compiler/rustc_middle/src/ty/diagnostics.rs

//! Diagnostics related methods for `Ty`.

use crate::ty::subst::{GenericArg, GenericArgKind};
use crate::ty::TyKind::*;
use crate::ty::{
    ConstKind, ExistentialPredicate, ExistentialProjection, ExistentialTraitRef, InferTy,
    ProjectionTy, Term, Ty, TyCtxt, TypeAndMut,
};

use rustc_errors::{Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::{QPath, TyKind, WhereBoundPredicate, WherePredicate};
use rustc_span::Span;

impl<'tcx> Ty<'tcx> {
    /// Similar to `Ty::is_primitive`, but also considers inferred numeric values to be primitive.
    pub fn is_primitive_ty(self) -> bool {
        matches!(
            self.kind(),
            Bool | Char
                | Str
                | Int(_)
                | Uint(_)
                | Float(_)
                | Infer(
                    InferTy::IntVar(_)
                        | InferTy::FloatVar(_)
                        | InferTy::FreshIntTy(_)
                        | InferTy::FreshFloatTy(_)
                )
        )
    }

    /// Whether the type is succinctly representable as a type instead of just referred to with a
    /// description in error messages. This is used in the main error message.
    pub fn is_simple_ty(self) -> bool {
        match self.kind() {
            Bool
            | Char
            | Str
            | Int(_)
            | Uint(_)
            | Float(_)
            | Infer(
                InferTy::IntVar(_)
                | InferTy::FloatVar(_)
                | InferTy::FreshIntTy(_)
                | InferTy::FreshFloatTy(_),
            ) => true,
            Ref(_, x, _) | Array(x, _) | Slice(x) => x.peel_refs().is_simple_ty(),
            Tuple(tys) if tys.is_empty() => true,
            _ => false,
        }
    }

    /// Whether the type is succinctly representable as a type instead of just referred to with a
    /// description in error messages. This is used in the primary span label. Beyond what
    /// `is_simple_ty` includes, it also accepts ADTs with no type arguments and references to
    /// ADTs with no type arguments.
    pub fn is_simple_text(self) -> bool {
        match self.kind() {
            Adt(_, substs) => substs.non_erasable_generics().next().is_none(),
            Ref(_, ty, _) => ty.is_simple_text(),
            _ => self.is_simple_ty(),
        }
    }

    /// Whether the type can be safely suggested during error recovery.
    pub fn is_suggestable(self) -> bool {
        fn generic_arg_is_suggestible(arg: GenericArg<'_>) -> bool {
            match arg.unpack() {
                GenericArgKind::Type(ty) => ty.is_suggestable(),
                GenericArgKind::Const(c) => const_is_suggestable(c.val()),
                _ => true,
            }
        }

        fn const_is_suggestable(kind: ConstKind<'_>) -> bool {
            match kind {
                ConstKind::Infer(..)
                | ConstKind::Bound(..)
                | ConstKind::Placeholder(..)
                | ConstKind::Error(..) => false,
                _ => true,
            }
        }

        // FIXME(compiler-errors): Some types are still not good to suggest,
        // specifically references with lifetimes within the function. Not
        //sure we have enough information to resolve whether a region is
        // temporary, so I'll leave this as a fixme.

        match self.kind() {
            Opaque(..)
            | FnDef(..)
            | Closure(..)
            | Infer(..)
            | Generator(..)
            | GeneratorWitness(..)
            | Bound(_, _)
            | Placeholder(_)
            | Error(_) => false,
            Dynamic(dty, _) => dty.iter().all(|pred| match pred.skip_binder() {
                ExistentialPredicate::Trait(ExistentialTraitRef { substs, .. }) => {
                    substs.iter().all(generic_arg_is_suggestible)
                }
                ExistentialPredicate::Projection(ExistentialProjection {
                    substs, term, ..
                }) => {
                    let term_is_suggestable = match term {
                        Term::Ty(ty) => ty.is_suggestable(),
                        Term::Const(c) => const_is_suggestable(c.val()),
                    };
                    term_is_suggestable && substs.iter().all(generic_arg_is_suggestible)
                }
                _ => true,
            }),
            Projection(ProjectionTy { substs: args, .. }) | Adt(_, args) | Tuple(args) => {
                args.iter().all(generic_arg_is_suggestible)
            }
            Slice(ty) | RawPtr(TypeAndMut { ty, .. }) | Ref(_, ty, _) => ty.is_suggestable(),
            Array(ty, c) => ty.is_suggestable() && const_is_suggestable(c.val()),
            _ => true,
        }
    }
}

pub fn suggest_arbitrary_trait_bound(
    generics: &hir::Generics<'_>,
    err: &mut DiagnosticBuilder<'_>,
    param_name: &str,
    constraint: &str,
) -> bool {
    let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
    match (param, param_name) {
        (Some(_), "Self") => return false,
        _ => {}
    }
    // Suggest a where clause bound for a non-type paremeter.
    let (action, prefix) = if generics.where_clause.predicates.is_empty() {
        ("introducing a", " where ")
    } else {
        ("extending the", ", ")
    };
    err.span_suggestion_verbose(
        generics.where_clause.tail_span_for_suggestion(),
        &format!(
            "consider {} `where` bound, but there might be an alternative better way to express \
             this requirement",
            action,
        ),
        format!("{}{}: {}", prefix, param_name, constraint),
        Applicability::MaybeIncorrect,
    );
    true
}

fn suggest_removing_unsized_bound(
    generics: &hir::Generics<'_>,
    err: &mut DiagnosticBuilder<'_>,
    param_name: &str,
    param: &hir::GenericParam<'_>,
    def_id: Option<DefId>,
) {
    // See if there's a `?Sized` bound that can be removed to suggest that.
    // First look at the `where` clause because we can have `where T: ?Sized`,
    // then look at params.
    for (where_pos, predicate) in generics.where_clause.predicates.iter().enumerate() {
        match predicate {
            WherePredicate::BoundPredicate(WhereBoundPredicate {
                bounded_ty:
                    hir::Ty {
                        kind:
                            hir::TyKind::Path(hir::QPath::Resolved(
                                None,
                                hir::Path {
                                    segments: [segment],
                                    res: hir::def::Res::Def(hir::def::DefKind::TyParam, _),
                                    ..
                                },
                            )),
                        ..
                    },
                bounds,
                span,
                ..
            }) if segment.ident.as_str() == param_name => {
                for (pos, bound) in bounds.iter().enumerate() {
                    match bound {
                        hir::GenericBound::Trait(poly, hir::TraitBoundModifier::Maybe)
                            if poly.trait_ref.trait_def_id() == def_id => {}
                        _ => continue,
                    }
                    let sp = match (
                        bounds.len(),
                        pos,
                        generics.where_clause.predicates.len(),
                        where_pos,
                    ) {
                        // where T: ?Sized
                        // ^^^^^^^^^^^^^^^
                        (1, _, 1, _) => generics.where_clause.span,
                        // where Foo: Bar, T: ?Sized,
                        //               ^^^^^^^^^^^
                        (1, _, len, pos) if pos == len - 1 => generics.where_clause.predicates
                            [pos - 1]
                            .span()
                            .shrink_to_hi()
                            .to(*span),
                        // where T: ?Sized, Foo: Bar,
                        //       ^^^^^^^^^^^
                        (1, _, _, pos) => {
                            span.until(generics.where_clause.predicates[pos + 1].span())
                        }
                        // where T: ?Sized + Bar, Foo: Bar,
                        //          ^^^^^^^^^
                        (_, 0, _, _) => bound.span().to(bounds[1].span().shrink_to_lo()),
                        // where T: Bar + ?Sized, Foo: Bar,
                        //             ^^^^^^^^^
                        (_, pos, _, _) => bounds[pos - 1].span().shrink_to_hi().to(bound.span()),
                    };
                    err.span_suggestion_verbose(
                        sp,
                        "consider removing the `?Sized` bound to make the \
                            type parameter `Sized`",
                        String::new(),
                        Applicability::MaybeIncorrect,
                    );
                }
            }
            _ => {}
        }
    }
    for (pos, bound) in param.bounds.iter().enumerate() {
        match bound {
            hir::GenericBound::Trait(poly, hir::TraitBoundModifier::Maybe)
                if poly.trait_ref.trait_def_id() == def_id =>
            {
                let sp = match (param.bounds.len(), pos) {
                    // T: ?Sized,
                    //  ^^^^^^^^
                    (1, _) => param.span.shrink_to_hi().to(bound.span()),
                    // T: ?Sized + Bar,
                    //    ^^^^^^^^^
                    (_, 0) => bound.span().to(param.bounds[1].span().shrink_to_lo()),
                    // T: Bar + ?Sized,
                    //       ^^^^^^^^^
                    (_, pos) => param.bounds[pos - 1].span().shrink_to_hi().to(bound.span()),
                };
                err.span_suggestion_verbose(
                    sp,
                    "consider removing the `?Sized` bound to make the type parameter \
                        `Sized`",
                    String::new(),
                    Applicability::MaybeIncorrect,
                );
            }
            _ => {}
        }
    }
}

/// Suggest restricting a type param with a new bound.
pub fn suggest_constraining_type_param(
    tcx: TyCtxt<'_>,
    generics: &hir::Generics<'_>,
    err: &mut DiagnosticBuilder<'_>,
    param_name: &str,
    constraint: &str,
    def_id: Option<DefId>,
) -> bool {
    let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);

    let Some(param) = param else {
        return false;
    };

    const MSG_RESTRICT_BOUND_FURTHER: &str = "consider further restricting this bound";
    let msg_restrict_type = format!("consider restricting type parameter `{}`", param_name);
    let msg_restrict_type_further =
        format!("consider further restricting type parameter `{}`", param_name);

    if def_id == tcx.lang_items().sized_trait() {
        // Type parameters are already `Sized` by default.
        err.span_label(param.span, &format!("this type parameter needs to be `{}`", constraint));
        suggest_removing_unsized_bound(generics, err, param_name, param, def_id);
        return true;
    }
    let mut suggest_restrict = |span| {
        err.span_suggestion_verbose(
            span,
            MSG_RESTRICT_BOUND_FURTHER,
            format!(" + {}", constraint),
            Applicability::MachineApplicable,
        );
    };

    if param_name.starts_with("impl ") {
        // If there's an `impl Trait` used in argument position, suggest
        // restricting it:
        //
        //   fn foo(t: impl Foo) { ... }
        //             --------
        //             |
        //             help: consider further restricting this bound with `+ Bar`
        //
        // Suggestion for tools in this case is:
        //
        //   fn foo(t: impl Foo) { ... }
        //             --------
        //             |
        //             replace with: `impl Foo + Bar`

        suggest_restrict(param.span.shrink_to_hi());
        return true;
    }

    if generics.where_clause.predicates.is_empty()
        // Given `trait Base<T = String>: Super<T>` where `T: Copy`, suggest restricting in the
        // `where` clause instead of `trait Base<T: Copy = String>: Super<T>`.
        && !matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. })
    {
        if let Some(span) = param.bounds_span_for_suggestions() {
            // If user has provided some bounds, suggest restricting them:
            //
            //   fn foo<T: Foo>(t: T) { ... }
            //             ---
            //             |
            //             help: consider further restricting this bound with `+ Bar`
            //
            // Suggestion for tools in this case is:
            //
            //   fn foo<T: Foo>(t: T) { ... }
            //          --
            //          |
            //          replace with: `T: Bar +`
            suggest_restrict(span);
        } else {
            // If user hasn't provided any bounds, suggest adding a new one:
            //
            //   fn foo<T>(t: T) { ... }
            //          - help: consider restricting this type parameter with `T: Foo`
            err.span_suggestion_verbose(
                param.span.shrink_to_hi(),
                &msg_restrict_type,
                format!(": {}", constraint),
                Applicability::MachineApplicable,
            );
        }

        true
    } else {
        // This part is a bit tricky, because using the `where` clause user can
        // provide zero, one or many bounds for the same type parameter, so we
        // have following cases to consider:
        //
        // 1) When the type parameter has been provided zero bounds
        //
        //    Message:
        //      fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
        //             - help: consider restricting this type parameter with `where X: Bar`
        //
        //    Suggestion:
        //      fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
        //                                           - insert: `, X: Bar`
        //
        //
        // 2) When the type parameter has been provided one bound
        //
        //    Message:
        //      fn foo<T>(t: T) where T: Foo { ... }
        //                            ^^^^^^
        //                            |
        //                            help: consider further restricting this bound with `+ Bar`
        //
        //    Suggestion:
        //      fn foo<T>(t: T) where T: Foo { ... }
        //                            ^^
        //                            |
        //                            replace with: `T: Bar +`
        //
        //
        // 3) When the type parameter has been provided many bounds
        //
        //    Message:
        //      fn foo<T>(t: T) where T: Foo, T: Bar {... }
        //             - help: consider further restricting this type parameter with `where T: Zar`
        //
        //    Suggestion:
        //      fn foo<T>(t: T) where T: Foo, T: Bar {... }
        //                                          - insert: `, T: Zar`
        //
        // Additionally, there may be no `where` clause whatsoever in the case that this was
        // reached because the generic parameter has a default:
        //
        //    Message:
        //      trait Foo<T=()> {... }
        //             - help: consider further restricting this type parameter with `where T: Zar`
        //
        //    Suggestion:
        //      trait Foo<T=()> where T: Zar {... }
        //                     - insert: `where T: Zar`

        if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. })
            && generics.where_clause.predicates.len() == 0
        {
            // Suggest a bound, but there is no existing `where` clause *and* the type param has a
            // default (`<T=Foo>`), so we suggest adding `where T: Bar`.
            err.span_suggestion_verbose(
                generics.where_clause.tail_span_for_suggestion(),
                &msg_restrict_type_further,
                format!(" where {}: {}", param_name, constraint),
                Applicability::MachineApplicable,
            );
        } else {
            let mut param_spans = Vec::new();

            for predicate in generics.where_clause.predicates {
                if let WherePredicate::BoundPredicate(WhereBoundPredicate {
                    span,
                    bounded_ty,
                    ..
                }) = predicate
                {
                    if let TyKind::Path(QPath::Resolved(_, path)) = &bounded_ty.kind {
                        if let Some(segment) = path.segments.first() {
                            if segment.ident.to_string() == param_name {
                                param_spans.push(span);
                            }
                        }
                    }
                }
            }

            match param_spans[..] {
                [&param_span] => suggest_restrict(param_span.shrink_to_hi()),
                _ => {
                    err.span_suggestion_verbose(
                        generics.where_clause.tail_span_for_suggestion(),
                        &msg_restrict_type_further,
                        format!(", {}: {}", param_name, constraint),
                        Applicability::MachineApplicable,
                    );
                }
            }
        }

        true
    }
}

/// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
pub struct TraitObjectVisitor<'tcx>(pub Vec<&'tcx hir::Ty<'tcx>>, pub crate::hir::map::Map<'tcx>);

impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
    fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
        match ty.kind {
            hir::TyKind::TraitObject(
                _,
                hir::Lifetime {
                    name:
                        hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static,
                    ..
                },
                _,
            ) => {
                self.0.push(ty);
            }
            hir::TyKind::OpaqueDef(item_id, _) => {
                self.0.push(ty);
                let item = self.1.item(item_id);
                hir::intravisit::walk_item(self, item);
            }
            _ => {}
        }
        hir::intravisit::walk_ty(self, ty);
    }
}

/// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
pub struct StaticLifetimeVisitor<'tcx>(pub Vec<Span>, pub crate::hir::map::Map<'tcx>);

impl<'v> hir::intravisit::Visitor<'v> for StaticLifetimeVisitor<'v> {
    fn visit_lifetime(&mut self, lt: &'v hir::Lifetime) {
        if let hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static =
            lt.name
        {
            self.0.push(lt.span);
        }
    }
}