Avoid more MetaItem-to-Attribute conversions.

There is code for converting `Attribute` (syntactic) to `MetaItem`
(semantic). There is also code for the reverse direction. The reverse
direction isn't really necessary; it's currently only used when
generating attributes, e.g. in `derive` code.

This commit adds some new functions for creating `Attributes`s directly,
without involving `MetaItem`s: `mk_attr_word`, `mk_attr_name_value_str`,
`mk_attr_nested_word`, and
`ExtCtxt::attr_{word,name_value_str,nested_word}`.

These new methods replace the old functions for creating `Attribute`s:
`mk_attr_inner`, `mk_attr_outer`, and `ExtCtxt::attribute`. Those
functions took `MetaItem`s as input, and relied on many other functions
that created `MetaItems`, which are also removed: `mk_name_value_item`,
`mk_list_item`, `mk_word_item`, `mk_nested_word_item`,
`{MetaItem,MetaItemKind,NestedMetaItem}::token_trees`,
`MetaItemKind::attr_args`, `MetaItemLit::{from_lit_kind,to_token}`,
`ExtCtxt::meta_word`.

Overall this cuts more than 100 lines of code and makes thing simpler.

compiler/rustc_builtin_macros/src/alloc_error_handler.rs

@@ -95,9 +95,7 @@ fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span
         body,
     }));
 
-    let special = sym::rustc_std_internal_symbol;
-    let special = cx.meta_word(span, special);
-    let attrs = thin_vec![cx.attribute(special)];
+    let attrs = thin_vec![cx.attr_word(sym::rustc_std_internal_symbol, span)];
 
     let item = cx.item(span, Ident::from_str_and_span("__rg_oom", span), attrs, kind);
     cx.stmt_item(sig_span, item)

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -1,5 +1,4 @@
 use rustc_ast::{
-    attr,
     ptr::P,
     token,
     tokenstream::{DelimSpan, TokenStream, TokenTree},
@@ -118,10 +117,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             self.cx.item(
                 self.span,
                 Ident::empty(),
-                thin_vec![self.cx.attribute(attr::mk_list_item(
-                    Ident::new(sym::allow, self.span),
-                    vec![attr::mk_nested_word_item(Ident::new(sym::unused_imports, self.span))],
-                ))],
+                thin_vec![self.cx.attr_nested_word(sym::allow, sym::unused_imports, self.span)],
                 ItemKind::Use(UseTree {
                     prefix: self.cx.path(self.span, self.cx.std_path(&[sym::asserting])),
                     kind: UseTreeKind::Nested(vec![

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -68,8 +68,7 @@ pub fn expand_deriving_clone(
         _ => cx.span_bug(span, "`#[derive(Clone)]` on trait item or impl item"),
     }
 
-    let inline = cx.meta_word(span, sym::inline);
-    let attrs = thin_vec![cx.attribute(inline)];
+    let attrs = thin_vec![cx.attr_word(sym::inline, span)];
     let trait_def = TraitDef {
         span,
         path: path_std!(clone::Clone),

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -5,7 +5,7 @@ use crate::deriving::path_std;
 use rustc_ast::{self as ast, MetaItem};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
-use rustc_span::symbol::{sym, Ident};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 use thin_vec::thin_vec;
 
@@ -18,11 +18,11 @@ pub fn expand_deriving_eq(
     is_const: bool,
 ) {
     let span = cx.with_def_site_ctxt(span);
-    let inline = cx.meta_word(span, sym::inline);
-    let hidden = rustc_ast::attr::mk_nested_word_item(Ident::new(sym::hidden, span));
-    let doc = rustc_ast::attr::mk_list_item(Ident::new(sym::doc, span), vec![hidden]);
-    let no_coverage = cx.meta_word(span, sym::no_coverage);
-    let attrs = thin_vec![cx.attribute(inline), cx.attribute(doc), cx.attribute(no_coverage)];
+    let attrs = thin_vec![
+        cx.attr_word(sym::inline, span),
+        cx.attr_nested_word(sym::doc, sym::hidden, span),
+        cx.attr_word(sym::no_coverage, span)
+    ];
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Eq),

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -15,8 +15,7 @@ pub fn expand_deriving_ord(
     push: &mut dyn FnMut(Annotatable),
     is_const: bool,
 ) {
-    let inline = cx.meta_word(span, sym::inline);
-    let attrs = thin_vec![cx.attribute(inline)];
+    let attrs = thin_vec![cx.attr_word(sym::inline, span)];
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Ord),

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -68,8 +68,7 @@ pub fn expand_deriving_partial_eq(
 
     // No need to generate `ne`, the default suffices, and not generating it is
     // faster.
-    let inline = cx.meta_word(span, sym::inline);
-    let attrs = thin_vec![cx.attribute(inline)];
+    let attrs = thin_vec![cx.attr_word(sym::inline, span)];
     let methods = vec![MethodDef {
         name: sym::eq,
         generics: Bounds::empty(),

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -19,8 +19,7 @@ pub fn expand_deriving_partial_ord(
     let ret_ty =
         Path(Path::new_(pathvec_std!(option::Option), vec![Box::new(ordering_ty)], PathKind::Std));
 
-    let inline = cx.meta_word(span, sym::inline);
-    let attrs = thin_vec![cx.attribute(inline)];
+    let attrs = thin_vec![cx.attr_word(sym::inline, span)];
 
     let partial_cmp_def = MethodDef {
         name: sym::partial_cmp,

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -20,8 +20,7 @@ pub fn expand_deriving_default(
 ) {
     item.visit_with(&mut DetectNonVariantDefaultAttr { cx });
 
-    let inline = cx.meta_word(span, sym::inline);
-    let attrs = thin_vec![cx.attribute(inline)];
+    let attrs = thin_vec![cx.attr_word(sym::inline, span)];
     let trait_def = TraitDef {
         span,
         path: Path::new(vec![kw::Default, sym::Default]),

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

@@ -718,7 +718,7 @@ impl<'a> TraitDef<'a> {
         let path = cx.path_all(self.span, false, vec![type_ident], self_params);
         let self_type = cx.ty_path(path);
 
-        let attr = cx.attribute(cx.meta_word(self.span, sym::automatically_derived));
+        let attr = cx.attr_word(sym::automatically_derived, self.span);
         let attrs = thin_vec![attr];
         let opt_trait_ref = Some(trait_ref);
 

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -188,7 +188,7 @@ fn inject_impl_of_structural_trait(
             .cloned(),
     );
     // Mark as `automatically_derived` to avoid some silly lints.
-    attrs.push(cx.attribute(cx.meta_word(span, sym::automatically_derived)));
+    attrs.push(cx.attr_word(sym::automatically_derived, span));
 
     let newitem = cx.item(
         span,

compiler/rustc_builtin_macros/src/global_allocator.rs

@@ -115,9 +115,7 @@ impl AllocFnFactory<'_, '_> {
     }
 
     fn attrs(&self) -> AttrVec {
-        let special = sym::rustc_std_internal_symbol;
-        let special = self.cx.meta_word(self.span, special);
-        thin_vec![self.cx.attribute(special)]
+        thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
     }
 
     fn arg_ty(

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -1,6 +1,3 @@
-use std::mem;
-
-use rustc_ast::attr;
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, Visitor};
 use rustc_ast::{self as ast, NodeId};
@@ -13,6 +10,7 @@ use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use smallvec::smallvec;
+use std::mem;
 
 struct ProcMacroDerive {
     id: NodeId,
@@ -365,14 +363,8 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
             cx.expr_array_ref(span, decls),
         )
         .map(|mut i| {
-            let attr = cx.meta_word(span, sym::rustc_proc_macro_decls);
-            i.attrs.push(cx.attribute(attr));
-
-            let deprecated_attr = attr::mk_nested_word_item(Ident::new(sym::deprecated, span));
-            let allow_deprecated_attr =
-                attr::mk_list_item(Ident::new(sym::allow, span), vec![deprecated_attr]);
-            i.attrs.push(cx.attribute(allow_deprecated_attr));
-
+            i.attrs.push(cx.attr_word(sym::rustc_proc_macro_decls, span));
+            i.attrs.push(cx.attr_nested_word(sym::allow, sym::deprecated, span));
             i
         });
 

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -52,7 +52,7 @@ pub fn inject(
             cx.item(
                 span,
                 ident,
-                thin_vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
+                thin_vec![cx.attr_word(sym::macro_use, span)],
                 ast::ItemKind::ExternCrate(None),
             ),
         );
@@ -79,7 +79,7 @@ pub fn inject(
     let use_item = cx.item(
         span,
         Ident::empty(),
-        thin_vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
+        thin_vec![cx.attr_word(sym::prelude_import, span)],
         ast::ItemKind::Use(ast::UseTree {
             prefix: cx.path(span, import_path),
             kind: ast::UseTreeKind::Glob,

compiler/rustc_builtin_macros/src/test.rs

@@ -2,7 +2,6 @@
 /// Ideally, this code would be in libtest but for efficiency and error messages it lives here.
 use crate::util::{check_builtin_macro_attribute, warn_on_duplicate_attribute};
 use rustc_ast as ast;
-use rustc_ast::attr;
 use rustc_ast::ptr::P;
 use rustc_ast_pretty::pprust;
 use rustc_errors::Applicability;
@@ -47,11 +46,7 @@ pub fn expand_test_case(
             tokens: None,
         };
         item.ident.span = item.ident.span.with_ctxt(sp.ctxt());
-        item.attrs.push(ecx.attribute(attr::mk_name_value_item_str(
-            Ident::new(sym::rustc_test_marker, sp),
-            test_path_symbol,
-            sp,
-        )));
+        item.attrs.push(ecx.attr_name_value_str(sym::rustc_test_marker, test_path_symbol, sp));
         item
     });
 
@@ -241,16 +236,9 @@ pub fn expand_test_or_bench(
         Ident::new(item.ident.name, sp),
         thin_vec![
             // #[cfg(test)]
-            cx.attribute(attr::mk_list_item(
-                Ident::new(sym::cfg, attr_sp),
-                vec![attr::mk_nested_word_item(Ident::new(sym::test, attr_sp))],
-            )),
+            cx.attr_nested_word(sym::cfg, sym::test, attr_sp),
             // #[rustc_test_marker = "test_case_sort_key"]
-            cx.attribute(attr::mk_name_value_item_str(
-                Ident::new(sym::rustc_test_marker, attr_sp),
-                test_path_symbol,
-                attr_sp,
-            )),
+            cx.attr_name_value_str(sym::rustc_test_marker, test_path_symbol, attr_sp),
         ]
         .into(),
         // const $ident: test::TestDescAndFn =

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -185,13 +185,12 @@ impl<'a> MutVisitor for EntryPointCleaner<'a> {
         let item = match entry_point_type(self.sess, &item, self.depth) {
             EntryPointType::MainNamed | EntryPointType::RustcMainAttr | EntryPointType::Start => {
                 item.map(|ast::Item { id, ident, attrs, kind, vis, span, tokens }| {
-                    let allow_ident = Ident::new(sym::allow, self.def_site);
-                    let dc_nested =
-                        attr::mk_nested_word_item(Ident::new(sym::dead_code, self.def_site));
-                    let allow_dead_code_item = attr::mk_list_item(allow_ident, vec![dc_nested]);
-                    let allow_dead_code = attr::mk_attr_outer(
+                    let allow_dead_code = attr::mk_attr_nested_word(
                         &self.sess.parse_sess.attr_id_generator,
-                        allow_dead_code_item,
+                        ast::AttrStyle::Outer,
+                        sym::allow,
+                        sym::dead_code,
+                        self.def_site,
                     );
                     let attrs = attrs
                         .into_iter()
@@ -309,8 +308,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     );
 
     // #[rustc_main]
-    let main_meta = ecx.meta_word(sp, sym::rustc_main);
-    let main_attr = ecx.attribute(main_meta);
+    let main_attr = ecx.attr_word(sym::rustc_main, sp);
 
     // pub fn main() { ... }
     let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(vec![]));