Rollup merge of #37198 - jseyfried:future_proof_macros_11, r=nrc

macros 1.1: future proofing and cleanup

This PR
 - uses the macro namespace for custom derives (instead of a dedicated custom derive namespace),
 - relaxes the shadowing rules for `#[macro_use]`-imported custom derives to match the shadowing rules for ordinary `#[macro_use]`-imported macros, and
 - treats custom derive `extern crate`s like empty modules so that we can eventually allow, for example, `extern crate serde_derive; use serde_derive::Serialize;` backwards compatibly.

r? @alexcrichton

2 files changed, 30 insertions, 7 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index ff1986cb4a8..f3272960e83 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -15,7 +15,7 @@ use attr::HasAttrs;
 use codemap::{self, CodeMap, ExpnInfo, Spanned, respan};
 use syntax_pos::{Span, ExpnId, NO_EXPANSION};
 use errors::DiagnosticBuilder;
-use ext::expand::{self, Invocation, Expansion};
+use ext::expand::{self, Expansion};
 use ext::hygiene::Mark;
 use fold::{self, Folder};
 use parse::{self, parser};
@@ -508,6 +508,8 @@ pub enum SyntaxExtension {
     /// the block.
     ///
     IdentTT(Box<IdentMacroExpander>, Option<Span>, bool),
+
+    CustomDerive(Box<MultiItemModifier>),
 }
 
 pub type NamedSyntaxExtension = (Name, SyntaxExtension);
@@ -522,9 +524,8 @@ pub trait Resolver {
     fn add_expansions_at_stmt(&mut self, id: ast::NodeId, macros: Vec<Mark>);
 
     fn find_attr_invoc(&mut self, attrs: &mut Vec<Attribute>) -> Option<Attribute>;
-    fn resolve_invoc(&mut self, scope: Mark, invoc: &Invocation, force: bool)
+    fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy>;
-    fn resolve_derive_mode(&mut self, ident: ast::Ident) -> Option<Rc<MultiItemModifier>>;
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -545,8 +546,7 @@ impl Resolver for DummyResolver {
     fn add_expansions_at_stmt(&mut self, _id: ast::NodeId, _macros: Vec<Mark>) {}
 
     fn find_attr_invoc(&mut self, _attrs: &mut Vec<Attribute>) -> Option<Attribute> { None }
-    fn resolve_derive_mode(&mut self, _ident: ast::Ident) -> Option<Rc<MultiItemModifier>> { None }
-    fn resolve_invoc(&mut self, _scope: Mark, _invoc: &Invocation, _force: bool)
+    fn resolve_macro(&mut self, _scope: Mark, _path: &ast::Path, _force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy> {
         Err(Determinacy::Determined)
     }
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 363ceebf0f4..6aeb46fd522 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -240,7 +240,17 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
             let scope =
                 if self.monotonic { invoc.expansion_data.mark } else { orig_expansion_data.mark };
-            let ext = match self.cx.resolver.resolve_invoc(scope, &invoc, force) {
+            let resolution = match invoc.kind {
+                InvocationKind::Bang { ref mac, .. } => {
+                    self.cx.resolver.resolve_macro(scope, &mac.node.path, force)
+                }
+                InvocationKind::Attr { ref attr, .. } => {
+                    let ident = ast::Ident::with_empty_ctxt(intern(&*attr.name()));
+                    let path = ast::Path::from_ident(attr.span, ident);
+                    self.cx.resolver.resolve_macro(scope, &path, force)
+                }
+            };
+            let ext = match resolution {
                 Ok(ext) => Some(ext),
                 Err(Determinacy::Determined) => None,
                 Err(Determinacy::Undetermined) => {
@@ -354,7 +364,15 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 let tok_result = mac.expand(self.cx, attr.span, attr_toks, item_toks);
                 self.parse_expansion(tok_result, kind, name, attr.span)
             }
-            _ => unreachable!(),
+            SyntaxExtension::CustomDerive(_) => {
+                self.cx.span_err(attr.span, &format!("`{}` is a derive mode", name));
+                kind.dummy(attr.span)
+            }
+            _ => {
+                let msg = &format!("macro `{}` may not be used in attributes", name);
+                self.cx.span_err(attr.span, &msg);
+                kind.dummy(attr.span)
+            }
         }
     }
 
@@ -429,6 +447,11 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 return kind.dummy(span);
             }
 
+            SyntaxExtension::CustomDerive(..) => {
+                self.cx.span_err(path.span, &format!("`{}` is a derive mode", extname));
+                return kind.dummy(span);
+            }
+
             SyntaxExtension::ProcMacro(ref expandfun) => {
                 if ident.name != keywords::Invalid.name() {
                     let msg =