path: root/src/librustc/ty/error.rs

use crate::ty::{self, BoundRegion, Region, Ty, TyCtxt};
use rustc_ast::ast;
use rustc_errors::{pluralize, Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_span::Span;
use rustc_target::spec::abi;

use std::borrow::Cow;
use std::fmt;

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

impl<T> ExpectedFound<T> {
    pub fn new(a_is_expected: bool, a: T, b: T) -> Self {
        if a_is_expected {
            ExpectedFound { expected: a, found: b }
        } else {
            ExpectedFound { expected: b, found: a }
        }
    }
}

// Data structures used in type unification
#[derive(Clone, Debug, TypeFoldable)]
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>),
    RegionsPlaceholderMismatch,

    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::List<ty::ExistentialPredicate<'tcx>>>),
    ObjectUnsafeCoercion(DefId),
    ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),

    IntrinsicCast,
}

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: &str,
            found: &str,
        ) -> 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)
            }
        }

        let br_string = |br: ty::BoundRegion| match br {
            ty::BrNamed(_, name) => format!(" {}", name),
            _ => String::new(),
        };

        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"),
            TupleSize(values) => write!(
                f,
                "expected a tuple with {} element{}, \
                           found one with {} element{}",
                values.expected,
                pluralize!(values.expected),
                values.found,
                pluralize!(values.found)
            ),
            FixedArraySize(values) => write!(
                f,
                "expected an array with a fixed size of {} element{}, \
                           found one with {} element{}",
                values.expected,
                pluralize!(values.expected),
                values.found,
                pluralize!(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",
                br_string(br)
            ),
            RegionsOverlyPolymorphic(br, _) => write!(
                f,
                "expected concrete lifetime, found bound lifetime parameter{}",
                br_string(br)
            ),
            RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
            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.def_path_str(values.expected)),
                    &format!("trait `{}`", tcx.def_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.def_path_str(values.expected),
                    tcx.def_path_str(values.found)
                )
            }),
            ProjectionBoundsLength(ref values) => write!(
                f,
                "expected {} associated type binding{}, found {}",
                values.expected,
                pluralize!(values.expected),
                values.found
            ),
            ExistentialMismatch(ref values) => report_maybe_different(
                f,
                &format!("trait `{}`", values.expected),
                &format!("trait `{}`", values.found),
            ),
            ConstMismatch(ref values) => {
                write!(f, "expected `{}`, found `{}`", values.expected, values.found)
            }
            IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
            ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
        }
    }
}

impl<'tcx> TypeError<'tcx> {
    pub fn must_include_note(&self) -> bool {
        use self::TypeError::*;
        match self {
            CyclicTy(_) | UnsafetyMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
            | Sorts(_) | IntMismatch(_) | FloatMismatch(_) | VariadicMismatch(_) => false,

            Mutability
            | TupleSize(_)
            | ArgCount
            | RegionsDoesNotOutlive(..)
            | RegionsInsufficientlyPolymorphic(..)
            | RegionsOverlyPolymorphic(..)
            | RegionsPlaceholderMismatch
            | Traits(_)
            | ProjectionMismatched(_)
            | ProjectionBoundsLength(_)
            | ExistentialMismatch(_)
            | ConstMismatch(_)
            | IntrinsicCast
            | ObjectUnsafeCoercion(_) => true,
        }
    }
}

impl<'tcx> ty::TyS<'tcx> {
    pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
        match self.kind {
            ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
                format!("`{}`", self).into()
            }
            ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),

            ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
            ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
            ty::Array(t, n) => {
                let n = tcx.lift(&n).unwrap();
                match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
                    _ if t.is_simple_ty() => format!("array `{}`", self).into(),
                    Some(n) => format!("array of {} element{} ", n, pluralize!(n)).into(),
                    None => "array".into(),
                }
            }
            ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
            ty::Slice(_) => "slice".into(),
            ty::RawPtr(_) => "*-ptr".into(),
            ty::Ref(_, ty, mutbl) => {
                let tymut = ty::TypeAndMut { ty, mutbl };
                let tymut_string = tymut.to_string();
                if tymut_string != "_"
                    && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
                {
                    format!("`&{}`", tymut_string).into()
                } else {
                    // Unknown type name, it's long or has type arguments
                    match mutbl {
                        hir::Mutability::Mut => "mutable reference",
                        _ => "reference",
                    }
                    .into()
                }
            }
            ty::FnDef(..) => "fn item".into(),
            ty::FnPtr(_) => "fn pointer".into(),
            ty::Dynamic(ref inner, ..) => {
                if let Some(principal) = inner.principal() {
                    format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
                } else {
                    "trait object".into()
                }
            }
            ty::Closure(..) => "closure".into(),
            ty::Generator(..) => "generator".into(),
            ty::GeneratorWitness(..) => "generator witness".into(),
            ty::Tuple(..) => "tuple".into(),
            ty::Infer(ty::TyVar(_)) => "inferred type".into(),
            ty::Infer(ty::IntVar(_)) => "integer".into(),
            ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
            ty::Placeholder(..) => "placeholder type".into(),
            ty::Bound(..) => "bound type".into(),
            ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
            ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
            ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
            ty::Projection(_) => "associated type".into(),
            ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
            ty::Param(p) => format!("type parameter `{}`", p).into(),
            ty::Opaque(..) => "opaque type".into(),
            ty::Error => "type error".into(),
        }
    }

    pub fn prefix_string(&self) -> Cow<'static, str> {
        match self.kind {
            ty::Infer(_)
            | ty::Error
            | ty::Bool
            | ty::Char
            | ty::Int(_)
            | ty::Uint(_)
            | ty::Float(_)
            | ty::Str
            | ty::Never => "type".into(),
            ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
            ty::Adt(def, _) => def.descr().into(),
            ty::Foreign(_) => "extern type".into(),
            ty::Array(..) => "array".into(),
            ty::Slice(_) => "slice".into(),
            ty::RawPtr(_) => "raw pointer".into(),
            ty::Ref(.., mutbl) => match mutbl {
                hir::Mutability::Mut => "mutable reference",
                _ => "reference",
            }
            .into(),
            ty::FnDef(..) => "fn item".into(),
            ty::FnPtr(_) => "fn pointer".into(),
            ty::Dynamic(..) => "trait object".into(),
            ty::Closure(..) => "closure".into(),
            ty::Generator(..) => "generator".into(),
            ty::GeneratorWitness(..) => "generator witness".into(),
            ty::Tuple(..) => "tuple".into(),
            ty::Placeholder(..) => "higher-ranked type".into(),
            ty::Bound(..) => "bound type variable".into(),
            ty::Projection(_) => "associated type".into(),
            ty::UnnormalizedProjection(_) => "associated type".into(),
            ty::Param(_) => "type parameter".into(),
            ty::Opaque(..) => "opaque type".into(),
        }
    }
}

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

        match err {
            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");
                }
                if expected_str == found_str && expected_str == "opaque type" {
                    // Issue #63167
                    db.note("distinct uses of `impl Trait` result in different opaque types");
                    let e_str = values.expected.to_string();
                    let f_str = values.found.to_string();
                    if e_str == f_str && &e_str == "impl std::future::Future" {
                        // FIXME: use non-string based check.
                        db.help(
                            "if both `Future`s have the same `Output` type, consider \
                                 `.await`ing on both of them",
                        );
                    }
                }
                match (&values.expected.kind, &values.found.kind) {
                    (ty::Float(_), ty::Infer(ty::IntVar(_))) => {
                        if let Ok(
                            // Issue #53280
                            snippet,
                        ) = self.sess.source_map().span_to_snippet(sp)
                        {
                            if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
                                db.span_suggestion(
                                    sp,
                                    "use a float literal",
                                    format!("{}.0", snippet),
                                    Applicability::MachineApplicable,
                                );
                            }
                        }
                    }
                    (ty::Param(expected), ty::Param(found)) => {
                        let generics = self.generics_of(body_owner_def_id);
                        let e_span = self.def_span(generics.type_param(expected, self).def_id);
                        if !sp.contains(e_span) {
                            db.span_label(e_span, "expected type parameter");
                        }
                        let f_span = self.def_span(generics.type_param(found, self).def_id);
                        if !sp.contains(f_span) {
                            db.span_label(f_span, "found type parameter");
                        }
                        db.note(
                            "a type parameter was expected, but a different one was found; \
                                 you might be missing a type parameter or trait bound",
                        );
                        db.note(
                            "for more information, visit \
                                 https://doc.rust-lang.org/book/ch10-02-traits.html\
                                 #traits-as-parameters",
                        );
                    }
                    (ty::Projection(_), ty::Projection(_)) => {
                        db.note("an associated type was expected, but a different one was found");
                    }
                    (ty::Param(_), ty::Projection(_)) | (ty::Projection(_), ty::Param(_)) => {
                        db.note("you might be missing a type parameter or trait bound");
                    }
                    (ty::Param(p), _) | (_, ty::Param(p)) => {
                        let generics = self.generics_of(body_owner_def_id);
                        let p_span = self.def_span(generics.type_param(p, self).def_id);
                        if !sp.contains(p_span) {
                            db.span_label(p_span, "this type parameter");
                        }
                        db.help("type parameters must be constrained to match other types");
                        if self.sess.teach(&db.get_code().unwrap()) {
                            db.help(
                                "given a type parameter `T` and a method `foo`:
```
trait Trait<T> { fn foo(&self) -> T; }
```
the only ways to implement method `foo` are:
- constrain `T` with an explicit type:
```
impl Trait<String> for X {
    fn foo(&self) -> String { String::new() }
}
```
- add a trait bound to `T` and call a method on that trait that returns `Self`:
```
impl<T: std::default::Default> Trait<T> for X {
    fn foo(&self) -> T { <T as std::default::Default>::default() }
}
```
- change `foo` to return an argument of type `T`:
```
impl<T> Trait<T> for X {
    fn foo(&self, x: T) -> T { x }
}
```",
                            );
                        }
                        db.note(
                            "for more information, visit \
                                 https://doc.rust-lang.org/book/ch10-02-traits.html\
                                 #traits-as-parameters",
                        );
                    }
                    (ty::Projection(_), _) => {
                        db.note(&format!(
                            "consider constraining the associated type `{}` to `{}` or calling a \
                             method that returns `{}`",
                            values.expected, values.found, values.expected,
                        ));
                        if self.sess.teach(&db.get_code().unwrap()) {
                            db.help(
                                "given an associated type `T` and a method `foo`:
```
trait Trait {
    type T;
    fn foo(&self) -> Self::T;
}
```
the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
```
impl Trait for X {
    type T = String;
    fn foo(&self) -> Self::T { String::new() }
}
```",
                            );
                        }
                        db.note(
                            "for more information, visit \
                                 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
                        );
                    }
                    (_, ty::Projection(_)) => {
                        db.note(&format!(
                            "consider constraining the associated type `{}` to `{}`",
                            values.found, values.expected,
                        ));
                        db.note(
                            "for more information, visit \
                                 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
                        );
                    }
                    _ => {}
                }
                debug!(
                    "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
                    values.expected, values.expected.kind, values.found, values.found.kind,
                );
            }
            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 issue #46062 <https://github.com/rust-lang/rust/issues/46062>\n\
                         for more information",
                    );
                }
            }
            _ => {}
        }
    }
}