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Auto merge of #87220 - petrochenkov:derivecfglimit2, r=Aaron1011
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Make `#[derive(A, B, ...)]` cfg-eval its input only for `A, B, ...` and stabilize `feature(macro_attributes_in_derive_output)`

Stabilization report: #87220 (comment)

Closes #81119
r? `@Aaron1011`
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bors committed Sep 25, 2021
2 parents 6867dd2 + 85f0290 commit 60fe8b3
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Showing 9 changed files with 124 additions and 157 deletions.
29 changes: 14 additions & 15 deletions compiler/rustc_builtin_macros/src/cfg_eval.rs
Expand Up @@ -2,17 +2,18 @@ use crate::util::check_builtin_macro_attribute;

use rustc_ast as ast;
use rustc_ast::mut_visit::MutVisitor;
use rustc_ast::ptr::P;
use rustc_ast::tokenstream::CanSynthesizeMissingTokens;
use rustc_ast::visit::Visitor;
use rustc_ast::{mut_visit, visit};
use rustc_ast::{AstLike, Attribute};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_expand::config::StripUnconfigured;
use rustc_expand::configure;
use rustc_feature::Features;
use rustc_parse::parser::ForceCollect;
use rustc_session::utils::FlattenNonterminals;

use rustc_ast::ptr::P;
use rustc_session::Session;
use rustc_span::symbol::sym;
use rustc_span::Span;
use smallvec::SmallVec;
Expand All @@ -24,21 +25,19 @@ crate fn expand(
annotatable: Annotatable,
) -> Vec<Annotatable> {
check_builtin_macro_attribute(ecx, meta_item, sym::cfg_eval);
vec![cfg_eval(ecx, annotatable)]
vec![cfg_eval(ecx.sess, ecx.ecfg.features, annotatable)]
}

crate fn cfg_eval(ecx: &ExtCtxt<'_>, annotatable: Annotatable) -> Annotatable {
CfgEval {
cfg: &mut StripUnconfigured {
sess: ecx.sess,
features: ecx.ecfg.features,
config_tokens: true,
},
}
.configure_annotatable(annotatable)
// Since the item itself has already been configured by the `InvocationCollector`,
// we know that fold result vector will contain exactly one element.
.unwrap()
crate fn cfg_eval(
sess: &Session,
features: Option<&Features>,
annotatable: Annotatable,
) -> Annotatable {
CfgEval { cfg: &mut StripUnconfigured { sess, features, config_tokens: true } }
.configure_annotatable(annotatable)
// Since the item itself has already been configured by the `InvocationCollector`,
// we know that fold result vector will contain exactly one element.
.unwrap()
}

struct CfgEval<'a, 'b> {
Expand Down
40 changes: 33 additions & 7 deletions compiler/rustc_builtin_macros/src/derive.rs
@@ -1,12 +1,13 @@
use crate::cfg_eval::cfg_eval;

use rustc_ast::{self as ast, attr, token, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
use rustc_ast as ast;
use rustc_ast::{attr, token, GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
use rustc_errors::{struct_span_err, Applicability};
use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
use rustc_feature::AttributeTemplate;
use rustc_parse::validate_attr;
use rustc_session::Session;
use rustc_span::symbol::sym;
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;

crate struct Expander;
Expand All @@ -26,8 +27,7 @@ impl MultiItemModifier for Expander {
return ExpandResult::Ready(vec![item]);
}

let item = cfg_eval(ecx, item);

let (sess, features) = (ecx.sess, ecx.ecfg.features);
let result =
ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
let template =
Expand All @@ -40,7 +40,8 @@ impl MultiItemModifier for Expander {
template,
);

attr.meta_item_list()
let mut resolutions: Vec<_> = attr
.meta_item_list()
.unwrap_or_default()
.into_iter()
.filter_map(|nested_meta| match nested_meta {
Expand All @@ -56,8 +57,21 @@ impl MultiItemModifier for Expander {
report_path_args(sess, &meta);
meta.path
})
.map(|path| (path, item.clone(), None))
.collect()
.map(|path| (path, dummy_annotatable(), None))
.collect();

// Do not configure or clone items unless necessary.
match &mut resolutions[..] {
[] => {}
[(_, first_item, _), others @ ..] => {
*first_item = cfg_eval(sess, features, item.clone());
for (_, item, _) in others {
*item = first_item.clone();
}
}
}

resolutions
});

match result {
Expand All @@ -67,6 +81,18 @@ impl MultiItemModifier for Expander {
}
}

// The cheapest `Annotatable` to construct.
fn dummy_annotatable() -> Annotatable {
Annotatable::GenericParam(ast::GenericParam {
id: ast::DUMMY_NODE_ID,
ident: Ident::invalid(),
attrs: Default::default(),
bounds: Default::default(),
is_placeholder: false,
kind: GenericParamKind::Lifetime,
})
}

fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
let item_kind = match item {
Annotatable::Item(item) => Some(&item.kind),
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/accepted.rs
Expand Up @@ -295,6 +295,8 @@ declare_features! (
(accepted, const_fn_union, "1.56.0", Some(51909), None),
/// Allows explicit discriminants on non-unit enum variants.
(accepted, arbitrary_enum_discriminant, "1.56.0", Some(60553), None),
/// Allows macro attributes to observe output of `#[derive]`.
(accepted, macro_attributes_in_derive_output, "1.57.0", Some(81119), None),

// -------------------------------------------------------------------------
// feature-group-end: accepted features
Expand Down
3 changes: 0 additions & 3 deletions compiler/rustc_feature/src/active.rs
Expand Up @@ -592,9 +592,6 @@ declare_features! (
/// Lessens the requirements for structs to implement `Unsize`.
(active, relaxed_struct_unsize, "1.51.0", Some(81793), None),

/// Allows macro attributes to observe output of `#[derive]`.
(active, macro_attributes_in_derive_output, "1.51.0", Some(81119), None),

/// Allows associated types in inherent impls.
(incomplete, inherent_associated_types, "1.52.0", Some(8995), None),

Expand Down
32 changes: 0 additions & 32 deletions compiler/rustc_resolve/src/macros.rs
Expand Up @@ -311,38 +311,6 @@ impl<'a> ResolverExpand for Resolver<'a> {
self.create_stable_hashing_context(),
);

if let Res::Def(_, _) = res {
// Gate macro attributes in `#[derive]` output.
if !self.session.features_untracked().macro_attributes_in_derive_output
&& kind == MacroKind::Attr
&& ext.builtin_name != Some(sym::derive)
{
let mut expn_id = parent_scope.expansion;
loop {
// Helper attr table is a quick way to determine whether the attr is `derive`.
if self.helper_attrs.contains_key(&expn_id) {
feature_err(
&self.session.parse_sess,
sym::macro_attributes_in_derive_output,
path.span,
"macro attributes in `#[derive]` output are unstable",
)
.emit();
break;
} else {
let expn_data = expn_id.expn_data();
match expn_data.kind {
ExpnKind::Root
| ExpnKind::Macro(MacroKind::Bang | MacroKind::Derive, _) => {
break;
}
_ => expn_id = expn_data.parent.expect_local(),
}
}
}
}
}

Ok(ext)
}

Expand Down
37 changes: 0 additions & 37 deletions src/test/ui/proc-macro/attribute-after-derive-feature-gate.rs

This file was deleted.

30 changes: 0 additions & 30 deletions src/test/ui/proc-macro/attribute-after-derive-feature-gate.stderr

This file was deleted.

2 changes: 0 additions & 2 deletions src/test/ui/proc-macro/attribute-after-derive.rs
Expand Up @@ -5,8 +5,6 @@
// compile-flags: -Z span-debug
// aux-build: test-macros.rs

#![feature(macro_attributes_in_derive_output)]

#![no_std] // Don't load unnecessary hygiene information from std
extern crate std;

Expand Down

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