miri: backtraces with instances

src/librustc/ich/impls_ty.rs

@@ -387,10 +387,10 @@ impl_stable_hash_for!(enum mir::interpret::ErrorHandled {
     TooGeneric
 });
 
-impl_stable_hash_for!(struct mir::interpret::FrameInfo {
+impl_stable_hash_for!(struct mir::interpret::FrameInfo<'tcx> {
     span,
     lint_root,
-    location
+    instance
 });
 
 impl_stable_hash_for!(struct ty::ClosureSubsts<'tcx> { substs });

src/librustc/mir/interpret/error.rs

@@ -10,8 +10,9 @@
 
 use std::{fmt, env};
 
+use hir::map::definitions::DefPathData;
 use mir;
-use ty::{Ty, layout};
+use ty::{self, Ty, layout};
 use ty::layout::{Size, Align, LayoutError};
 use rustc_target::spec::abi::Abi;
 
@@ -19,7 +20,6 @@ use super::{Pointer, Scalar};
 
 use backtrace::Backtrace;
 
-use ty;
 use ty::query::TyCtxtAt;
 use errors::DiagnosticBuilder;
 
@@ -52,16 +52,30 @@ pub type ConstEvalResult<'tcx> = Result<&'tcx ty::Const<'tcx>, ErrorHandled>;
 pub struct ConstEvalErr<'tcx> {
     pub span: Span,
     pub error: ::mir::interpret::EvalErrorKind<'tcx, u64>,
-    pub stacktrace: Vec<FrameInfo>,
+    pub stacktrace: Vec<FrameInfo<'tcx>>,
 }
 
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
-pub struct FrameInfo {
+pub struct FrameInfo<'tcx> {
     pub span: Span,
-    pub location: String,
+    pub instance: ty::Instance<'tcx>,
     pub lint_root: Option<ast::NodeId>,
 }
 
+impl<'tcx> fmt::Display for FrameInfo<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        ty::tls::with(|tcx| {
+            if tcx.def_key(self.instance.def_id()).disambiguated_data.data
+                == DefPathData::ClosureExpr
+            {
+                write!(f, "inside call to closure")
+            } else {
+                write!(f, "inside call to `{}`", self.instance)
+            }
+        })
+    }
+}
+
 impl<'a, 'gcx, 'tcx> ConstEvalErr<'tcx> {
     pub fn struct_error(&self,
         tcx: TyCtxtAt<'a, 'gcx, 'tcx>,
@@ -135,8 +149,13 @@ impl<'a, 'gcx, 'tcx> ConstEvalErr<'tcx> {
             struct_error(tcx, message)
         };
         err.span_label(self.span, self.error.to_string());
-        for FrameInfo { span, location, .. } in &self.stacktrace {
+        // Skip the last, which is just the environment of the constant.  The stacktrace
-            err.span_label(*span, format!("inside call to `{}`", location));
+        // is sometimes empty because we create "fake" eval contexts in CTFE to do work
+        // on constant values.
+        if self.stacktrace.len() > 0 {
+            for frame_info in &self.stacktrace[..self.stacktrace.len()-1] {
+                err.span_label(frame_info.span, frame_info.to_string());
+            }
         }
         Ok(err)
     }

src/librustc_mir/interpret/eval_context.rs

@@ -14,7 +14,6 @@ use std::mem;
 use syntax::source_map::{self, Span, DUMMY_SP};
 use rustc::hir::def_id::DefId;
 use rustc::hir::def::Def;
-use rustc::hir::map::definitions::DefPathData;
 use rustc::mir;
 use rustc::ty::layout::{
     self, Size, Align, HasDataLayout, LayoutOf, TyLayout
@@ -654,11 +653,10 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
         }
     }
 
-    pub fn generate_stacktrace(&self, explicit_span: Option<Span>) -> Vec<FrameInfo> {
+    pub fn generate_stacktrace(&self, explicit_span: Option<Span>) -> Vec<FrameInfo<'tcx>> {
         let mut last_span = None;
         let mut frames = Vec::new();
-        // skip 1 because the last frame is just the environment of the constant
+        for &Frame { instance, span, mir, block, stmt, .. } in self.stack().iter().rev() {
-        for &Frame { instance, span, mir, block, stmt, .. } in self.stack().iter().skip(1).rev() {
             // make sure we don't emit frames that are duplicates of the previous
             if explicit_span == Some(span) {
                 last_span = Some(span);
@@ -671,13 +669,6 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
             } else {
                 last_span = Some(span);
             }
-            let location = if self.tcx.def_key(instance.def_id()).disambiguated_data.data
-                == DefPathData::ClosureExpr
-            {
-                "closure".to_owned()
-            } else {
-                instance.to_string()
-            };
             let block = &mir.basic_blocks()[block];
             let source_info = if stmt < block.statements.len() {
                 block.statements[stmt].source_info
@@ -688,7 +679,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
                 mir::ClearCrossCrate::Set(ref ivs) => Some(ivs[source_info.scope].lint_root),
                 mir::ClearCrossCrate::Clear => None,
             };
-            frames.push(FrameInfo { span, location, lint_root });
+            frames.push(FrameInfo { span, instance, lint_root });
         }
         trace!("generate stacktrace: {:#?}, {:?}", frames, explicit_span);
         frames