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Special case derive(Debug) for fieldless enums

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This commit is contained in:
clubby789 2023-01-19 15:52:29 +00:00
parent 97cf1713d1
commit 95a824c02c
2 changed files with 55 additions and 7 deletions
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51
compiler/rustc_builtin_macros/src/deriving/debug.rs
View File

@ -2,6 +2,7 @@ use crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::path_std;
use ast::EnumDef;
use rustc_ast::{self as ast, MetaItem};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident, Symbol};
@ -31,7 +32,8 @@ pub fn expand_deriving_debug(
nonself_args: vec![(fmtr, sym::f)],
ret_ty: Path(path_std!(fmt::Result)),
attributes: ast::AttrVec::new(),
fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
fieldless_variants_strategy:
FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
combine_substructure: combine_substructure(Box::new(|a, b, c| {
show_substructure(a, b, c)
})),
@ -49,7 +51,8 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
let (ident, vdata, fields) = match substr.fields {
Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
AllFieldlessEnum(..) | EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
AllFieldlessEnum(enum_def) => return show_fieldless_enum(cx, span, enum_def, substr),
EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
}
};
@ -174,3 +177,47 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
BlockOrExpr::new_mixed(stmts, Some(expr))
}
}
/// Special case for enums with no fields. Builds:
/// ```text
/// impl ::core::fmt::Debug for A {
/// fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
/// ::core::fmt::Formatter::write_str(f,
/// match self {
/// A::A => "A",
/// A::B() => "B",
/// A::C {} => "C",
/// })
/// }
/// }
/// ```
fn show_fieldless_enum(
cx: &mut ExtCtxt<'_>,
span: Span,
def: &EnumDef,
substr: &Substructure<'_>,
) -> BlockOrExpr {
let fmt = substr.nonselflike_args[0].clone();
let arms = def
.variants
.iter()
.map(|v| {
let variant_path = cx.path(span, vec![substr.type_ident, v.ident]);
let pat = match &v.data {
ast::VariantData::Tuple(fields, _) => {
debug_assert!(fields.is_empty());
cx.pat_tuple_struct(span, variant_path, vec![])
}
ast::VariantData::Struct(fields, _) => {
debug_assert!(fields.is_empty());
cx.pat_struct(span, variant_path, vec![])
}
ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
};
cx.arm(span, pat, cx.expr_str(span, v.ident.name))
})
.collect::<Vec<_>>();
let name = cx.expr_match(span, cx.expr_self(span), arms);
let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]))
}

11
tests/ui/deriving/deriving-all-codegen.stdout
View File

@ -731,11 +731,12 @@ impl ::core::marker::Copy for Fieldless { }
#[automatically_derived]
impl ::core::fmt::Debug for Fieldless {
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match self {
Fieldless::A => ::core::fmt::Formatter::write_str(f, "A"),
Fieldless::B => ::core::fmt::Formatter::write_str(f, "B"),
Fieldless::C => ::core::fmt::Formatter::write_str(f, "C"),
}
::core::fmt::Formatter::write_str(f,
match self {
Fieldless::A => "A",
Fieldless::B => "B",
Fieldless::C => "C",
})
}
}
#[automatically_derived]