Rename NestedMetaItem::name_value_literal.

It's a highly misleading name, because it's completely different to
`MetaItem::name_value_literal`. Specifically, it doesn't match
`MetaItemKind::NameValue` (e.g. `#[foo = 3]`), it matches
`MetaItemKind::List` (e.g. `#[foo(3)]`).

compiler/rustc_ast/src/attr/mod.rs

@@ -464,8 +464,9 @@ impl NestedMetaItem {
         self.meta_item().and_then(|meta_item| meta_item.meta_item_list())
     }
 
-    /// Returns a name and single literal value tuple of the `MetaItem`.
-    pub fn name_value_literal(&self) -> Option<(Symbol, &MetaItemLit)> {
+    /// If it's a singleton list of the form `foo(lit)`, returns the `foo` and
+    /// the `lit`.
+    pub fn singleton_lit_list(&self) -> Option<(Symbol, &MetaItemLit)> {
         self.meta_item().and_then(|meta_item| {
             meta_item.meta_item_list().and_then(|meta_item_list| {
                 if meta_item_list.len() == 1

compiler/rustc_attr/src/builtin.rs

@@ -986,7 +986,7 @@ pub fn parse_repr_attr(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
                     recognised = true;
                     acc.push(h);
                 }
-            } else if let Some((name, value)) = item.name_value_literal() {
+            } else if let Some((name, value)) = item.singleton_lit_list() {
                 let mut literal_error = None;
                 let mut err_span = item.span();
                 if name == sym::align {

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -435,7 +435,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
             sym::repr => {
                 codegen_fn_attrs.alignment = if let Some(items) = attr.meta_item_list()
                     && let [item] = items.as_slice()
-                    && let Some((sym::align, literal)) = item.name_value_literal()
+                    && let Some((sym::align, literal)) = item.singleton_lit_list()
                 {
                     rustc_attr::parse_alignment(&literal.kind)
                         .map_err(|msg| {