remove Panic variant from InterpError

src/librustc/mir/interpret/error.rs

@@ -139,7 +139,6 @@ impl<'tcx> ConstEvalErr<'tcx> {
         lint_root: Option<hir::HirId>,
     ) -> Result<(), ErrorHandled> {
         let must_error = match self.error {
-            InterpError::MachineStop(_) => bug!("CTFE does not stop"),
             err_inval!(Layout(LayoutError::Unknown(_))) | err_inval!(TooGeneric) => {
                 return Err(ErrorHandled::TooGeneric);
             }
@@ -149,9 +148,18 @@ impl<'tcx> ConstEvalErr<'tcx> {
         };
         trace!("reporting const eval failure at {:?}", self.span);
 
+        let err_msg = match &self.error {
+            InterpError::MachineStop(msg) => {
+                // A custom error (`ConstEvalErrKind` in `librustc_mir/interp/const_eval/error.rs`).
+                // Should be turned into a string by now.
+                msg.downcast_ref::<String>().expect("invalid MachineStop payload").clone()
+            }
+            err => err.to_string(),
+        };
+
         let add_span_labels = |err: &mut DiagnosticBuilder<'_>| {
             if !must_error {
-                err.span_label(self.span, self.error.to_string());
+                err.span_label(self.span, err_msg.clone());
             }
             // 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
@@ -183,7 +191,7 @@ impl<'tcx> ConstEvalErr<'tcx> {
             );
         } else {
             let mut err = if must_error {
-                struct_error(tcx, &self.error.to_string())
+                struct_error(tcx, &err_msg)
             } else {
                 struct_error(tcx, message)
             };
@@ -259,6 +267,9 @@ impl<'tcx> From<InterpError<'tcx>> for InterpErrorInfo<'tcx> {
     }
 }
 
+/// Information about a panic.
+///
+/// FIXME: this is not actually an InterpError, and should probably be moved to another module.
 #[derive(Clone, RustcEncodable, RustcDecodable, HashStable, PartialEq)]
 pub enum PanicInfo<O> {
     Panic { msg: Symbol, line: u32, col: u32, file: Symbol },
@@ -616,8 +627,6 @@ impl fmt::Debug for ResourceExhaustionInfo {
 }
 
 pub enum InterpError<'tcx> {
-    /// The program panicked.
-    Panic(PanicInfo<u64>),
     /// The program caused undefined behavior.
     UndefinedBehavior(UndefinedBehaviorInfo),
     /// The program did something the interpreter does not support (some of these *might* be UB
@@ -650,8 +659,7 @@ impl fmt::Debug for InterpError<'_> {
             InvalidProgram(ref msg) => write!(f, "{:?}", msg),
             UndefinedBehavior(ref msg) => write!(f, "{:?}", msg),
             ResourceExhaustion(ref msg) => write!(f, "{:?}", msg),
-            Panic(ref msg) => write!(f, "{:?}", msg),
-            MachineStop(_) => write!(f, "machine caused execution to stop"),
+            MachineStop(_) => bug!("unhandled MachineStop"),
         }
     }
 }

src/librustc/mir/interpret/mod.rs

@@ -37,15 +37,6 @@ macro_rules! err_ub_format {
     ($($tt:tt)*) => { err_ub!(Ub(format!($($tt)*))) };
 }
 
-#[macro_export]
-macro_rules! err_panic {
-    ($($tt:tt)*) => {
-        $crate::mir::interpret::InterpError::Panic(
-            $crate::mir::interpret::PanicInfo::$($tt)*
-        )
-    };
-}
-
 #[macro_export]
 macro_rules! err_exhaust {
     ($($tt:tt)*) => {
@@ -80,11 +71,6 @@ macro_rules! throw_ub_format {
     ($($tt:tt)*) => { throw_ub!(Ub(format!($($tt)*))) };
 }
 
-#[macro_export]
-macro_rules! throw_panic {
-    ($($tt:tt)*) => { return Err(err_panic!($($tt)*).into()) };
-}
-
 #[macro_export]
 macro_rules! throw_exhaust {
     ($($tt:tt)*) => { return Err(err_exhaust!($($tt)*).into()) };

src/librustc_mir/const_eval/error.rs

@@ -2,32 +2,39 @@ use std::error::Error;
 use std::fmt;
 
 use super::InterpCx;
-use crate::interpret::{ConstEvalErr, InterpErrorInfo, Machine};
+use crate::interpret::{ConstEvalErr, InterpError, InterpErrorInfo, Machine, PanicInfo};
+
+/// The CTFE machine has some custom error kinds.
 #[derive(Clone, Debug)]
-pub enum ConstEvalError {
+pub enum ConstEvalErrKind {
     NeedsRfc(String),
     ConstAccessesStatic,
+    Panic(PanicInfo<u64>),
 }
 
-impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
+// The errors become `MachineStop` with plain strings when being raised.
+// `ConstEvalErr` (in `librustc/mir/interpret/error.rs`) knows to
+// handle these.
+impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalErrKind {
     fn into(self) -> InterpErrorInfo<'tcx> {
-        err_unsup!(Unsupported(self.to_string())).into()
+        InterpError::MachineStop(Box::new(self.to_string())).into()
     }
 }
 
-impl fmt::Display for ConstEvalError {
+impl fmt::Display for ConstEvalErrKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        use self::ConstEvalError::*;
+        use self::ConstEvalErrKind::*;
         match *self {
             NeedsRfc(ref msg) => {
                 write!(f, "\"{}\" needs an rfc before being allowed inside constants", msg)
             }
             ConstAccessesStatic => write!(f, "constant accesses static"),
+            Panic(ref msg) => write!(f, "{:?}", msg),
         }
     }
 }
 
-impl Error for ConstEvalError {}
+impl Error for ConstEvalErrKind {}
 
 /// Turn an interpreter error into something to report to the user.
 /// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.

src/librustc_mir/const_eval/machine.rs

@@ -9,10 +9,11 @@ use std::hash::Hash;
 use rustc_data_structures::fx::FxHashMap;
 
 use rustc_span::source_map::Span;
+use rustc_span::symbol::Symbol;
 
 use crate::interpret::{
     self, snapshot, AllocId, Allocation, AssertMessage, GlobalId, ImmTy, InterpCx, InterpResult,
-    Memory, MemoryKind, OpTy, PlaceTy, Pointer, Scalar,
+    Memory, MemoryKind, OpTy, PanicInfo, PlaceTy, Pointer, Scalar,
 };
 
 use super::error::*;
@@ -56,6 +57,32 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
         self.dump_place(*dest);
         return Ok(true);
     }
+
+    /// "Intercept" a function call to a panic-related function
+    /// because we have something special to do for it.
+    /// Returns `true` if an intercept happened.
+    pub fn hook_panic_fn(
+        &mut self,
+        span: Span,
+        instance: ty::Instance<'tcx>,
+        args: &[OpTy<'tcx>],
+    ) -> InterpResult<'tcx, bool> {
+        let def_id = instance.def_id();
+        if Some(def_id) == self.tcx.lang_items().panic_fn()
+            || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
+        {
+            // &'static str
+            assert!(args.len() == 1);
+
+            let msg_place = self.deref_operand(args[0])?;
+            let msg = Symbol::intern(self.read_str(msg_place)?);
+            let span = self.find_closest_untracked_caller_location().unwrap_or(span);
+            let (file, line, col) = self.location_triple_for_span(span);
+            Err(ConstEvalErrKind::Panic(PanicInfo::Panic { msg, file, line, col }).into())
+        } else {
+            Ok(false)
+        }
+    }
 }
 
 /// Number of steps until the detector even starts doing anything.
@@ -212,7 +239,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             Ok(body) => *body,
             Err(err) => {
                 if let err_unsup!(NoMirFor(ref path)) = err.kind {
-                    return Err(ConstEvalError::NeedsRfc(format!(
+                    return Err(ConstEvalErrKind::NeedsRfc(format!(
                         "calling extern function `{}`",
                         path
                     ))
@@ -246,7 +273,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         }
         // An intrinsic that we do not support
         let intrinsic_name = ecx.tcx.item_name(instance.def_id());
-        Err(ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into())
+        Err(ConstEvalErrKind::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into())
     }
 
     fn assert_panic(
@@ -256,7 +283,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         _unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx> {
         use rustc::mir::interpret::PanicInfo::*;
-        Err(match msg {
+        // Convert `PanicInfo<Operand>` to `PanicInfo<u64>`.
+        let err = match msg {
             BoundsCheck { ref len, ref index } => {
                 let len = ecx
                     .read_immediate(ecx.eval_operand(len, None)?)
@@ -268,21 +296,21 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                     .expect("can't eval index")
                     .to_scalar()?
                     .to_machine_usize(&*ecx)?;
-                err_panic!(BoundsCheck { len, index })
+                BoundsCheck { len, index }
             }
-            Overflow(op) => err_panic!(Overflow(*op)),
-            OverflowNeg => err_panic!(OverflowNeg),
-            DivisionByZero => err_panic!(DivisionByZero),
-            RemainderByZero => err_panic!(RemainderByZero),
-            ResumedAfterReturn(generator_kind) => err_panic!(ResumedAfterReturn(*generator_kind)),
-            ResumedAfterPanic(generator_kind) => err_panic!(ResumedAfterPanic(*generator_kind)),
+            Overflow(op) => Overflow(*op),
+            OverflowNeg => OverflowNeg,
+            DivisionByZero => DivisionByZero,
+            RemainderByZero => RemainderByZero,
+            ResumedAfterReturn(generator_kind) => ResumedAfterReturn(*generator_kind),
+            ResumedAfterPanic(generator_kind) => ResumedAfterPanic(*generator_kind),
             Panic { .. } => bug!("`Panic` variant cannot occur in MIR"),
-        }
-        .into())
+        };
+        Err(ConstEvalErrKind::Panic(err).into())
     }
 
     fn ptr_to_int(_mem: &Memory<'mir, 'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx, u64> {
-        Err(ConstEvalError::NeedsRfc("pointer-to-integer cast".to_string()).into())
+        Err(ConstEvalErrKind::NeedsRfc("pointer-to-integer cast".to_string()).into())
     }
 
     fn binary_ptr_op(
@@ -291,7 +319,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         _left: ImmTy<'tcx>,
         _right: ImmTy<'tcx>,
     ) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
-        Err(ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into())
+        Err(ConstEvalErrKind::NeedsRfc("pointer arithmetic or comparison".to_string()).into())
     }
 
     fn find_foreign_static(
@@ -321,7 +349,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _dest: PlaceTy<'tcx>,
     ) -> InterpResult<'tcx> {
-        Err(ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into())
+        Err(ConstEvalErrKind::NeedsRfc("heap allocations via `box` keyword".to_string()).into())
     }
 
     fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
@@ -355,7 +383,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         if memory_extra.can_access_statics {
             Ok(())
         } else {
-            Err(ConstEvalError::ConstAccessesStatic.into())
+            Err(ConstEvalErrKind::ConstAccessesStatic.into())
         }
     }
 }

src/librustc_mir/interpret/intrinsics.rs

@@ -376,32 +376,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(true)
     }
 
-    /// "Intercept" a function call to a panic-related function
-    /// because we have something special to do for it.
-    /// Returns `true` if an intercept happened.
-    pub fn hook_panic_fn(
-        &mut self,
-        span: Span,
-        instance: ty::Instance<'tcx>,
-        args: &[OpTy<'tcx, M::PointerTag>],
-    ) -> InterpResult<'tcx, bool> {
-        let def_id = instance.def_id();
-        if Some(def_id) == self.tcx.lang_items().panic_fn()
-            || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
-        {
-            // &'static str
-            assert!(args.len() == 1);
-
-            let msg_place = self.deref_operand(args[0])?;
-            let msg = Symbol::intern(self.read_str(msg_place)?);
-            let span = self.find_closest_untracked_caller_location().unwrap_or(span);
-            let (file, line, col) = self.location_triple_for_span(span);
-            throw_panic!(Panic { msg, file, line, col })
-        } else {
-            return Ok(false);
-        }
-    }
-
     pub fn exact_div(
         &mut self,
         a: ImmTy<'tcx, M::PointerTag>,

src/librustc_mir/interpret/intrinsics/caller_location.rs

@@ -54,12 +54,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         location
     }
 
-    pub fn alloc_caller_location_for_span(&mut self, span: Span) -> MPlaceTy<'tcx, M::PointerTag> {
-        let (file, line, column) = self.location_triple_for_span(span);
-        self.alloc_caller_location(file, line, column)
-    }
-
-    pub(super) fn location_triple_for_span(&self, span: Span) -> (Symbol, u32, u32) {
+    crate fn location_triple_for_span(&self, span: Span) -> (Symbol, u32, u32) {
         let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
         let caller = self.tcx.sess.source_map().lookup_char_pos(topmost.lo());
         (
@@ -68,4 +63,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             caller.col_display as u32 + 1,
         )
     }
+
+    pub fn alloc_caller_location_for_span(&mut self, span: Span) -> MPlaceTy<'tcx, M::PointerTag> {
+        let (file, line, column) = self.location_triple_for_span(span);
+        self.alloc_caller_location(file, line, column)
+    }
 }