Auto merge of #39572 - jseyfried:fix_inert_attributes, r=nrc

macros: fix inert attributes from `proc_macro_derives` with `#![feature(proc_macro)]`

This PR refactors collection of `proc_macro_derive` invocations to fix #39347.

After this PR, the input to a `#[proc_macro_derive]` function no longer sees `#[derive]`s on the underlying item. For example, consider:
```rust
extern crate my_derives;
use my_derives::{Trait, Trait2};

#[derive(Copy, Clone)]
#[derive(Trait)]
#[derive(Trait2)]
struct S;
```

Today, the input to the `Trait` derive is `#[derive(Copy, Clone, Trait2)] struct S;`, and the input to the `Trait2` derive is `#[derive(Copy, Clone)] struct S;`. More generally, a `proc_macro_derive` sees all builtin derives, as well as all `proc_macro_derive`s listed *after* the one being invoked.

After this PR, both `Trait` and `Trait2` will see `struct S;`.
This is a [breaking-change], but I believe it is highly unlikely to cause breakage in practice.

r? @nrc

src/librustc_metadata/creader.rs

@@ -616,10 +616,9 @@ impl<'a> CrateLoader<'a> {
                                       trait_name: &str,
                                       expand: fn(TokenStream) -> TokenStream,
                                       attributes: &[&'static str]) {
-                let attrs = attributes.iter().cloned().map(Symbol::intern).collect();
-                let derive = SyntaxExtension::ProcMacroDerive(
-                    Box::new(ProcMacroDerive::new(expand, attrs))
-                );
+                let attrs = attributes.iter().cloned().map(Symbol::intern).collect::<Vec<_>>();
+                let derive = ProcMacroDerive::new(expand, attrs.clone());
+                let derive = SyntaxExtension::ProcMacroDerive(Box::new(derive), attrs);
                 self.0.push((Symbol::intern(trait_name), Rc::new(derive)));
             }
 

src/librustc_resolve/macros.rs

@@ -27,10 +27,10 @@ use syntax::ext::base::{NormalTT, Resolver as SyntaxResolver, SyntaxExtension};
 use syntax::ext::expand::{Expansion, mark_tts};
 use syntax::ext::hygiene::Mark;
 use syntax::ext::tt::macro_rules;
-use syntax::feature_gate::{emit_feature_err, GateIssue, is_builtin_attr};
+use syntax::feature_gate::{self, emit_feature_err, GateIssue};
 use syntax::fold::{self, Folder};
 use syntax::ptr::P;
-use syntax::symbol::keywords;
+use syntax::symbol::{Symbol, keywords};
 use syntax::util::lev_distance::find_best_match_for_name;
 use syntax::visit::Visitor;
 use syntax_pos::{Span, DUMMY_SP};
@@ -130,12 +130,16 @@ impl<'a> base::Resolver for Resolver<'a> {
         self.whitelisted_legacy_custom_derives.contains(&name)
     }
 
-    fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion) {
+    fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion, derives: &[Mark]) {
         let invocation = self.invocations[&mark];
         self.collect_def_ids(invocation, expansion);
 
         self.current_module = invocation.module.get();
         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
+        self.current_module.unresolved_invocations.borrow_mut().extend(derives);
+        for &derive in derives {
+            self.invocations.insert(derive, invocation);
+        }
         let mut visitor = BuildReducedGraphVisitor {
             resolver: self,
             legacy_scope: LegacyScope::Invocation(invocation),
@@ -172,7 +176,9 @@ impl<'a> base::Resolver for Resolver<'a> {
         ImportResolver { resolver: self }.resolve_imports()
     }
 
-    fn find_attr_invoc(&mut self, attrs: &mut Vec<ast::Attribute>) -> Option<ast::Attribute> {
+    // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
+    fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<ast::Attribute>)
+                              -> Option<ast::Attribute> {
         for i in 0..attrs.len() {
             match self.builtin_macros.get(&attrs[i].name()).cloned() {
                 Some(binding) => match *binding.get_macro(self) {
@@ -183,11 +189,50 @@ impl<'a> base::Resolver for Resolver<'a> {
                 },
                 None => {}
             }
+        }
 
-            if self.proc_macro_enabled && !is_builtin_attr(&attrs[i]) {
-                return Some(attrs.remove(i));
+        // Check for legacy derives
+        for i in 0..attrs.len() {
+            if attrs[i].name() == "derive" {
+                let mut traits = match attrs[i].meta_item_list() {
+                    Some(traits) if !traits.is_empty() => traits.to_owned(),
+                    _ => continue,
+                };
+
+                for j in 0..traits.len() {
+                    let legacy_name = Symbol::intern(&match traits[j].word() {
+                        Some(..) => format!("derive_{}", traits[j].name().unwrap()),
+                        None => continue,
+                    });
+                    if !self.builtin_macros.contains_key(&legacy_name) {
+                        continue
+                    }
+                    let span = traits.remove(j).span;
+                    self.gate_legacy_custom_derive(legacy_name, span);
+                    if traits.is_empty() {
+                        attrs.remove(i);
+                    } else {
+                        attrs[i].value = ast::MetaItem {
+                            name: attrs[i].name(),
+                            span: attrs[i].span,
+                            node: ast::MetaItemKind::List(traits),
+                        };
+                    }
+                    return Some(ast::Attribute {
+                        value: ast::MetaItem {
+                            name: legacy_name,
+                            span: span,
+                            node: ast::MetaItemKind::Word,
+                        },
+                        id: attr::mk_attr_id(),
+                        style: ast::AttrStyle::Outer,
+                        is_sugared_doc: false,
+                        span: span,
+                    });
+                }
             }
         }
+
         None
     }
 
@@ -236,7 +281,7 @@ impl<'a> base::Resolver for Resolver<'a> {
                 Ok(binding) => Ok(binding.get_macro(self)),
                 Err(Determinacy::Undetermined) if !force => return Err(Determinacy::Undetermined),
                 _ => {
-                    let msg = format!("macro undefined: '{}!'", name);
+                    let msg = format!("macro undefined: `{}`", name);
                     let mut err = self.session.struct_span_err(span, &msg);
                     self.suggest_macro_name(&name.as_str(), &mut err);
                     err.emit();
@@ -251,13 +296,6 @@ impl<'a> base::Resolver for Resolver<'a> {
         result
     }
 
-    fn resolve_builtin_macro(&mut self, tname: Name) -> Result<Rc<SyntaxExtension>, Determinacy> {
-        match self.builtin_macros.get(&tname).cloned() {
-            Some(binding) => Ok(binding.get_macro(self)),
-            None => Err(Determinacy::Undetermined),
-        }
-    }
-
     fn resolve_derive_macro(&mut self, scope: Mark, path: &ast::Path, force: bool)
                             -> Result<Rc<SyntaxExtension>, Determinacy> {
         let ast::Path { span, .. } = *path;
@@ -540,4 +578,14 @@ impl<'a> Resolver<'a> {
                              `use {}::{};`", crate_name, name))
             .emit();
     }
+
+    fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
+        if !self.session.features.borrow().custom_derive {
+            let sess = &self.session.parse_sess;
+            let explain = feature_gate::EXPLAIN_CUSTOM_DERIVE;
+            emit_feature_err(sess, "custom_derive", span, GateIssue::Language, explain);
+        } else if !self.is_whitelisted_legacy_custom_derive(name) {
+            self.session.span_warn(span, feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE);
+        }
+    }
 }

src/libsyntax/ext/base.rs

@@ -514,7 +514,7 @@ pub enum SyntaxExtension {
     /// The input is the annotated item.
     /// Allows generating code to implement a Trait for a given struct
     /// or enum item.
-    ProcMacroDerive(Box<MultiItemModifier>),
+    ProcMacroDerive(Box<MultiItemModifier>, Vec<Symbol> /* inert attribute names */),
 
     /// An attribute-like procedural macro that derives a builtin trait.
     BuiltinDerive(BuiltinDeriveFn),
@@ -528,15 +528,15 @@ pub trait Resolver {
     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item>;
     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool;
 
-    fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion);
+    fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion, derives: &[Mark]);
     fn add_ext(&mut self, ident: ast::Ident, ext: Rc<SyntaxExtension>);
     fn add_expansions_at_stmt(&mut self, id: ast::NodeId, macros: Vec<Mark>);
 
     fn resolve_imports(&mut self);
-    fn find_attr_invoc(&mut self, attrs: &mut Vec<Attribute>) -> Option<Attribute>;
+    // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
+    fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<Attribute>) -> Option<Attribute>;
     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy>;
-    fn resolve_builtin_macro(&mut self, tname: Name) -> Result<Rc<SyntaxExtension>, Determinacy>;
     fn resolve_derive_macro(&mut self, scope: Mark, path: &ast::Path, force: bool)
                             -> Result<Rc<SyntaxExtension>, Determinacy>;
 }
@@ -555,19 +555,16 @@ impl Resolver for DummyResolver {
     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> { item }
     fn is_whitelisted_legacy_custom_derive(&self, _name: Name) -> bool { false }
 
-    fn visit_expansion(&mut self, _invoc: Mark, _expansion: &Expansion) {}
+    fn visit_expansion(&mut self, _invoc: Mark, _expansion: &Expansion, _derives: &[Mark]) {}
     fn add_ext(&mut self, _ident: ast::Ident, _ext: Rc<SyntaxExtension>) {}
     fn add_expansions_at_stmt(&mut self, _id: ast::NodeId, _macros: Vec<Mark>) {}
 
     fn resolve_imports(&mut self) {}
-    fn find_attr_invoc(&mut self, _attrs: &mut Vec<Attribute>) -> Option<Attribute> { None }
+    fn find_legacy_attr_invoc(&mut self, _attrs: &mut Vec<Attribute>) -> Option<Attribute> { None }
     fn resolve_macro(&mut self, _scope: Mark, _path: &ast::Path, _force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy> {
         Err(Determinacy::Determined)
     }
-    fn resolve_builtin_macro(&mut self, _tname: Name) -> Result<Rc<SyntaxExtension>, Determinacy> {
-        Err(Determinacy::Determined)
-    }
     fn resolve_derive_macro(&mut self, _scope: Mark, _path: &ast::Path, _force: bool)
                             -> Result<Rc<SyntaxExtension>, Determinacy> {
         Err(Determinacy::Determined)