compiler/rustc_hir_analysis/src/astconv/lint.rs

use rustc_ast::TraitObjectSyntax;
use rustc_errors::{Diagnostic, StashKey};
use rustc_hir as hir;
use rustc_lint_defs::{builtin::BARE_TRAIT_OBJECTS, Applicability};
use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;

use super::AstConv;

impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
    /// Make sure that we are in the condition to suggest the blanket implementation.
    pub(super) fn maybe_lint_blanket_trait_impl(
        &self,
        self_ty: &hir::Ty<'_>,
        diag: &mut Diagnostic,
    ) {
        let tcx = self.tcx();
        let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
        if let hir::Node::Item(hir::Item {
            kind:
                hir::ItemKind::Impl(hir::Impl {
                    self_ty: impl_self_ty,
                    of_trait: Some(of_trait_ref),
                    generics,
                    ..
                }),
            ..
        }) = tcx.hir().get_by_def_id(parent_id)
            && self_ty.hir_id == impl_self_ty.hir_id
        {
            if !of_trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
                return;
            }
            let of_trait_span = of_trait_ref.path.span;
            // make sure that we are not calling unwrap to abort during the compilation
            let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else {
                return;
            };
            let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else {
                return;
            };
            // check if the trait has generics, to make a correct suggestion
            let param_name = generics.params.next_type_param_name(None);

            let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
                (span, format!(", {param_name}: {impl_trait_name}"))
            } else {
                (generics.span, format!("<{param_name}: {impl_trait_name}>"))
            };
            diag.multipart_suggestion(
                format!(
                    "alternatively use a blanket \
                     implementation to implement `{of_trait_name}` for \
                     all types that also implement `{impl_trait_name}`"
                ),
                vec![(self_ty.span, param_name), add_generic_sugg],
                Applicability::MaybeIncorrect,
            );
        }
    }

    pub(super) fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
        let tcx = self.tcx();
        if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
            self_ty.kind
        {
            let needs_bracket = in_path
                && !tcx
                    .sess
                    .source_map()
                    .span_to_prev_source(self_ty.span)
                    .ok()
                    .is_some_and(|s| s.trim_end().ends_with('<'));

            let is_global = poly_trait_ref.trait_ref.path.is_global();

            let mut sugg = Vec::from_iter([(
                self_ty.span.shrink_to_lo(),
                format!(
                    "{}dyn {}",
                    if needs_bracket { "<" } else { "" },
                    if is_global { "(" } else { "" },
                ),
            )]);

            if is_global || needs_bracket {
                sugg.push((
                    self_ty.span.shrink_to_hi(),
                    format!(
                        "{}{}",
                        if is_global { ")" } else { "" },
                        if needs_bracket { ">" } else { "" },
                    ),
                ));
            }

            if self_ty.span.edition().at_least_rust_2021() {
                let msg = "trait objects must include the `dyn` keyword";
                let label = "add `dyn` keyword before this trait";
                let mut diag =
                    rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
                if self_ty.span.can_be_used_for_suggestions() {
                    diag.multipart_suggestion_verbose(
                        label,
                        sugg,
                        Applicability::MachineApplicable,
                    );
                }
                // check if the impl trait that we are considering is a impl of a local trait
                self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
                diag.stash(self_ty.span, StashKey::TraitMissingMethod);
            } else {
                let msg = "trait objects without an explicit `dyn` are deprecated";
                tcx.struct_span_lint_hir(
                    BARE_TRAIT_OBJECTS,
                    self_ty.hir_id,
                    self_ty.span,
                    msg,
                    |lint| {
                        lint.multipart_suggestion_verbose(
                            "use `dyn`",
                            sugg,
                            Applicability::MachineApplicable,
                        );
                        self.maybe_lint_blanket_trait_impl(&self_ty, lint);
                        lint
                    },
                );
            }
        }
    }
}