rustc_span: Ident::invalid -> Ident::empty

The equivalent for `Symbol`s was renamed some time ago (`kw::Invalid` -> `kw::Empty`), and it makes sense to do the same thing for `Ident`s.

compiler/rustc_builtin_macros/src/asm.rs

@@ -812,7 +812,7 @@ pub fn expand_global_asm<'cx>(
         Ok(args) => {
             if let Some(inline_asm) = expand_preparsed_asm(ecx, args) {
                 MacEager::items(smallvec![P(ast::Item {
-                    ident: Ident::invalid(),
+                    ident: Ident::empty(),
                     attrs: Vec::new(),
                     id: ast::DUMMY_NODE_ID,
                     kind: ast::ItemKind::GlobalAsm(inline_asm),

compiler/rustc_builtin_macros/src/derive.rs

@@ -85,7 +85,7 @@ impl MultiItemModifier for Expander {
 fn dummy_annotatable() -> Annotatable {
     Annotatable::GenericParam(ast::GenericParam {
         id: ast::DUMMY_NODE_ID,
-        ident: Ident::invalid(),
+        ident: Ident::empty(),
         attrs: Default::default(),
         bounds: Default::default(),
         is_placeholder: false,

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -724,7 +724,7 @@ impl<'a> TraitDef<'a> {
 
         cx.item(
             self.span,
-            Ident::invalid(),
+            Ident::empty(),
             a,
             ast::ItemKind::Impl(Box::new(ast::ImplKind {
                 unsafety,

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -178,7 +178,7 @@ fn inject_impl_of_structural_trait(
 
     let newitem = cx.item(
         span,
-        Ident::invalid(),
+        Ident::empty(),
         attrs,
         ItemKind::Impl(Box::new(ImplKind {
             unsafety: ast::Unsafe::No,

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -77,7 +77,7 @@ pub fn inject(
 
     let use_item = cx.item(
         span,
-        Ident::invalid(),
+        Ident::empty(),
         vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
         ast::ItemKind::Use(ast::UseTree {
             prefix: cx.path(span, import_path),