-                if last == span {
+                if last == frame.span {
                     continue;
                 }
             } else {
-                last_span = Some(span);
+                last_span = Some(frame.span);
             }
 
-            let lint_root = block.and_then(|block| {
-                let block = &body.basic_blocks()[block];
-                let source_info = if stmt < block.statements.len() {
-                    block.statements[stmt].source_info
-                } else {
-                    block.terminator().source_info
-                };
-                match &body.source_scopes[source_info.scope].local_data {
+            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),
                     mir::ClearCrossCrate::Clear => None,
                 }
             });
 
-            frames.push(FrameInfo { call_site: span, instance, lint_root });
+            frames.push(FrameInfo { call_site: frame.span, instance: frame.instance, lint_root });
         }
         trace!("generate stacktrace: {:#?}, {:?}", frames, explicit_span);
         frames