Rollup merge of rust-lang#102049 - fee1-dead-contrib:derive_const, r=…

…oli-obk

Add the `#[derive_const]` attribute

Closes rust-lang#102371. This is a minimal patchset for the attribute to work. There are no restrictions on what traits this attribute applies to.

r? ```@oli-obk```

compiler/rustc_builtin_macros/src/cfg_accessible.rs

@@ -34,6 +34,7 @@ impl MultiItemModifier for Expander {
  span: Span,
  meta_item: &ast::MetaItem,
  item: Annotatable,
+ _is_derive_const: bool,
  ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  let template = AttributeTemplate { list: Some("path"), ..Default::default() };
  let attr = &ecx.attribute(meta_item.clone());

compiler/rustc_builtin_macros/src/derive.rs

@@ -10,7 +10,7 @@ use rustc_session::Session;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
 
-pub(crate) struct Expander;
+pub(crate) struct Expander(pub bool);
 
 impl MultiItemModifier for Expander {
  fn expand(
@@ -19,6 +19,7 @@ impl MultiItemModifier for Expander {
  span: Span,
  meta_item: &ast::MetaItem,
  item: Annotatable,
+ _: bool,
  ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  let sess = ecx.sess;
  if report_bad_target(sess, &item, span) {
@@ -58,20 +59,20 @@ impl MultiItemModifier for Expander {
  report_path_args(sess, &meta);
  meta.path
  })
- .map(|path| (path, dummy_annotatable(), None))
+ .map(|path| (path, dummy_annotatable(), None, self.0))
  .collect();
 
  // Do not configure or clone items unless necessary.
  match &mut resolutions[..] {
  [] => {}
- [(_, first_item, _), others @ ..] => {
+ [(_, first_item, ..), others @ ..] => {
  *first_item = cfg_eval(
  sess,
  features,
  item.clone(),
  ecx.current_expansion.lint_node_id,
  );
- for (_, item, _) in others {
+ for (_, item, _, _) in others {
  *item = first_item.clone();
  }
  }

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -12,6 +12,7 @@ pub fn expand_deriving_copy(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let trait_def = TraitDef {
  span,
@@ -22,6 +23,7 @@ pub fn expand_deriving_copy(
  supports_unions: true,
  methods: Vec::new(),
  associated_types: Vec::new(),
+ is_const,
  };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -14,6 +14,7 @@ pub fn expand_deriving_clone(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  // The simple form is `fn clone(&self) -> Self { *self }`, possibly with
  // some additional `AssertParamIsClone` assertions.
@@ -87,6 +88,7 @@ pub fn expand_deriving_clone(
  combine_substructure: substructure,
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -15,6 +15,7 @@ pub fn expand_deriving_eq(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let span = cx.with_def_site_ctxt(span);
  let inline = cx.meta_word(span, sym::inline);
@@ -42,6 +43,7 @@ pub fn expand_deriving_eq(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  super::inject_impl_of_structural_trait(cx, span, item, path_std!(marker::StructuralEq), push);

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -13,6 +13,7 @@ pub fn expand_deriving_ord(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let inline = cx.meta_word(span, sym::inline);
  let attrs = thin_vec![cx.attribute(inline)];
@@ -34,6 +35,7 @@ pub fn expand_deriving_ord(
  combine_substructure: combine_substructure(Box::new(|a, b, c| cs_cmp(a, b, c))),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -14,6 +14,7 @@ pub fn expand_deriving_partial_eq(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  fn cs_eq(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
  let base = true;
@@ -89,6 +90,7 @@ pub fn expand_deriving_partial_eq(
  supports_unions: false,
  methods,
  associated_types: Vec::new(),
+ is_const,
  };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -13,6 +13,7 @@ pub fn expand_deriving_partial_ord(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let ordering_ty = Path(path_std!(cmp::Ordering));
  let ret_ty =
@@ -43,6 +44,7 @@ pub fn expand_deriving_partial_ord(
  supports_unions: false,
  methods: vec![partial_cmp_def],
  associated_types: Vec::new(),
+ is_const,
  };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -13,6 +13,7 @@ pub fn expand_deriving_debug(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  // &mut ::std::fmt::Formatter
  let fmtr = Ref(Box::new(Path(path_std!(fmt::Formatter))), ast::Mutability::Mut);
@@ -37,6 +38,7 @@ pub fn expand_deriving_debug(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/decodable.rs

@@ -16,6 +16,7 @@ pub fn expand_deriving_rustc_decodable(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let krate = sym::rustc_serialize;
  let typaram = sym::__D;
@@ -55,6 +56,7 @@ pub fn expand_deriving_rustc_decodable(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -16,6 +16,7 @@ pub fn expand_deriving_default(
  mitem: &ast::MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  item.visit_with(&mut DetectNonVariantDefaultAttr { cx });
 
@@ -47,6 +48,7 @@ pub fn expand_deriving_default(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/encodable.rs

@@ -100,6 +100,7 @@ pub fn expand_deriving_rustc_encodable(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let krate = sym::rustc_serialize;
  let typaram = sym::__S;
@@ -139,6 +140,7 @@ pub fn expand_deriving_rustc_encodable(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -171,7 +171,7 @@ use rustc_ast::{GenericArg, GenericParamKind, VariantData};
 use rustc_attr as attr;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 use std::cell::RefCell;
 use std::iter;
 use std::ops::Not;
@@ -204,6 +204,8 @@ pub struct TraitDef<'a> {
  pub methods: Vec<MethodDef<'a>>,
 
  pub associated_types: Vec<(Ident, Ty)>,
+
+ pub is_const: bool,
 }
 
 pub struct MethodDef<'a> {
@@ -730,7 +732,7 @@ impl<'a> TraitDef<'a> {
  unsafety: ast::Unsafe::No,
  polarity: ast::ImplPolarity::Positive,
  defaultness: ast::Defaultness::Final,
- constness: ast::Const::No,
+ constness: if self.is_const { ast::Const::Yes(DUMMY_SP) } else { ast::Const::No },
  generics: trait_generics,
  of_trait: opt_trait_ref,
  self_ty: self_type,

compiler/rustc_builtin_macros/src/deriving/hash.rs

@@ -13,6 +13,7 @@ pub fn expand_deriving_hash(
  mitem: &MetaItem,
  item: &Annotatable,
  push: &mut dyn FnMut(Annotatable),
+ is_const: bool,
 ) {
  let path = Path::new_(pathvec_std!(hash::Hash), vec![], PathKind::Std);
 
@@ -39,6 +40,7 @@ pub fn expand_deriving_hash(
  })),
  }],
  associated_types: Vec::new(),
+ is_const,
  };
 
  hash_trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -38,9 +38,10 @@ pub mod partial_ord;
 
 pub mod generic;
 
-pub(crate) struct BuiltinDerive(
- pub(crate) fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable)),
-);
+pub(crate) type BuiltinDeriveFn =
+ fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable), bool);
+
+pub(crate) struct BuiltinDerive(pub(crate) BuiltinDeriveFn);
 
 impl MultiItemModifier for BuiltinDerive {
  fn expand(
@@ -49,6 +50,7 @@ impl MultiItemModifier for BuiltinDerive {
  span: Span,
  meta_item: &MetaItem,
  item: Annotatable,
+ is_derive_const: bool,
  ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  // FIXME: Built-in derives often forget to give spans contexts,
  // so we are doing it here in a centralized way.
@@ -57,21 +59,28 @@ impl MultiItemModifier for BuiltinDerive {
  match item {
  Annotatable::Stmt(stmt) => {
  if let ast::StmtKind::Item(item) = stmt.into_inner().kind {
- (self.0)(ecx, span, meta_item, &Annotatable::Item(item), &mut |a| {
- // Cannot use 'ecx.stmt_item' here, because we need to pass 'ecx'
- // to the function
- items.push(Annotatable::Stmt(P(ast::Stmt {
- id: ast::DUMMY_NODE_ID,
- kind: ast::StmtKind::Item(a.expect_item()),
- span,
- })));
- });
+ (self.0)(
+ ecx,
+ span,
+ meta_item,
+ &Annotatable::Item(item),
+ &mut |a| {
+ // Cannot use 'ecx.stmt_item' here, because we need to pass 'ecx'
+ // to the function
+ items.push(Annotatable::Stmt(P(ast::Stmt {
+ id: ast::DUMMY_NODE_ID,
+ kind: ast::StmtKind::Item(a.expect_item()),
+ span,
+ })));
+ },
+ is_derive_const,
+ );
  } else {
  unreachable!("should have already errored on non-item statement")
  }
  }
  _ => {
- (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a));
+ (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a), is_derive_const);
  }
  }
  ExpandResult::Ready(items)

compiler/rustc_builtin_macros/src/lib.rs

@@ -99,7 +99,8 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
  bench: test::expand_bench,
  cfg_accessible: cfg_accessible::Expander,
  cfg_eval: cfg_eval::expand,
- derive: derive::Expander,
+ derive: derive::Expander(false),
+ derive_const: derive::Expander(true),
  global_allocator: global_allocator::expand,
  test: test::expand_test,
  test_case: test::expand_test_case,

compiler/rustc_expand/src/base.rs

@@ -250,6 +250,7 @@ pub trait MultiItemModifier {
  span: Span,
  meta_item: &ast::MetaItem,
  item: Annotatable,
+ is_derive_const: bool,
  ) -> ExpandResult<Vec<Annotatable>, Annotatable>;
 }
 
@@ -263,6 +264,7 @@ where
  span: Span,
  meta_item: &ast::MetaItem,
  item: Annotatable,
+ _is_derive_const: bool,
  ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  ExpandResult::Ready(self(ecx, span, meta_item, item))
  }
@@ -873,7 +875,7 @@ impl SyntaxExtension {
 /// Error type that denotes indeterminacy.
 pub struct Indeterminate;
 
-pub type DeriveResolutions = Vec<(ast::Path, Annotatable, Option<Lrc<SyntaxExtension>>)>;
+pub type DeriveResolutions = Vec<(ast::Path, Annotatable, Option<Lrc<SyntaxExtension>>, bool)>;
 
 pub trait ResolverExpand {
  fn next_node_id(&mut self) -> NodeId;