rust/compiler/rustc_lint/src/internal.rs

//! Some lints that are only useful in the compiler or crates that use compiler internals, such as
//! Clippy.

use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
use rustc_ast as ast;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{def_id::DefId, Expr, ExprKind, GenericArg, PatKind, Path, PathSegment, QPath};
use rustc_hir::{HirId, Impl, Item, ItemKind, Node, Pat, Ty, TyKind};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::hygiene::{ExpnKind, MacroKind};
use rustc_span::symbol::{kw, sym, Symbol};
use rustc_span::Span;
use tracing::debug;

declare_tool_lint! {
    pub rustc::DEFAULT_HASH_TYPES,
    Allow,
    "forbid HashMap and HashSet and suggest the FxHash* variants",
    report_in_external_macro: true
}

declare_lint_pass!(DefaultHashTypes => [DEFAULT_HASH_TYPES]);

impl LateLintPass<'_> for DefaultHashTypes {
    fn check_path(&mut self, cx: &LateContext<'_>, path: &Path<'_>, hir_id: HirId) {
        let Res::Def(rustc_hir::def::DefKind::Struct, def_id) = path.res else { return };
        if matches!(cx.tcx.hir().get(hir_id), Node::Item(Item { kind: ItemKind::Use(..), .. })) {
            // don't lint imports, only actual usages
            return;
        }
        let replace = match cx.tcx.get_diagnostic_name(def_id) {
            Some(sym::HashMap) => "FxHashMap",
            Some(sym::HashSet) => "FxHashSet",
            _ => return,
        };
        cx.struct_span_lint(DEFAULT_HASH_TYPES, path.span, |lint| {
            let msg = format!(
                "prefer `{}` over `{}`, it has better performance",
                replace,
                cx.tcx.item_name(def_id)
            );
            lint.build(&msg)
                .note(&format!("a `use rustc_data_structures::fx::{}` may be necessary", replace))
                .emit();
        });
    }
}

/// Helper function for lints that check for expressions with calls and use typeck results to
/// get the `DefId` and `SubstsRef` of the function.
fn typeck_results_of_method_fn<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &Expr<'_>,
) -> Option<(Span, DefId, ty::subst::SubstsRef<'tcx>)> {
    // FIXME(rustdoc): Lints which use this function use typecheck results which can cause
    // `rustdoc` to error if there are resolution failures.
    //
    // As internal lints are currently always run if there are `unstable_options`, they are added
    // to the lint store of rustdoc. Internal lints are also not used via the `lint_mod` query.
    // Crate lints run outside of a query so rustdoc currently doesn't disable them.
    //
    // Instead of relying on this, either change crate lints to a query disabled by rustdoc, only
    // run internal lints if the user is explicitly opting in or figure out a different way to
    // avoid running lints for rustdoc.
    if cx.tcx.sess.opts.actually_rustdoc {
        return None;
    }

    match expr.kind {
        ExprKind::MethodCall(segment, _, _)
            if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) =>
        {
            Some((segment.ident.span, def_id, cx.typeck_results().node_substs(expr.hir_id)))
        },
        _ => {
            match cx.typeck_results().node_type(expr.hir_id).kind() {
                &ty::FnDef(def_id, substs) => Some((expr.span, def_id, substs)),
                _ => None,
            }
        }
    }
}

declare_tool_lint! {
    pub rustc::POTENTIAL_QUERY_INSTABILITY,
    Allow,
    "require explicit opt-in when using potentially unstable methods or functions",
    report_in_external_macro: true
}

declare_lint_pass!(QueryStability => [POTENTIAL_QUERY_INSTABILITY]);

impl LateLintPass<'_> for QueryStability {
    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
        let Some((span, def_id, substs)) = typeck_results_of_method_fn(cx, expr) else { return };
        if let Ok(Some(instance)) = ty::Instance::resolve(cx.tcx, cx.param_env, def_id, substs) {
            let def_id = instance.def_id();
            if cx.tcx.has_attr(def_id, sym::rustc_lint_query_instability) {
                cx.struct_span_lint(POTENTIAL_QUERY_INSTABILITY, span, |lint| {
                    let msg = format!(
                        "using `{}` can result in unstable query results",
                        cx.tcx.item_name(def_id)
                    );
                    lint.build(&msg)
                        .note("if you believe this case to be fine, allow this lint and add a comment explaining your rationale")
                        .emit();
                })
            }
        }
    }
}

declare_tool_lint! {
    pub rustc::USAGE_OF_TY_TYKIND,
    Allow,
    "usage of `ty::TyKind` outside of the `ty::sty` module",
    report_in_external_macro: true
}

declare_tool_lint! {
    pub rustc::USAGE_OF_QUALIFIED_TY,
    Allow,
    "using `ty::{Ty,TyCtxt}` instead of importing it",
    report_in_external_macro: true
}

declare_lint_pass!(TyTyKind => [
    USAGE_OF_TY_TYKIND,
    USAGE_OF_QUALIFIED_TY,
]);

impl<'tcx> LateLintPass<'tcx> for TyTyKind {
    fn check_path(
        &mut self,
        cx: &LateContext<'tcx>,
        path: &'tcx rustc_hir::Path<'tcx>,
        _: rustc_hir::HirId,
    ) {
        if let Some(segment) = path.segments.iter().nth_back(1)
        && let Some(res) = &segment.res
        && lint_ty_kind_usage(cx, res)
        {
            let span = path.span.with_hi(
                segment.args.map_or(segment.ident.span, |a| a.span_ext).hi()
            );
            cx.struct_span_lint(USAGE_OF_TY_TYKIND, path.span, |lint| {
                lint.build("usage of `ty::TyKind::<kind>`")
                    .span_suggestion(
                        span,
                        "try using `ty::<kind>` directly",
                        "ty",
                        Applicability::MaybeIncorrect, // ty maybe needs an import
                    )
                    .emit();
            });
        }
    }

    fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx Ty<'tcx>) {
        match &ty.kind {
            TyKind::Path(QPath::Resolved(_, path)) => {
                if lint_ty_kind_usage(cx, &path.res) {
                    cx.struct_span_lint(USAGE_OF_TY_TYKIND, path.span, |lint| {
                        let hir = cx.tcx.hir();
                        match hir.find(hir.get_parent_node(ty.hir_id)) {
                            Some(Node::Pat(Pat {
                                kind:
                                    PatKind::Path(qpath)
                                    | PatKind::TupleStruct(qpath, ..)
                                    | PatKind::Struct(qpath, ..),
                                ..
                            })) => {
                                if let QPath::TypeRelative(qpath_ty, ..) = qpath
                                    && qpath_ty.hir_id == ty.hir_id
                                {
                                    lint.build("usage of `ty::TyKind::<kind>`")
                                        .span_suggestion(
                                            path.span,
                                            "try using `ty::<kind>` directly",
                                            "ty",
                                            Applicability::MaybeIncorrect, // ty maybe needs an import
                                        )
                                        .emit();
                                    return;
                                }
                            }
                            Some(Node::Expr(Expr {
                                kind: ExprKind::Path(qpath),
                                ..
                            })) => {
                                if let QPath::TypeRelative(qpath_ty, ..) = qpath
                                    && qpath_ty.hir_id == ty.hir_id
                                {
                                    lint.build("usage of `ty::TyKind::<kind>`")
                                        .span_suggestion(
                                            path.span,
                                            "try using `ty::<kind>` directly",
                                            "ty",
                                            Applicability::MaybeIncorrect, // ty maybe needs an import
                                        )
                                        .emit();
                                    return;
                                }
                            }
                            // Can't unify these two branches because qpath below is `&&` and above is `&`
                            // and `A | B` paths don't play well together with adjustments, apparently.
                            Some(Node::Expr(Expr {
                                kind: ExprKind::Struct(qpath, ..),
                                ..
                            })) => {
                                if let QPath::TypeRelative(qpath_ty, ..) = qpath
                                    && qpath_ty.hir_id == ty.hir_id
                                {
                                    lint.build("usage of `ty::TyKind::<kind>`")
                                        .span_suggestion(
                                            path.span,
                                            "try using `ty::<kind>` directly",
                                            "ty",
                                            Applicability::MaybeIncorrect, // ty maybe needs an import
                                        )
                                        .emit();
                                    return;
                                }
                            }
                            _ => {}
                        }
                        lint.build("usage of `ty::TyKind`").help("try using `Ty` instead").emit();
                    })
                } else if !ty.span.from_expansion() && let Some(t) = is_ty_or_ty_ctxt(cx, &path) {
                    if path.segments.len() > 1 {
                        cx.struct_span_lint(USAGE_OF_QUALIFIED_TY, path.span, |lint| {
                            lint.build(&format!("usage of qualified `ty::{}`", t))
                                .span_suggestion(
                                    path.span,
                                    "try importing it and using it unqualified",
                                    t,
                                    // The import probably needs to be changed
                                    Applicability::MaybeIncorrect,
                                )
                                .emit();
                        })
                    }
                }
            }
            _ => {}
        }
    }
}

fn lint_ty_kind_usage(cx: &LateContext<'_>, res: &Res) -> bool {
    if let Some(did) = res.opt_def_id() {
        cx.tcx.is_diagnostic_item(sym::TyKind, did) || cx.tcx.is_diagnostic_item(sym::IrTyKind, did)
    } else {
        false
    }
}

fn is_ty_or_ty_ctxt(cx: &LateContext<'_>, path: &Path<'_>) -> Option<String> {
    match &path.res {
        Res::Def(_, def_id) => {
            if let Some(name @ (sym::Ty | sym::TyCtxt)) = cx.tcx.get_diagnostic_name(*def_id) {
                return Some(format!("{}{}", name, gen_args(path.segments.last().unwrap())));
            }
        }
        // Only lint on `&Ty` and `&TyCtxt` if it is used outside of a trait.
        Res::SelfTy { trait_: None, alias_to: Some((did, _)) } => {
            if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
                if let Some(name @ (sym::Ty | sym::TyCtxt)) = cx.tcx.get_diagnostic_name(adt.did())
                {
                    // NOTE: This path is currently unreachable as `Ty<'tcx>` is
                    // defined as a type alias meaning that `impl<'tcx> Ty<'tcx>`
                    // is not actually allowed.
                    //
                    // I(@lcnr) still kept this branch in so we don't miss this
                    // if we ever change it in the future.
                    return Some(format!("{}<{}>", name, substs[0]));
                }
            }
        }
        _ => (),
    }

    None
}

fn gen_args(segment: &PathSegment<'_>) -> String {
    if let Some(args) = &segment.args {
        let lifetimes = args
            .args
            .iter()
            .filter_map(|arg| {
                if let GenericArg::Lifetime(lt) = arg {
                    Some(lt.name.ident().to_string())
                } else {
                    None
                }
            })
            .collect::<Vec<_>>();

        if !lifetimes.is_empty() {
            return format!("<{}>", lifetimes.join(", "));
        }
    }

    String::new()
}

declare_tool_lint! {
    pub rustc::LINT_PASS_IMPL_WITHOUT_MACRO,
    Allow,
    "`impl LintPass` without the `declare_lint_pass!` or `impl_lint_pass!` macros"
}

declare_lint_pass!(LintPassImpl => [LINT_PASS_IMPL_WITHOUT_MACRO]);

impl EarlyLintPass for LintPassImpl {
    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
        if let ast::ItemKind::Impl(box ast::Impl { of_trait: Some(lint_pass), .. }) = &item.kind {
            if let Some(last) = lint_pass.path.segments.last() {
                if last.ident.name == sym::LintPass {
                    let expn_data = lint_pass.path.span.ctxt().outer_expn_data();
                    let call_site = expn_data.call_site;
                    if expn_data.kind != ExpnKind::Macro(MacroKind::Bang, sym::impl_lint_pass)
                        && call_site.ctxt().outer_expn_data().kind
                            != ExpnKind::Macro(MacroKind::Bang, sym::declare_lint_pass)
                    {
                        cx.struct_span_lint(
                            LINT_PASS_IMPL_WITHOUT_MACRO,
                            lint_pass.path.span,
                            |lint| {
                                lint.build("implementing `LintPass` by hand")
                                    .help("try using `declare_lint_pass!` or `impl_lint_pass!` instead")
                                    .emit();
                            },
                        )
                    }
                }
            }
        }
    }
}

declare_tool_lint! {
    pub rustc::EXISTING_DOC_KEYWORD,
    Allow,
    "Check that documented keywords in std and core actually exist",
    report_in_external_macro: true
}

declare_lint_pass!(ExistingDocKeyword => [EXISTING_DOC_KEYWORD]);

fn is_doc_keyword(s: Symbol) -> bool {
    s <= kw::Union
}

impl<'tcx> LateLintPass<'tcx> for ExistingDocKeyword {
    fn check_item(&mut self, cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
        for attr in cx.tcx.hir().attrs(item.hir_id()) {
            if !attr.has_name(sym::doc) {
                continue;
            }
            if let Some(list) = attr.meta_item_list() {
                for nested in list {
                    if nested.has_name(sym::keyword) {
                        let v = nested
                            .value_str()
                            .expect("#[doc(keyword = \"...\")] expected a value!");
                        if is_doc_keyword(v) {
                            return;
                        }
                        cx.struct_span_lint(EXISTING_DOC_KEYWORD, attr.span, |lint| {
                            lint.build(&format!(
                                "Found non-existing keyword `{}` used in \
                                     `#[doc(keyword = \"...\")]`",
                                v,
                            ))
                            .help("only existing keywords are allowed in core/std")
                            .emit();
                        });
                    }
                }
            }
        }
    }
}

declare_tool_lint! {
    pub rustc::UNTRANSLATABLE_DIAGNOSTIC,
    Allow,
    "prevent creation of diagnostics which cannot be translated",
    report_in_external_macro: true
}

declare_tool_lint! {
    pub rustc::DIAGNOSTIC_OUTSIDE_OF_IMPL,
    Allow,
    "prevent creation of diagnostics outside of `SessionDiagnostic`/`AddSubdiagnostic` impls",
    report_in_external_macro: true
}

declare_lint_pass!(Diagnostics => [ UNTRANSLATABLE_DIAGNOSTIC, DIAGNOSTIC_OUTSIDE_OF_IMPL ]);

impl LateLintPass<'_> for Diagnostics {
    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
        let Some((span, def_id, substs)) = typeck_results_of_method_fn(cx, expr) else { return };
        debug!(?span, ?def_id, ?substs);
        if let Ok(Some(instance)) = ty::Instance::resolve(cx.tcx, cx.param_env, def_id, substs) &&
            !cx.tcx.has_attr(instance.def_id(), sym::rustc_lint_diagnostics)
        {
            return;
        }

        let mut found_impl = false;
        for (_, parent) in cx.tcx.hir().parent_iter(expr.hir_id) {
            debug!(?parent);
            if let Node::Item(Item { kind: ItemKind::Impl(impl_), .. }) = parent &&
                let Impl { of_trait: Some(of_trait), .. } = impl_ &&
                let Some(def_id) = of_trait.trait_def_id() &&
                let Some(name) = cx.tcx.get_diagnostic_name(def_id) &&
                matches!(name, sym::SessionDiagnostic | sym::AddSubdiagnostic)
            {
                found_impl = true;
                break;
            }
        }
        debug!(?found_impl);
        if !found_impl {
            cx.struct_span_lint(DIAGNOSTIC_OUTSIDE_OF_IMPL, span, |lint| {
                lint.build("diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls")
                    .emit();
            })
        }

        let mut found_diagnostic_message = false;
        for ty in substs.types() {
            debug!(?ty);
            if let Some(adt_def) = ty.ty_adt_def() &&
                let Some(name) =  cx.tcx.get_diagnostic_name(adt_def.did()) &&
                matches!(name, sym::DiagnosticMessage | sym::SubdiagnosticMessage)
            {
                found_diagnostic_message = true;
                break;
            }
        }
        debug!(?found_diagnostic_message);
        if !found_diagnostic_message {
            cx.struct_span_lint(UNTRANSLATABLE_DIAGNOSTIC, span, |lint| {
                lint.build("diagnostics should be created using translatable messages").emit();
            })
        }
    }
}