rust/src/librustc/mir/interpret/error.rs

use std::{fmt, env};

use crate::hir;
use crate::hir::map::definitions::DefPathData;
use crate::mir;
use crate::ty::{self, Ty, layout};
use crate::ty::layout::{Size, Align, LayoutError};
use rustc_target::spec::abi::Abi;
use rustc_macros::HashStable;

use super::{RawConst, Pointer, CheckInAllocMsg, ScalarMaybeUndef};

use backtrace::Backtrace;

use crate::ty::query::TyCtxtAt;
use errors::DiagnosticBuilder;

use syntax_pos::{Pos, Span};
use syntax::symbol::Symbol;

#[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, RustcEncodable, RustcDecodable)]
pub enum ErrorHandled {
    /// Already reported a lint or an error for this evaluation.
    Reported,
    /// Don't emit an error, the evaluation failed because the MIR was generic
    /// and the substs didn't fully monomorphize it.
    TooGeneric,
}

impl ErrorHandled {
    pub fn assert_reported(self) {
        match self {
            ErrorHandled::Reported => {},
            ErrorHandled::TooGeneric => bug!("MIR interpretation failed without reporting an error \
                                              even though it was fully monomorphized"),
        }
    }
}

CloneTypeFoldableImpls! {
    ErrorHandled,
}

pub type ConstEvalRawResult<'tcx> = Result<RawConst<'tcx>, ErrorHandled>;
pub type ConstEvalResult<'tcx> = Result<&'tcx ty::Const<'tcx>, ErrorHandled>;

#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
pub struct ConstEvalErr<'tcx> {
    pub span: Span,
    pub error: crate::mir::interpret::InterpError<'tcx>,
    pub stacktrace: Vec<FrameInfo<'tcx>>,
}

#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable)]
pub struct FrameInfo<'tcx> {
    /// This span is in the caller.
    pub call_site: Span,
    pub instance: ty::Instance<'tcx>,
    pub lint_root: Option<hir::HirId>,
}

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)?;
            }
            if !self.call_site.is_dummy() {
                let lo = tcx.sess.source_map().lookup_char_pos(self.call_site.lo());
                write!(f, " at {}:{}:{}", lo.file.name, lo.line, lo.col.to_usize() + 1)?;
            }
            Ok(())
        })
    }
}

impl<'tcx> ConstEvalErr<'tcx> {
    pub fn struct_error(
        &self,
        tcx: TyCtxtAt<'tcx>,
        message: &str,
    ) -> Result<DiagnosticBuilder<'tcx>, ErrorHandled> {
        self.struct_generic(tcx, message, None)
    }

    pub fn report_as_error(&self, tcx: TyCtxtAt<'tcx>, message: &str) -> ErrorHandled {
        let err = self.struct_error(tcx, message);
        match err {
            Ok(mut err) => {
                err.emit();
                ErrorHandled::Reported
            },
            Err(err) => err,
        }
    }

    pub fn report_as_lint(
        &self,
        tcx: TyCtxtAt<'tcx>,
        message: &str,
        lint_root: hir::HirId,
        span: Option<Span>,
    ) -> ErrorHandled {
        let lint = self.struct_generic(
            tcx,
            message,
            Some(lint_root),
        );
        match lint {
            Ok(mut lint) => {
                if let Some(span) = span {
                    let primary_spans = lint.span.primary_spans().to_vec();
                    // point at the actual error as the primary span
                    lint.replace_span_with(span);
                    // point to the `const` statement as a secondary span
                    // they don't have any label
                    for sp in primary_spans {
                        if sp != span {
                            lint.span_label(sp, "");
                        }
                    }
                }
                lint.emit();
                ErrorHandled::Reported
            },
            Err(err) => err,
        }
    }

    fn struct_generic(
        &self,
        tcx: TyCtxtAt<'tcx>,
        message: &str,
        lint_root: Option<hir::HirId>,
    ) -> Result<DiagnosticBuilder<'tcx>, ErrorHandled> {
        match self.error {
            err_inval!(Layout(LayoutError::Unknown(_))) |
            err_inval!(TooGeneric) =>
                return Err(ErrorHandled::TooGeneric),
            err_inval!(Layout(LayoutError::SizeOverflow(_))) |
            err_inval!(TypeckError) =>
                return Err(ErrorHandled::Reported),
            _ => {},
        }
        trace!("reporting const eval failure at {:?}", self.span);
        let mut err = if let Some(lint_root) = lint_root {
            let hir_id = self.stacktrace
                .iter()
                .rev()
                .filter_map(|frame| frame.lint_root)
                .next()
                .unwrap_or(lint_root);
            tcx.struct_span_lint_hir(
                crate::rustc::lint::builtin::CONST_ERR,
                hir_id,
                tcx.span,
                message,
            )
        } else {
            struct_error(tcx, message)
        };
        err.span_label(self.span, self.error.to_string());
        // 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.len() > 0 {
            for frame_info in &self.stacktrace[..self.stacktrace.len()-1] {
                err.span_label(frame_info.call_site, frame_info.to_string());
            }
        }
        Ok(err)
    }
}

pub fn struct_error<'tcx>(tcx: TyCtxtAt<'tcx>, msg: &str) -> DiagnosticBuilder<'tcx> {
    struct_span_err!(tcx.sess, tcx.span, E0080, "{}", msg)
}

/// Packages the kind of error we got from the const code interpreter
/// up with a Rust-level backtrace of where the error occured.
/// Thsese should always be constructed by calling `.into()` on
/// a `InterpError`. In `librustc_mir::interpret`, we have `throw_err_*`
/// macros for this.
#[derive(Debug, Clone)]
pub struct InterpErrorInfo<'tcx> {
    pub kind: InterpError<'tcx>,
    backtrace: Option<Box<Backtrace>>,
}


impl fmt::Display for InterpErrorInfo<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.kind)
    }
}

impl InterpErrorInfo<'_> {
    pub fn print_backtrace(&mut self) {
        if let Some(ref mut backtrace) = self.backtrace {
            print_backtrace(&mut *backtrace);
        }
    }
}

fn print_backtrace(backtrace: &mut Backtrace) {
    backtrace.resolve();
    eprintln!("\n\nAn error occurred in miri:\n{:?}", backtrace);
}

impl<'tcx> From<InterpError<'tcx>> for InterpErrorInfo<'tcx> {
    fn from(kind: InterpError<'tcx>) -> Self {
        let backtrace = match env::var("RUST_CTFE_BACKTRACE") {
            // Matching `RUST_BACKTRACE` -- we treat "0" the same as "not present".
            Ok(ref val) if val != "0" => {
                let mut backtrace = Backtrace::new_unresolved();

                if val == "immediate" {
                    // Print it now.
                    print_backtrace(&mut backtrace);
                    None
                } else {
                    Some(Box::new(backtrace))
                }
            },
            _ => None,
        };
        InterpErrorInfo {
            kind,
            backtrace,
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
pub enum PanicInfo<O> {
    Panic {
        msg: Symbol,
        line: u32,
        col: u32,
        file: Symbol,
    },
    BoundsCheck {
        len: O,
        index: O,
    },
    Overflow(mir::BinOp),
    OverflowNeg,
    DivisionByZero,
    RemainderByZero,
    GeneratorResumedAfterReturn,
    GeneratorResumedAfterPanic,
}

/// Type for MIR `Assert` terminator error messages.
pub type AssertMessage<'tcx> = PanicInfo<mir::Operand<'tcx>>;

impl<O> PanicInfo<O> {
    /// Getting a description does not require `O` to be printable, and does not
    /// require allocation.
    /// The caller is expected to handle `Panic` and `BoundsCheck` separately.
    pub fn description(&self) -> &'static str {
        use PanicInfo::*;
        match self {
            Overflow(mir::BinOp::Add) =>
                "attempt to add with overflow",
            Overflow(mir::BinOp::Sub) =>
                "attempt to subtract with overflow",
            Overflow(mir::BinOp::Mul) =>
                "attempt to multiply with overflow",
            Overflow(mir::BinOp::Div) =>
                "attempt to divide with overflow",
            Overflow(mir::BinOp::Rem) =>
                "attempt to calculate the remainder with overflow",
            OverflowNeg =>
                "attempt to negate with overflow",
            Overflow(mir::BinOp::Shr) =>
                "attempt to shift right with overflow",
            Overflow(mir::BinOp::Shl) =>
                "attempt to shift left with overflow",
            Overflow(op) =>
                bug!("{:?} cannot overflow", op),
            DivisionByZero =>
                "attempt to divide by zero",
            RemainderByZero =>
                "attempt to calculate the remainder with a divisor of zero",
            GeneratorResumedAfterReturn =>
                "generator resumed after completion",
            GeneratorResumedAfterPanic =>
                "generator resumed after panicking",
            Panic { .. } | BoundsCheck { .. } =>
                bug!("Unexpected PanicInfo"),
        }
    }
}

impl<O: fmt::Debug> fmt::Debug for PanicInfo<O> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use PanicInfo::*;
        match self {
            Panic { ref msg, line, col, ref file } =>
                write!(f, "the evaluated program panicked at '{}', {}:{}:{}", msg, file, line, col),
            BoundsCheck { ref len, ref index } =>
                write!(f, "index out of bounds: the len is {:?} but the index is {:?}", len, index),
            _ =>
                write!(f, "{}", self.description()),
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
pub enum InvalidProgramInfo<'tcx> {
    /// Resolution can fail if we are in a too generic context.
    TooGeneric,
    /// Cannot compute this constant because it depends on another one
    /// which already produced an error.
    ReferencedConstant,
    /// Abort in case type errors are reached.
    TypeckError,
    /// An error occurred during layout computation.
    Layout(layout::LayoutError<'tcx>),
}

impl fmt::Debug for InvalidProgramInfo<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use InvalidProgramInfo::*;
        match self {
            TooGeneric =>
                write!(f, "encountered overly generic constant"),
            ReferencedConstant =>
                write!(f, "referenced constant has errors"),
            TypeckError =>
                write!(f, "encountered constants with type errors, stopping evaluation"),
            Layout(ref err) =>
                write!(f, "rustc layout computation failed: {:?}", err),
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
pub enum UndefinedBehaviorInfo {
    /// Handle cases which for which we do not have a fixed variant.
    Ub(String),
    /// Unreachable code was executed.
    Unreachable,
}

impl fmt::Debug for UndefinedBehaviorInfo {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use UndefinedBehaviorInfo::*;
        match self {
            Ub(ref msg) =>
                write!(f, "{}", msg),
            Unreachable =>
                write!(f, "entered unreachable code"),
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
pub enum UnsupportedOpInfo<'tcx> {
    /// Handle cases which for which we do not have a fixed variant.
    Unsupported(String),

    // -- Everything below is not classified yet --
    FunctionAbiMismatch(Abi, Abi),
    FunctionArgMismatch(Ty<'tcx>, Ty<'tcx>),
    FunctionRetMismatch(Ty<'tcx>, Ty<'tcx>),
    FunctionArgCountMismatch,
    UnterminatedCString(Pointer),
    DanglingPointerDeref,
    DoubleFree,
    InvalidMemoryAccess,
    InvalidFunctionPointer,
    InvalidBool,
    InvalidDiscriminant(ScalarMaybeUndef),
    PointerOutOfBounds {
        ptr: Pointer,
        msg: CheckInAllocMsg,
        allocation_size: Size,
    },
    InvalidNullPointerUsage,
    ReadPointerAsBytes,
    ReadBytesAsPointer,
    ReadForeignStatic,
    InvalidPointerMath,
    ReadUndefBytes(Size),
    DeadLocal,
    InvalidBoolOp(mir::BinOp),
    UnimplementedTraitSelection,
    CalledClosureAsFunction,
    NoMirFor(String),
    DerefFunctionPointer,
    ExecuteMemory,
    InvalidChar(u128),
    OutOfTls,
    TlsOutOfBounds,
    AlignmentCheckFailed {
        required: Align,
        has: Align,
    },
    ValidationFailure(String),
    VtableForArgumentlessMethod,
    ModifiedConstantMemory,
    ModifiedStatic,
    AssumptionNotHeld,
    TypeNotPrimitive(Ty<'tcx>),
    ReallocatedWrongMemoryKind(String, String),
    DeallocatedWrongMemoryKind(String, String),
    ReallocateNonBasePtr,
    DeallocateNonBasePtr,
    IncorrectAllocationInformation(Size, Size, Align, Align),
    HeapAllocZeroBytes,
    HeapAllocNonPowerOfTwoAlignment(u64),
    ReadFromReturnPointer,
    PathNotFound(Vec<String>),
}

impl fmt::Debug for UnsupportedOpInfo<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use UnsupportedOpInfo::*;
        match self {
            PointerOutOfBounds { ptr, msg, allocation_size } => {
                write!(f, "{} failed: pointer must be in-bounds at offset {}, \
                          but is outside bounds of allocation {} which has size {}",
                    msg, ptr.offset.bytes(), ptr.alloc_id, allocation_size.bytes())
            },
            ValidationFailure(ref err) => {
                write!(f, "type validation failed: {}", err)
            }
            NoMirFor(ref func) => write!(f, "no mir for `{}`", func),
            FunctionAbiMismatch(caller_abi, callee_abi) =>
                write!(f, "tried to call a function with ABI {:?} using caller ABI {:?}",
                    callee_abi, caller_abi),
            FunctionArgMismatch(caller_ty, callee_ty) =>
                write!(f, "tried to call a function with argument of type {:?} \
                           passing data of type {:?}",
                    callee_ty, caller_ty),
            FunctionRetMismatch(caller_ty, callee_ty) =>
                write!(f, "tried to call a function with return type {:?} \
                           passing return place of type {:?}",
                    callee_ty, caller_ty),
            FunctionArgCountMismatch =>
                write!(f, "tried to call a function with incorrect number of arguments"),
            ReallocatedWrongMemoryKind(ref old, ref new) =>
                write!(f, "tried to reallocate memory from {} to {}", old, new),
            DeallocatedWrongMemoryKind(ref old, ref new) =>
                write!(f, "tried to deallocate {} memory but gave {} as the kind", old, new),
            InvalidChar(c) =>
                write!(f, "tried to interpret an invalid 32-bit value as a char: {}", c),
            AlignmentCheckFailed { required, has } =>
               write!(f, "tried to access memory with alignment {}, but alignment {} is required",
                      has.bytes(), required.bytes()),
            TypeNotPrimitive(ty) =>
                write!(f, "expected primitive type, got {}", ty),
            PathNotFound(ref path) =>
                write!(f, "Cannot find path {:?}", path),
            IncorrectAllocationInformation(size, size2, align, align2) =>
                write!(f, "incorrect alloc info: expected size {} and align {}, \
                           got size {} and align {}",
                    size.bytes(), align.bytes(), size2.bytes(), align2.bytes()),
            InvalidDiscriminant(val) =>
                write!(f, "encountered invalid enum discriminant {}", val),
            InvalidMemoryAccess =>
                write!(f, "tried to access memory through an invalid pointer"),
            DanglingPointerDeref =>
                write!(f, "dangling pointer was dereferenced"),
            DoubleFree =>
                write!(f, "tried to deallocate dangling pointer"),
            InvalidFunctionPointer =>
                write!(f, "tried to use a function pointer after offsetting it"),
            InvalidBool =>
                write!(f, "invalid boolean value read"),
            InvalidNullPointerUsage =>
                write!(f, "invalid use of NULL pointer"),
            ReadPointerAsBytes =>
                write!(f, "a raw memory access tried to access part of a pointer value as raw \
                    bytes"),
            ReadBytesAsPointer =>
                write!(f, "a memory access tried to interpret some bytes as a pointer"),
            ReadForeignStatic =>
                write!(f, "tried to read from foreign (extern) static"),
            InvalidPointerMath =>
                write!(f, "attempted to do invalid arithmetic on pointers that would leak base \
                    addresses, e.g., comparing pointers into different allocations"),
            DeadLocal =>
                write!(f, "tried to access a dead local variable"),
            DerefFunctionPointer =>
                write!(f, "tried to dereference a function pointer"),
            ExecuteMemory =>
                write!(f, "tried to treat a memory pointer as a function pointer"),
            OutOfTls =>
                write!(f, "reached the maximum number of representable TLS keys"),
            TlsOutOfBounds =>
                write!(f, "accessed an invalid (unallocated) TLS key"),
            CalledClosureAsFunction =>
                write!(f, "tried to call a closure through a function pointer"),
            VtableForArgumentlessMethod =>
                write!(f, "tried to call a vtable function without arguments"),
            ModifiedConstantMemory =>
                write!(f, "tried to modify constant memory"),
            ModifiedStatic =>
                write!(f, "tried to modify a static's initial value from another static's \
                    initializer"),
            AssumptionNotHeld =>
                write!(f, "`assume` argument was false"),
            ReallocateNonBasePtr =>
                write!(f, "tried to reallocate with a pointer not to the beginning of an \
                    existing object"),
            DeallocateNonBasePtr =>
                write!(f, "tried to deallocate with a pointer not to the beginning of an \
                    existing object"),
            HeapAllocZeroBytes =>
                write!(f, "tried to re-, de- or allocate zero bytes on the heap"),
            ReadFromReturnPointer =>
                write!(f, "tried to read from the return pointer"),
            UnimplementedTraitSelection =>
                write!(f, "there were unresolved type arguments during trait selection"),
            InvalidBoolOp(_) =>
                write!(f, "invalid boolean operation"),
            UnterminatedCString(_) =>
                write!(f, "attempted to get length of a null terminated string, but no null \
                    found before end of allocation"),
            ReadUndefBytes(_) =>
                write!(f, "attempted to read undefined bytes"),
            HeapAllocNonPowerOfTwoAlignment(_) =>
                write!(f, "tried to re-, de-, or allocate heap memory with alignment that is \
                    not a power of two"),
            Unsupported(ref msg) =>
                write!(f, "{}", msg),
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
pub enum ResourceExhaustionInfo {
    /// The stack grew too big.
    StackFrameLimitReached,
    /// The program ran into an infinite loop.
    InfiniteLoop,
}

impl fmt::Debug for ResourceExhaustionInfo {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use ResourceExhaustionInfo::*;
        match self {
            StackFrameLimitReached =>
                write!(f, "reached the configured maximum number of stack frames"),
            InfiniteLoop =>
                write!(f, "duplicate interpreter state observed here, const evaluation will never \
                    terminate"),
        }
    }
}

#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
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
    /// but the interpreter is not sure).
    Unsupported(UnsupportedOpInfo<'tcx>),
    /// The program was invalid (ill-typed, not sufficiently monomorphized, ...).
    InvalidProgram(InvalidProgramInfo<'tcx>),
    /// The program exhausted the interpreter's resources (stack/heap too big,
    /// execution takes too long, ..).
    ResourceExhaustion(ResourceExhaustionInfo),
    /// Not actually an interpreter error -- used to signal that execution has exited
    /// with the given status code.  Used by Miri, but not by CTFE.
    Exit(i32),
}

pub type InterpResult<'tcx, T = ()> = Result<T, InterpErrorInfo<'tcx>>;

impl fmt::Display for InterpError<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Forward `Display` to `Debug`
        write!(f, "{:?}", self)
    }
}

impl fmt::Debug for InterpError<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use InterpError::*;
        match *self {
            Unsupported(ref msg) =>
                write!(f, "{:?}", msg),
            InvalidProgram(ref msg) =>
                write!(f, "{:?}", msg),
            UndefinedBehavior(ref msg) =>
                write!(f, "{:?}", msg),
            ResourceExhaustion(ref msg) =>
                write!(f, "{:?}", msg),
            Panic(ref msg) =>
                write!(f, "{:?}", msg),
            Exit(code) =>
                write!(f, "exited with status code {}", code),
        }
    }
}