Auto merge of #63248 - petrochenkov:nomarker, r=matthewjasper

Move special treatment of `derive(Copy, PartialEq, Eq)` from expansion infrastructure to elsewhere

As described in https://github.com/rust-lang/rust/pull/62086#issuecomment-515195477.

Reminder:
- `derive(PartialEq, Eq)` makes the type it applied to a "structural match" type, so constants of this type can be used in patterns (and const generics in the future).
- `derive(Copy)` notifies other derives that the type it applied to implements `Copy`, so `derive(Clone)` can generate optimized code and other derives can generate code working with `packed` types and types with `rustc_layout_scalar_valid_range` attributes.

First, the special behavior is now enabled after properly resolving the derives, rather than after textually comparing them with `"Copy"`, `"PartialEq"` and `"Eq"` in `fn add_derived_markers`.

The markers are no longer kept as attributes in AST since derives cannot modify items and previously did it through hacks in the expansion infra.
Instead, the markers are now kept in a "global context" available from all the necessary places, namely - resolver.

For `derive(PartialEq, Eq)` the markers are created by the derive macros themselves and then consumed during HIR lowering to add the `#[structural_match]` attribute in HIR.
This is still a hack, but now it's a hack local to two specific macros rather than affecting the whole expansion infra.
Ideally we should find the way to put `#[structural_match]` on the impls rather than on the original item, and then consume it in `rustc_mir`, then no hacks in expansion and lowering will be required.
(I'll make an issue about this for someone else to solve, after this PR lands.)

The marker for `derive(Copy)` cannot be emitted by the `Copy` macro itself because we need to know it *before* the `Copy` macro is expanded for expanding other macros.
So we have to do it in resolve and block expansion of any derives in a `derive(...)` container until we know for sure whether this container has `Copy` in it or not.
Nasty stuff.

r? @eddyb or @matthewjasper

4 files changed, 12 insertions, 7 deletions

diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs
index 2340238aaea..3b1edf90d6b 100644
--- a/src/libsyntax_ext/deriving/clone.rs
+++ b/src/libsyntax_ext/deriving/clone.rs
@@ -3,8 +3,7 @@ use crate::deriving::generic::*;
 use crate::deriving::generic::ty::*;
 
 use syntax::ast::{self, Expr, GenericArg, Generics, ItemKind, MetaItem, VariantData};
-use syntax::attr;
-use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::ext::base::{Annotatable, ExtCtxt, SpecialDerives};
 use syntax::ptr::P;
 use syntax::symbol::{kw, sym, Symbol};
 use syntax_pos::Span;
@@ -36,7 +35,8 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt<'_>,
             match annitem.node {
                 ItemKind::Struct(_, Generics { ref params, .. }) |
                 ItemKind::Enum(_, Generics { ref params, .. }) => {
-                    if attr::contains_name(&annitem.attrs, sym::rustc_copy_clone_marker) &&
+                    let container_id = cx.current_expansion.id.parent();
+                    if cx.resolver.has_derives(container_id, SpecialDerives::COPY) &&
                         !params.iter().any(|param| match param.kind {
                             ast::GenericParamKind::Type { .. } => true,
                             _ => false,
diff --git a/src/libsyntax_ext/deriving/cmp/eq.rs b/src/libsyntax_ext/deriving/cmp/eq.rs
index 0c34599814a..1909729f4a9 100644
--- a/src/libsyntax_ext/deriving/cmp/eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/eq.rs
@@ -3,7 +3,7 @@ use crate::deriving::generic::*;
 use crate::deriving::generic::ty::*;
 
 use syntax::ast::{self, Expr, MetaItem, GenericArg};
-use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::ext::base::{Annotatable, ExtCtxt, SpecialDerives};
 use syntax::ptr::P;
 use syntax::symbol::{sym, Symbol};
 use syntax_pos::Span;
@@ -13,6 +13,8 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt<'_>,
                           mitem: &MetaItem,
                           item: &Annotatable,
                           push: &mut dyn FnMut(Annotatable)) {
+    cx.resolver.add_derives(cx.current_expansion.id.parent(), SpecialDerives::EQ);
+
     let inline = cx.meta_word(span, sym::inline);
     let hidden = cx.meta_list_item_word(span, sym::hidden);
     let doc = cx.meta_list(span, sym::doc, vec![hidden]);
diff --git a/src/libsyntax_ext/deriving/cmp/partial_eq.rs b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
index 337f7c5cfe2..7d7c4ae22a8 100644
--- a/src/libsyntax_ext/deriving/cmp/partial_eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
@@ -3,7 +3,7 @@ use crate::deriving::generic::*;
 use crate::deriving::generic::ty::*;
 
 use syntax::ast::{BinOpKind, Expr, MetaItem};
-use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::ext::base::{Annotatable, ExtCtxt, SpecialDerives};
 use syntax::ptr::P;
 use syntax::symbol::sym;
 use syntax_pos::Span;
@@ -13,6 +13,8 @@ pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt<'_>,
                                   mitem: &MetaItem,
                                   item: &Annotatable,
                                   push: &mut dyn FnMut(Annotatable)) {
+    cx.resolver.add_derives(cx.current_expansion.id.parent(), SpecialDerives::PARTIAL_EQ);
+
     // structures are equal if all fields are equal, and non equal, if
     // any fields are not equal or if the enum variants are different
     fn cs_op(cx: &mut ExtCtxt<'_>,
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index cb89a68b9f2..7e6d9126c87 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -186,7 +186,7 @@ use rustc_target::spec::abi::Abi;
 use syntax::ast::{self, BinOpKind, EnumDef, Expr, Generics, Ident, PatKind};
 use syntax::ast::{VariantData, GenericParamKind, GenericArg};
 use syntax::attr;
-use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::ext::base::{Annotatable, ExtCtxt, SpecialDerives};
 use syntax::source_map::{self, respan};
 use syntax::util::map_in_place::MapInPlace;
 use syntax::ptr::P;
@@ -425,8 +425,9 @@ impl<'a> TraitDef<'a> {
                         return;
                     }
                 };
+                let container_id = cx.current_expansion.id.parent();
                 let is_always_copy =
-                    attr::contains_name(&item.attrs, sym::rustc_copy_clone_marker) &&
+                    cx.resolver.has_derives(container_id, SpecialDerives::COPY) &&
                     has_no_type_params;
                 let use_temporaries = is_packed && is_always_copy;