mbe: Handle applying attribute rules with paths

Add infrastructure to apply an attribute macro given argument tokens and
body tokens.

Teach the resolver to consider `macro_rules` macros when looking for an
attribute via a path.

This does not yet handle local `macro_rules` attributes.

2 files changed, 9 insertions, 4 deletions

diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 2a75070ef54..8a190bf06ed 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -1028,13 +1028,14 @@ struct DeriveData {
 
 struct MacroData {
     ext: Arc<SyntaxExtension>,
+    attr_ext: Option<Arc<SyntaxExtension>>,
     nrules: usize,
     macro_rules: bool,
 }
 
 impl MacroData {
     fn new(ext: Arc<SyntaxExtension>) -> MacroData {
-        MacroData { ext, nrules: 0, macro_rules: false }
+        MacroData { ext, attr_ext: None, nrules: 0, macro_rules: false }
     }
 }
 
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index ecf4f797434..0692f368ade 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -835,7 +835,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
                 _ => None,
             },
-            None => self.get_macro(res).map(|macro_data| Arc::clone(&macro_data.ext)),
+            None => self.get_macro(res).map(|macro_data| match kind {
+                Some(MacroKind::Attr) if let Some(ref ext) = macro_data.attr_ext => Arc::clone(ext),
+                _ => Arc::clone(&macro_data.ext),
+            }),
         };
         Ok((ext, res))
     }
@@ -1168,7 +1171,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         node_id: NodeId,
         edition: Edition,
     ) -> MacroData {
-        let (mut ext, mut nrules) = compile_declarative_macro(
+        let (mut ext, mut attr_ext, mut nrules) = compile_declarative_macro(
             self.tcx.sess,
             self.tcx.features(),
             macro_def,
@@ -1185,13 +1188,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 // The macro is a built-in, replace its expander function
                 // while still taking everything else from the source code.
                 ext.kind = builtin_ext_kind.clone();
+                attr_ext = None;
                 nrules = 0;
             } else {
                 self.dcx().emit_err(errors::CannotFindBuiltinMacroWithName { span, ident });
             }
         }
 
-        MacroData { ext: Arc::new(ext), nrules, macro_rules: macro_def.macro_rules }
+        MacroData { ext: Arc::new(ext), attr_ext, nrules, macro_rules: macro_def.macro_rules }
     }
 
     fn path_accessible(