rustc_builtin_macros/deriving/

clone.rs

use rustc_ast::{self as ast, Generics, ItemKind, Safety, VariantData};
use rustc_data_structures::fx::FxHashSet;
use rustc_expand::base::ExtCtxt;
use rustc_span::{DUMMY_SP, Ident, Span, sym};
use thin_vec::{ThinVec, thin_vec};

use crate::deriving::generic::*;
use crate::deriving::path_std;

pub(crate) fn expand_deriving_clone(
    cx: &ExtCtxt<'_>,
    span: Span,
    item: &ast::Item,
    push: &mut dyn FnMut(Box<ast::Item>),
    is_const: bool,
) {
    // The simple form is `fn clone(&self) -> Self { *self }`, possibly with
    // some additional `AssertParamIsClone` assertions.
    //
    // We can use the simple form if either of the following are true.
    // - The type derives Copy and there are no generic parameters. (If we
    //   used the simple form with generics, we'd have to bound the generics
    //   with Clone + Copy, and then there'd be no Clone impl at all if the
    //   user fills in something that is Clone but not Copy. After
    //   specialization we can remove this no-generics limitation.)
    // - The item is a union. (Unions with generic parameters still can derive
    //   Clone because they require Copy for deriving, Clone alone is not
    //   enough. Whether Clone is implemented for fields is irrelevant so we
    //   don't assert it.)
    let bounds;
    let substructure;
    let is_simple;
    match &item.kind {
        ItemKind::Struct(_, Generics { params, .. }, _)
        | ItemKind::Enum(_, Generics { params, .. }, _) => {
            let container_id = cx.current_expansion.id.expn_data().parent.expect_local();
            let has_derive_copy = cx.resolver.has_derive_copy(container_id);
            bounds = smallvec![];
            if has_derive_copy
                && !params
                    .iter()
                    .any(|param| matches!(param.kind, ast::GenericParamKind::Type { .. }))
            {
                is_simple = true;
                substructure = combine_substructure(|c, s, sub| cs_clone_simple(c, s, sub, false));
            } else {
                is_simple = false;
                substructure = combine_substructure(|c, s, sub| {
                    cs_clone(c, s, sub, item.kind.ident().unwrap())
                });
            }
        }
        ItemKind::Union(..) => {
            bounds = smallvec![path_std!(cx, span, marker::Copy)];
            is_simple = true;
            substructure = combine_substructure(|c, s, sub| cs_clone_simple(c, s, sub, true));
        }
        _ => cx.dcx().span_bug(span, "`derive(Clone)` on wrong item kind"),
    }

    // If the clone method is just copying the value, also mark the type as
    // `TrivialClone` to allow some library optimizations.
    if is_simple {
        let trivial_def = TraitDef {
            span,
            path: path_std!(cx, span, clone::TrivialClone),
            needs_copy_as_bound_if_packed: true,
            additional_bounds: bounds.clone(),
            supports_unions: true,
            methods: SmallVec::new(),
            is_const,
            safety: Safety::Unsafe(DUMMY_SP),
            // `TrivialClone` is not part of an API guarantee, so it shouldn't
            // appear in rustdoc output.
            document: false,
            ..
        };

        trivial_def.expand(cx, item, push);
    }

    let trait_def = TraitDef {
        span,
        path: path_std!(cx, span, clone::Clone),
        needs_copy_as_bound_if_packed: true,
        additional_bounds: bounds,
        supports_unions: true,
        methods: smallvec![MethodDef {
            name: sym::clone,
            generics: cx.empty_generics(span),
            explicit_self: true,
            nonself_args: SmallVec::new(),
            has_other_selflike_arg: false,
            ret_ty: cx.ty_self(span),
            attributes: thin_vec![cx.generated_attr(span, ast::GeneratedAttr::Inline)],
            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
            combine_substructure: substructure,
        }],
        is_const,
        ..
    };

    trait_def.expand_ext(cx, item, push, is_simple)
}

fn cs_clone_simple(
    cx: &ExtCtxt<'_>,
    trait_span: Span,
    substr: Substructure<'_>,
    is_union: bool,
) -> BlockOrExpr {
    let mut stmts = ThinVec::new();
    let mut seen_type_names = FxHashSet::default();
    let mut process_variant = |variant: &VariantData| {
        for field in variant.fields() {
            // This basic redundancy checking only prevents duplication of
            // assertions like `AssertParamIsClone<Foo>` where the type is a
            // simple name. That's enough to get a lot of cases, though.
            if let Some(name) = field.ty.kind.is_simple_path()
                && !seen_type_names.insert(name)
            {
                // Already produced an assertion for this type.
                // Anonymous structs or unions must be eliminated as they cannot be
                // type parameters.
            } else {
                // let _: AssertParamIsClone<FieldTy>;
                super::assert_ty_bounds(
                    cx,
                    &mut stmts,
                    field.ty.clone(),
                    field.span,
                    &[sym::clone, sym::AssertParamIsClone],
                );
            }
        }
    };

    if is_union {
        // Just a single assertion for unions, that the union impls `Copy`.
        // let _: AssertParamIsCopy<Self>;
        let self_ty = cx.ty_self(DUMMY_SP);
        super::assert_ty_bounds(
            cx,
            &mut stmts,
            self_ty,
            trait_span,
            &[sym::clone, sym::AssertParamIsCopy],
        );
    } else {
        match substr {
            StaticStruct(vdata, ..) => {
                process_variant(vdata);
            }
            StaticEnum(enum_def, ..) => {
                for variant in &enum_def.variants {
                    process_variant(&variant.data);
                }
            }
            _ => cx.dcx().span_bug(trait_span, "unexpected substructure in simple `derive(Clone)`"),
        }
    }
    BlockOrExpr::new_mixed(stmts, Some(cx.expr_deref(trait_span, cx.expr_self(trait_span))))
}

fn cs_clone(
    cx: &ExtCtxt<'_>,
    trait_span: Span,
    substr: Substructure<'_>,
    type_ident: Ident,
) -> BlockOrExpr {
    let subcall = |field: FieldInfo| {
        let args = thin_vec![field.self_expr];
        cx.expr_call_global(
            field.span,
            cx.std_path(field.span, &[sym::clone, sym::Clone, sym::clone]),
            args,
        )
    };

    let ctor_path;
    let all_fields;
    let vdata;
    // We need to use `type_ident` instead of `Self` here,
    // see https://github.com/rust-lang/rust/issues/163800
    match substr {
        Struct(vdata_, af) => {
            ctor_path = cx.path(trait_span, &[type_ident]);
            all_fields = af;
            vdata = vdata_;
        }
        EnumMatching(.., variant, af) => {
            ctor_path = cx.path(trait_span, &[type_ident, variant.ident]);
            all_fields = af;
            vdata = &variant.data;
        }
        _ => cx.dcx().span_bug(trait_span, "unexpected substructure in `derive(Clone)`"),
    }

    let expr = match *vdata {
        VariantData::Struct { .. } => {
            let fields = all_fields
                .into_iter()
                .map(|field| cx.field_imm(field.span, field.name.unwrap(), subcall(field)))
                .collect::<ThinVec<_>>();

            cx.expr_struct(trait_span, ctor_path, fields)
        }
        VariantData::Tuple(..) => {
            let subcalls = all_fields.into_iter().map(subcall).collect();
            let path = cx.expr_path(ctor_path);
            cx.expr_call(trait_span, path, subcalls)
        }
        VariantData::Unit(..) => cx.expr_path(ctor_path),
    };
    BlockOrExpr::new_expr(expr)
}