Rename the exp field to mirror its uses

Author: oli-obk

src/librustc_plugin/registry.rs

@@ -110,8 +110,8 @@ impl<'a> Registry<'a> {
                     edition,
                 }
             }
-            IdentTT { ext, span: _, allow_internal_unstable } => {
-                IdentTT { ext, span: Some(self.krate_span), allow_internal_unstable }
+            IdentTT { expander, span: _, allow_internal_unstable } => {
+                IdentTT { expander, span: Some(self.krate_span), allow_internal_unstable }
             }
             _ => extension,
         }));

src/libsyntax/ext/base.rs

@@ -658,7 +658,7 @@ pub enum SyntaxExtension {
     /// A function-like syntax extension that has an extra ident before
     /// the block.
     IdentTT {
-        ext: Box<dyn IdentMacroExpander + sync::Sync + sync::Send>,
+        expander: Box<dyn IdentMacroExpander + sync::Sync + sync::Send>,
         span: Option<Span>,
         allow_internal_unstable: Vec<Symbol>,
     },

src/libsyntax/ext/expand.rs

@@ -784,7 +784,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
             }
 
-            IdentTT { ext: ref expander, span: tt_span, ref allow_internal_unstable } => {
+            IdentTT { ref expander, span: tt_span, ref allow_internal_unstable } => {
                 if ident.name == keywords::Invalid.name() {
                     self.cx.span_err(path.span,
                                     &format!("macro {}! expects an ident argument", path));