rust/src/librustc/ty/error.rs

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use hir::def_id::DefId;
use ty::{self, BoundRegion, Region, Ty, TyCtxt};
use std::fmt;
use rustc_target::spec::abi;
use syntax::ast;
use errors::{Applicability, DiagnosticBuilder};
use syntax_pos::Span;

use hir;

#[derive(Clone, Copy, Debug)]
pub struct ExpectedFound<T> {
    pub expected: T,
    pub found: T,
}

// Data structures used in type unification
#[derive(Clone, Debug)]
pub enum TypeError<'tcx> {
    Mismatch,
    UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
    AbiMismatch(ExpectedFound<abi::Abi>),
    Mutability,
    TupleSize(ExpectedFound<usize>),
    FixedArraySize(ExpectedFound<u64>),
    ArgCount,

    RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
    RegionsInsufficientlyPolymorphic(BoundRegion, Region<'tcx>),
    RegionsOverlyPolymorphic(BoundRegion, Region<'tcx>),

    Sorts(ExpectedFound<Ty<'tcx>>),
    IntMismatch(ExpectedFound<ty::IntVarValue>),
    FloatMismatch(ExpectedFound<ast::FloatTy>),
    Traits(ExpectedFound<DefId>),
    VariadicMismatch(ExpectedFound<bool>),

    /// Instantiating a type variable with the given type would have
    /// created a cycle (because it appears somewhere within that
    /// type).
    CyclicTy(Ty<'tcx>),
    ProjectionMismatched(ExpectedFound<DefId>),
    ProjectionBoundsLength(ExpectedFound<usize>),
    ExistentialMismatch(ExpectedFound<&'tcx ty::Slice<ty::ExistentialPredicate<'tcx>>>),

    OldStyleLUB(Box<TypeError<'tcx>>),
}

#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Debug, Copy)]
pub enum UnconstrainedNumeric {
    UnconstrainedFloat,
    UnconstrainedInt,
    Neither,
}

/// Explains the source of a type err in a short, human readable way. This is meant to be placed
/// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
/// afterwards to present additional details, particularly when it comes to lifetime-related
/// errors.
impl<'tcx> fmt::Display for TypeError<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use self::TypeError::*;
        fn report_maybe_different(f: &mut fmt::Formatter,
                                  expected: String, found: String) -> fmt::Result {
            // A naive approach to making sure that we're not reporting silly errors such as:
            // (expected closure, found closure).
            if expected == found {
                write!(f, "expected {}, found a different {}", expected, found)
            } else {
                write!(f, "expected {}, found {}", expected, found)
            }
        }

        match *self {
            CyclicTy(_) => write!(f, "cyclic type of infinite size"),
            Mismatch => write!(f, "types differ"),
            UnsafetyMismatch(values) => {
                write!(f, "expected {} fn, found {} fn",
                       values.expected,
                       values.found)
            }
            AbiMismatch(values) => {
                write!(f, "expected {} fn, found {} fn",
                       values.expected,
                       values.found)
            }
            Mutability => write!(f, "types differ in mutability"),
            FixedArraySize(values) => {
                write!(f, "expected an array with a fixed size of {} elements, \
                           found one with {} elements",
                       values.expected,
                       values.found)
            }
            TupleSize(values) => {
                write!(f, "expected a tuple with {} elements, \
                           found one with {} elements",
                       values.expected,
                       values.found)
            }
            ArgCount => {
                write!(f, "incorrect number of function parameters")
            }
            RegionsDoesNotOutlive(..) => {
                write!(f, "lifetime mismatch")
            }
            RegionsInsufficientlyPolymorphic(br, _) => {
                write!(f,
                       "expected bound lifetime parameter{}{}, found concrete lifetime",
                       if br.is_named() { " " } else { "" },
                       br)
            }
            RegionsOverlyPolymorphic(br, _) => {
                write!(f,
                       "expected concrete lifetime, found bound lifetime parameter{}{}",
                       if br.is_named() { " " } else { "" },
                       br)
            }
            Sorts(values) => ty::tls::with(|tcx| {
                report_maybe_different(f, values.expected.sort_string(tcx),
                                       values.found.sort_string(tcx))
            }),
            Traits(values) => ty::tls::with(|tcx| {
                report_maybe_different(f,
                                       format!("trait `{}`",
                                               tcx.item_path_str(values.expected)),
                                       format!("trait `{}`",
                                               tcx.item_path_str(values.found)))
            }),
            IntMismatch(ref values) => {
                write!(f, "expected `{:?}`, found `{:?}`",
                       values.expected,
                       values.found)
            }
            FloatMismatch(ref values) => {
                write!(f, "expected `{:?}`, found `{:?}`",
                       values.expected,
                       values.found)
            }
            VariadicMismatch(ref values) => {
                write!(f, "expected {} fn, found {} function",
                       if values.expected { "variadic" } else { "non-variadic" },
                       if values.found { "variadic" } else { "non-variadic" })
            }
            ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
                write!(f, "expected {}, found {}",
                       tcx.item_path_str(values.expected),
                       tcx.item_path_str(values.found))
            }),
            ProjectionBoundsLength(ref values) => {
                write!(f, "expected {} associated type bindings, found {}",
                       values.expected,
                       values.found)
            },
            ExistentialMismatch(ref values) => {
                report_maybe_different(f, format!("trait `{}`", values.expected),
                                       format!("trait `{}`", values.found))
            }
            OldStyleLUB(ref err) => {
                write!(f, "{}", err)
            }
        }
    }
}

impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
    pub fn sort_string(&self, tcx: TyCtxt<'a, 'gcx, 'lcx>) -> String {
        match self.sty {
            ty::TyBool | ty::TyChar | ty::TyInt(_) |
            ty::TyUint(_) | ty::TyFloat(_) | ty::TyStr | ty::TyNever => self.to_string(),
            ty::TyTuple(ref tys) if tys.is_empty() => self.to_string(),

            ty::TyAdt(def, _) => format!("{} `{}`", def.descr(), tcx.item_path_str(def.did)),
            ty::TyForeign(def_id) => format!("extern type `{}`", tcx.item_path_str(def_id)),
            ty::TyArray(_, n) => {
                match n.assert_usize(tcx) {
                    Some(n) => format!("array of {} elements", n),
                    None => "array".to_string(),
                }
            }
            ty::TySlice(_) => "slice".to_string(),
            ty::TyRawPtr(_) => "*-ptr".to_string(),
            ty::TyRef(region, ty, mutbl) => {
                let tymut = ty::TypeAndMut { ty, mutbl };
                let tymut_string = tymut.to_string();
                if tymut_string == "_" ||         //unknown type name,
                   tymut_string.len() > 10 ||     //name longer than saying "reference",
                   region.to_string() != ""       //... or a complex type
                {
                    format!("{}reference", match mutbl {
                        hir::Mutability::MutMutable => "mutable ",
                        _ => ""
                    })
                } else {
                    format!("&{}", tymut_string)
                }
            }
            ty::TyFnDef(..) => "fn item".to_string(),
            ty::TyFnPtr(_) => "fn pointer".to_string(),
            ty::TyDynamic(ref inner, ..) => {
                inner.principal().map_or_else(|| "trait".to_string(),
                    |p| format!("trait {}", tcx.item_path_str(p.def_id())))
            }
            ty::TyClosure(..) => "closure".to_string(),
            ty::TyGenerator(..) => "generator".to_string(),
            ty::TyGeneratorWitness(..) => "generator witness".to_string(),
            ty::TyTuple(..) => "tuple".to_string(),
            ty::TyInfer(ty::TyVar(_)) => "inferred type".to_string(),
            ty::TyInfer(ty::IntVar(_)) => "integral variable".to_string(),
            ty::TyInfer(ty::FloatVar(_)) => "floating-point variable".to_string(),
            ty::TyInfer(ty::CanonicalTy(_)) |
            ty::TyInfer(ty::FreshTy(_)) => "skolemized type".to_string(),
            ty::TyInfer(ty::FreshIntTy(_)) => "skolemized integral type".to_string(),
            ty::TyInfer(ty::FreshFloatTy(_)) => "skolemized floating-point type".to_string(),
            ty::TyProjection(_) => "associated type".to_string(),
            ty::TyParam(ref p) => {
                if p.is_self() {
                    "Self".to_string()
                } else {
                    "type parameter".to_string()
                }
            }
            ty::TyAnon(..) => "anonymized type".to_string(),
            ty::TyError => "type error".to_string(),
        }
    }
}

impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
    pub fn note_and_explain_type_err(self,
                                     db: &mut DiagnosticBuilder,
                                     err: &TypeError<'tcx>,
                                     sp: Span) {
        use self::TypeError::*;

        match err.clone() {
            Sorts(values) => {
                let expected_str = values.expected.sort_string(self);
                let found_str = values.found.sort_string(self);
                if expected_str == found_str && expected_str == "closure" {
                    db.note("no two closures, even if identical, have the same type");
                    db.help("consider boxing your closure and/or using it as a trait object");
                }
                match (&values.found.sty, &values.expected.sty) { // Issue #53280
                    (ty::TyInfer(ty::IntVar(_)), ty::TyFloat(_)) => {
                        if let Ok(snippet) = self.sess.source_map().span_to_snippet(sp) {
                            if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
                                db.span_suggestion_with_applicability(
                                    sp,
                                    "use a float literal",
                                    format!("{}.0", snippet),
                                    Applicability::MachineApplicable
                                );
                            }
                        }
                    },
                    _ => {}
                }
            },
            OldStyleLUB(err) => {
                db.note("this was previously accepted by the compiler but has been phased out");
                db.note("for more information, see https://github.com/rust-lang/rust/issues/45852");

                self.note_and_explain_type_err(db, &err, sp);
            }
            CyclicTy(ty) => {
                // Watch out for various cases of cyclic types and try to explain.
                if ty.is_closure() || ty.is_generator() {
                    db.note("closures cannot capture themselves or take themselves as argument;\n\
                             this error may be the result of a recent compiler bug-fix,\n\
                             see https://github.com/rust-lang/rust/issues/46062 for more details");
                }
            }
            _ => {}
        }
    }
}